Cross-Reactions of Hl-A Antibodies

Cross-reactive HL-A antibodies were initially produced by subject BC in response to alloimmunization with leukocytes from a single donor. After six cycles of immunization with leukocytes from the original donor a second immunizing cell was substituted. A brisk anamnestic response resulted. The antibody response was primarily associated with antigens found on the original immunizing cells, but not present in the second donor. Sera obtained after immunization with each donor were further compared. Both samples contained high titered cross-reactive HL-A3 antibodies and HL-A3 platelets could completely absorb cytotoxins from both serum samples. In addition, pH gradient elution studies indicated that the serum obtained after challenge with the second cell donor had a lower binding avidity for the HL-A3 antigen. These results extend the observations of the original antigenic sin phenomenon to include such responses with major histocompatibility antigens.