1. Immunology

2. Definition
Branch of science that deals with immune system: Use of antibody – antigen reactions in diagnosis.

3. General or Non specific host immune defense mechanisms
Host defense can be grouped into four major categories:
1. General Physical Chemical and 4. Biological barriers
General barriers
Direct factors like nutrition, fever, age, genetic factors and indirect factors like personal hygiene and living conditions.
2. Physical barriers
First line of host defence against infection skin and mucous membranes. Intact skin forms a very effective mechanical barrier. Mucous secretions of the respiratory, digestive and urino-genital systems form a protective covering.

4. Chemical barriers
Gastric juices, salivary glycoproteins, lysozyme, oleic acid on the skin, urea etc.
Body fluids contain antibodies and complements, fibronectin, hormones, beta-lysin other polypeptides, interferons, bacteriocins.

5. Microbial and Biological barriers
Involves cells derived from bone marrow cells.
Phagocytes.
Normal microbiota
Inflammation: increased blood supply, increased capillary permeability, leukocyte migration and phagocytosis.

6. Specific immunity
(Lymphocytes) that can recognize foreign molecules forming specialized protein (antibodies) that target the antigens with other components of the immune system.

7. Phagocytosis
Leukocytes (white blood cells) protect the body against infection by the process of phagocytosis.
Granulocytes and agranulocytes:
Granunolocytes include basophils, eosinophils and neutrophils and agranulocytes include monocytes and lymphocytes.

8. Immune Response Antigen Characters: Immunogenicity specific reactivity
An antigen is any macromolecule that activates the immune system.
Proteins, polysaccharides, nucleoproteins, lipids.
Characters: Immunogenicity specific reactivity
An antigen can elicit the formation of an antibody to form antigen-antibody complex or immune complex.
Epitope or antigenic determinant
Bacterial cell can have numerous antigens.
‘O’ antigen
‘H’ antigens
Haptens

9. Antibody Immunoglobulins are glycoproteins Antibodies
Produced by ‘B’ lymphoid cells
Immunoglobulins constitute approximately 1 to 2% of the total serum proteins

10. Structure of antibody
Each immunoglobulin is composed of four peptide chains, two identical large or heavy (H) chains and two identical light (L) chains.
Gamma for Ig G,alpha for Ig A,mu for Ig M,delta for Ig D and,epsilon for Ig E
L chains exist either as kappa or lamda chains called ‘L’ chain allotypes.
Functionally antibodies have two protein fragments namely Fc and Fab fragments.
Fc enables the immunoglobulin to bind to complement or host.
Fab contains the antigen binding sites
‘H’ & ‘L’ chains have both variable and constant regions (domains).
Variable domain provides the specificity of an immunoglobulin

11. Immunity Specific immunity – types Acquired immunity:
Immunity after exposure to a suitable antigen -antibodies or lymphocytes from immune donor
Naturally acquired active immunity
immunity after an infection can be either life long or for only a few years.
ii. Naturally acquired passive immunity
Transfer of antibody from one host to another for eg. Mother to fetus short time.
iii. Artificially acquired – active immunity : Vaccines
iv. Artificially acquired – passive immunity: Antibodies produced in vitro are introduced into a host).. Botulinum antitoxin
Humoral Immunity presence of soluble antibodies in blood and lymph antibody-mediated immunity.
Cell – mediated immunity
Immunity that results from T-cells coming into close contact with foreign cells or infected cells

12. Immunological methods of detection of Microbial pathogens
Serotyping
Method is widely applied to Gram negative enteric bacterial specific antibodies to indentify homologous antigens. In case of food borne pathogens, the antigens are particulate and agglutination methods are employed. For soluble antigens like toxins gel diffusion assays may be used.

13. Radio immunoassay
Consists of adding a radioactive label to an antigen, allowing to react with specific antibody and measuring use of a radio activity counter 125 I.

14. Immunofluorescence ELISA – Enzyme Linked Immuno-Sorbant Assy
Conjugation of an enzyme to either antigen or antibody allows detection simple, versatile and highly sensitive test for detection of antigen or antibody

15. ELISA and related assays depend on four major principles
1. Simple ELISA (Simple 2 layer assays)
2. Sandwich ELISA (Two site assay)
3. Indirect ELISA