Acute in vivo exposure to interferon-γ enables resident brain dendritic cells to become effective antigen presenting cells

Dendritic cells (DC) are the professional antigen presenting cells (APC) that bridge the innate and adaptive immune system. Previously, in a CD11c/EYFP transgenic mouse developed to study DC functions, we anatomically mapped and phenotypically characterized a discrete population of EYFP+ cells within the microglia that we termed brain dendritic cells (bDC). In this study, we advanced our knowledge of the function of these cells in the CD11c/EYFP transgenic mouse and its chimeras, using acute stimuli of stereotaxically inoculated IFN gamma or IL-4 into the CNS. The administration of IFN gamma increased the number of EYFP+ bDC but did not recruit peripheral DC into the CNS. IFN gamma, but not IL-4, upregulated the expression levels of major histocompatibility class II (MHC-II). In addition, IFN gamma-activated EYFP(+)bDC induced antigen-specific naive CD4 T cells to proliferate and secrete Th1/Th17 cytokines. Activated bDC were also able to stimulate naive CD8 T cells. Collectively, these data reveal the Th1 cytokine IFN gamma, but not the Th2 cytokine IL4, induces bDC to up-regulate MHC-II and become competent APC.