Immunochemical Studies on Blood Groups

Abstract

The basis for the difference between A1 and A2 specificity has been in dispute from the moment of its discovery (1-5). An excellent review of the earlier studies may be found in the thesis of Gammelgaard, recently available in English (6). One view holds that the A~ and A~ antigenic determinants are chemically identical, differences being essentially quantitative and ascribable to the presence of many more determinants on an A1 than on an A~ erythrocyte (7-11). Based on hemagglutination-inhibition titers of salivas from A~ and As secretors, B oettcher (11) proposed that individual molecules of A substance from A1 secretors have a higher ratio of A:H antigenic determinants than those from A~ secretors. He also proposed that the A~ gene is a duplication of the As gene. Bar-Shany et al. (12) found only a small, although significant, difference between A~ and A2 saliva in absorption studies. A proportion of A2 bloods contain anti-A~ (13-17). M~ikelii et al. (18) recently attempted to explain why anti-A~ does not agglutinate A2 cells without assuming that the A~ and A~ determinants differ. Hypothesizing the receptor density to be higher on A1 than on A2 erythrocytes, Miikel~i suggests that anti-A~ antibodies have a low affinity for A receptors and cannot form firm bridges between red cells using only one valence per cell. Thus they would only agglutinate A1 cells on which the receptors are close together. A~-specific antibodies therefore would have to be multivalent and of the 7M type and bivalent antibodies such as 7G would not distinguish between AI and A2 erythrocytes.The other view contends that there is a qualitative difference between the antigenic determinants in A1 and As individuals (19)(20)(21)(22)(23). Friedenreich and Worsaae (23) suggested that A~ and A~ are qualitatively different but related antigens. Their assumption was based mainly on absorption experiments showing that anti-A serum contained at least two kinds of antibodies, anti-A and anti-A~. A1 cells reacted strongly with anti-A

Immunochemical studies on blood groups LXVI. Competitive binding assays of A1 and A2 blood group substances with insolubilized anti-A serum and insolubilized A agglutinin from Dolichos biflorus.

“…2 b), indicating a qualitative difference. This is supported by the quantitative precipitin finding that although both A~ and A2 substances reach equivalence in the same region and decrease as more antigen is added, the amount of AbN precipitated at equivalence by A2 substance is less than that precipitated by A1 substance (4). If the difference were only quantitative, one would expect to reach the same maximum with A2 substance and the inhibition lines to be parallel in CBA.…”

“…The IgM eluates were not tested. A2 substance precipitated a larger proportion of antibodies from the IgG GalNAc eluate than from the IgG ARL 0.52 eluate (4). The GalNAc eluate would be expected to have more sites specific for the smaller trisaccharide structure LFucal 2 DGalNAca--~3DGal which A1 and A~ share, whereas the ARL 0.52 eluate would have more sites of larger size.…”

“…The absorbed, A-active material was eluted with vGalNAc as previously described (26,27). Inhibiters used in CBA included human blood group A, substances MSM 10%, MSS 10% (28), and Cyst 9 from Dr. Harold Baer (29), and human blood group .%2 substance Cyst 14 phenol insoluble (4). Cyst 14 fucose eluate and Cyst 14 effluent are fractions from Cyst 14 phenol insoluble separated by affinity chromatography on Lotus-Sepharose (30).…”

“…Chris and Jos partially absorbed on PL-Hog A, which is like htunan A1 substances (4,30), have lower binding affinities for [~H]HGM GaINAc eluate than the unabsorbed sera. This is reflected in the lower slopes, 36 for Chris (Fig.…”

Macro- and Microdiíferences in Blood Group Antigens and Antibodies

“…On the other hand, no such chemi cal basis has been found for the difference between Ai and A>. For both Ai and A2 the determinant group appears to be the same, namely, N-acetyl-Dgalactosamine, and the differences in their serological behavior appears to be due to some minor difference -perhaps differences in the length of the subjacent polysaccharide chain [9,29], As von D u ng crn and H irszfeld [2] showed, when anti-A serum (human group B serum) is absorbed with A2 cells, a fraction of antibody is left behind, designated anti-Ai because it agglutinates Ai cells but not A2 cells1. Thus, anti-A serum does not consist merely of a population of antibodies, all of identical structure, since it can be fractionated by absorption into antibodies of at least two specificitiesnamely, anti-A proper, reactive for both Ai and A2 cells and anti-Aj, reactive for Ai cells alone.…”