Possible Mechanisms by which Alloantisera Inhibit in the MLC Test

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Abstract
MLC inhibition studies were performed with two human alloantisera: one specific for HLA‐B7, the other for HLA‐DRw7. The stimulator cell inhibitory effects of these sera were tested in primary and secondary MLC tests. Both sera inhibited in the primary MLC, whereas only the anti‐DRw7 serum was capable of blocking the secondary MLC test. The difference in inhibiting properties of these sera was further analyzed in primary MLC tests using selected MLC combinations, Fc receptor negative cell populations and pepsin digests of the anti‐B7 serum. Anti‐DRw7 antibodies could inhibit by masking the stimulatory DR antigens. The inhibition of the anit‐B7 antiserum was dependent on Fc, which suggested that anti HLA‐B antibodies inhibited by some other mechanism. This inhibition could have been caused by antibody dependent cellular lympholysis of the stimulator cells or by the induction of suppressor cell activity.