IMMUNOLOGY DEN

Organs of the immune system

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 20:07:00 +0000

The immune system can be distinguished by function as the:

Primary Lymphoid organs --> Thymus & Bone marrow
Secondary lymphoid organs –> Lymph nodes, Spleen & Various Mucosal Lymphoid Tissues (MALT), such as Gut-Associated Lymphoid Tissue (GALT).
Tertiary lymphoid organs –> Cutaneous-associated lymphoid tissues

Primary Lymphoid organs:

Only after a lymphocyte has matured a primary lymphoid organ is the cell immune competent.
In mammals, T-cells mature in the "Thymus" and B-cells mature in the "Bone marrow” (in Bursa of Fabricus in birds).
There are TWO cells in the Primary Lymphoid Organs – Thymus and Bone Marrow.

Secondary lymphoid organs

Lymph nodes and the spleen are the most highly organized of the secondary lymphoid organs.
Less-organized lymphoid tissue, collectively called "Mucosal-Associated lymphoid Tissue"(MALT), is found in various body sites.
MALT includes -> Peyer's patches (in the small intestine), the tonsils, & the Appendix.
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Thymus

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:58:00 +0000

The thymus is a flat, bi-lobed organ situated above the heart.
Immature T-cells are simply referred as "Thymocyte", these are densely packed outer compartment (or) cortex of the thymus lobule.
Some of the thymic epithelial cells in the outer cortex, called "nurse cells", have long membrane extensions that surround as many as so thymocytes, forming large multicellular complexes
The average weight of the thymus is 70 grams in infants; its age dependent involution levels an organ with an average weight of only 3 grams in the elderly.

Explanations about Thymus:

The thymus covered by a fibrous capsule. It is formed of two lobes.
Each lobe of the thymus is organized into lobule which is separated from one another by septa called trabeculae.
With in each lobule, the cells are arranged into an outer cortex and an inner medulla.
The cortex is tightly packed with proliferating immature lymphocytes while the medulla contains more mature cells.
As the cells mature, they move from the cortex to the medulla.
The cortex consists of lymphocytes (thymocytes) and reticular cells.
The medulla consists of vascular structure, reticular epithelial cells and scattered lymphocytes.
There are also some interdigitating cells associated with the epithelial network and these cells are rich in MHC class II antigens.

Bone marrow

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:44:00 +0000

In birds, a lymphoid organ called the "Bursa of fabricius", which is a gut-associated lymphoid tissue, is the primary site of B-cell maturation.
In mammals, such as primates and rodents, there is no Bursa, but Bone marrow serve as the "Bursal equivalent", where B-cell maturation occurs.
In rabbits, uses gut-associated tissues such as the Appendix as primary lymphoid tissue for important steps in the proliferation and diversification of B-cells.

Spleen

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:42:00 +0000

It is largest secondary lymphoid organ.
The spleen is a large, ovoid secondary lymphoid organ, situated at high in the left abdominal cavity.
Spleen specializes in filtering blood and trapping blood-borne antigens.
It can respond to systemic infections.
The spleen is surrounded by a capsule that extends a number of projections into the interior to form a compartmentalized structure.
They are of two types: a) Red pulp b)White pulp

a) Red pulp:

Populated by macrophages & numerous red blood cells (erythrocytes).
It is the site where old and defective RBC are destroyed and removed.

b) White pulp:

Populated mainly by T-Lymphocytes.

Mucosal - Associated Lymphoid Tissue (MALT):

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:30:00 +0000

It is non-encapsulated clusters of lymphoid tissue with immune function is the "mucosal immune system".
It is common around the membrane lining the respiratory, digestive and urogenital tracts (gateways to the body for involving organisms)
The MALT of the gut is called "Gut-Associated lymphoid tissues"(GALT).
It includes payer's patches and focal accumulations of lymphocytes in the lamina propria.
The MALT filters out antigens that enter in air and food (or) come from microorganisms growing in the intestines.
The antigen activated B-Lymphocytes of the bodies first line defense against infection by microorganisms.
These B-cells also make Ig.E as a main response to helminthes.
The mucosal layer of the alimentary canal, respiratory and urinogential tracts is provided with dispersed groups of lymphoid tissues known as MALT.

These tissues are usually without a capsule (uncapsulated). In human beings the payers patches, the tonsils and appendix are good examples of lymphoid tissues found in the mucosal layer of the alimentary canal. Hence these are also referred to as GALT (Gut Associated Lymphoid Tissue).

Peyer’s Patches

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:29:00 +0000

Peyer’s patches are secondary lympoid tissues. They are MALT (Mucosa Associated Lymphoid Tissue).
They are collection of lymphoid nodules packed together to form oblong elevations of the mucus membrane of the small intestine.
They consist of a mixture of T and B lymphocytes where the T-cells predominate.
The cells secrete Ig.A , gets transported across the mucosa into the intestinal lumen where it neutralizes viruses, bacteria and toxins and blocks the entry of these antigens into circulation by acting as an antiseptic paint.

Lymph node

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:22:00 +0000

Lymph nodes are encapsulated bean-shaped structures containing a reticular network placed with lymphocytes, macrophages & dendritic cells.
The overall architecture of a lymph node supports an ideal micro environment for lymphocytes to effectively encounter and respond to trapped antigens.
The lymph node can be divided into three roughly concentric regions based on morphology:

Cortex:

The Cortex contains lymphocytes (mostly B-cells), macrophages & follicular dendritic cells arranged in primary follicles.
This cortex region some times referred to as "Thymus-independent area.

Medulla:

It is innermost layer of lymph node

Para-cortex:

Beneath the cortex, which is populated largely by T-Lymphocytes and also contains interdigitating dendritic cells thought to have migrated from tissues to the node.
These interdigitating dendritic cells express high levels of class n MHC molecules, which are necessary for presenting antigen to T_H-cells.
These paracortex regions sometimes referred to as a "Thymus dependent area".

Tonsils

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:16:00 +0000

Tonsils are lymphoid tissues encircling the pharynx.
These are secondary lymphoid tissues.
They are very similar to Thymus internal structure.
There are 3 types of tonsils palatine tonsils, lingual tonsils and pharyngeal tonsils.
The tonsils also setup resistance to infection microbes.
The tonsils sample the microbes in the inhaled air form suitable antibiotics.

Requirements for Immunogenesity (or) Factors affecting on Immunogenecity

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:12:00 +0000

A substance most possess the following three characteristics to be immunologic.

1) Foreignness
2) High Molecular weight
3) Chemical Complexity
4) Solubility (biodegradability)

1) Foreignness:

Animals normally do not respond immunologically to “self”, for example, if a RABBIT is injected with its own serum albumin, it will not mount an immune response. It recognizes the albumin as self. In contrast, if rabbit serum albumin as “foreign” and mount an immune response against it. To prove that the rabbit, which did not respond to its own serum albumin because it recognizes the substance as foreign. Thus, the first requirement for a compound to be immunogenic is foreignness. The substance as foreign. Thus, the first requirement for a compound to be immunogenic is foreignness. The more foreign the substance the more immunogenic it is.

2) High Molecular Weight:

Compounds that have a molecular weight of less than 1000 daltons are not immunogenic (e.g: Penicillin, Progesterone, Aspirin)
Compounds that have molecular weight between 1000 and 6000 daltons may (or) may not be immunogenic. (e.g: Insulin, Adrenocorticotropic Hormone (ACTH))
Compounds that have molecular weight greater than 6000 daltons are generally immunogenic. (e.g: Albumin, Tetanus toxin)

3) Chemical Complexity:

It is necessary for compound to be immunogenic is a certain degree of physiological complexity.

Eg: Homopolymer of Amino Acids, such as

Polymer of Lysine (mol.wt. 30,000dt)- Seldom is good immunogen
Poly D-Glutamate (mol.wt. 50,000dt)- It is not immunogen

If the complexity is increased by the attachment of various such as “Dinitrophenol” or other low molecular weight compounds which by themselves are not immunogenic, to be epsilon amino group of polylysine, the entire macromolecule becomes immunogenic.

In general, an increase in the chemical complexity of a compound is accompanied by an increase in its immunogenicity. Thus copolymers of several amino acids such as “polyglutamic acid, Alanine and lysine” are highly immunogenic.

4) Solubility (biodegradability):

Intact antigens must be broken down into immunogenic pieces. Cells must interact with antigens before acquired immunity can induce. Antigen presenting cells (APC) degrade the substances in a manner that enhances the immunogenecity of the antigenic substances, this is called antigenic processing.

Antigen

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 19:11:00 +0000

a substance (usually foreign) that binds specifically to an antibody (or) a T-cell receptor, often is used as an synonym for “Immunogen”.

(or)

An organism (or) a macromolecule, which stimulates a specific immune response, is called an “Immunogen” or “antigen”.

The molecular properties of antigens and the way these properties ultimately contribute to immune activation to our understanding of the immune system.

Immunogenicity:

Immunogenicity is the ability to induce a humoral and /or cell-mediated immune response.

B-cells + Antigen –> Effector B-cells (plasma cells) + Memory cells

T-cells + Antigen –> Effector T-cells + Memory cells

Although a substance that induces a specific immune response is usually called an “antigen”, is more approximately called on “Immunogen” (Immune response inducing substance).

Antigenecity:

It is the ability to combine specifically with the final products of the above responses (i.e., antibodies and/or cell surface receptors). Although all molecules that have the property of immunogenicity also have the property of antigenicity, the reverse is not true.

Haptens: Low molecular weight molecules that can be made immunologic by conjugation to suitable carrier. These lake immunogenicity. Haptens are antigenic but not immunogenic. Haptens are incomplete antigens.

Requirements for Immunogenesity (or) Factors affecting on Immunogenecity

Cells of the Immune System

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 14:30:00 +0000

Lymphocytes are the central cells of the immune system, responsible for acquired immunity & the immunologic attributes of diversity, specificity, many and self/non-self recognition.
Lymphocytes constitute 20% to 40% of the body's WBC and 99% of the cells in the lymph.
Resting B & T-lymphocytes are small, motile, nonphagocytic cells, which can't be distinguished morphologically.
In Go - phase of the cell cycle, B and T- lymphocytes are not interacted with antigen-referred to as "naive cells", which have generally short life span.
Certain cytokines induces the naive cells to enter the cell cycle by progressing from G₀into G₁ & subsequently into S, G₂ & M.
Lymphoblasts proliferate and differentiate into "Effector cells" (or) into "Memory cells".
Effector cells: The functions in various ways to estimate the antigen. These cells have short life spans, generally ranging from a few days to few weeks
Plasma cells: The antibody-secreting effector cells of the B-cell lineage have a characteristic cytoplasm that contains abundant ER(to support their rate of protein synthesis).

The lymphocytes can be broadly subdivided into three populations - B-cells, T-cells, Null cells-on the basis of function and cell membrane components.

B-Cells (or) B-Lymphocytes

T-Cells (or) T-Lymphocytes

Null cells

Other Cells are

Granulocytic Cells

Mast Cells

B-Cells are involved in Humoral Immune response and

T-cells are involved in Cell mediated immune response.

Mast cells

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 14:23:00 +0000

Mast cells were first described by Paul Ehrlich in his 1878 doctoral thesis on the basis of their unique staining characteristics and large granules
A mast cell is also known as Mastocyte and Labrocyte
The cells contains many granules rich in Histamine and Heparin
Mast cells play a key role in the inflammatory process
These cell precursors are formed in the bone marrow by hematopoiesis.
Mast cells known for their role in Allergy and Anaphylaxix.
The major function of Mast cells are involved in Wound Healing and Defense against Pathogens.
The mast cell is very similar in both appearance and function to the basophil, a type of white blood cell
These are found in a wide variety of tissues, including The skin.Connective tissues of various organs, Mucosal epithelial tissue of respiratory, Genitourinary & digestive tracts.
These cells have large number of cytoplasmic granules that contain "Histamine" and other pharmacologically active Substances.
It plays an important role in the development of allergies

Role in disease

Allergic disease

Many forms of cutaneous and mucosal allergy are mediated for a large part by mast cells; they play a central role in asthma, eczema, itch (from various causes) and allergic rhinitis and allergic conjunctivitis. Antihistamine drugs act by blocking the action of histamine on nerve endings. Cromoglicate-based drugs (sodium cromoglicate, nedocromil) block a calcium channel essential for mast cell degranulation, stabilizing the cell and preventing release of histamine and related mediators. Leukotriene antagonists (such as montelukast and zafirlukast) block the action of leukotriene mediators, and are being used increasingly in allergic diseases.

Anaphylaxis

In anaphylaxis (a severe systemic reaction to allergens, such as nuts, bee stings or drugs), body-wide degranulation of mast cells leads to vasodilation and, if severe, symptoms of life-threatening shock.

Autoimmunity

Mast cells are implicated in the pathology associated with the autoimmune disorders rheumatoid arthritis, bullous pemphigoid, and multiple sclerosis. They have been shown to be involved in the recruitment of inflammatory cells to the joints (e.g. rheumatoid arthritis) and skin (e.g. bullous pemphigoid) and this activity is dependent on antibodies and complement components.

Reproductive disorders

Mast cells are present within the endometrium, with increased activation and release of mediators in endometriosis. In males, mast cells are present in the testes and are increased in oligo- and azoospermia, with mast cell mediators directly suppressing sperm motility in a potentially reversible manner.

Mast cell disorders

Mastocytosis is a rare condition featuring proliferation of mast cells. It exists in a cutaneous and systemic form, with the former being limited to the skin and the latter involving multiple organs. Mast cell tumors are often seen in dogs and cats.

Watch this Video on MAST CELLS:

Macrophages antimicrobial and cytotoxic activities

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 13:52:00 +0000

Antimicrobicia! & cytotoxic substances produced by activated macrophages can destroy phagocytosed microorganisms.

Mediators of antimicrobial and cytotoxic activity of macrophages and neutrophils

Oxygen-dependent killing

Oxygen-independent killing

Reactive oxygen intermediates

O₂^.-(Superoxide anion)

OH^- (Hydroxide radicals)

H₂O₂ (Hydrogm peroxide)

ClO^- (Hypochlorite anion)

Defensins

Tumor necrosis factor -alpha

(macrophage only)

Lysozyme

Hydrolytie enzymes

Reactive nitrogen intermediates

NO (nitric oxide)

NO₂ (nitrogen dioxide)

HNO₂ (nitrous oxide)

Others

NH₂Cl (monochloramine)

A) Oxygen-dependent killing mechanism:

Activated phagocytes produce a number of "Reactive Oxygen Intermediates (ROIs)" & "reactive nitrogen intermediates" that have potent antimicrobial activity.
During phagocytosis, a metabolic process known as the "Respiratory Burst" occurs in activated macrophages.
Due to the respiratory burst, membrane - bound enzyme "Oxidase" will activate, that catalyzes the reduction of oxygen to superoxide anion (powerful oxidizing agent), a reactive oxygen intermediate & hydroxyl radicals &H₂O_2.
As the lysosomes fuses with the phagosomes, the activity of "Myeloperoxidase" produces hypochlorite from hydrogen peroxide and chloride ions.
Hypochlorite, the active agent of household bleach, is toxic to ingested microbes.
When the macrophages are activated with bacterial cell wall components. The T-cell derived cytokine (IFN-γ), they begin to express high levels of “Nitric Oxide synthatase"(NOS), an enzyme that oxidizes L-arginine to yield L-Citrulline & nitric oxide (NO), a gas.

L-Arginine + O₂ + NADPH -> NO + L-Citrulline +NADP⁺

No has potent anti-microbial activity.

B) Oxygen-independent killing mechanism:

Activated macrophages also synthesize 'lysozyme' and various hydrolytic enzymes whose degradative activities do not require Oxygen.
The activated macrophages produce a group of antimicrobials cytotoxic peptides, commonly known as "Defensin", these Molecules are cystine- rich cationic peptides containing 29-35 Amino acids residues.
The defensin is circularized protein.
The peptide form ion-permeable channel in bacterial cell membrane.

Intracellular pathogens:

Some microorganism can survive & multiply within pathogens include:
- Listeria monocytogenes
- Salmonella typhimurium
- Neisseria gonorrhoeae &
- Mycobacterium aviutn
- Mycobacteriura tuberculosis
- Mycobacterium leprea
- Brucella abortus &
- Candida albicans
Some intracellular pathogens prevent the fusion of lysosomes with phagosome and proliferate with in phagosomes.

T-Lymphocytes

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 13:49:00 +0000

The letter "T" designates from its site of maturation, in the "Thymus". T-cells regulate the "Cell-mediated immunity". The cells operates against cells bearing intracellular organisms, T-cells recognize antigen only when it is on the surface of a body cells. T-cells have receptors on their membrane surface (cell markers), which belongs to an important group of molecules known as the “Major Histocompatibility Complex (MHC)”.

There are 4 types of t-lymphocytes are present in immune system. They are :

i) T-Helper cells (T_H-Cells):

The T_H-cells recognize and bind to the combination of the antigen with the class -II MHC on the macrophage surface.
T_H-cells produce a variety of soluble factors known as "Cytokines". The cytokines induce gamma-interferon" and other "Macrophage activating factors".
The cytokines restore the microbicidal mechanism of the macrophage and bring about the death of the intracellular microorganisms.

II) Cytotoxic T-Cells (Tc -Cells):

The cells clonally express a large number of different surface receptors.
Each Tc recognizes antigen only association with a cell marker, the class-l MHC.
Tc also releases gamma-interferon.
The cells recognize virally infected cells, which are killed before the virus replicates.
Like B-cells, Tc - cells require help from Th-cells.
These cells attack infected cells and cancer cells.
The cells discharge a protein called "Perforin", which lyses the infected cell.

iii) T-Suppressor cells (Ts-cells):

The Ts-cells promote immune response.
The cells suppress a specific antibody formation (Infectious tolerance).
The "Infectious tolerance" phenomenon was shown that mice could be made unresponsive by infection of a heavy dose of sheep RBC into them; their T-cells suppressed specific antibody formation in the recipient mice.

T-cell receptor:

The T-cell receptor was elucidated through the powerful recombinant DMA technology.
The T-cell receptor called "Ti" (which is a made up of two non-identical polypeptides- α & β chains and joined by a disulfide bond).
The Ti associated with another protein called "CD3".

Ti +CD3 –> Ti-CD3 complex

(T-cell receptor complex)

After many years, the immunologists identified second type of receptor composed of gamma and 6-chains.

The CDs is made up of at least three polypeptide chains (γ,δ and Є).

iv) T_s-lymphocytes: (T suppressor Cells):

Ts cells are a sub population of T cells that suppresses the activity of B-cells and other T-cells.
They are the regulatory T cells.
They inhibit antibody production by B cells.
They suppress the functions of the T killer cells and T helper cells.

Development of T-lymphocytes:

The T-lymphocytes are derived from "Hemopoietic stem cells" of bone marrow. Some of these cells turn into "Lymphopoietic progenitor". The lymphoid progenitor cells turn into "Pre-T-lymphocytes". The Pre-T-cells leave the bone marrow and enter the thymus. In the thymus they mature into T-lymphocytes through the influence of thymic hormones. The mature T-lymphocytes enter the blood and colonies the secondary lymphoid organs such as spleen, lymph nodes, payer’s patches, etc. Here they become functional on exposure to antigens.

B-Lymphocytes

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 13:43:00 +0000

The letter "B" designate from its site of maturation, in the "Bursa of fabricius" in the birds; and "Bone marrow" in the mammalian species, including humans & mice.
B-Lymphocytes carries out "Humoral-immune response" by producing antibodies.
B-Lymphocytes is stimulated by "T_h -lymphocytes".
When the antigen stimulate, the B-cell divides repeatedly & differentiate over a 4 to 5 day period, generating a population of Plasma cells & Memory cells.
Plasma cells lack membrane-bound antibody, synthesize and secrete one of the five classes of antibody.
Each of the approximately 1.5X10⁵ molecules of antibody on the membrane of a single B- cell has an identical binding site for antigen.

Development of B-Lymphocytes:

B-cell differentiation as assessed by membrane immunoglobulin expression can be divided into antigen-independent and antigen-dependent phases. Surrounding microenvironment influences of the bone marrow i.e. drives antigen-independent differentiation of B-cells: B-cells develop "Clonal diversity" in the absence of antibody receptors for antigens.

B-cell development moves through several stages marked by the rearrangement of immunoglobulin genes, "bone marrow stromal cells" in two ways influence all of these stages:

1. By direct contact of the stromal cells with B-cell precursors in early stages of B-cell development and
2. by stromal cell-derived growth factors in later stages of B-cell development.

Progenetor B-cells use their surface molecules to bind to stromal cell "hyaluronic acid". This activity promotes "C-kit ligand" (stem cell factor) binding to C-kit encoded "Tyrosine kinase" membrane receptors.

B-lymphocyte differentiate from stem cells to pre-progenitor B-cells undergoing heavy V-region gene rearrangements, and then to progenitor B-cell that contain "Cytoplasmic -n-Chains".in the next stage , pre-B-cells undergo light chain V-J-arrangement and express low levels of membrane n-heavy chains associated with surrogate light chains. These surrogate light chains associate with each other to form a "light chain like structure". At this time, the immature B-cells express both n-heavy chains and light chains as surface Ig.M molecules. Finally, the B-cells also start to express Ig.D in addition to Ig.M. These cells are called "Mature B-cells", and exit to the periphery.

Focus point: Once stimulated antigen, the B-cells lose Ig.D immunoglobuiins A portion of the cells becomes a memory cell. B-cells then progress into plasma cells that secrete the class of Immunoglobulin lost represented on their surfaces.

Granulocytic cells

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 09:52:00 +0000

The granulocytes are classified as Neutrophils, Eosinophils and Basophils on the basis of cellular morphology and cytoplasmic staining characteristics.

a) Neutrophils:

It has a multi-lobed nucleus & granulated cytoplasm that stains with both acid & basic dyes.
It is often called a "Poly-morphonuclear leukocyte'(PMN)
These are produced by hematopoiesis in the bone marrow, which are released into the tissues, where they have a life span of only a few days.
Movement of circulating neutrophils into tissues called "Extravasation".
The neutrophils contains primary & Secondary granules:

Larger, denser primary granules

Peroxidase, Lysozyme, Various hydrolytic enzymes

Smaller, secondary granules

Collagenase, Lactofemn & Lysozyme

Both primary & secondary granules are fuse with phagosomes.
The cells exhibit a larger "Respiratory Burst" than macrophages & express higher levels of "defensins" than macrophages do.

b) Eosinophils:

The cells are motile phagocytic cells that can migrate from the blood into the tissue spaces.
It has a bi-lobes nucleus & a granulated cytoplasm that stains with the acid dye "Eosin" red (hence its name).
Play a significant role like phagocytic role like macrophages.
The secreted contents of eosinophilic granules may damage the parasite membrane.

c) Basophils:

It has a lobed nucleus and heavily granulated cytoplasm that stains with the basic dye "methylene Blue".
These are nonophagocytic granulocytes, which release pharmacologically active substances from their cytoplasmic granules. These substances play a major role in certain "Allergic responses".

Null cells

noreply@blogger.com (Indian Government Jobs) — Mon, 05 Nov 2012 09:51:00 +0000

Null cells are lymphocytes with cytotoxic properties.
They are neither B-cells not T cell. They are intermediate between T and B cells.
They form less than 3%.
There are two types of Null cells namely, Natural Killer Cells (NK cells) and Killer Cells.

Natural Killer Cells:

NK cells are a group of null cells.
They form the third population of lymphocytes.
The NK cells have 2 or 3 large granules in the cytoplasm. Hence they are also Large Granular Lymphocytes (LGL).
They have a kidney shaped nucleus.
The NK cells kill the target cells without the aid of antibody or complement. So they are antibody independent.
They destroy the cancer cells and cells infected with herpes and mumps virus.
They are activated by Interferons and Interleukins-2.

Killer Cells (K cells):

Killer cells are antibody dependent.
These cells possess Fc receptors for binding with IgG antibodies. Hence they can bind with cells coated with IgG antibodies and can kill them.
These cells can combine with specific antibody with it is in complex with antigen. If the complex is on the surface of a target cell, these lymphocytes become activated destroying the target cell.
This cell can kill a variety of cells such as tumor cells, bacteria, viruses, fungi and parasites.

Elements of Immunity: Acquired Immunity

noreply@blogger.com (Indian Government Jobs) — Sat, 03 Nov 2012 10:21:00 +0000

The resistance developed by man during his life is known as Acquired immunity or Adaptive immunity.
This is distinct from innate immunity in that it is due to specific antibodies or sensitized lymphocytes produces in response to specific antigens. Hence, this immunity is also known as specific immunity.
This acquired specific immunity is of two types namely Active and Passive.
Both active and passive immunity may be Natural or Artificial.

I) ACTIVE IMMUNITY
Active immunity is the resistance developed by an individual in response to an antigenic stimulus.

The antigen may gain entrance either by natural infection or through any other sources such as artificial immunization by vaccination.

a) Natural Active Immunity:

Immunity is developed by the host in response to the antigen that enters by natural infections.
For example, a person attacked by measles or smallpox develops natural active immunity as he recovers from the diseases.
The immunity acquired by way of such infections is also long lasting in many cases. For example, life time immunity is got following certain viral infections such as smallpox, measles and mumps.

b) Artificial Active Immunity:

In artificial active immunity, immunity is attained by the host in response to the antigen got by vaccination. Vaccines are preparations of live (attenuated) or killed microorganism or their products (toxoids).

Live Vaccine (attenuated): in this preparation, live microorganisms are attenuated by different methods. Attenuation results in the loss of pathogenicity without the loss of antigenicity of the microorganisms.
                      E.g.: Anthrax vaccine,
                               BCG (Bacille Calmette Guerin),
                               Sabin Vaccine (oral Poliomyelities Vaccine),
                               Measels Vaccine.
Vaccines prepared with killed microorganisms: In this vaccines, microorganisms are killed in their virulent phase either by heat or antiseptics. While killing, care is taken not to denature the antigen by excessive heat or strong detergents.
                   E.g.: Salk vaccine,
                             Influenza vaccine,
                             TAB vaccine,
                             Pertussis vaccine,
                             Toxoid,
                             Tetanus Toxoid (TT),
                             Diptheria Toxoid,
                            Triple Vaccine (DPT).

Immunization schedule for Children

Age	Vaccine
From 3^rd day after birth	BCG
3 months	DPT (1) OPV (1)
4 months	DPT (2) OPV (2)
5 months	DPT (3) OPV (3)
10 months	Measles
16 months	Booster dose or DPT and OPV

DPT = Diptheria, Pertussis, Tetanus vaccine (Triple vaccine)
OPV = Oral polio vaccine

II) PASSIVE IMMUNITY
The immunity that non-immune individual acquires by receiving antibodies or sensitized white blood cells from another immune individual is known as passive immunity.
The immunity is caused by passive immunization is less effective and inferior than that caused by active immunization. The main advantage of passive immunization is that it is immediate in its action of producing immunization and so this method would be used when immediate immunity is needed.
Passive immunity is also two types namely Natural and artificial.

a) Natural Passive immunity:
The immunity transferred from the mother to the child passively is known as natural passive immunity.

In human beings, this natural passive immunity occurs mainly by the passage of antibodies from the mother to her unborn child through the placenta during the later part of pregnancy.

The antibodies that are transferred are entirely Ig.G as other immunoglobulin sub-types (A, D, E and M) do not pass the placental barrier.

In other primates and in most of the other mammals such as pig the transfer of antibodies from the mother to the young one occurs mainly orally through the colostrums (the first milk produced by the mother after the birth of the offspring).

b) Artificial Passive Immunity:

Transfer of immunity from an immunized donor to a non immune recipient by transferring antibodies or immunized lymphocytes is known as artificial passive immunity.

Artificially passive immunity is therapeutically (science of treating diseases) used in the treatment of tetanus, diphtheria, gas gangrene, snake bite and immuno deficiency states.

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Elements of Immunity: Innate Immunity

noreply@blogger.com (Indian Government Jobs) — Sat, 03 Nov 2012 09:49:00 +0000

The elements of the innate (non-specific) immune system include anatomical barriers, secretory molecules and cellular components. Among the mechanical anatomical barriers are the skin and internal epithelial layers, the movement of the intestines and the oscillation of broncho-pulmonary cilia. Associated with these protective surfaces are chemical and biological agents.

It is a non-specific immunity.
This mechanism of immunity is similar for most types of infections, hence its name.
Its resistance to infection is by blocking the entry of pathogens into the body or by destroying the microbes through means other then antibodies.
Thus no-specific defense mechanism provides innate immunity which operates through many factors.

1) First line Defense (External Defense):

The external defense comprises physical and chemical barriers to the entry of pathogens into the body.

SKIN:

Skin is the largest (9.7m²) water proof, germ proof, self-disinfecting, defensive organ
The skin is providing a protective cover to the body.
It secretes some acids like Pyruvic acid and Lactic acid by sweat glands, which creates acidic environment on the skin.
In this environment some pathogens does not survive on the skin and it can not penetrate through the skin.

MUCUS MEMBRANE:

It resists the penetration of parasites into tissues.
Mucus secreted by mucus glands traps the pathogen and immobilizes them.
Mucus is a clear sticky mixture of mucin (glycoprotein) and water.
It is present in all internal tracks.

Vaginal Bacterias:

These bacteria produce lactic acid from the Glycogen thereby producing acidic environment to vagina as female’s best natural defense against pathogens.

2) Second line Defense (Internal defense) :

Body’s internal defense involves the participation of cellular and non-cellular factors possessing anti-bacterial property which have been found in blood and tissue.

I) Biochemical Factors:

The major biochemical factors are Interferon and Complement system.

Interferon:

These are group of soluble non-toxic glycoproteins produced in small amount by all cells of the body.

A special defense works specially against viral infection.

They offer resistance by blocking viral m-RNA transcription there by disrupting the viral life-cycle.

Cells involved by a virus produce an antiviral protein Interferon.

The interferon reaches the uninfected cells; it makes them resistant to the viral infection.

Complement System:

This system comprising set of 11 proteins found in the serum.

It is activated characteristically by antigen-antibody complexes.

Activation of the complement increases phagocytosis and destruction of the microbial organisms that enter the body of an individual.

The system perform functions in different ways:

Complement proteins rupture the cell membrane of microbe.

Stimulate mast cells to produce histamine

Strengthens the inflammatory reaction.

Act as Chemokines

Attract the phagocytes to the infected area.

Lysozyme :

Lysozyme breaks down the cell wall of bacteria.

Coagulation system :

Depending on the severity of the tissue injury, the coagulation system may or may not be activated. Some products of the coagulation system can contribute to the non-specific defenses because of their ability to increase vascular permeability and act as chemotactic agents for phagocytic cells.

Lactoferrin and transferrin:

By binding iron, an essential nutrient for bacteria, these proteins limit bacterial growth.

Interleukin-1:

IL-1 induces fever and the production of acute phase proteins, some of which are antimicrobial because they can opsonize bacteria.

II) Cellular Factors:

The natural defense mechanism against microorganisms and other foreign particles is carried out mainly by phagocytic cells were originally discovered by Mitchnikoff (1883). The process of eating the cells is known as Phagocytosis.

These phagocytic cells are of TWO types:

a) Microphages
b) Macrophages

a) Microphages:

Microphages are also called “Granulocytes”.
Microphages are polymorphonuclear leucocytes.
These are of three types: Neutrophils, Basophils, Eosinophils (Acidophils)
These calls possess multilobed nuclei and hence called polymorphonuclear leucocytes
They do not divide and short lived.

b) Macrophages:

These are mononuclear phagocytic system which was originally called as Reticuloendothelial system.
The pahgocytic cells of this system reach the site of inflammation in large number attracted by chemotactic substance and ingest the particulate materials.
Macrophages are phagocytic cells, derived from the blood monocyte.
The Macrophages are amoeboid cells having Bi-lobed nucleus & prominent cytoplasmic lysosomes.
Macrophages like cells serve different functions in different tissues & are named according to their tissue location.
Mononuclear phagocytic cell - monocyte circulating in the blood up to 8 hours, during which time they enlarge; they then migrate into the tissues & differentiate into specific tissue Macrophages

Macrophages	Location
Alveolar Macrophages	In the Lungs
Histocytes	In Connective tissues
Kupffer cells	In the Liver
Mesangial cells	In the Kidney
Microglial cells	In the Brain
Osteoclasts	In the Bone

Elements of Immunity

noreply@blogger.com (Indian Government Jobs) — Sat, 03 Nov 2012 03:06:00 +0000

The term immunity is defined as the resistance shown by the host against the adverse effects caused by microbes and their toxic products. In vertebrates two types of defense mechanisms work together to contact infection.

1. Innate Immunity (or) Non-Specific resistance
2. Acquired immunity or Specific resistance

I) Innate Immunity:

a) It is a non-specific immunity.
b) This mechanism of immunity is similar for most types of infections, hence its name.
c) Its resistance to infection is by blocking the entry of pathogens into the body or by destroying the microbes through means other then antibodies.
d) Thus no-specific defense mechanism provides innate immunity which operates through many factors.
1) First line Defense (External Defense):
First line defenses are physical barriers like SKIN, MUCUS MEMBRANE, Vaginal Bacterias
2) Second line Defense (Internal Defense):
Second line defenses are Biochemical factors and Cellular factors

II) Acquired Immunity:

The resistance developed by man during his life is known as Acquired immunity or adaptive immunity. This is distinct from innate immunity in that it is due to specific antibodies or sensitized lymphocytes produces in response to specific antigens. Hence, this immunity is also known as specific immunity.
This acquired specific immunity is of two types namely Active and Passive.
Both active and passive immunity may be Natural or Artificial.

What is Immunology

noreply@blogger.com (Indian Government Jobs) — Sat, 03 Nov 2012 01:56:00 +0000

Immunology is the study of the immune response. It has tremendous advances in the last 3 decades. In Latin “Immunitis” means “Freedom from Burdens” It is the slogan of second world war soldiers. The Father of Immunology and microbiology is Louis Pasteur” (1822 to 1895).

Animal encounter many potentially dangerous microbes in air, water and food. They have evolved co-operative types of defense mechanism against the disease causing microbes. These mechanisms maintain homeostasis to keep the animals alive. In fact human body is a closed container. If a parasite is to establish it must first penetrate the layer of this container. Intact skin and its extension into the gastrointestinal, respiratory and urinary tracts represent the major form of infection and diseases