W.W. Socha

Molecular biology and evolution of blood group and MHC antigens in primates

Contents: Taxonomy and Phylogeny of Primates Red Blood Cell Antigens Major Histocompatibility Complex.

Blood groups of anthropoid apes and their relationship to human blood groups

Abstract Affinity between blood groups of man and those of anthropoid apes is reflected not only in similarities or identities of reactions of the red cells with many specific typing reagents, but also in overall structures of some of the main blood group systems defined in man and in apes. Besides specificities of human-type, such as A-B-O, M-N, Rh-Hr, I-i, etc. known to be present on the red cells of various species of apes, specific reagents were produced by iso- or cross-immunization of chimpanzees that detect red cell specificities characteristic for apes only. Some of those specificities were found to be shared by several ape species and to fall into separate blood group systems that are counterparts of the human blood group systems. Recently obtained serological, as well as population data, indicate that the chimpanzee R-C-E-F blood group system is the counterpart of the human Rh-Hr system. Similarly to the Rh-Hr system, it is built around a main antigen, the Rc antigen, to which secondary specificities are attached by means of multiple allelic genes. The Rc is not only the principal factor of the chimpanzee R-C-E-F group system, but also constitutes a direct link with the human Rh-Hr blood group system, since anti-Rc reagents also detect Rh0 specificity on the human red cells. Another chimpanzee blood group system, the V-A-B-D system, is counterpart of the M-N-S-s system, and is built around the central antigen Vc. the Vc is not only the principal specificity of the chimpanzee V-A-B-D system, but it also constitutes the direct link with the human M-N-S-s system since anti-Vc reagent gives with chimpanzee red cells reactions parralleling those obtained with anti-N lectin (Nv) while in tests with human red cells it detects specificity identical or closely related to the Mia specificity.

BLOOD GROUPS OF APES AND MONKEYS

The study of red cell antigens of primate animals was initiated by Landsteiner and Miller in 1925. It was intensified in 1940 when it was recognized that not only apes’ and monkeys’ red cells contained antigens similar to those already known in humans, but that immunizations of laboratory animals with the red cells of monkeys resulted in a production of antibodies that defined a new, hitherto unrecognized allogenic property of the human red cells. The discovery of the Rh factor (Landsteiner and Wiener, 1940) was to be one of the most important chapters in the history of human blood groups.

Molecular genetics of chimpanzee Rh-related genes: their relationship with the R-C-E-F blood group system, the chimpanzee counterpart of the human rhesus system.

As the chimpanzee R-C-E-F blood group system appears to be the chimpanzee counterpart of the human Rhesus (RH) system, we have tried to determine whether chimpanzee Rh-like genes encode R-C-E-F-related proteins. Chimpanzee genomic DNA, digested by any of eight endonucleases and hybridized with three Rh exon-specific probes, exhibits a high degree of polymorphism. Analysis of DNA from unrelated individuals of different R-C-E-F types revealed that the presence of some restriction fragments is correlated with particular R-C-E-F types. The cosegregation of these fragments with R-C-E-F haplotypes was confirmed by family studies. Oligonucleotides complementary to regions flanking human exons were used as PCR primers on chimpanzee DNA; the resulting amplified fragments were identical in size to their human counterparts. Moreover, the nucleotide sequences of the fragments present a high degree of similarity to the corresponding human regions.

The chimpanzee M blood-group antigen is a variant of the human M-N glycoproteins

Chimpanzee erythrocytes express strong M but weak, occasional N blood-group activity, as detected by anti-M and anti-N reagents. We have found that the M activity is carried by a major membrane glycoprotein that is similar but not identical to the human MM glycoprotein (glycophorin A). We have isolated and characterized this glycoprotein from erythrocyte membranes of four individual chimpanzees. The purified glycoproteins strongly inhibited agglutination of M cells by rabbit anti-human M sera and only weakly inhibited the agglutination of N cells by rabbit anti-human N sera. They also displayed medium-to-strong inhibitory activity against chimpanzee iso- and crossimmune antisera tested with chimpanzee erythrocytes of various V-A-B-D and Wc specificities, which are known as chimpanzee extensions of the human type M-N system and the Miltenberger counterpart, respectively. Each glycoprotein was cleaved with CNBr into three fragments, whose size, solubility, and composition were analogous to those obtained by similar treatment of the human M-N antigens. The amino-terminal fragment was found to be a glycooctapeptide whose amino acid composition and partial sequence indicated that it is an intermediate form of the human M and N glycooctapeptides. Its carbohydrate content comprised two threonine-linked saccharide units that, although similar in composition to the human threonine-linked units, were fewer in number than the three units found in the corresponding human glycooctapeptides. Structural similarities to the human antigens strongly suggest that the amino terminus bears the major antigenic determinants of the molecule, and the occurrence in this region of numerous, albeit rare, variants among humans and in chimpanzees indicates that the corresponding coding sequence of the structural gene is particularly susceptible to mutational events. We conclude that the chimpanzee M gene product is a variant of the human type and that the chimpanzee gene is an allele of the human polymorphic M-N locus.

Chimpanzee R-C-E-F Blood Group System: a Counterpart of the Human Rh-Hr Blood Groups

A chimpanzee blood group system is defined by a set of isoimmune antisera, anti-Rc, anti-Cc, anti-Ec, anti-Fc, anti-Cc and anti-Cc1, that distinguish 19 blood types. Population analysis of 285 unrelated animals and the study of 21 chimpanzee families support the postulated model of inheritance by 9 allelic genes. There is a close relationship between the R-C-E-F blood group system and human Rh-Hr blood groups as indicated by overall structural resemblance of both systems and by serological similarity of their principal antigens, Rc and Rho. There are indications that R-like structures are also present on the red cells of other anthropoid apes, and possibly on those of the Old World monkeys.

Blood groups of macaques:a comparative study.

Distribution of the human-type and of the simian-type blood groups in rhesus, crab-eating, bonnet, pig-tailed and stump-tailed macaques revealed significant similarities and differences among these species. Human-type A--B-O blood groups cut across taxonomic lines and seem less value for taxonomic purposes than the simian-type blood groups detected by cross-reacting isoimmune rhesus monkey sera.

Diversity of Human Anti-D Monoclonal Antibodies Revealed by Reactions with Chimpanzee Red Blood Cells

Fifty‐three human anti‐D monoclonal antibodies (mAbs) revealed a striking diversity of reactions in tests with panels of chimpanzee red blood cells (RBCs) of various R‐C‐E‐F blood group phenotypes (counterparts of the human Rh‐Hr groups). The reactivities of these antibodies, which depended on the agglutination technique used, could be classified into four main types. These patterns of reactivity of anti‐D mAbs with chimpanzee RBCs showed only limited correlation with types of reactions observed with human D variant RBCs. Primate red cells may, therefore, constitute an independent test system for subclassification of human monoclonal antibodies. Comparison of reactivities of human anti‐D mAbs with chimpanzee and human D variant RBCs confirms the homology between the chimpanzee Rc, and the human D antigens. The chimpanzee Rc shares with human D the epitopes epD5, epD6/7 and epD8, but lacks epitopes epD1, epD2, epD3 and epD4 of the Rh mosaic, thus resembling the human D variants IVb and Vc.

Polymorphism of glycophorins in nonhuman primate erythrocytes

Using immunoblotting techniques and polyclonal antisera to human erythrocyte α glycophorin, we show that erythrocytes of several species of nonhuman primates, including representatives of anthropoid apes (19 chimpanzees, 3 gorillas, 6 orangutans, and 3 gibbons) and Old World monkeys (3 baboons, 5 rhesus monkeys, and 6 cynomologus macaques), contain human α glycophorin-like molecules. Each species displays a unique glycophorin profile; in anthropoid apes the profile is more complex than in Old World monkeys and more similar to that seen in humans. The chimpanzee was the only species in which human δ-like glycophorin was detected but it differed from its human counterpart in electrophoretic mobility and reaction with M-specific monoclonal antibody. In contrast to humans, highly polymorphic glycophorin profiles were observed in each species of anthropoid apes and three distinct patterns were defined in each. No such polymorphism has been found so far among the Old World monkeys in the limited number of animals studied. The major glycophorins in all species but the chimpanzees failed to react with M- or N-specific monoclonal antibodies, suggesting structural differences from the human within the amino terminal regions. The reaction with the minor glycophorins showed inter- and intraspecies variability. All glycophorins, except δ-like glycophorin in the chimpanzee, reacted with the antiserum to the carboxyl terminal fragment of human α glycophorin, indicating a structural relation to the human in this region. An unexpected correlation was observed, in the chimpanzee, between the patterns of electrophoretically resolved glycophorins and the V-A-B-D blood-group phenotypes, allowing the assignment of each determinant to specific glycophorin bands. The basis for the differences observed between human and nonhuman primate glycophorins is not clear but the possibilities include a common nonpolymorphic ancestor and differences in selective pressures.

Rh Antibodies Produced by an Isoimmunized Chimpanzee; Reciprocal Relationship between Chimpanzee Simian-Type Isoimmune Sera and Human Anti-Rh₀Reagents

An isoimmune chimpanzee serum was found to contain, in addition to expected antibodies of the simian-type specificity anti-Lc, a fraction of anti-Rho specificity, as proved by parallel tests with standard human anti-Rho sera as well as by absorption experiments using human and chimpanzee red cells. On the other hand, the two human anti-Rho sera tested in parallel were found to contain not only antibodies of specificity anti-Rho but also antibodies capable of detecting Lc specificity on the chimpanzee red cells. The reciprocal relationship between human and chimpanzee isoimmune sera constitutes the first example of symmetrical cross-reactivity between closely related species. The new source of anti-Rho reagents is expected to contribute additional information on the human Rh-Hr blood group system.