Inhibition of mixed leukocyte culture reactivity by sera from hemodialysis patients and transplant recipients as an indicator of isoimmunization

A system has been designed to determine the mixed leukocyte culture (MLC) inhibitory activity of sera from patients presensitized by hemodialysis or transplantation. Monthly samples of sera were screened for blocking factors on 10 different one way MLC, using a constant panel of responding lymphocytes and a standard stimulating cell mixture. In addition, the reactivity of the patients' lymphocytes to the same stimulating cell mixture was tested. MLC inhibitory activity was detectable before appearance or following the disappearance of lymphocytotoxic antibodies in sera from hemodialysis patients. In transplant recipients MLC inhibitory activity was strongly associated with cytotoxic antibodies and humoral rejection. These data suggest the value of MLC inhibition as a sensitive test for detection of presensitization.