EVIDENCE FOR EXPRESSION OF THE JO(A) BLOOD-GROUP ANTIGEN ON THE GY(A)HY-ACTIVE GLYCOPROTEIN/

The phenotypic association between the non-assigned high-incidence ant igen Jo(a) and the Gy(a) collection antigens Gy(a) and Hy was investig ated by haemagglutination studies, now cytometric analysis, immune pre cipitation and immunoblotting experiments. In haemagglutination tests anti-Jo(a) gave the same pattern of reactivity with erythrocytes pre-t reated with pronase, trypsin, alpha-chymotrypsin and thiol reducing ag ents as did anti-Gy(a) and anti-Hy. In addition, similar to that found for anti-Gy(a) and anti-Hy, anti Jo(a) also showed reduced binding, a s determined by haemagglutination and flow cytometric analysis, to ery throcytes from patients with paroxysmal nocturnal haemoglobinuria. Imm une precipitates prepared from radio-iodinated antigen-positive red ce lls with anti-Jo(a), anti-Gy(a) and anti-Hy gave similar results - a m ajor component of M(r) 49,000-60,000 (the Gy(a)/Hy-active glycoprotein ) and a second component of M(r) 85,000-92,000 (this may be a dimer of the Gy(a)/Hy-active glycoprotein, or a coprecipitated protein). These immune precipitates, when probed with both anti-Gy(a) and anti-Hy und er non-reducing conditions, gave a positive immunoblotting reaction to both the M(r) 49,000-60,000 and the M, 85,000-92,000 components. Thes e results strongly suggest that the Jo(a) antigen is expressed on the same glycoprotein that carries the Gy(a) and Hy antigens.