Protection from respiratory virus infections can be mediated by antigen-specific CD4+ T cells that persist in the lungs

Abstract

Although CD4+ T cells have been shown to mediate protective cellular immunity against respiratory virus infections, the underlying mechanisms are poorly understood. For example, although phenotypically distinct populations of memory CD4+ T cells have been identified in different secondary lymphoid tissues, it is not known which subpopulations mediate protective cellular immunity. In this report, we demonstrate that virus-specific CD4+ T cells persist in the lung tissues and airways for several months after Sendai virus infection of C57BL/6 mice. A large proportion of these cells possess a highly activated phenotype (CD44hi, CD62Llo, CD43hi, and CD25hi) and express immediate effector function as indicated by the production of interferon γ after a 5-h restimulation in vitro. Furthermore, intratracheal adoptive transfer of lung memory cells into β2m-deficient mice demonstrated that lung-resident virus-specific CD4+ T cells mediated a substantial degree of protection against secondary virus infection. Taken together, these data demonstrate that activated memory CD4+ T cells persisting at mucosal sites play a critical role in mediating protective cellular immunity.