EVIDENCE FOR ACTIVELY ACQUIRED TOLERANCE TO Rh ANTIGENS

Abstract

Data were collected on the mothers of 2 groups of Rh-negative women; those who did not develop Rh sensitization within 3 Rh-positive pregnancies (classified as relatively "tolerant" to Rh antigens), and those who showed evidence of Rh sensitization during or before the 3rd Rh-positive pregnancy (classified as relatively "intolerant" to Rh antigens). In the tolerant group 32 women had Rh positive mothers and 9 had Rh negative mothers. In the intolerant group 27 had Rh positive mothers and 29 had Rh negative mothers. A Chi-square test for homogeneity indicated heterogeneity for these 2 samples. Similar results were obtained after excluding all cases in which blood may have been transfused or injected. Data obtained through the Pasadena Rh Testing Laboratory indicated that the tendency to develop Rh antibody in an early Rh-positive pregnancy was greater among Rh-negative daughters or Rh-negative women than among Rh-negative daughters of Rh-positive women. In these cases "tolerance" was classified according to the development of detectable Rh antibody, without regard to the effects of this antibody on the infants. A 2nd source of data was the Hematology Clinic at the Los Angeles Childrens Hospital, where only women giving birth to erythroblastotic infants came to the attention of the study. In this group there was no evidence of association between the production of an erythroblastotic child by an Rh-negative woman and the Rh type of the maternal grandmother. The conflict in results between the two sources of data is interpreted by the fact that the tolerance developed toward Rh-positive antigens by Rh-negative daughters of Rh-positive mothers is sometimes overridden in an early Rh-positive pregnancy, resulting in erythroblastosis. In the case of Rh-negative daughters of Rh-positive mothers, the kind or amount of antibody produced in an early Rh-positive pregnancy is such that a considerable proportion of infants may not be diagnosed as erythroblastotic. This interpretation has been confirmed tentatively by limited tests.