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ANTIGEN
Antigen:-These are the substance which when entered inside host produces antibodies with
which they react specifically in an observable manner
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Immunogen:- substance which stimulates immune response when entered inside body
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Antigenicity:- The property of eliciting production of Abs and reacting specifically in an
observable manner
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Attributes if antigen:i
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ii
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Types of antigen:i
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Hapten:-they can react with specific Abs but cannot produce immune
response(Once they combine with larger molecule carrier they are
immunogenic)
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complex(precipitating)(polyvalent)
ii
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Epitope are two types:
i
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Conformational
T cell recognizes linear eiptope while B cell recognize Conformational epitope
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Some of the LMW antigens non antigenic but if they are absorbed in large molecular
weight substance (like-bentonite and kaolin) they render Antigenicity
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They are like haptens
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The Antigenicity depends on diversity of antigens
For ex:- Proteins are more antigenic than polysaccharides as they are made up of 20 aa
while polysaccharides are made up of 4 or 5 monosaccharide’s
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Susceptible to tissue enzyme: The antigens which are susceptible to tissue enzymes are
antigenic
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Those

which are not susceptible to enzymatic degradation are not antigenic and even those who do
quickly
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Foreignness: Antigens which are foreign only induce immune response
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Antigenic specificity: The ability of host cell to recognize specific antigen
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(cross reactions occurs depending on
there resemblance of stereochemical nature
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Species specificity-All individual of a species have species specific antigen
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There immunological
reaction follows phylogenetic relation
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Ex- When an individual is sensitized by horse serum it shows
hypersensitivity reaction to other equine serum but not bovine serum
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Iso specificity-These antigens are present in some but not all individual of
species
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Ex- human erythrocyte antigen
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3
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Ex; Eye lens protein, Sperm
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Organ specificity-Some of the tissue antigens are present in different
species
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ExBrain Kidney And Lens protein
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Heterogenic Specificity;-some of the antigens are present in different species, class,
family kingdoms and phylum
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They are absent in rabbit so they are used to prepare antibodies
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For ex- Weil Felix test (Typhus Fever) PaulBunnel Test (Infectious mononucleosis) cold Agglutination test (atypical Pneumonia)
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T cell dependent(TD)
2
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They need to be mediated by T cell
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This MHCII receptor causes T cell to differentiate into T(h) cells
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It interact with CD40 receptor on B cell to
produce Ab
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They interact
with BCRs of innate immunity
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Type 1- Directly mitogenic and cause polyclonal B cell activation
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Type 2- They activate B cell to generate Abs with help of cytokinines and also activate
complement system
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[These are
usually lipids sugar and nucleic acid]
Superantigens- These are antigenic molecules which when introduced activates massive
number of T cells
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They have high molecular weight
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They don’t bind in the groove between  and  chains of MHCII receptor, they rather
bind lateral to  chain and V chain of TCR
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Determinant recognized by innate immune system:Adaptive immunity they recognize discrete determinants and demonstrate high degree
specificity
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These molecular patterns are pathogen associated molecular patterns
(PAMPs) and receptors are pattern recognition receptors (PRRs)
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Toll like receptors-Trans membrane receptors on macrophages and
dendritic cells
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2
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3
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