LAUSR

Both respiratory syncytial virus (RSV) and influenza A virus (IAV) may infect human peripheral blood mononuclear leukocytes (PBMC) during the immune response to viral challenge as the cells are recruited to the respiratory tract. The current studies demonstrated differences in PBMC responses to the two viruses very early after exposure, including reduced fos protein and CD69 expression and IL‐2 production by RSV‐exposed T lymphocytes. Exposure to RSV resulted in reduced lymphocyte proliferation despite evidence of a virus‐specific T lymphocyte frequency equivalent to that for influenza virus. Reduced RSV‐induced proliferation was not due to apoptosis, which was itself reduced relative to that of influenza virus‐exposed T lymphocytes. The data indicate that differential immune responses to RSV and influenza virus are determined early after exposure of human PBMC and support the concept that the anamnestic immune response that might prevent clinically evident reinfection is attenuated very soon after exposure to RSV. Thus, candidate RSV vaccines should be expected to reduce but not prevent clinical illness upon subsequent infection by RSV. Furthermore, effective therapeutic agents for RSV are likely to be needed, especially for high‐risk populations, even after vaccine development.