Immunologic recognition of influenza virus-infected cells. II. Expression of influenza A matrix protein on the infected cell surface and its role in recognition by cross-reactive cytotoxic T cells

Two distinct subpopulations of cytotoxic T cells are generated in the primary or secondary response of mice to type A influenza viruses. One subpopulation is specific for the immunizing virus strain. The other subpopulation shows a high degree of cross-reactivity for heterologous type A virus of a different subtype. This report examines the possibility that distinct influenza virus antigens, expressed on the surface of the infected cell, are recognized by the different subpopulations of influenza-specific cytotoxic T cells. Data are presented which demonstrate that influenza A matrix protein, an internal virion antigen, is detectable on the surface of target cells infected with influenza A viruses of different subtypes. Since this viral antigen is type specific, i.e., serologically cross-reactive among all type A influenza viruses, it could serve as the target for cross-reactive cytotoxic T cells. To further examine the specificity of the two cytotoxic T-cell subpopulations, experiments were carried out by using the inhibitor of glycoprotein synthesis - 2-Deoxy-D-Glucose 2-DG. These experiments examine first the effect of 2-DG on the expression of influenza matrix protein and viral glycoprotein on the infected cell surface and second, the susceptibility of 2-DG-treated target cells to lysis by cytotoxic T cells. 2-DG inhibits the expression of the viral hemagglutinin glycoprotein on the cell surface but does not inhibit the expression of the nonglycosylated matrix protein. Furthermore, inhibition of glycoprotein synthesis in infected target cells abrogates the reactivity of infected target cells to lysis by virus strain-specific but not cross- reactive cytotoxic T cells. These findings suggest that the influenza glycoproteins (hemagglutinin and/or neuraminidase) and the nonglycosylated matrix protein are the targets for the virus strain- specific and cross-reactive cytotoxic T cells, respectively. These results are discussed in the light of available information on influenza virus structure and the biology of influenza infection and in terms of current models for cytotoxic T-cell recognition of virus-infected cells.