Antigen Processing: A Beginner’s Guide

Here’s a simplified overview of MHC class I antigen processing. The ultimate product of the pathway is expression of the class I major histocompatibility complex at the surface of a cell. Cytotoxic T lymphocytes recognize the complex, and can respond by destroying abnormal cells.

Here I’ve shown a virus-infected cell, but the antigen presentation pathway goes on all the time, even in normal cells. Normal (”self”) proteins are presented on MHC class I but are ignored by CTL, because self-reactive T cells are eliminated during maturation in the thymus.