Platelets inhibit antigen presentation by dendritic cells and tumor cells / 中国实验血液学杂志

ABSTRACT

This study was aimed to investigate the effects of intact platelets on antigen presentation by either tumor cells or bone-marrow derived dendritic cells (BMDCs). The antigen presentation assay models included BMDC stimulated mixed allogenic lymphocyte reaction and antigen presentation by OVA-harboring EG7 cells to OVA-specific TCR transgenic OT-I T lymphocytes. Fresh platelets prepared from hemogenic murine bloods were added to the culture systems to different levels. Lymphocyte proliferation, level of secreted cytokines in the culture and phenotype of BMDCs were measured by isotope incorporation, ELISA and flow cytometry respectively. The results indicated that when platelets at certain concentrations were added in co-culture system containing both OVA-harboring EG7 cells and OVA-specific TCR transgenic OT-I T lymphocytes, both lymphocyte proliferation and IFNγ production were inhibited. The addition of platelets to the BMDC culture followed by LPS or CpG ODN treatment blocked B7-2 upregulation, cytokine production of the BMDCs, and stimulation potency of such BMDCs for allogenic lymphocytes. Furthermore, platelets inhibited the ability of BMDCs to present both soluble and cellular antigens to clonal specific T lymphocytes, which reflected by decreased lymphocyte proliferation and cytokine production. All these platelet-dependent effects were related to the concentrations of platelets in culture. FACS analysis also revealed that platelets bound to BMDCs induced slightly higher cell death rate of BMDCs. It is concluded that under certain conditions, platelets may affect antigen presentation and the overall outcome of immune responses in a negative way, providing new evidence for the hypothesis that platelets play much more complicated roles in the regulation of immune compartments than originally believed.