An antigen is a substance which, when introduced into a body evokes immune response to produce a specific antibody with which is reacts in an observable manner.
Types of Antigen
Antigen can be classified as "Complete" And "Haptens/Incomplete Antigen"
These substances which can induce antibody formation by themselves and can react specifically with these antibodies
Haptens are substance unable to induce antibody formation on its own but can become immunogenic (capable of inducing antibodies) when covalently linked to proteins, called carrier proteins. However Haptens can react specifically with induced antibodies.
These antibodies are produced not only aganist the hapten but also aganist the carrier protein.
Complex Haptens are produced not only aganist the Haptens antibodies to from precipitates, example capsular polysaccharide of pneumococci.
Simple Haptens combined with specific antibodies but no precipitate is produced. This is due to univalent character of simple Haptens, whereas complex Haptens are polyvalent.
Proantigens are low molecular weight substance which do not induce antibody formation but can cause delayed hypersensitivity reaction, example: dinitrocholro-benzene (DNCB).
Antigenic determinant (epitope) is the smallest unit of antigenicity. Antigen possesses a number of these determinants. Each type of determinant induces a specific antibody formation.
The same or closely related antigens present in different tissues of more than one specific are known as heterophile Antigens.
Antibodies to those antigens produced by one specific cross react with antigens of other species.
Example included
-- Forssman antigen
Weli-Felix reaction
Serum of patients suffering from typhus fever aggulutinates strains of Proteus species. This is due to presence of heterophile antigen on Rickettsiae causing typhus fever, shared by proteins strains.
Paul Bunnel test
In infection mononucleosis, heterophile antibodies aggulutinate sheep erythrocytes. This is because Epstein Barr virus ( causative agent of infectious money nucleosis ) shares antigen with sheep erythrocytes.
Types of Antigen
Antigen can be classified as "Complete" And "Haptens/Incomplete Antigen"
I. Complete Antigen
These substances which can induce antibody formation by themselves and can react specifically with these antibodies
II. Haptens/Incomplete
Haptens are substance unable to induce antibody formation on its own but can become immunogenic (capable of inducing antibodies) when covalently linked to proteins, called carrier proteins. However Haptens can react specifically with induced antibodies.
These antibodies are produced not only aganist the hapten but also aganist the carrier protein.
Complex Haptens are produced not only aganist the Haptens antibodies to from precipitates, example capsular polysaccharide of pneumococci.
Simple Haptens combined with specific antibodies but no precipitate is produced. This is due to univalent character of simple Haptens, whereas complex Haptens are polyvalent.
Proantigens are low molecular weight substance which do not induce antibody formation but can cause delayed hypersensitivity reaction, example: dinitrocholro-benzene (DNCB).
Antigenic determinant (epitope) is the smallest unit of antigenicity. Antigen possesses a number of these determinants. Each type of determinant induces a specific antibody formation.
Heterophile Antigens
The same or closely related antigens present in different tissues of more than one specific are known as heterophile Antigens.
Antibodies to those antigens produced by one specific cross react with antigens of other species.
Example included
-- Forssman antigen
Weli-Felix reaction
Serum of patients suffering from typhus fever aggulutinates strains of Proteus species. This is due to presence of heterophile antigen on Rickettsiae causing typhus fever, shared by proteins strains.
Paul Bunnel test
In infection mononucleosis, heterophile antibodies aggulutinate sheep erythrocytes. This is because Epstein Barr virus ( causative agent of infectious money nucleosis ) shares antigen with sheep erythrocytes.
