IMMUNE CD4(-CELLS PROMOTE THE CLEARANCE OF INFLUENZA-VIRUS FROM MAJORHISTOCOMPATIBILITY COMPLEX CLASS-II -() T)- RESPIRATORY EPITHELIUM/

The experiments described establish that CD4(+) T-cell-dependent effec tor mechanisms can eliminate an H3N2 influenza A virus from lung cells that are unable to express class II major histocompatibility complex (MHC) glycoproteins. Radiation chimeras were made by using CD4+ T cell s and bone marrow from CD8-depleted, MHC class II +/+ mice and irradia ted (950 rads) MHC class II -/- recipients. The influenza virus-specif ic CD4(+) T-cell responses in these +/+-->-/- mice were not obviously different from those in the +/+-->+/+ controls: the cytokine profiles, the spectra of plasma cells producing the various immunoglobulin isot ypes, and the frequencies of virus-specific CD4(+) T cells were simila r for the two groups. Expression of class II MHC glycoproteins on stim ulator cells, B lymphocytes, and monocytes/macrophages is apparently s ufficient for CD4(+) T cells to terminate influenza virus infection of MHC class II -/- respiratory epithelium. A possible explanation is th at the local spread of this lytic virus in the lung is limited by cyto kines and/or antibody.