Activated antigen-specific CD8(+) T cells persist in the lungs following recovery from respiratory virus infections

The poor correlation between cellular immunity to respiratory virus infecti ons and the numbers of memory CD8(+) T cells in the secondary lymphoid orga ns suggests that there may be additional reservoirs of T cell memory to thi s class of infection. Here we identify a substantial population of Ag-speci fic T cells in the lung that persist for several months after recovery from an influenza or Sendai virus infection. These cells are present in high nu mbers in both the airways and lung parenchyma and fan be distinguished from memory cell populations in the spleen and peripheral lymph nodes in terms of the relative frequencies among CD8(+) T cells, activation status, and ki netics of persistence. In addition, these cells are functional in terms of their ability to proliferate, express cytolytic activity, and secrete cytok ines, although they do not express constitutive cytolytic activity. Adoptiv e transfer experiments demonstrated that the long-term establishment of act ivated T cells in the lung did not require infection in the lung by a patho gen carrying the inducing Ag, The kinetics of persistence of Ag-specific CD 8(+) T cells in the lung suggests that they play a key role in protective c ellular immunity to respiratory virus infections.