Antigens Flashcards
Describe the definition of antigen.
-antibody generator
-induce immune response when in body
-molecules that bind to antibodies, MHC, or lymphocyte receptors (TCR/BCR)
Describe the two subcategories of antigens.
- immunogens
-can stimulate immune response - haptens
-cant by themself stimulate immune response but can when complexed w larger molecule like a host protein
Describe immunogenicity & antigenicity in antigens.
- immunogenicity
-antigens that induce immune response in form of T cell, B cell, antibodies - antigenicity
-antigens that bind products of immune response (ex. lymphocyte or Ab)
Describe epitope/antigenic determinant.
-part of antigen that induces immune response & binds to products of immune response
EX: proteins, polysaccharide, antibody
Describe the sources of antigens.
- infectious (microbial - foreign)
-bacteria
-virus
>structural antigen - structure of virus (envelope etc)
>nonstructural antigen - proteins that virus makes when infects cell (uses host system to make their own structures)
-parasite (each stage of development has diff antigen)
-fungi - altered self antigen
-tumors (from host)
Describe non-microbial antigens.
-venom
-bugs
-food
-cat dander
-cell surface antigens (blood type, MHC class)
Describe the factors affecting immunogenicity of antigens.
- Foreigness = non self is immunogenic
- Size = larger antigen -> more immunogenic
- Chemical composition = complex usually immunogenic (diverse epitopes)
- Physical properties
>particulate antigens - more immunogenic than soluble antigens
>denatured antigens - more immunogenic than native forms (more epitopes) - Degradability = antigens easily degraded more immunogenic
- Genetic factors = some antigens more immunogenic than other species
- Age = young/old less capable to have immune response than middle with the same antigen
Describe the chemical nature of antigens and their immunogenicity.
- Proteins = largest group of antigens that are mostly immunogenic
- Polysaccharides = good immunogens
- Nucleic acids = weak antigens may be immunogenic when conjugated to proteins
- Lipids = not immunogenic (some can be haptens)
Define adjuvant.
Substance that enhances body’s immune response to antigen
-acts as irritant
-recruits macrophages & dendritic cells at site
Describe T-independent antigens.
-antigens that directly stimulate B lymphocytes to make antibodies without the need of T helper cells
-ex: lipopolisaccharides
Describe the properties of T-independent antigens.
-polymeric structure with the same antigenic determinant repeats
-activate lymphocytes polyclonally
-resistant to degradation
Describe T-dependent antigens.
-antigens that indirectly stimulate B lymphocytes to make antibodies
-presence of T helper cells
-proteins mostly T-dependent
-contain few copies of various antigenic determinants
Describe superantigens.
-superantigens can activate lg # of lymphocytes at once non specifically
>derived from bacteria/virus
>bind to variable domain of B chain in TCR or CD4+ T cells & a chain of MHC class II on APCs
>binding of superantigen to TCR & MHC II = signal that activates T cells polyclonally
—polyclonal activation of T helper lymphocytes = production of IL1, IL2, Il6, TNFa, MIP1a, MIP1B (systemic toxicity via inflammation)
Describe haptens.
-nonimmunogenic substance like penicilloyl
-cant induce immune response unless conjugated to carrier like a protein
-incomplete antigens
Describe autoantigens.
-natural self/host antigens
-autoimmunity
