Chapter 11 Flashcards
In humoral immune responses, B lymphocytes are
activated by what?
antigen and secrete antibodies that act
to eliminate the antigen. Both protein and nonprotein antigens can stimulate antibody responses.
B cell responses to protein antigens require the
contribution of CD4+
helper T cells specific for the
antigen
Helper T cell–dependent B cell responses to protein
antigens require initial activation of naive T cells
in the T cell zones and of B cells in lymphoid follicles in lymphoid organs. The activated lymphocytes migrate toward where?
toward one another and interact at
the edges of follicles, where the B cells present the
antigen to helper T cells
Activated helper T cells express CD40L, which
engages what?
CD40 on the B cells, and the T cells secrete
cytokines that bind to cytokine receptors on the B
cells. The combination of CD40 and cytokine
signals stimulates initial B cell proliferation and
differentiation
Stimulation of activated B cells at extrafollicular
sites by helper T cells leads to what?
the formation of
extrafollicular foci where some isotype switching
occurs and short-lived plasma cells are generated
Some activated helper T cells differentiate into
specialized TFH cells that express high levels of what?
ICOS and CXCR5 and secrete IL-21. TFH cells and
activated B cells migrate into the follicle, and TFH
cells activate these specific B cells to initiate the
268 Chapter 11 – B Cell Activation and Antibody Production
formation of germinal centers
The late events in
T cell–dependent antibody responses, including what other events?
extensive isotype switching, somatic mutation,
affinity maturation, generation of memory B cells,
and induction of long-lived plasma cells, take place
within germinal centers
Helper T cell–derived signals, including CD40L and
cytokines, induce what?
isotype switching in B cells by a
process of switch recombination, leading to the
production of various Ig isotypes.
Isotype switching requires the induction of what?
AID, a cytidine deaminase that converts cytosine to uracil in
single-stranded DNA, and different cytokines
allow AID to access distinct downstream heavy
chain loci
Affinity maturation occurs in germinal centers and
leads to what?
increased affinity of antibodies during the
course of a T cell–dependent humoral response
Affinity maturation is a result of somatic mutation
of what?
Ig heavy and light chain genes induced by AID,
followed by selective survival of the B cells that
produce the high-affinity antibodies and bind to
antigen displayed by FDCs in the germinal centers.
TFH cells also participate in selection of high-affinity
B cells
Some of the progeny of germinal center B cells
differentiate into what?
antibody-secreting plasma cells
that migrate to the bone marrow. Other progeny
become memory B cells that live for long periods,
recirculate between lymph nodes and spleen, and
respond rapidly to subsequent exposures to antigen
by differentiating into high-affinity antibody secretors.
The differentiation of activated B cells into
plasma cells or memory cells is controlled by what?
the
expression of various transcription factors.
TI antigens are generally what?
nonprotein antigens that
induce humoral immune responses without the
involvement of helper T cells
Many TI antigens,
including polysaccharides, membrane glycolipids,
and nucleic acids, are what?
multivalent, can cross-link
multiple membrane Ig molecules on a B cell, and
activate complement, thereby activating the B cells
without T cell help
TLR activation on B cells by
microbial products facilitates T-independent B cell
activation. TI antigens stimulate antibody responses
in which there is limited what?
limited heavy chain class switching, affinity maturation, or memory B cell generation because these features are largely dependent on helper T cells, which are not activated by nonprotein antigens
