antigens Flashcards
how was the word antigen come about
it was a combination of the words antibody and generator
what are antigens
- antigens are molecules or pieces of molecules that bind to antibodies, MHC molecules or TCRs
- Molecules that induce an immune response when introduced into the body
what are the two sub categories of antigens
- immunogens
- haptens
what are immunogens
immunogens are a substance capable of stimulating an immune response
what are haptens
haptens are substances that will not by themselves stimulate an immune response but can do so when complexed with a larger molecules, such as a host protein
what are the two cardinal features of antigens
- Immunogenicity
- antigenicity
what is immunogenicity
antigens are capable of inducing an immune response (t cells, B cells - Ab)
What is antigenicity
antigenicity is when antigens are capable of binding with products of the immune response that they induced (i.e., Lymphocytes or antibodies)
What are the functions of Epitope or antigenic determinant
Epitope or antigenic determinant is a part of an antigen that is actually responsible for inducing the immune response and binding to the products of the immune response (lymphocyte receptors and antibodies)
what are the sources of antigens
- Infectious agents such as (microbial antigens)
- bacteria
- viruses
- parasites
- Fungi
- Altered self-antigens
- Tumors
what are the factors that affect the immunogenicity of antigens
- Foreignness
- size
- chemical composition
- Physical properties
- Degradability
- genetic factors
- age
How does Foreignness affect the immunogenicity of antigens
The immune system distinguishes between self and non-self and only self substances are immunogenic and induce immune response (with exceptions)
How does size affect the immunogenicity of antigens
there is no absolute size at which antigens become more immunogenic, however, the larger the antigen the more immunogenic is can be
How does chemical composition affect the immunogenicity of antigens
complex molecules are usually immunogenic (chance of diverse antigenic determinants)
what are the two physical properties that affect immunogenicity of antigens
- Particulate antigens
- are more immunogenic than soluble antigens
- Denatured antigens
- are more immunogenic than native forms (denaturation exposes more antigenic determinants)
How does Degradability affect the immunogenicity of antigens
antigens that are phagocytosed and easily degraded are usually highly immunogenic
How does Genetic factors affect the immunogenicity of antigens
- some antigens are more immunogenic for a given species than for the other. Similarly, some antigens are more immunogenic for an individual than the other
- species or individuals may have genetic variations in genes encoding antigen receptors or both T or B cells
How does age affect the immunogenicity of antigens
young or old individuals usually have less capability to mount an immune response compared to the middle-aged in relation to the same antigen
what are the chemical nature of antigens we are concerned with
- Proteins
- by far the largest group of antigens
- polysaccharides
- Nucleic acids
- Lipids
how do the proteins affect the chemical nature of antigens
most proteins are highly immunogenic (pure proteins, glycoproteins or lipoproteins)
how do the polysaccharides affect the chemical nature of antigens
pure polysaccharides and lipopolysaccharides are usually good immunogens (pneumococcal polysaccharides may require conjunction)
how do the nucleic acids affect the chemical nature of antigens
weak antigens may become highly immunogenic when conjugated to proteins
how do the Lipids affect the chemical nature of antigens
generally not immunogenic but some may be heptanes
what are adjuvants
a substance that enhances the body’s immune response to an antigen
