Dendritic cell-T cell interactions: CD8αα expressed on dendritic cells regulates T cell proliferation

Expression of the CD8αα homodimer has been used to differentiate lymphoid (CD8α+) from myeloid (CD8α−) dendritic cells (DCs). We have reported that CD8α+ and CD8α− DCs have differential abilities to stimulate proliferation in allogeneic T cells. However, no specific function has been attributed to DC-derived CD8α. The current study examines the hypothesis that CD8αα expression on DCs regulates DC-induced T cell activation. CD8α− transduced bone marrow-derived DCs were more potent stimulators of T cell proliferation, and produced significantly greater quantities of IL-12 in co-culture with T cells. LCK, a kinase whose expression is reported to be T cell-restricted and known to bind to the cytoplasmic tail of CD8αβ in T cells, was detected readily in primary CD8α+ splenic DCs and at greater levels than CD8α− DCs from the same tissues. LCK also co-precipitated with CD8α on immunblots strongly suggesting its role in CD8α+ DC-induced T cell activation. Collectively, these data show that CD8α expressed on DC may not only be a lineage/maturation marker but also contribute to DC function.