Soluble proteins and haptens on bone marrow-derived dendritic cells are presented to host CD4 T cells in an MHC-restricted manner.

Because of their potent antigen-presenting capacity, dendritic cells (DC) have been used extensively in immunotherapy protocols. Our purpose was to functionally characterize mouse bone marrow-derived DC (BMDC) in vitro (in protein antigen- and hapten-specific assays) and in vivo (injecting soluble protein- and hapten-pulsed DC) to determine their suitability for the generation of T(h) cell responses. Furthermore, we determined whether there is cross-presentation on MHC class II molecules during in vivo protein and hapten sensitization. Co-culture of protein-pulsed [with hen egg lysozyme (HEL) or with pigeon cytochrome c (CYT)] DC with T cells from HEL- or CYT- sensitized mice induced antigen-specific T cell proliferation, but compared to cultured Langerhans cells (LC), BMDC required higher protein antigen-pulsing concentrations (100 microg and 1 mg/ml). In contrast, at low protein concentrations (10 microg/ml), BMDC stimulated an HEL-specific hybridoma very efficiently. Using an in vitro T cell proliferation assay and in vivo delayed-type hypersensitivity and contact sensitivity assays, we found that protein- and hapten-pulsed BMDC were able to sensitize syngeneic but not allogeneic hosts. Furthermore, if we injected BALB/c- and C57BL/6-derived HEL-pulsed BMDC into F1 mice, specific secondary proliferation of primed T cells occurred only when antigen-pulsed stimulator cells syngeneic to the injected BMDC were used. Using this model system we found that soluble proteins and haptens are presented by injected BMDC to host T cells in an MHC-restricted manner in vivo.