Intranasal exposure to protein antigen induces immunological tolerance mediated by functionally disabled CD4+ T cells.

In this study we examined the immunological parameters underlying the natural immunity to inhaled nonpathogenic proteins. We addressed this question by examining the effect of intranasal exposure to OVA in both wild-type mice and mice reconstituted with OVA-TCR transgenic CD4+ T cells. Intranasal administration of OVA induced an initial phase of activation during which CD4+ T cells were capable of proliferating and producing cytokines. Although many of the OVA-specific CD4+ T cells were subsequently depleted from the lymphoid organs, a stable population of such T cells survived but remained refractory to antigenic rechallenge. The unresponsive state was not associated with immune deviation due to selective secretion of Th1- or Th2-type cytokines, and the presence of regulatory CD8+ T cells was not required. Moreover, neutralization of the immunosuppressive cytokines IL-10 and TGF-beta did not abrogate the induction of tolerance. Inhibition of the interaction of T cells with CD86, but not CD80, at the time of exposure to intranasal Ag prevented the development of unresponsiveness, while selective blockade of CTLA-4 had no effect. Our results suggest that intranasal exposure to Ags results in immunological tolerance mediated by functionally impaired CD4+ T cells via a costimulatory pathway that requires CD86.