Download - Antigen Antibody reactions
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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
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IgG – Protects the body fluids
IgA – Protects the body surface
IgM – Protects the blood stream
IgE – Mediates reaginic
hypersensitivity
Immunoglobulin roles..
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Specific Antigen
Specific Antibod
y
Antigen-Antibody reaction
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Types(Serological reactions)
• Precipitation
• Agglutination
• Complement fixation test
• Immunofluorescence
• ELISA
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• Highly specific• Entire molecules react,not fragment• Both participates - formation of
precipitates & agglutinates
Characteristics..(Ag-Ab)
Ag-Ab
SurfaceFirm &
Reversible
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(Ag-Ab) contd..
Affinity
Avidity
Intensity of attraction between Ag-Ab
Binding strength of Ag-Ab
Ab-----Bivalent-------
Ab
Ag—multivalent—Ag
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• 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)
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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
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• 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
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PrecipitationAgglutination
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Precipitation..
Precipitinogen + Precipitin Insoluble precipitate (Soluble Ag) (Ab) (Ag-Ab)
ElectrolytespH:7.4/37*c
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Precipitation
Suspended as
Floccules
Flocculation
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Mech.of Precipitation..(Lattice Hypothesis)
Ab-----Bivalent-------Ab Ag—multivalent—Ag
MultiMolecul
arlattice
Opt
imum
pr
opor
tion
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Zone Phenomenon
Prozone Postzone
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Identification
--Human blood--Seminal fluid--Bacteria--Microbial components
Detection
--Antigen--Antibody
Standardization
--Toxins--Antitoxins
Apps..
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CRP test
Ring Test
VDRL-Syphilis
Slide Flocculation test
Kahn test-Syphilis
Tube flocculation test
Techniques
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• 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
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Types..Single diffusion in one dimension(Oudin’s procedure)
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Double diffusion in one dimension(Oakley-Fulthrope procedure)
Use:To determine the no. of antigens
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Single diffusion in two dimensions(Radial immunodiffusion)
Uses: For quantitation of Ags & Abs
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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
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Immunoelectrophoresis
Use:Analysis of Human serum in diseases such as Myeloma,Heavy chain disease
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Countercurrent Immunoelectrophoresis
Use : Used for detection of various Ags in body fluids Diagnosis of Infectious diseases such as meningococcal,streptococcal
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Rocket electrophoresis(One dimensional single
electroimmunodiffusion)
Uses : Quantitation of Proteins and other Ags in various clinical problems
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Two dimensional Immunoelectrophoresis(Laurell
’s Procedure)
Uses:To detect and quantitate human serum proteins To detect abnormal proteins in various body fluids
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Agglutination..
Agglutinogen + Agglutinin Ag-Ab complex (ParticulateAg) (Ab) (Agglutination)
Nacl
pH:7.4/37*c
Mechanism same as Precipitation---LATTICE HYPOTHESIS
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Use:Blood grouping&Cross matching
Use:Diagnosis of Typhoid,Typhus,Brucellosi
s
Agglutination..Types
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• To detect Antibodies 1)Fail to Agglutinate corresponding Antigens 2)Inhibit Agglutination
Coomb’s Antiglobulin test
Incomplete/ Blocking Abs
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Direct(Invivo) Indirect(Invitro)Hemolytic disease of new born(Rh incompatibility)
To demonstrate non agglutinating Abs in Brucellosis
Indirect Coomb’s test
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PrecipitationAgglutination
Coating soluble Ag onto surface of
Carrier molecule
Instead of Ag-----Ab=Reverse Passive Agglutination
Passive Agglutination tests
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Ag Adsorbed Latex(milk)
Latex Agglutination test
Specific Ab
Milky white liquid
Coarse suspensi
on of granules
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Haemagglutination test
Eg:Treponema pallidium haemagglutination test for serodiagnosis of Syphilis
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Coagglutination test
Uses:Detection of bacterial Ags in blood,CSF in pneumococcal,gonococcal infections etc.,
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Tq…u…..
by S.Vigneshwaran