Activation of lymphocytes after platelet allotransfusion possessing only class I MHC product.

After platelet allotransfusion, we found a characteristic increase in the expression of interleukin-2 receptor, dipeptydilpeptidase IV (CD26), activation-inducer molecule (AIM, CD69) and transferrin receptors (CD71) on day 3 indicating that important functional molecules expressed on the activation of lymphocytes by allogeneic platelets. At the same time, no consistent increase of other activation molecules such as Ki-l (CD30), intercellular adhesion molecule (ICAM-1, CD54) and Ki-24 (CDw70) antigen expression was detected, probably as a result of the selective activation of some lymphocyte subsets. In order to obtain further evidence for the in vivo activation triggered by allogeneic platelets, subsequent step of T cell activation towards differentiation was investigated with monoclonal antibodies to leucocyte common antigens. A sharp expression of the UCHL1, coupled with a decrease of the CD45R molecule was detected on day 7 or 14, suggesting a T cell priming.