T Cell Subsets Flashcards
What do T cells do in the lymph node
In the cortex, T cells monitor antigen presented by macorphages and dendritic cells
T cells that do not encounter specific antigen leave lymph node through the lymphatics
T cells that encounter antigen proliferate into effector cells
What are CCR7 and L selectin and what they do
cell adhesion molecules, trafficking of naive T cells into lymphoid organs
What does ICAM-1 and LFA-1 do
ICAM 1 is n APC, LFA 1 on T cell, they stabilise the interaction and prolong cell-cell conntact during antigen presentation
What is costimulation? What is the physiologic significance of costimulation? What are
some of the ligand-receptor pairs involved in costimulation?
Costimulation refers to signals delivered to a lymphocyte that are required for
lymphocyte activation but are independent of antigen receptor signalling.
Costimulatory signals are commonly referred to as a “second signal” and provide
lymphocytes with the information that the antigen they are recognizing may be of
microbial (or foreign) origin. B7-1 and B7-2 are the major costimulators on antigenpresenting cells, which bind to CD28 on T cells.
What are some of the molecules in addition to the TCR that T cells use to initiate their
responses to antigens, and what are the functions of these molecules?
Molecules other than the TCR used by T cells to respond to antigens include the CD4
and CD8 coreceptors, which bind to class II and class I MHC molecules, respectively;
costimulatory receptors such as CD28, which bind to costimulators expressed on
activated APCs; and adhesion molecules such as the integrin LFA-1, which mediate Tcell adhesion to APCs and also control the migration of the T cells.
What is the principal growth factor for T cells? Why do antigen-specific T cells expand
more than other (bystander) T cells on exposure to an antigen?
The major growth factor for T cells is interleukin-2 (IL-2). It is produced by T cells in
response to antigen receptor signals and costimulation. T cells that have recognized
antigens express increased levels of receptors for IL-2 and thus preferentially respond
to the growth factor during immune responses to the antigens.
Why do naive T cells migrate preferentially to lymphoid organs and differentiated
effector T cells migrate preferentially to tissues that are sites of infection?
Naive T cells express the adhesion molecule L-selectin and the chemokine receptor
CCR7, which mediate homing to lymph nodes. Differentiated effector cells lose
expression of these molecules and instead express adhesion molecules that bind to
molecules on endothelium exposed to inflammatory cytokines. The effector cells also
express receptors for chemokines produced at sites of inflammation, thus preferentially
migrating to these sites.
What are the mechanisms by which T cells activate macrophages, and what are the
responses of macrophages that result in the killing of ingested microbes?
Activated Th1 cells secrete cytokines such as interferon-gamma that activate
macrophages. These helper T cells also express CD40 ligand, which can activate
macrophages by engaging CD40. Activated macrophages generate reactive oxygen
species and make nitric oxide. These free radicals can destroy ingested microbes.
Activated macrophages also produce increased amounts of lysosomal enzymes, which
help to destroy microbes, and other molecules that promote inflammation and recruit
more leukocytes into the reaction.
How do CD8+ CTLs kill cells that are infected with viruses?
CD8+ T cells that recognize antigen on an infected tissue cell release granules that
contain perforin and granzymes, which enter the infected cells recognized by the T
lymphocytes and induce apoptosis of these infected cells. They can also express FasL
to induce apoptosis of the infected cells through Fas-FasL interaction.
Function of Th2
Produce:
IL4 and IL13 which act on B cells to stimulate production of IgE
IL5 activates eosinophils
Function of Th17
Produce: IL17 which induces production of chemokines and other cytokines which recruit neutrophils to site of inflammation
