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

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Abstract
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.