Fig. 4: Production of Co-stimulatory
Molecules by Antgen-Presenting Cells (APCs)
Antigen-presenting cells such as dendritic cells and macrophages can produce
both MHC-I and MHC-II molecules. MHC-I molecules with bound peptides can be
recognized by a complementary-shaped TCR/CD8 on the surface of a naive T8-lymphocyte
while MHC-II molecules with bound peptides can be recognized by a complementary-shaped
TCR/CD4 on the surface of a naive T4-lymphocyte.
This represents the first signal necessary for activation of the naive T4-
or T8-lymphocyte. Co-stimulatory signals involving the interaction
of co-stimulatory molecules such as CD40 and B7 molecules on the APC with
their corresponding ligands on the T4- or T8-lymphocyte are also necessary
for activation. These co-stimulatory molecules are only synthesized when toll-like
receptors on APCs bind to pathogen-associated molecular patterns of microbes.
This is another backup system to help assure that the TCR of the lymphocyte
is recognizing a nonself peptide and not a self peptide
on the MHC molecules of the APC. Without the interaction of the co-stimulatory
molecules, the naive T4- or T8-lymphocyte is not activated and undergoes apoptosis.
Kaiser's Microbiology Home Page
Copyright © Gary E. Kaiser
All Rights Reserved
Updated: May 2, 2005
Please send comments and inquiries to Dr.