Competitive inhibition of T‐cell mediated lympholysis by platelets

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Abstract
Platelets are known to possess serologically detectable HLA-A, B, C (class I) antigens, but not HLA-DR (class II) antigens. Platelets were used as nonlabeled (cold) competitors for cell-mediated lympholysis directed against determinants on PHA [phytohemagglutinin] (3 days) and PWM [pokeweed mitogen] (7 days) 51Cr-labeled (hot) lymphoblasts, i.e., T and B lymphoblasts, respectively. Platelets were able to incompletely inhibit cytolysis against T-lymphoblasts, but not B-lymphoblasts. The inhibition is immunologically specific in the sense that only platelets autologous to the original stimulator cell block, while platelets autologus to the original stimulator cell block, while platelets autologous to the original responder cell do not. The immunogenetic specificity of platelet blocking is unknown at present, since no allogeneic 3rd party platelets were investigated. Platelets do not inhibit cytolysis by cytotoxic lymphocytes previously shown to identify HLA-non A, B, C, D/DR determinants on T-lymphoblasts. Platelets must be mature (.gtoreq. 7 days) for optimal results to be obtained. Since platelets are easy to procure and maintain their reactivity for months by simple storage in saline at 4.degree. C, platelets may be used to screen for cell-mediated lympholysis against HLA-class I, II or new determinants.