Platelets inhibit in vitro response of lymphocytes to mitogens

Recent studies proposed that besides their role in thrombosis, platelets are involved in modulation of immune response of organisms to foreign bodies through platelet–leukocyte cross-talks at different levels. In the present study, we compared the response of T and B lymphocytes to mitogens in the presence or absence of platelets in cell cultures. Proliferation of T cells in response to lower concentrations of anti-CD3 or ConA stimulation as well as IL2 production of ConA-induced T blasts were inhibited by platelets. Similarly, proliferation and IL6 production of B blasts stimulated with low dose lipopolysaccharide (LPS) or CpG oligodeoxynucleotide 1826 were also dramatically inhibited by platelets. Over-expression of early activation marker CD69 induced by mitogens was blocked by platelets in both T blasts and B blasts. Platelets in culture also blocked production of IgM and IgE in B cells that were induced by anti-CD40/IL4 or LPS/IL4 treatments. These observations provided new evidence for the theory that platelets play more complicated roles in immune compartments. More efforts should be made to address the issue whether such platelet–lymphocyte interactions have any physiological significance in human and animals.