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The knowledge of the potential clinical significance of alloantibodies to blood group antigens is essential for selecting appropriate red blood cell (RBC) products for transfusion. This article provides a summary of clinical and technical aspects of many alloantibodies.

Anti-Lu 14 has been found in the serum of a gravida 2 pregnant woman who had not been given any blood transfusions. Her husband is Lu:14 but otherwise of common Lutheran blood type. Maternal immunization probably occurred during the first pregnancy. The second child did not inherit the father's Lu14 gene and was not affected by the maternal antibody.

A case of hemolytic disease in a newborn infant caused by anti-Dia is described. The parents are Japanese. The antibody was an IgG of subclasses IgG1 and IgG3, did not bind complement, and gave a 27 percent phagocytosis rate when used to sensitize red blood cells for a macrophage binding assay. The antibody was not detected during antenatal serologic testing. This case suggests the need for reagent red blood cell panels selected to match antibody specificities likely to be encountered in a particular population.

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 alpha-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.

A healthy 38-year-old white woman had two abortions and three live children. Red cells from each of her living children at birth had a strongly positive direct antiglobulin test. Detailed studies on the third child showed that the cells were sensitized by IgG. Maternal serum, tested by a range of techniques against reagent red cells and the husband's cells, showed no unusual antibody. Maternal serum and eluates prepared from red cells of the third child did not react with fresh cells from the older siblings (aged 7 and 10 years). Follow-up on the third child showed that the direct antiglobulin test was positive at 2 months, weakly positive at 4 months, and negative at 8 months. Red cells collected at 8 months of age did not react with the stored eluate prepared from the baby's sensitized red cells at birth. The most likely explanation of these data is that the children inherited a paternal antigen that is only present as a red cell surface-active structure during fetal development.

A 'new' Lutheran-related antibody, named anti-Lu14, reacts with approximately 2.4% of random bloods. Red cells of the rare Lu:-8 phenotype are Lu:14. The data indicate, with a high probability, that the Lu 14 antigen is a product of an allele of Lu8 and that Lu14 and Lu8 comprise a third pair of alleles at the Lutheran locus. Red cells of the original Sw (a+) propositus are Lu:14. By coincidence, he has inherited two low-incidence genes. This observation may explain the discrepancy in different families concerning a possible relationship between Swa and Lutheran. Pedigree information now suggests that Swa is not a Lutheran gene.

A new antibody, designated anti-K18, reacts with a high frequency red cell antigen that is related to the Kell blood group system. All of more than 2,000 bloods were K:18 but K-0 phenotype red cells are K:-18.