Investigations on six males with naturally occurring Rh antibodies are described. In two subjects in whom the antibody (one anti-E and one anti-D) could be detected only by a two-stage papain technique, the survival of incompatible red cells was normal. In the remaining four subjects, the antibodies (two anti-E and two anti-D) could be detected by the indirect antiglobulin test and, in these, incompatible red cells were destroyed at an accelerated rate; in two of the subjects, 75-99% of the cells were cleared within 24 h; in the other two, 50% of the cells were cleared within 24 h and the remaining cells were cleared far more slowly. All six antibodies were mainly or wholly IgG; a clear-cut immune response was observed in only one case.

The treatment regimen that we adopted may prove useful in other cases of unplanned ABO-incompatible organ transplants. The successful outcome suggests that planned ABO-incompatible lung transplants may be possible.

Rh-negative women, immunized to Rh by previous pregnancies, with only low concentrations of IgG anti-Rh(D) in their plasma were assigned at random to test and control groups (7 subjects in each group). Both groups were challenged with an intravenous injection of 0.28 ml of Rh-positive red cells; in addition, the test group received 500 µg anti-Rh intramuscularly. 2 weeks after the injections, all subjects showed an increase in plasma anti-Rh concentration; levels in test and control groups were similar. It is concluded that in Rh-immunized subjects with low levels of IgG anti-Rh a secondary response to Rh cannot be prevented by giving passively administered anti-Rh with the red cells.

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At the North London Blood Transfusion Centre, red cells from accredited Rh-D-positive donors, matched for all antigens capable of inducing clinically significant antibodies, are used to stimulate immune plasma donors to achieve higher anti-D levels. Despite such careful matching, antibody to the relatively non-immunogenic M antigen developed in 3 out of 20 NN donors (15%) stimulated with M-positive cells. In general, good responders to the Rh antigen D are good responders to other red cell antigens; our report exemplifies the importance of using fully matched accredited red cells for immune stimulation and the need to perform thorough antibody screening after each stimulation.