51. Antigens - definition, characteristics, different types

Question 1

Antigen - a foreign substance that induces an immune response

Answer 1

Antigen - a foreign substance that induces an immune response

Question 2

Characteristic features of antigens:

Immunogenicity: the ability of the antigen to indue immunity, it mainly refers to infectious agents. Immunogenicity may increase at the simultaneous injection of substances, which increase the immune reaction

Antigenicity: expresses the strength of the antigen and its ability to induce a stronger or weaker immune response. Antigens are .’. characterised as strong/ weak

Specificity: antigens have active places called epitope. The epitope is the distinct molecular surface features of an antigen capable of being bound by an antibody - antigenic determinant. Specificity is the ability of the host cells to recognise an antigen specifically as a unique molecular entity and distinguish if from another with exquisite precision

Answer 2

Characteristic features of antigens:

Immunogenicity: the ability of the antigen to indue immunity, it mainly refers to infectious agents. Immunogenicity may increase at the simultaneous injection of substances, which increase the immune reaction

Antigenicity: expresses the strength of the antigen and its ability to induce a stronger or weaker immune response. Antigens are .’. characterised as strong/ weak

Specificity: antigens have active places called epitope. The epitope is the distinct molecular surface features of an antigen capable of being bound by an antibody - antigenic determinant. Specificity is the ability of the host cells to recognise an antigen specifically as a unique molecular entity and distinguish if from another with exquisite precision

Question 3

Types:

T - independant antigens

• activate B cells without MHC class II T help
• ex. pneumococcal polysaccharides
• flagella

T-dependant antigens

• require T help to activate B cells
• ex. microbial proteins

Superantigens

• polyclonal T cell response
• ex. staphylycoccal enterotoxins
• activate a large fraction of T cells in contrast to conventional T-dependant antigens

Alloantigens

• an antigen that is part of an animals self-recognition system. They are the products of polymorphic genes. ex. blood group antigens

Characteristic:

foreign origin - only foreign molecules are immunogenic

Answer 3

Types:

T - independant antigens

• activate B cells without MHC class II T help
• ex. pneumococcal polysaccharides
• flagella

T-dependant antigens

• require T help to activate B cells
• ex. microbial proteins

Superantigens

• polyclonal T cell response
• ex. staphylycoccal enterotoxins
• activate a large fraction of T cells in contrast to conventional T-dependant antigens

Alloantigens

• an antigen that is part of an animals self-recognition system. They are the products of polymorphic genes. ex. blood group antigens

Characteristic:

foreign origin - only foreign molecules are immunogenic

Question 4

Antigens are classified according to the following criteria:

• Chemical composition: the more complex a substance is, the more immunogenic it will be, proteins, semi-sugars, nucleoproteins
• Physical form: particulate > soluble, denatured > native
• Localisation: superficial - surface antigen, intracellular - internal antigen
• Origin: Autoantigen - target of humoral / cell mediated immune response Alloantigen - an antigen present only in some individuals of a particular blood group

Xenoantigen - an antigen occurring in organisms of more that one species

Immunogens include polysaccharides, nucleic acids (poorly immunogenic) and lipids (non-immunogenic) some glycollipids and phospholipids can be immunogenic for T Cells

Answer 4

Antigens are classified according to the following criteria:

• Chemical composition: the more complex a substance is, the more immunogenic it will be, proteins, semi-sugars, nucleoproteins
• Physical form: particulate > soluble, denatured > native
• Localisation: superficial - surface antigen, intracellular - internal antigen
• Origin: Autoantigen - target of humoral / cell mediated immune response Alloantigen - an antigen present only in some individuals of a particular blood group

Xenoantigen - an antigen occurring in organisms of more that one species

Immunogens include polysaccharides, nucleic acids (poorly immunogenic) and lipids (non-immunogenic) some glycollipids and phospholipids can be immunogenic for T Cells