Identification of the respiratory syncytial virus-induced immunosuppressive factor produced by human peripheral blood mononuclear cells in vitro as interferon-alpha.

Respiratory syncytial virus (RSV) can inhibit the proliferative response of human peripheral blood mononuclear cells (PBMC) in vitro. This inhibition is mediated by an extracellular RSV-induced factor. In the present study, the factor was clearly identified as interferon (IFN)-alpha. The RSV-induced IFN-alpha bound strongly to PBMC and inhibited the anti-RSV proliferative response only when added within the first few days of stimulation. There was, however, no concomitant decrease in the production of interleukin (IL)-2 nor in the cell surface expression of CD25, CD71, and HLA-DR. Inhibition by RSV-induced IFN-alpha was unrelated to the levels of IL-1, -2, and -6 or of IFN-gamma induced by RSV in vitro or to the presence of IL-1 inhibitor, tumor necrosis factor-alpha, prostaglandin, or IL-10. Immunosuppression by IFN-alpha may significantly affect the outcome of infection and reinfection with RSV.