Further Experimental Studies on the Prevention of Rh Haemolytic Disease

Abstract

In a previous report (Finn et al., 1961) we gave reasons for thinking that the rapid removal of Rh-positive foetal erythrocytes from the circulation of a mother who was Rh-negative would prevent her from becoming immunized and producing Rh antibodies. We have now investigated the matter further, and the present paper describes the completed results of the earlier work (Experiment I) and then gives details of some subsequent observations (Experiments II and III). The reasoning involved and the scope of the investigations are first discussed. Levine (1943) demonstrated the marked degree of protection against Rh haemolytic disease afforded by ABO incompatibility between mother and foetus. We agreed with Race and Sanger (1950) that the probable mechanism lay in the rapid destruction of the incompatible foetal cells in the circulation by the anti-A and anti-B. Experiment I was therefore designed to determine whether immunization resulting from injection of ABO compatible Rh-positive blood into Rh-negative male volunteers could be prevented by the infusion of plasma containing high-titre saline-reacting (complete) anti-D antibodies, simulating the effect of anti-A and anti-B. Some initial results of this experiment have been briefly reported (Finn et al., 1962). It was found that, compared with control subjects, antibody formation was enhanced rather than prevented and we noted that in some cases nearly half the injected cells survived in the circulation for over a week, though at that time free complete anti-D could be detected in the recipients' sera. On the basis of these results a second approach which forms the substance of Experiment II was tried. Stern et al. (1961) had shown that prior in vitro coating of Rh-positive erythrocytes with incomplete anti-D would prevent antibody formation after subsequent injection *Now Research Fellow, Johns Hopkins Hospital, Baltimore. tNow Senior Medical Registrar, Sefton General Hospital Liverpool. into Rh-negative males. It was thought that the mechanism operating here might be the complete blocking of the D-antigen sites by incomplete antibody. Mollison (1959) had shown that this was associated with the rapid clearing of such cells from the circulation. Our experiment thus involved the use of plasma containing high titres of incomplete anti-D antibodies and a study of its effectiveness in preventing Rh immunization by previously injected Rh-positive blood. Further studies were carried out in Baltimore (Experi-ment III) to elucidate the relationships between differing amounts and types of Rh antibody, the rapidity of clearance of injected Rh-positive cells, and subsequent immunization. Materials and Methods The experiments were carried out on groups of Rh-negative male volunteers. Those in Liverpool were blood donors and those in Baltimore were inmates of the Maryland State Penitentiary. The method of giving the blood and plasma was the same as that described in Finn et al. (1961). In Experiments I and II the men were dealt with in groups of six; as a rule, three received 5 ml. of Rh-positive blood and then half an hour later were given the antibody-containing plasma, while the other three received only the Rh-positive blood and thus acted as controls. The details of what was given to each of the 24 men in Experiment I are shown in Table I and to each of the 42 men in Experiment II in Table II. It was the aim in the second experiment to use 50 ml. of plasma with a high titre of incomplete antibody, thus attempting to achieve rapid clearance of injected blood, but because of practical difficulties this dose was not always possible.