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Antigen processing and presentation: modulation by innate immune signals
A selection of talks on Immunology & Inflammation
Lymphocyte homing: getting lymphocytes to the right place at the right time
- Prof. Ann Ager
- Cardiff University, UK
This is a talk on antigen processing and presentation, and in particular how it's regulated by innate immune signals. And it's given by Colin Watts from the University of Dundee.
Antigen presentation refers to the display of short process peptides on so-called MHC, or major histocompatibility complex molecules. Seen here is a class I MHC molecule with the short 8-residue peptide found in a peptide binding groove. Class I MHC molecules generally have peptides between 8 and 10 amino acid residues. Whereas class II MHC molecules display considerably longer peptides due to a more open ended peptide-binding groove. It's the recognition of these peptide MHC complexes by the T cell antigen receptors that initiates most immune responses. We can distinguish the two classes of MHC molecule by the types of peptide they present. As simply diagrammed here, class I MHC molecules display peptides which are derived from intracellular, i.e. cytosolic or nuclear proteins, which as we'll see in a moment, become loaded in the endoplasmic reticulum and transported to the cell surface where they're recognized by CD8 T cells. Usually the outcome of recognition is killing, for example, of the virally infected or a tumor cells. In contrast, class II MHC molecules capture and display peptides derived from exogenous proteins, i.e. proteins taken up into the cell by one or more forms of endocytosis, for example, bacterial toxins like tetanus toxin. Here the endocytic pathway acts as the site for peptide loading. And then following transport to the cell's surface, the CD4 T cell can perform various functions, for example can help a B lymphocyte to differentiate and become an antibody producing cell. The two T cells seen in this slide are so-called effector T cells. They have previously been activated and are primed to perform an effector function, which was just described. But these T cells must have already been activated by a different type of antigen presenting cell. And it's clear, and as well discussed elsewhere in the series, that dendritic cells are uniquely able to prime naive T cells.