A multilaboratory investigation during several years has identified a low incidence antigen JAL on the red cells of 7 propositi. JAL appears to be associated with two unusual Rh complexes, one of which produces a depressed C antigen and the other a depressed c antigen. Family studies strongly suggest that the JAL antigen is encoded by the RH locus. Anti-JAL has been implicated in haemolytic disease of the newborn and is thus considered to be a clinically significant antibody.

This study describes the comparative measurement of D antigen site density using a fluorescent indirect antiglobulin test (FIAT) read by flow cytometry. The test results confirmed the continuum of D antigen strength from weakest D through to R2R2 and also allowed the majority of weak D samples to be adequately distinguished from D-negative samples.

Haemaglobin separation was carried out by isoelectric focusing using precast polyacrylamide gels with a pH range of 5 5-8 5, supplied by Pharmacia Biotechnology Ltd. Haemoglobin A2 was measured by elution from cellulose acetate electrophoresis strips2 and Hb F measured by alkali denaturation using a modification of Betke's method.3 Globin chain synthesis was assessed by tritiated leucine incorporation using a modification of the method of Weatherall, Clegg, and Naughton.4

SUMMARY A fourth human blood group chimaera studied in Birmingham is an example of haemopoietic (twin) chimaerism in which the subject was unaware of being a twin. Chimarerism was discovered during routine antenatal serological investigation in which it was shown that the proposita has two red cell populations, one of the rhesus genotype rr, and the other R1r. Further studies showed that she has two populations of lymphocytes, one with the female karyotye, 46XX, and the other with the male karyotype, 46XY. Skin fibroblasts were all 46XX.

The phenotypic association between the non-assigned high-incidence antigen Joa and the Gya collection antigens Gya and Hy was investigated by haemagglutination studies, flow cytometric analysis, immune precipitation and immunoblotting experiments. In haemagglutination tests anti-Joa gave the same pattern of reactivity with erythrocytes pre-treated with pronase, trypsin, alpha-chymotrypsin and thiol reducing agents as did anti-Gya and anti-Hy. In addition, similar to that found for anti-Gya and anti-Hy, anti Joa also showed reduced binding, as determined by haemagglutination and flow cytometric analysis, to erythrocytes from patients with paroxysmal nocturnal haemoglobinuria. Immune precipitates prepared from radio-iodinated antigen-positive red cells with anti-Joa, anti-Gya and anti-Hy gave similar results--a major component of M(r) 49,000-60,000 (the Gya/Hy-active glycoprotein) and a second component of M(r) 85,000-92,000 (this may be a dimer of the Gya/Hy-active glycoprotein, or a coprecipitated protein). These immune precipitates, when probed with both anti-Gya and anti-Hy under non-reducing conditions, gave a positive immunoblotting reaction to both the M(r) 49,000-60,000 and the M(r) 85,000-92,000 components. These results strongly suggest that the Joa antigen is expressed on the same glycoprotein that carries the Gya and Hy antigens.