Some biological effects of IgM anti-Rh (D).

Twelve previously uninjected D-negative subjects were given 1 ml of D-positive cells together with 30–90 μg IgM anti-D intravenously; about 50 per cent of the cells were cleared within 48 hours, and the remainder were cleared far more slowly; at 6 months two of the subjects had formed anti-D. All subjects were then given a second injection of D-positive red cells but without passive antibody; two subjects without demonstrable anti-D at the time of this injection showed accelerated clearance within the first week and developed anti-D within 6 weeks. The proportion of subjects forming anti-D (four out of twelve) was not significantly different from that found in a previous series injected with red cells alone and it was concluded that these doses of IgM anti-D had failed to suppress immunization. It has previously been proposed that the proper criterion for judging augmentation of immune responses in D-negative subjects is not the proportion of subjects becoming immunized but rather the characteristics of the response in subjects capable of responding. In the present series no definite evidence was obtained that antibody formation was brisker or greater in those subjects who received passive IgM antibody together with their first injection of D-positive red cells.