Antigen-presenting dendritic cells rescue CD4-depleted CCR2^-/- mice from lethal histoplasma capsulatum infection

Excessive production of interleukin-4 impairs clearance of the fungal pathogen Histoplasma capsulatum in mice lacking the chemokine receptor CCR2. An increase in the interleukin-4 level is associated with decreased recruitment of dendritic cells to lungs; therefore, we investigated the possibility that these cells influence interleukin-4 production. Adoptive transfer of wild-type or CCR2^-/- bone marrow-derived dendritic cells loaded with heat-killed yeast cells to infected CCR2^-/- mice suppressed interkeukin-4 transcription. Surprisingly, transfer of cells did not reduce the fungal burden despite the fact that it limited interleukin-4 transcription. Yeast cell-loaded bone marrow-derived dendritic cell-mediated regulation of interleukin-4 transcription was dependent on major histocompatibility complex II antigen presentation to CD4⁺ T cells. We previously showed that CD4 ⁺ T cells were a source of interleukin-4 in infected CCR2 ^-/- mice, but their contribution to the TH2 phenotype was unclear. Here we demonstrated that these cells were functionally important since elimination of them prior to infection, but not elimination of them at the time of infection, reduced the interleukin-4 level in infected CCR2^-/- mice. However, the fungal burden was reduced only in CD4-depleted CCR2 ^-/- mice that received yeast cell-loaded bone marrow-derived dendritic cells. Taken together, the data indicate that generation of excess interleukin-4 in lungs of H. capsulatum-infected CCR2^-/- mice is at least partially a consequence of decreased recruitment of dendritic cells capable of antigen presentation. Furthermore, CD4⁺ T cells had a deleterious impact on immunity in infected CCR2^-/- mice.