Chapter 9 Flashcards
T cell responses are initiated by signals that are
generated by TCR recognition of what?
peptide-MHC
complexes on the surface of an APC and through
signals provided at the same time by costimulators
expressed on APCs
The best-defined costimulators are members of the
B7 family, which are recognized by what?
receptors of
the CD28 family expressed on T cells. The expression of B7 costimulators on APCs is increased by
encounter with microbes, providing a mechanism
for generating optimal responses against infectious
pathogens
Some members of the CD28 family
inhibit T cell responses, and the outcome of T cell
antigen recognition is determined by what?
the balance
between engagement of activating and inhibitory
receptors of this family
T cell responses to antigen and costimulators
include changes in the expression of what?
surface molecules, synthesis of cytokines and cytokine
SUMMARY 223
receptors, cellular proliferation, and differentiation into effector and memory cells
The surface molecules whose expression is induced
on T cell activation include what?
proteins that are
involved in retention of T cells in lymphoid organs,
growth factors for cytokines, effector and regulatory molecules, and molecules that influence the
migration of the T cells
Shortly after activation, T cells produce what cytokine?
IL-2 and express high levels of the functional
IL-2 receptor. IL-2 drives the proliferation of the
cells, which can result in marked expansion of
antigen-specific clones
CD4+
helper T lymphocytes may differentiate into
specialized effector TH1 cells that secrete what?
IFN-γ,
which mediate defense against intracellular
microbes, or into TH2 cells that secrete IL-4 and
IL-5, which favor IgE- and eosinophil/mast cell–
mediated immune reactions against helminths, or
into TH17 cells, which promote inflammation and
mediate defense against extracellular fungi and
bacteria.
The differentiation of naive CD4+
T cells into
subsets is induced by what?
y cytokines produced by APCs
and by the T cells themselves. The differentiation
program is governed by transcription factors that
promote cytokine gene expression in the T cells
and epigenetic changes in cytokine gene loci,
which may be associated with stable commitment
to a particular subset
Y T cells of the CD8+
subset proliferate and differentiate into what?
cytotoxic T lymphocytes (CTLs), which
express cytotoxic granules and can kill infected
cells.
Some activated T cells may differentiate into
memory cells, which survive for long periods and
respond rapidly to antigen challenge. The maintenance of memory cells is dependent on what?
cytokines
such as IL-7, which may promote the expression
of antiapoptotic proteins and stimulate low-level
cycling. Memory T cells are heterogeneous and
consist of populations that differ in migration
properties and functional responses.
