Overview of Antibody-Mediated Immunity Flashcards
Describe the characteristics of mature B cells
-express IgM or IgD on cell surface
Describe the roles of the major subsets of mature B cells in antibody-mediated immunity
- antigen specificity (IgM and IgD)
- alternatively splice Ig H chain transcript C(micro) to C(delta) to allow coexpression of IgM and IgD
- recirculate thru the blood and secondary lymphoid tissues
Describe the presentation of protein antigens by B cells to helper T cells
- IgM and IgD
- BCR coreceptors
- react with T cells, more responsive to cytokines, migrate to T cell zone
Describe the key components of T cell help
1) antogen binds to membrane bound Ig
2) endocytozed
3) protein antigens broken down and peptides are displayed on MHC class II and presented to helper T cells
4) bind at edge of lymphoid follicle
- both must be specific for epitopes of same antigen (but not same epitope)
- B cell can present many MHC class II:antigen complexes at once (12 possible MHC class II’s and each bind multiple antigens)
Describe the results of T cell help for B cells, including germinal centers
- where antibody response develops fully
- intense proliferation
- Ig isotype switching
- somatic hypermutation
- affinity maturation
- generate memory B cells
- generate long-lived plasma cells
Explain the general process and significance of immunoglobulin heavy chain isotype switching
- refers to the switching of C segments (constant)
- stop codon is moved or altered
- changes the function of the B cell
Explain somatic hypermutation of immunoglobulin genes
- changes C bases to U bases at varying intervals
- results in C-G to A-T mutations
- may inactivate or increase affinity for another antigen
Explain affinity maturation of antibody responses
- B cells with highest affinity survive
- hypermutations allow trial and error of affinity for antigens
Compare and contrast the characteristics and functions of plasma cells and memory B cells
Plasma:
-long-lived antibody-secreting cells
-found in medulla of lymph nodes, splenic red oulp, and bone marrow
-terminally differentiated (no cell division; only job is to secrete antibody until it dies)
-hihghly developed secretory apparatus as it only secretes (no membrane bound antibodies)
Memory B cells:
-long-lived and slowly divide (if at all)
-only display antibodies (doesn’t secrete)
-inherit all genetic mutations from germinal center
-provide rapid, robust and high-affinity antibody response upon secondary exposure to antigen
Compare and contrast antibody responses to T cell-dependent and T cell-independent antigens
Dependent: -bind protein antigens -isotype switching -affinity maturation -produce long-lived plasma cells -make memory B cells for secondary response Independent: -bind polysaccharide antigens -isotype switching between IgM and IgG -little or no affinity maturation -produce short-lived plasma cells -for some polysaccharide antigens -- produce memory B cells for secondary response
Compare and contrast the characteristics and effector functions of the different antibody isotypes
IgM -half life of 5 days -naive B cell antigen receptor -complement activation IgD -half-life of 3 days -Naive B cell antigen receptor IgG -subtypes 1-4 -half-life of 23 days -opsonization -complement activation -ADCC -neonatal immunity -feedback inhibition of B cells IgA -subtypes 1 & 2 -half-life of 6 days mucosal immunity IgE -half-life of 2 days -defense against helminthic parasites -immediate hypersensitivity
Explain the functions of the neonatal Fc receptor in neonatal immunity
- in placenta, transports IgG from mother to baby (binds to Fc region)
- contributes of long half-life of the circulating IgG
- binds to IgG in endosomes and prevents degradation – then returns to cell surface
Explain the functions of the role of maternal IgG in neonatal immunity
-gives same range of antigen specificity to baby to help fight infections/not be immunocompromised when baby enters the world
