Competitive inhibition of T-cell mediated lympholysis by platelets

Platelets are known to possess serologically detectable HLA-A, B, C (class I) antigens, but not HLA-DR (class II) antigens. We have used platelets as non-labelled (cold) competitors for cell-mediated lympholysis directed against determinants on PHA (3 days) and PWM (7 days) 51Cr-labelled (hot) lymphoblasts, i.e. T and B lymphoblasts, respectively. It is found that platelets are 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 responder cell do not. The immunogenetic specificity of platelet blocking is unknown at present, since no allogeneic third party platelets have been investigated. It is further found that platelets do not inhibit cytolysis by cytotoxic lymphocytes previously qualified to identify HLA-non A, B, C, D/DR determinants on T-lymphoblasts. Like in serology, platelets have to mature (greater than or equal to 7 days) in order to obtain optimal results. Since platelets are easy to procure and maintain their reactivity for months by simple storage in saline at 4 degrees C, platelets may be used to screen for cell-mediated lympholysis against HLA-class I, II or "new" determinants.