Brief Definitive Report Influenza Virus Subtype-specific Cytotoxic T Lymphocytes Lyse Target Cells Coated with a Protein Produced in E. Coli

Virus-specific cytotoxic T cells (CTL) recognize viral antigen in conjunction with products of genes of the major histocompatibility complex (MHC) (1); however, the nature of the viral antigen(s) recognized by specific CTL is not clear, identification of viral determinant(s) recognized by CTL is an important issue; however, it has been difficult to demonstrate CTL recognition of target cells exposed to viral antigens. Previous studies (2) have indicated that the surface glycoproteins of Sendal virus were recognized by CTL, providing the fusion (F) protein was cleaved. Isolated viral surface glycoproteins were recognized on cell surfaces by CTL after incorporation into the cell membrane by liposomal carriers (3, 4), and by DNA-mediated gene transfer (5). CTL responses to internal influenza viral proteins have also been reported (6, 7). Extensive studies have been conducted (8) using influenza A virus infection as a model system, and two different subpopulations of CTL, crossreactive and subtype-specific, are induced. We previously reported (9) that an influenza virus-specific polypeptide (designated c13 protein) produced in E. coli induced H1 influenza subtype-specific memory and secondary H-2-restricted CTL responses in mice. The cl 3 protein is a hybrid protein of the first 81 amino acids of the NS1 viral nonstructural protein and the HA2 subunit of viral hemagglutinin (HA) derived using genes from an H1 N1 virus. It is, therefore, conceivable that the c l 3 protein interacts with cellular membrane to be presented to CTL precursors along with MHC products. In this study, we examined the ability of c 13 protein to render target cells susceptible to lytic activity of influenza virus-specific CTL. The results showed that target cells exposed to c 13 protein were lysed by CTL in a subtypespecific and H-2-restricted manner, suggesting that this protein interacts with target cell membrane with its hydrophobic region, and is presented on the cell membrane in proper conformation with H-2 antigens for recognition by the influenza virus subtype-specific CTL.