Brefeldin A specifically inhibits presentation of protein antigens to cytotoxic T lymphocytes.

Cytotoxic T lymphocytes (CTLs) recognize foreign antigens, including viral proteins, in association with major histocompatibility complex (MHC) class I molecules. Brefeldin A, a specific inhibitor of exocytosis, completely and reversibly inhibited the presentation of viral proteins, but not exogenous peptides, to MHC class I-restricted CTLs directed against influenza virus antigens. The effect of brefeldin A on antigen presentation correlated with its inhibition of intracellular transport of newly synthesized class I molecules. Brefeldin A is thus a specific inhibitor of antigen processing for class I-restricted T cell recognition. Its effect on antigen presentation supports the idea that exogenous peptide antigens associate with cell surface class I molecules, whereas protein antigens processed via the cytosolic route associate with nascent class I molecules before they leave the trans-Golgi complex.