Expression of blood group-like antigens on the T lymphocytes of acute leukaemia patients in remission.

A number of previous studies have described antibodies in normal sera reactive to human leukaemia cells. In the course of studies on humoral immunity to acute myeloid leukaemia (AML) cells it was noticed that sera from normal subjects were cytotoxic in complement lysis and leucocyte dependent antibody (LDA) assays to blood leucocytes from patients with AML in remission. Investigation of these reactions in eleven patients with acute leukaemia in complete or partial remission revealed that reactivity occurred most frequently between sera from normal blood group O or B subjects and leucocytes from patients of blood group A (five patients). Leucocytes from blood group O patients were largely unreactive. Blood leucocytes from five of six patients in relapse did not react with normal sera. Subsequent studies revealed that the antigens were detected only on T lymphocytes. Reactivity could be removed by absorption on red cells of blood group A but not sheep or Ox red blood cells suggesting the antigens concerned were closely related to blood group A antigens. Some reactivity with antisera to the blood group H antigens was also evident in these studies. Gel filtration studies indicated that lymphocyte dependent antibody mediated cytotoxicity was mediated by IgG antibodies while complement dependent lysis was mainly mediated by IgM antibodies. The biological significance of these findings has yet to be determined but these results suggest that reactivity with blood group antigens needs to be considered in in vitro cytotoxicity studies involving leucocytes from leukaemia patients.