Synthesis of Inflammatory Cytokines and Expression of Adhesion Molecules in Megakaryocytes

Inflammatory cytokines and platelet adhesion molecules may play a major role in hemostasis and immuno-pathological processes. Hematopoietic cells of myeloid and lymphoid lineages are known to be important sources of a variety of inflammatory cytokines. However, the immunological role of megakaryocytes is not well known. This project studied the involvement of megakaryocytes on immuno-inflammatory processes and the possible mechanism via the adhesion molecules and the synthesis of relevant cytokines. The expression of interleukin (IL)-1 to IL-10, TNF-a, TNF-g and IFN-g in primary megakaryocytes and four megakaryocytic cell lines: Meg-01, Dami, CHRF-288-11 and M-07e were determined by RT-PCR. The effect of IL-1b, IL-3, IL-6 and TPO on megakaryocyte colony formation (CFU-MK) was studied by using a plasma clot culture system. The CFU-MK was confirmed by AchE staining. The expression of adhesion protein CD36 on human platelets, megakaryocytes and megakaryocytic cell lines was also analyzed by using flow cytometry, ELISA and immunocytochemical methods. Our results showed that CD36 was expressed on platelets, megakaryocytes and the four megakaryocytic cell lines. The relative expression level is as follows: platelets > megakaryocytes > Meg-01 > Dami > CHRF-288-11 > M-07e, suggesting that the level of CD36 expression correlates with the degree of maturity of megakaryocytic differentiation. Inflammatory cytokines TNF-a, IL-1b, IL-3 and IL-6 were detected in primary megakaryocytes and all the four megakaryocytic cell lines, suggesting that different stages of megakaryocytes can be as a source of inflammatory cytokines. IL-1b, IL-3 and IL-6, as well as TPO, play a stimulating effect on CFU-MK formation, suggesting that there is an "autocrine" effect on megakaryopoiesis. Megakaryocytes may involve in immuno-inflammatory processes via the synthesis of inflammatory cytokines and platelet adhesion molecules.