Interaction of penicillin with HLA-A and -B antigens.

When lymphocytes of healthy donors were incubated with penicillin and washed before HLA typing, the cytotoxic reactivity of some typing sera with their corresponding antigen was blocked. When the penicillin was added to the cytotoxicity assay at different times, competition between penicillin and alloantiserum for binding on or near the same epitope on the HLA molecule could be observed. On the basis of the inhibition experiments, HLA antigens can be divided into three groups: 1. Antibody reactivity blocked by penicillin (Bw35) 2. Antibody reactivity not blocked by penicillin (B14) 3. Antibody reactivity blocked by penicillin in some donors but not in others (A2). This third group may provide an opportunity to determine structural differences among, until now, serologically indistinguishable HLA molecules. By adding penicillin to a multispecific serum, containing both antibodies that can and cannot be blocked, a monospecific typing serum can be obtained. The differential effect of penicillin on the HLA antigens was not restricted to complement-dependent cytotoxicity on lymphocytes. Similar results were obtained when the HLA antisera were tested with indirect immunofluorescence on platelets or in absorption experiments.