Immunology Definition Branch of science that deals with
Immunology
Definition • Branch of science that deals with immune system: Use of antibody – antigen reactions in diagnosis.
General or Non specific host immune defense mechanisms Host defense can be grouped into four major categories: 1. General 2. Physical 3. Chemical and 4. Biological barriers 1. 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.
Chemical barriers • Gastric juices, salivary glycoproteins, lysozyme, oleic acid on the skin, urea etc. • Body fluids contain antibodies and complements, fibronectin, hormones, betalysin other polypeptides, interferons, bacteriocins.
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.
Specific immunity • (Lymphocytes) that can recognize foreign molecules forming specialized protein (antibodies) that target the antigens with other components of the immune system.
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.
Immune Response • Antigen • 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
Antibody • Immunoglobulins are glycoproteins Antibodies • Produced by ‘B’ lymphoid cells • Immunoglobulins constitute approximately 1 to 2% of the total serum proteins
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
Immunity • Specific immunity – types • Acquired immunity: • Immunity after exposure to a suitable antigen -antibodies or lymphocytes from immune donor i. Naturally acquired active 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
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.
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.
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
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
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