IL-12 increases CD80 expression and the stimulatory capacity of bone marrow-derived dendritic cells

Dendritic cells (DC) are potent antigen-presenting cells derived from CD34bone marrow stem cells. They undergo a series of maturational steps thatallow them to stimulate primary T cell responses. Several cytokines areknown to contribute to this process. In this study murine DC maturing frombone marrow progenitors under the influence of granulocyte macrophagecolony stimulating factor and tumour necrosis factor-alpha were found toproduce IL-12 as measured by ELISA and by flow cytometry to detectintracellular cytokine. Administration of additional IL-12 from day 3 to 7of culture altered the function and phenotype of DC; enhanced stimulationof T cell proliferation by DC in allogeneic mixed leukocyte reactions wasassociated with an increase in the surface expression of CD80 on DC. Theseeffects were dose dependent, and were consistently seen with IL-12 at 25ng/ml and were less marked with IL-12 at 50 ng/ml. These results show thatIL-12 is both produced by DC and can increase their stimulatory capacity.The findings suggest that there may be an autocrine effect of IL-12 on DCmaturation and function.