Blocking of HLA and B lymphocyte alloantigens with F (ab')2 fragments of rabbit antibodies.

F(ab')2 fragments of rabbit antibodies specific for human B lymphocytes will block human anti-B lymphocyte alloantibodies. F(ab')2 of anti-beta2m will block HLA alloantibodies. The F(ab')2 fragments can be used to improve the typing of B cell lines and certain leukemia cells which express both HLA and B lymphocyte alloantigens. Pretreatment of these cells with anti-beta2m F(ab')2 preparations allows the observation of B cell alloantigen reactions independently of HLA reactions. Similar use of rabbit anti-B cell F (ab')2 allows HLA reactions to be observed free from the "extra reactions" caused by B alloantibodies that are present in many HLA typing sera.