Expression and function of DNAM-1 on human B-lineage cells.

BACKGROUND: Although DNAM-1 is an activating receptor constitutively expressed on the majority of NK cells, CD8+ T cells, CD4+ T cells, monocytes, and platelets in human, several evidences demonstrated that a small population in B-lineage cells also expressed DNAM-1. However, the expression profile of DNAM-1 on B-lineage cells and its function remain obscure. Previous reports revealed that a considerable number of leukocytes including B cells in the peripheral blood conjugated to platelet. Thus, the proportion of DNAM-1+ B-lineage cells determined by flow cytometry analysis in the previous reports might be overestimated. METHODS: We examined whether platelets conjugate B cells and then analyzed the expression of DNAM-1 on the subpopulations of B-lineage cells according to their maturation stages after exclusion of platelet-conjugated B cells. We also assessed the involvement of DNAM-1 in IL-10 and antibody production from cultured B-lineage cells stimulated with CpG-ODN. RESULTS: Approximately 10% of human DNAM-1+ CD19+ B cells in the peripheral blood conjugated to platelets, resulting in the overestimation of the proportion of DNAM-1+ B cells. After exclusion of platelet-conjugating B cells, we show that DNAM-1 expression was detected on subpopulations of memory B cells, plasmablasts, and plasma cells and upregulated by stimulation with CpG-ODN. Moreover, DNAM-1 was involved in IL-10 and antibody productions by B cells after CpG-ODN stimulation. CONCLUSIONS: DNAM-1 may be involved in B-lineage cell-mediated immune responses.