Glycosylation of native MHC class Ia molecules is required for recognition by allogeneic cytotoxic T lymphocytes.

The question whether or not target cell N-linked carbohydrate participates in cytotoxic T lymphocyte (CTL) mediated cytolysis has been in contention for well over a decade. Much of the evidence supporting a role for N-linked carbohydrate stems from the treatment of target cells with the glycosylation inhibitor tunicamycin (TM). In this report, we show that treatment of targets with TM, but not other inhibitors of complex carbohydrate formation (swainsonine, 1-deoxynojirimycin, and 1-deoxymannojirimycin), abrogates the lytic response. We conclude that N-linked complex carbohydrates are not absolutely required for the maturation or function of any target cell glycoconjugate directly involved in the lytic process. However, we show that TM treatment of target cells leads to the loss of an MHC class Ia epitope known to be required for T cell triggering. Further, we show that only target cells expressing class Ia molecules with functional glycosylation sequons are subject to the TM effect. From these results we conclude that while N-linked glycosylation of native MHC class Ia molecules is required for antigen presentation, the exact structural motif of the glycan is not important.