Influenza virus infection of mouse lymphoblasts alters the binding affinity of anti‐H‐2 antibody: Requirement for viral neuraminidase

The requirement for histocompatibility in the T lymphocyte killing of virus‐infected cells has led us to investigate the effect of influenza virus infection on mouse cell surface histocompatibility (H‐2) antigens. Monoclonal anti‐H‐2 antibody made it possible to develop equilibrium binding conditions for the assay of H‐2 antigen‐antibody interactions on intact cells. Scatchard analysis of anti‐H‐2 binding with normal and virus‐infected cells yielded linear curves indicating homogeneity of the interaction at varied concentrations of antibody through saturating levels. The estimated number of 2 × 105 ‐ 5 × 105 H‐2 antigenic sites per mouse lymphoblast does not appear to change during the course of influenza virus infection. However, the Ka (binding affinity constant) of anti‐H‐2 binding is rapidly elevated by virus infection (“0” time), continues to increase for 3 h post infection, then decreases. Control cells, treated with normal egg allantoic fluid, show no change in Ka during similar incubation. This change in Ka requires the presence of active viral neuraminidase. Thermal denaturation of the neuraminidase of the virus particles abolishes their ability to induce Ka alteration, even though hemagglutinin activity is retained. Treatment of cells with neuraminidase of bacterial origin led to an elevation of Ka, but did not mimic the viral effect in time dependence and magnitude of peak responses. The time‐dependent lowering of Ka from peak values appeared to relate to virus replication, since UV light‐inactivated virus‐induced Ka elevation, but did not produce the typical Ka decline at 4‐5 h post infection. The changes in Ka of anti‐H‐2 binding during influenza infection reflects a virus‐ induced alteration of the H‐2 molecule or its environment in the host cell membrane. The molecular basis of this change and its relation to H‐2‐restricted recognition of influenza virus‐infected cells by cytotoxic T cells requires further study.