Concanamycin B inhibits the expression of newly-synthesized MHC class II molecules on the cell surface.

We screened natural chemical compounds which inhibit the expression of newly-synthesized MHC class II molecules on the cell surface. IFN-gamma stimulates Colo 205 adenocarcinoma cells to induce the expression of MHC class I, MHC class II, and ICAM-1 molecules on the cell surface. We show here that concanamycin B inhibits the expression of MHC class II molecules on Colo 205 cells, whereas it does not affect the expression of MHC class I and ICAM-1 molecules. Concanamycin B also abrogates the enhancement of the MHC class II expression by IL-4 on mouse lymphocytes. Furthermore, concanamycin B suppresses the antigen presentation by MHC class II molecules.