Heterogeneity of anti‐U demonstrable by the use of papain‐treated red cells

When red cells (RBCs) are treated with papain, one form of the U antigen, which we have named UPS (U papain-sensitive), is almost completely removed or denatured. A second form, UPR (U papain-resistant), remains unaltered on the treated RBCs. Tests on 42 examples of anti-U showed that two contained only anti-UPS, 19 contained only -UPR, and 21 contained separable -UPS and -UPR. In those sera containing both antibodies, anti-UPR was always the stronger of the two. These findings suggest 1) that UPS is located on the Ss sialoglycoprotein (glycophorin B) at a position distal to a papain-sensitive site or that the cleavage point is within the portion of the SGP that comprises UPS, and 2) that UPR is located between the papain-sensitive site and the RBC membrane. The UPS determinant was not denatured by neuraminidase, L-cysteine, trypsin, ficin, or α-chymotrypsin, and it was only partially denatured by pronase. The finding that RBCs treated with para-chloromercuribenzoic acid or para-chloromercuriphenyl sulfonic acid did not react with anti-UPR but did continue to react with anti-UPS suggests that the in situ configuration of UPR, but not UPS, is dependent on the presence of one or more disulfide bonds. RBCs of the S−s−U+(weak) phenotype were shown to carry markedly reduced amounts of both UPS and UPR.