Antigen –Antibody Reaction

Abhishek Routray

Points to focus on……………………….

• Introduction• Stages of reaction• General features of the reaction• Measurement of the reaction

INTRODUCTION

• In the body they form antibody mediated immunity.• In laboratory they help in diagnosis of infections.• In epidemiological surveys it differentiates the

infectious from the non infectious one and screen the population for particular infection.• In general these reaction can be used for detection

and quantitation of either antigen and antibody

Antigen antibody reaction in vitro is known as serological reaction

STAGES

stag

es

primary

secondary

tertiary

Primary stages Secondary stages Tertiary stagesInitial reaction rapid Visible effect Neutralization and

destruction of infectious agent or tissue damage

Reversible Precipitation Involves humoral immunity against infectious diseases as well as clinical allergy.

No visible effect agglutinationWeak intermolecular bond Neutralization of toxinDetected by estimating bound Ag & Ab and other method llike Radioactive isotope Fluroscent dyes ferritin

Complement fixation,Immbolizaation of motile organism

General features

• Reaction is specific.• Entire molecule not fragment reacts.• No denaturation of the antigen on the antibody during

reaction.• The combination occurs at the surface,firm but reversible.

avidity affinityStrength of bond after formation of Ag-Ab complex

Describe intensity of interaction of Ag-Ab complexIt is the function of closeness of fit between the epitope and antigen binding region of its antibody

• Both antigen and antibody participates in the formation of agglutinates• Antigen antibody can combine in varying proportion unlike

chemicals with fixed valency• Both antigens and antibodies are multivalent and antibodies

are generally bivalent

MEASUREMENT OF ANTIGEN AND

ANTIBODY

Measurement Is in the term of mass or unit or titre.Antibody titre of the serum is the highest dilution of serum which shows an

observable reaction with antigen

sensitivity• The ability of test to detect even

minute quantity of antigen and antibody

• When the test is highly sensitive false negative result may be absent or minimal

specificity• ability of the test to detect homologus

antigen and antibody• In highly specific test false positive

reactions are absent or minimal.

In generally sensitivity and specificity of a test is in inverse proportion