Effect of measles virus infection on MHC class II expression and antigen presentation in human monocytes.

We studied the effect of measles virus (MV) infection on the expression of MHC class II molecules and on the antigen-presenting function in human peripheral blood monocytes in vitro. The expression of HLA-DR, -DQ, and -DP molecules was up to 10-fold higher in MV-infected than that in uninfected monocytes. This effect did not change upon stimulation of monocytes with LPS, and was not mediated by IFN-gamma. In contrast to results obtained with peripheral monocytes, MV infection in a human monocytic cell line, THP-1, did not enhance the basic MHC class II expression, but strongly inhibited the IFN-gamma-induced expression. High levels of MHC class II expression in MV-infected monocytes were associated with capacity to present MV antigens, but the capacity to present unrelated antigens was strongly reduced. These results indicate how MV infection in monocytes may suppress the antigen-mediated T cell proliferation, still allowing the expansion of MV-specific T cell clones.