HLA class II-restricted presentation of cytoplasmic measles virus antigens to cytotoxic T cells.

To analyze the nature of the HLA class II-restricted cytotoxic T-lymphocyte (CTL) response to measles virus, murine fibroblasts were transfected with expressible cDNA clones for human HLA-DR antigen and for measles virus matrix or nucleocapsid proteins. DR-positive murine fibroblasts transfected with measles virus matrix or nucleocapsid genes were lysed by class II-restricted measles virus-specific CTL lines. Lysis was as efficient as with infected autologous B-cell lines, even though the measles virus cytoplasmic proteins were undetectable by antibodies in the transfected target cells. These results demonstrate that cytoplasmic viral antigens can be presented to CTL in the context of HLA class II antigens and that measles virus matrix and nucleocapsid proteins contribute to class II-restricted measles virus-specific CTL responses. These results also show that endogenously synthesized measles virus proteins can be efficiently presented by class II antigens. The implications of these findings for measles virus pathogenesis and for antigen processing are discussed.