Antigen targeting of Fc-receptors induces strong T cell responses in vivo independent of ITAM signaling but dependent on dendritic cell subsets

Dendritic cells (DCs) are important antigen presenting cells (APCs) and responsible for the induction of immune responses and preserving peripheral tolerance. We showed that targeting of antigens via C-type lectin receptors to different specialized DC subpopulations induced either CD4+ or CD8+ T cell responses in vivo. Fc receptors are also highly active in endocytosis enabling APCs to take up antigens in form of immune complexes. As they are expressed on various APCs, we aimed to identify responsible APCs for primary and secondary immune responses. Therefore, we assessed their expression in various organs and delivered antigens by specific recombinant antibodies. The targeting of the Fc receptors induced CD4+ and CD8+ T cell responses in a transgenic as well as a naïve system. Moreover, especially antigen delivery to the activating FcγRIV was superior in inducing CD4+ and CD8+ T cell responses at the same time, which could not be observed by classical targeting of the C-type lectin receptors DEC205 or DCIR2. Additionally, targeting of antigens to FcγRIV induced a pronounced CD4 helper response in naïve mice, whereas targeting to DCIR2 was inefficient. As FcγRIV is expressed on both major splenic DC subsets, we used this receptor to verify the subset intrinsic preference of DCs for CD4+ or CD8+ T cell responses. This was clearly shown by the induction of CD4+ T cell responses by splenic CD8− DCs, whereas splenic CD8+ DCs induced a CD8+ T cell response. The induced naïve CD8+ T cell responses were functional relevant, as we could demonstrate efficient dose-dependent killing of target cells in vivo. Therefore, we suggest this strategy as useful tool for the induction of de novo as well as the modulation of immune responses for therapeutic applications.