Humoral Immunity Flashcards
What is the difference between the recognition phase and effector phase of humoral immunity?
The recognition phase involves the identification of antigens via membrane-bound immunoglobulins (IgM and IgD) on the surface of the naive B cell. The effector phase is characterized by secretion of immunoglobulins from plasma cells (ie, mature B cells).
A primary response is generated when an antigen is first encountered. Second, exposure to that same ag is known as the secondary response. What are key differences between primary and secondary responses? What accounts for these differences?
The primary response has a longer lag period (time until ab is produced) and is typically characterized by IgM followed by low amounts of IgG. The secondary response is characterized by a faster and larger production of IgG that persists longer. These differences are due to antigen-specific memory B cells in the secondary response
What is affinity maturation?
Process that selects for B cells producing antibodies of highest affinity to an antigen of interest through successive exposure to that antigen in the periphery
What genetic process drives affinity maturation?
Somatic hypermutation results in random and rapid point mutations in variable gene segments of V(D)J genes, modifying the affinity of a B cell’s immunoglobulin. The B cells expressing immunoglobulins with highest affiities are then selected through interaction with antigen
What is the name of the process by which immature B cells expressing immunoglobulins with a high affinity for self-antigens are restricted from becoming mature?
Negative selection. An analogous process occurs with T cells
What type of cell stimulates B-cell clonal expansion, isotype switching, affinity maturation, and differentiation into memory B cells?
Helper T cells (CD4+/CD8-)
What are the two types of cells that may become activated B cells?
- Plasma cells, which are responsible for secretion of abs
- Memory B cells, which undergo affinity maturation and may differentiate into plasma cells upon reexposure to the antigen
Will a single antigen with a single epitope activate a B cell?
No. B-cell activation is dependent on the cross-linking of membrane bound IgM and IgD, which requires more than one epitope. (This is true of most ags but there are plenty of examples of monomeric soluble protein ags where cross linking is not required and T cells helps overcome this requirement)
How do B-cell and T cell receptors differ with respect to the native form (ie, three dimensional shape) of the antigen?
T-cell receptors recognize only a linear peptide sequence that results from processing within an ag-presenting cell (APC). The B-cell receptors can recognize the native form of the antigen.
B-cell proliferation, early ab secretion, and isotype switching occur in which area of the lymphoid follicle?
These early phase, T cell dependent responses occur in the marginal zone
B cell affinity maturation and isotype switching occur in which area of the lymphoid follicle?
These late phase events occur in the germinal centers. Isotype switching can occur in the early or late phases and in two separate locations
What processes result from interaction of CD40 on B cells with CD40L on T cells?
Isotype switching, B cell activation, and affinity maturation. The T-cell cytokines also play a role in these processes
The Th2 subset of T cells, which produce IL4 cause B cell expression of what isotype?
IgE
TGF-beta causes B-cell expression of what isotype?
IgA
What cytokine expressed by T cells also causes isotype switching to IgA?
IL-5
