antigen antibody reactions
TRANSCRIPT
DEFINITIONS
Antigen • Evokes specific immune response – Specific
antibody/specifically sensitised T-cells• Any foreign substance can act as an antigen
Antibody • Synthesized in response to a foreign
substance• Antibodies – Globulins – Immunoglobulins
IgG – Protects the body fluids
IgA – Protects the body surface
IgM – Protects the blood stream
IgE – Mediates reaginic
hypersensitivity
Immunoglobulin roles..
Specific Antigen
Specific Antibod
y
Antigen-Antibody reaction
Types(Serological reactions)
• Precipitation
• Agglutination
• Complement fixation test
• Immunofluorescence
• ELISA
• Highly specific• Entire molecules react,not fragment• Both participates - formation of
precipitates & agglutinates
Characteristics..(Ag-Ab)
Ag-Ab
SurfaceFirm &
Reversible
(Ag-Ab) contd..
Affinity
Avidity
Intensity of attraction between Ag-Ab
Binding strength of Ag-Ab
Ab-----Bivalent-------
Ab
Ag—multivalent—Ag
• Initial interaction• Rapid,reversible,weakPrimary
• Change in Physical state• Leads to
agglutination,precipitation etc.,Secondary
• Invivo initiate chain reactions• Leads to tissue
damage,hypersensitivityTertiary
Stages..(Ag-Ab)
Invivo
• Ab mediated immunity-Infectious diseases• Tissue injury-Hypersensitivity&Autoimmune
diseases
Invitro
• Diagnosis of Infectious & Non infectious diseases
• Epidemiological surveys
General
• Detection• Quantitation
Importance..(Ag-Ab)
Antigens/Antibodies
• Ability of test to detect even very minute quantities of Ag/Ab
Sensitivity
• Ability of test to detect reaction between homologous Ags&Abs
Selectivity
Parameters of sero reactions
PrecipitationAgglutination
Precipitation..
Precipitinogen + Precipitin Insoluble precipitate (Soluble Ag) (Ab) (Ag-Ab)
ElectrolytespH:7.4/37*c
Precipitation
Suspended as
Floccules
Flocculation
Mech.of Precipitation..(Lattice Hypothesis)
Ab-----Bivalent-------Ab Ag—multivalent—Ag
MultiMolecul
arlattice
Opt
imum
pr
opor
tion
Zone Phenomenon
Prozone Postzone
Identification
--Human blood--Seminal fluid--Bacteria--Microbial components
Detection
--Antigen--Antibody
Standardization
--Toxins--Antitoxins
Apps..
CRP test
Ring Test
VDRL-Syphilis
Slide Flocculation test
Kahn test-Syphilis
Tube flocculation test
Techniques
• Gel>specific>>sensitive>Liquid• Gel- porosity-Ag+Ab- Precipitation band
Immunodiffusion Test
Distinct for diff.Antigens
1)Identity2)Cross reaction3)Non identity between different antigens
Indications
Types..Single diffusion in one dimension(Oudin’s procedure)
Double diffusion in one dimension(Oakley-Fulthrope procedure)
Use:To determine the no. of antigens
Single diffusion in two dimensions(Radial immunodiffusion)
Uses: For quantitation of Ags & Abs
Double diffusion in two dimensions (Ouchterlony Procedure)
Use : To compare 2 Ag-Ab systems. Diagnosis of bacterial,viral,fungal,parasitic diseases. Eg:Elek’s test-Diptheria
Immunoelectrophoresis
Use:Analysis of Human serum in diseases such as Myeloma,Heavy chain disease
Countercurrent Immunoelectrophoresis
Use : Used for detection of various Ags in body fluids Diagnosis of Infectious diseases such as meningococcal,streptococcal
Rocket electrophoresis(One dimensional single
electroimmunodiffusion)
Uses : Quantitation of Proteins and other Ags in various clinical problems
Two dimensional Immunoelectrophoresis(Laurell
’s Procedure)
Uses:To detect and quantitate human serum proteins To detect abnormal proteins in various body fluids
Agglutination..
Agglutinogen + Agglutinin Ag-Ab complex (ParticulateAg) (Ab) (Agglutination)
Nacl
pH:7.4/37*c
Mechanism same as Precipitation---LATTICE HYPOTHESIS
Use:Blood grouping&Cross matching
Use:Diagnosis of Typhoid,Typhus,Brucellosi
s
Agglutination..Types
• To detect Antibodies 1)Fail to Agglutinate corresponding Antigens 2)Inhibit Agglutination
Coomb’s Antiglobulin test
Incomplete/ Blocking Abs
Direct(Invivo) Indirect(Invitro)Hemolytic disease of new born(Rh incompatibility)
To demonstrate non agglutinating Abs in Brucellosis
Indirect Coomb’s test
PrecipitationAgglutination
Coating soluble Ag onto surface of
Carrier molecule
Instead of Ag-----Ab=Reverse Passive Agglutination
Passive Agglutination tests
Ag Adsorbed Latex(milk)
Latex Agglutination test
Specific Ab
Milky white liquid
Coarse suspensi
on of granules
Haemagglutination test
Eg:Treponema pallidium haemagglutination test for serodiagnosis of Syphilis
Coagglutination test
Uses:Detection of bacterial Ags in blood,CSF in pneumococcal,gonococcal infections etc.,
Tq…u…..
by S.Vigneshwaran