Programmed death-1 receptor negatively regulates LPS-mediated IL-12 production and differentiation of murine macrophage RAW264.7 cells.

While programmed death-1 (PD-1), a co-inhibitory member of CD28 immunoglobulin superfamily plays negative roles in effector functions of T cells and B cells, little is known about the function of PD-1 expressed on innate immune cells. In this study, we demonstrate that IL-12 production was greatly suppressed in LPS-stimulated RAW264.7 cells upon PD-1 engagement with B7-H1.Fc fusion protein, and was restored in the presence of antagonistic anti-PD-1 mAb. PD-1-mediated suppression of IL-12 production in LPS-stimulated RAW264.7 cells was mediated by inhibition of Janus N-terminal-linked kinase (JNK) signaling pathway, and to a lesser extent, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway through the recruitment of SHP-2 to PD-1 cytoplasmic tail. B7-H1.Fc-mediated PD-1 engagement also downregulates the expression of co-stimulatory molecules such as CD80, CD86, MHC class I and II proteins in LPS-stimulated RAW264.7 cells. Furthermore, the endocytic activity is enhanced but the allostimulatory capacity is suppressed in LPS-treated RAW264.7 cells upon PD-1 engagement. Taken together, our results reveal a novel function of macrophage PD-1 in the negative regulation of IL-12 synthesis and differentiation into dendritic cell-like cells.