Conjugates of B-cells and platelet microparticles in the human peripheral blood

Background: Activated platelets shed microparticles [MPs] in vivo and certainly in vitro under storage. Like platelets, platelet-derived MPs contribute to hemostatic and inflammatory responses. We sought to determine the interactions between platelet MPs and peripheral B lymphocytes in the healthy blood circulation to propose a possible role for platelet MPs in the functioning of B cells

Materials and Methods: An enzyme-linked immunosorbent assay [ELISA] was established to determine the normal interactions between human peripheral blood B lymphocytes and platelet MPs. B cells were isolated and bound to the wells of microtiter plates using coated anti-CD19. Then the presence of attached MPs was surveyed. Also, platelet MPs were separated from human platelet concentrates and applied to confirm the new binding capacities of B cells for these microvesicles

Results: Platelet MPs were recognized in the wells of ELISA in which only B cells were isolated. So MPs were bound with peripheral blood B cells. Furthermore, using this method, the role of CD40/ CD40L interaction was displayed for the binding

Conclusion: It seemed that the binding of platelet MPs to B cells normally took place in vivo and a percent of B cells circulate in blood in connection with platelet MPs

Effects of platelet microparticles on the activation of B cells

Platelets are anucleated fragments derived from megakaryocytes. It has been demonstrated that platelets play a role in hemostasis and innate immunity. In addition, platelets have a CD40 ligand which is an important molecular marker in motivating immune cells. Thus, platelets also have a role in adaptive immunity as seen by their ability to activate B cells. Since human platelet microparticles [MPs] originate from platelets, we have chosen to examine the effects of MPs on B cell activation. Platelet MPs were isolated from platelet concentrates obtained from the Tehran Blood Transfusion Center. The MPs were co-cultured with B cells isolated from human whole blood with magnetic beads using negative selection. After seven days, the expression of activation markers CD27 and CD86, as well as IgD were evaluated by flow cytometry. In a comparison between test [B cells/MPs] and control [B cells] cells we observed that the expression of activation markers CD27 and CD86 increased during the seven-day co-culture period. However, the expression of IgD antibody decreased. As with platelets, MPs can affect B cell activation during in vitro co-culture