Lecture 12 - Part I Flashcards
What initiates the immune response for B lymphocytes?
Recognition of Ags by specific BCR on the B lymphocyte
As part of the humoral immune response, what do the progeny of the B cell clones differentiate to into?
- Plasma cells –> IgM
- Other Ig isotypes
- Affinity maturation
- Memory cells
Antigen binds to which membrane Ig isotype on mature, naive B cells? What does this binding cause?
Ag binds to IgM and IgD; activates these cells
What are the steps of B cell activation?
proliferation –> clonal expansion –> differentiation –> generation of Ab secreting plasma cells and memory B cells
One B cell could give rise to how many Ab secreting cells per week?
5000
What is heavy chain isotype switching?
when some activated B cells begin to produce Abs other than IgM and IgD
As humoral immune response develops, activated B cells produce Abs that bind to Ags with increasing affinity, progressively dominating the response, what is this called?
Affinity Maturation
What type of response is Ab response to protein Ags, that requires the help of CD4 helper T cells?
T-dependent
What type of T cell facilitates the formation of germinal centers?
Follicular helper T cells
What are germinal centers?
structures generated in secondary lymphoid organs. Several steps of T dependent humoral immune responses occur here
Steps of T dependent response:
- activated B cells differentiate into Ab secreting plasma cells
- plasma cells migrate from germinal centers (in peripheral lymphoid organs) to bone marrow (where they live for years)
- long-lived plasma cells continuously secrete Abs that provide immediate protection
Ab responses to multivalent non-protein Ags with repeating epitopes (polysaccharides, lipids, nucleic acids) that DO NOT require Ag specific helper T cells, indicate what type of response?
T independent response
T independent responses may be elicited by what?
engagement of BCR and may be potentiated by signals from other receptors on the B cells.
B cells activated by protein Ags differentiate into what type of cells?
Memory cells
Isotype switching and affinity maturation are typically seen in what type of response and in response to what?
humoral immune response; protein Ags
What types of signals drive isotype switching and affinity maturation?
T dependent signals
Primary or Secondary response? - elicited when the same Ag stimulates B cells, leading to production of greater quantities of specific Abs.
Seconary response
Primary or Secondary response? - Naive B cells stimulated by Ag become activated, then differentiate into Ab secreting cells that produce Abs specific for eliciting Ag.
Primary response
__________ B cells respond to protein Ags; and initiate ____________ Ab responses.
Follicular; T-dependent
T independent responses to multivalent Ags are mediated by what?
marginal zone B cells in the spleen, and B-1 cells in mucosal sites
What has to occur to initiate an Ab response?
Ags have to be captured and transported to the B cell areas of lymphoid organs
What are most naive B cells? What is another name for them?
follicular B cells (aka recirculating cells)
What tissues do follicular B cells migrate into the B cell zones of these tissues?
secondary lymphoid tissues
What chemokine guides the movement into lymphoid follicles, and what secretes this chemokine?
CXCL13; secreted by follicular DCs
What does chemokine CXCL13 do?
attracts naive B cells into the follicles
How are most Ags transported to lymph?
via lymphatic vessels that drain into subcapsular sinus of the LNs
Soluble Ags reach B cell zone of follicle and do what?
interact directly with specific B cells
Microbes and Ag-Ab complexes are captured by what?
subcapsular sinus macrophages (deliver Ags to follicles)
What is captured by resident DCs and transported into follicles, thus activating B cells?
Large Ags
