January 10, 2008
MIC519 – Immunology
Exam 2 – Redo
Toll-like receptors (TLRs) play a key role in the activation of the innate immune system.
The TLRs that are able to recognize many of the different types of pathogens and host-
derived proteins are the TLRs that are expressed mainly on macrophages and dendritic
Macrophages phagocytose debris and pathogens that enter the cell.
cells are the most potent antigen-presenting cells, inducing both naïve and memory
Macrophages and DCs are primarily involved in the innate immune
response, but they are also essential in the adaptive immune response as antigen-
presenting cells (APCs). Therefore, TLR signaling promotes activation of an innate
immune response and then triggers antigen-specific adaptive immunity (Medzhitov et al.,
1997, Kaisho et al., 2002, Akira et al., 2001, Aderm et al., 2001).
TLR signaling acts to
trigger the adaptive immune response by enhancing the expression of MHC molecules
and inducing tumor antigen-specific cytotoxic T lymphocytes (CTLs) which are
important for eliminating tumor cells. TLR signaling also increases the production of IL-
12 which is a major helper-T cell 1 (Th1)-inducing cytokine, on APCs (Kaisho et al.,
2002, Akira et al., 2001, Akira et al., 2001, Melief et al., 2002). IL-12 is one of the first
cytokines produced by macrophages during infection. The DCs matured by TLR
stimulation may induce T-cell differentiation toward a Th1 response by presenting
antigens to the T cells while promoting a Th1-leading situation in that environment.
T cell immunity to intracellular bacteria is triggered by phagocytic cells for both MHC
class I and II-restricted Ag presentation functions. These APC stimulate CD4+ T cells
specific for bacterial Ags which in turn feed back through the release of cytokines such as
IFN- to phagocytic cells harboring replicative intracellular bacteria by increasing their
bacteriostatic and bactericidal functions. Macrophages represent an APC partner for T
cells. Efficient uptake of bacteria by macrophages is mediated by various surface
molecules such as FcR. Activated macrophages are a source of IL-12 which plays a
pivotal role in host resistance to bacterial infection by stimulating IFN- production by NK
cells and by promoting Th1 responses. Dendritic cells represent the most potent APC for
priming naive T cells, an important source of IL-12 following microbial stimuli, and
consequently are highly efficient in inducing antiviral and antitumor immune responses.
(Jiao et al., 2002).
From the table, the T cells function is to detect memory effector T cells. If the
tyrosinase-specific T cells expressed high levels of CD45RA and not CD45RO, and low
levels of CD44, then the T cells that they were detecting would have been naive T cells.
MHC/peptide tetramers can be used to stain T cells in an antigen-specific manner to