PETER J. D'ADAMO
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THE SUB GROUPS OF A
See also: Sub groups of type A
Considerable numbers of variants of the A antigen are known, most of which are rare; the B antigen is less variable but several rare variants are known. The most important distinction is between A, the commonest antigen, and A2 which has a frequency of several per cent in most European, African, and West Asiatic populations. Though the distinction has been known for nearly 50 years. Its basic nature is still not completely understood, but most of the facts are covered by the following conventional account. Thomsen el al. (1930) observed that there were two varieties of the A antigen, A1 and A2, allowing the blood groups A and AB to be classified respectively as
A1 and A2, and as A1B and A2B. Both types of antigen react with the ordinary antibody anti-A, but only
A1 reacts with anti-A1, while A2, fails to do so. Reaction of antigens is shown, as usual, by agglutination. Anti-A1 is present in the serum of most B persons together with ordinary anti-A. The latter antibody can be absorbed from a serum containing it, by means of A2 cells, leaving only anti-A1 behind, so that the serum becomes a specific anti-A1 reagent. An excellent anti-A1 reagent can also be prepared by extracting the lectin from
Dolichos biflorus seeds with physiological saline.
The A1 and A2 antigens are produced by corresponding allelomorphic genes, so that what we have called the
A gene is really of two possible kinds, A1 and A2. In the genotype
A1A2 the A1 gene causes the production of A1 antigen, and thus the genotypes
A1A2, A1O, and A1A1 are indistinguishable by methods at present available, since all react both with anti-A and anti-A1.
As group A2 is intermediate in several of its properties between A1 and O, it would be of great interest to know whether this applies to its associations with disease, but unfortunately very few investigators of associations have determined the sub-groups of A in their patients.
THE RHESUS BLOOD GROUP
See also: Rhesus Blood Group
From a clinical point of view the Rhesus or Rh system is by far the most important system other than ABO. ABO-Rh incompatibility is the main cause of hemolytic disease of the newborn, and a major cause of transfusion reactions. As however hemolytic disease of the newborn is not being considered in detail here, and as the other disease associations of the system are few and relatively unimportant, only a brief account of the system will be given here. The principal antigen of the system Rh0 or D, was discovered by Landsteiner and Wiener (1940). Subsequently, very numerous other associated antigens were discovered, and considerable controversy arose both as to notation and as to the theoretical interpretation of the uncontroversial observations of geneticists. This is not the place to discuss the controversy and for the purpose of this book the CDE notation of Fisher (Race, 1944) will be used, and its genetic implications of closely linked genes will be assumed. Only the main features of this very complex system will be described. On this basis the principal antigen of the system is known as D, determined by a gene
D, the allele d of which behaves as an amorph very closely linked to the
Dd locus are two other loci each characterized by a pair of major alleles
Cc and Ee respectively. Each of these four genes gives rise to a correspondingly named antigen.
Them are thus eight possible chromosomic combinations of genes, all of which are known to exist, but of which
CDe cDE, cDe, and cde are the commonest.
Incompatibility with respect to the D antigen it, as already mentioned, the main cause of hemolytic disease of the newborn, but Cc and Ee incompatibilities are rare causes, as they am also of transfusion reactions. Unlike the antibodies of the ABO system, each of which is universally present in persons lacking the corresponding antigen, antibodies to the Rh antigens are virtually never found except as a result of immunization by pregnancy or transfusion, and reactions appear only at a second exposure to the antigen. This applies also to all the other blood-group systems except the ABO. Very few searches have been made for any other kinds of disease associations of the Rh groups, and nearly all of these are confined to a comparison of the D-positive and D-negative types.
Rh blood type might also influence NK cell activity. While some studies have not found an association, other researchers have observed a higher natural NK cytotoxicity against target cells in individuals with Rh- blood type.
It has recently been demonstrated
that two human Rh glycoproteins can correct ammonium transport deficiency in mutant yeast cells. Rh proteins are therefore ammonium transporters - a role that, in vertebrates, has remained previously uncharacterized. These data herald a new era in Rh protein research, beyond their role as blood group antigens, and into the characterization of ammonium transport mechanisms, notably in the kidney.
Pross HF, Baines MG. Studies of human natural killer cells. I. In vivo parameters affecting normal cytotoxic function. Int J Cancer 1982 Apr 15;29(4):383-90
Lasek W, Jakobisiak M, Plodziszewska M, Gorecki D. The influence of ABO blood groups, Rh antigens and cigarette smoking on the level of NK activity in normal population. Arch Immunol Ther Exp (Warsz) 1989;37(3-4):287-94
Hersey P, Edwards A, Trilivas C, et al. Relationship of natural killer-cell activity to rhesus antigens in man. Br J Cancer 1979 Mar;39(3):234-40
Marini AM, Matassi G, Raynal V, Andre B, Cartron JP, Cherif-Zahar B. The human Rhesus-associated RhAG protein and a kidney homologue promote ammonium transport in yeast. Nat Genet. 2000 Nov;26(3):341-4.
THE MN SYSTEM
See also: MNS Blood Group
Up to 1927 the term 'blood groups' meant simply the ABO groups, for few people had any idea that there could be others; one of these few was Landsteiner; he and Levine injected rabbits with red cells-each rabbit with cells from one person. The sera of these rabbits, after
suitable treatment, were found to contain any one of three antibodies, each
of which agglutinated some but not all human red cell; the substances
assumed to be be present on the red cells were given the symbols M, N,
and P, giving rise to agglutination of the cells by the respective antibodies anti-M,
anti-N, and anti-P.
When the MN system was first discovered it appeared rather uninteresting. It was of virtually no medical importance, and the frequencies of the M and N genes were closely similar, each near 50 per cent, in most populations available for testing. Only the American Indians, with much more M than N, relieved this uniformity. The discovery of the S and s antigens in 1947 and 1951 came at a fortunate time, for a model of
closely linked genes in the Rh system had been very thoroughly studied, and so it was soon realized that here again closely linked loci were involved, two irr number, one determining the alleles M and N and the other S and s. Thus in the MN system we now have the possibility of four haplotypes MS, Ms, NS, and Ns and, as we shall see, this expansion of the system greatly enhances its anthropological value.
A considerable number of other antigens are now known to be determined by genes closely linked to MN and Ss but only one of these, the Henshaw or He antigen, has any great anthropological value, for it appears to be totally limited to populations of African ancestry. The hypothetical allele of the He gene, which we may call he, has not yet been shown to give rise to an antigen.
The substances M and N on the red cells are inherited by means of two allelomorphic genes M and N at a single locus (independent of ABO and of P1P2) but there is no dominance or recessiveness, so that while the cells of MM homozygotes are agglutinated by anti-M and those of NN homozygotes by anti-N, those Of MN heterozygotes are agglutinated by both antisera.
Because anti-M and anti-N occur only extremely rarely in human serum there is almost no danger of their causing trouble in blood transfusion. Thus they have been recognized as of little importance in medicine, and testing has largely been left to geneticists. Thus data
on the distribution of the M and N groups has built up only very gradually
over the years.
Blumenfeld and Adamany (1978) found that the MM blood group polypeptide differs from the NN polypeptide in two amino acids, these being serine and glycine in MM and leucine and glutamic acid in NN. The MN individual shows all four amino acids. The two major sialoglycoproteins of the human red cell membrane, alpha and delta (glycophorins A and B), carry the MNSs antigenic specificities. They have identical amino acid sequences for the first 26 residues from the amino terminus. Alpha expresses M or N blood group activity; delta carries only blood group N activity. Furthermore, the asparagine at position 26 of the alpha carries an oligosaccharide chain which is absent from the same position of delta. The two sialoglycoproteins differ in their remaining amino acid sequence and delta expresses Ss activity. Using antibodies directed against different structural regions of the major sialoglycoprotein alpha, Mawby et al. (1981) confirmed that two variant forms (Miltenberger class V and Ph) represented hybrid sialoglycoprotein molecules, which arose from anomalous crossover events between the genes coding for alpha and delta. The genes appear to be closely linked, in the order alpha-delta (5-prime to 3-prime). Thus the family data on close linkage are confirmed. The sequence may be MN--Ss--Gc (Gedde-Dahl and Olaisen, 1981)
Rothman et al. (1995) used the GPA assay to evaluate the effects of occupational exposure to benzene. The GPA assay measures the frequency of variant erythrocytes that have lost expression of the blood type M in blood samples from heterozygous (MN) individuals. Variant cells are detected by treating sphered, fixed erythrocytes with fluorescent-labeled monoclonal antibodies specific for the M and N forms and, by flow cytometry, counting variant cells that bind the anti-N antibody but not the anti-M antibody. The variant cells possess the phenotype N-zero (single-copy expression of N and no expression of M) or NN (double-copy expression of N and no expression of M). These phenotypic variants arise from different mutational mechanisms in precursor cells: N-zero cells are thought to arise from point mutations, deletions, or gene inactivation, whereas NN cells presumably arise from mitotic recombination, chromosome loss and reduplication, or gene conversion. Rothman et al. (1995) used this GPA assay to evaluate DNA damage produced by benzene in 24 heavily exposed workers in Shanghai, China and 23 matched controls. A significant increase in the MN GPA variant cell frequency was found in benzene-exposed workers, but no significant difference existed between the 2 groups for N-zero cells. Furthermore, lifetime cumulative occupational exposure to benzene was associated with the NN frequency, but not with the N-zero frequency, suggesting that NN mutations occur in longer-lived bone marrow stem cells.
Springer and colleagues recently summarized the results of a clinical trial initiated in 1974 to examine the potential of T/Tn antigens (carbohydrate precursors of MN blood group
antigens) as vaccines for breast cancer. T/Tn antigen (10 mg) was admixed with 0.5 units of typhoid vaccine, USP (Salmonella typhi) and injected intradermally in 16 patients with stage II, III, or IV breast cancer. Mean survival exceeded 5 years; the 10 patients who survived more than 10 years included three stage III and three stage IV patients. MacLean and co-workers (149b) have undertaken a pilot study to determine whether human breast carcinoma patients immunized with a second carbohydrate epitope (sialyl-Tn-KLH plus DETOX) produce specific anti-sialyl-Tn antibody responses. Following immunization, all 12 patients developed increased titers of complement-mediated cytotoxic antibodies specific for sialyl-Tn. Five patients were alive 12 or more months after entry and another 4 patients were alive 6 or more months after entry into the study.
THE ABILITY TO TASTE PHENYLTHIOCARBAMIDE (PTC)
See also: PROP and PTC Taster Polymorphisms
In 1931 Fox observed that to some individuals the simple chemical compound phenylthiocarbamide (PTC), has an intensely bitter taste, while to others it is tasteless Being a chemist he also showed that a number of other closely related were tested by the PTC tasters but not by the non-tasters. The ability to taste these substances was shown by Blakeslee and Salmon (1931) and by Snyder (1932) to behave as a Mendelian dominant character.
Harris and Kalmus (1930) showed that the distinction was by no means absolute one, and that reliable results could be obtained only by the use of solutions or known concentration. They devised a method for ascertaining the lowest concentration that could be tasted by each person. They prepared a saturated solution of PTC in distilled water, and from this a series of twofold dilutions. Starting with the weakest solution, the various dilutions are successively presented to the subject until he claims to be able to taste one. Two glasses of this dilution and two of distilled water are then presented, and he is asked to say which are which. If be answers correctly the dilution is taken to mark his threshold, but if he gives the wrong answer the experiment is repeated with the next stronger solution, and so on.
Nearly every population shows a bimodal distribution of thresholds with a clear-cut intermediate dilution level at which few or no thresholds fall. Those who can taste solutions dilute than this critical value are classed as tasters and those whose thresholds fall at bow concentration as non- tasters.
The recognition that the substances which define the taster polymorphism are thyroid inhibitors, and that the polymorphism is associated with differences in susceptibility to thyroid diseases has been noted in the literature.
As already mentioned,
phenylthiocarbamide is a thyroid inhibitor, and knowledge of this led Professors Harry
Harris and H. Kalmus, and Dr W. R. Trotter, and later Dr F. D. Kitchin and his colleagues, to look for an association
between tasting and thyroid diseases.
They and others have shown that there is indeed such as association, for persons with ordinary nodular non-toxic
goiters include an excess of non-tasters while those with toxic goiters, and
over activity of the thyroid gland, include an excess of tasters. There is some evidence that even in persons who are clinically normal there is a higher frequency of tasters among those with higher thyroid activity, and that tasters tend to develop more rapidly at puberty than non-tasters.
In this system we have a particularly complete picture of the environmental factors involved. As we have seen, the thyroid hormone molecule contains iodine, so that, for normal thyroid activity, a certain level of iodine is needed in the diet. Such small quantities of iodine, normally occurring as iodide, are tasteless to all individuals. It is moreover known that unduly high levels of iodine can produce thyrotoxicosis. On the other hand there are often present in the diet, especially in cabbages, thiocarbamide derivatives which are thyroid inhibitors, and which PTC tasters taste as bitter. We may suppose therefore that tasters, but
non-tasters, will limit their intake of such substances, and so be more liable to thyroid oven, activity, and less to
under activity, than non-tasters. Since both under activity and over activity
can affect fertility and can indeed be fatal, we can envisage a delicately balanced polymorphism of the two allelic: genes, based on the levels of iodine and of thyroid inhibitors in the diet, such
that if iodine is deficient or inhibitors in excess, tasters will be favored
selectively, while if there is an excess of iodine, or a lack of inhibtors,
non-tasters will be favored.
Sunderland has drawn attention to a particular case where
differences in taster frequency are possibly of practical significance. The geology of north Lancashire and that of Derbyshire are closely similar, with a preponderance of lower Carboniferous limestones and, presumably in
both areas, with a deficiency of iodine in the drinking water. Yet simple
iodine deficiency goiter is much commoner in Derbyshire ('Derbyshire neck') than in
North Lancashire, and this is accompanied by an appreciably higher frequency of tasters in the
low-goiter area. On the above selective hypothesis we should expect that the excess of
goiter-susceptible non-tasters in Derbyshire would (in the absence of goiter
prophylaxis) be gradually reduced, and with it the incidence of goiter would also be lowered.
Mahunage, (1962) showed that the consistency of ear-wax is under genetic control. Cerumen (ear-wax) may be wet (sticky) or dry (hard); the types are controlled by a pair of allelic genes, that for the wet type expressing itself dominantly in relation to that for the dry. Petrakis et al. (1971) summing up his own observations and those of others on the distribution of the alleles, showed that there are wide variations in gene frequencies throughout the world, the dry allele being predominant in the Mongoloid peoples; in Caucasoids the wet allele usually predominates, and in Negroids the dry allele is almost totally absent. Since the cerumen glands of the ear and the mammary glands are both derived from the apocrine type of sweat glands, attempts have been made to show an association between carcinoma of the breast and wax type.
THE DUFFY BLOOD-GROUP SYSTEM
See also: Duffy_blood_group_system
Almost the only other blood-group system that appears to bear any important relation to disease incidence, other than hemolytic disease of the newborn, is the Duffy system. However, the indirect in which this probable association was discovered suggests that similar unexpected relations may in the future be discovered with other systems. The antigen known as Fya was discovered by Cutbush et al. (1950) and the Fyb antigen, the product of its allelic gene, by Ikin et al. (1951). The allelic genes
Fya and Fyb account for nearly all the phenotypes found in European populations, but it was observed by Sanger et al. (1955) that a high proportion of American Negroes are of the phenotype
Fy(a-b-). An inspection of the latest tables of Mourant et al (1976) will show that, except in the South African Republic, over 95 per cent of African Negroes are of this type, which represents the homozygote of a third allelic gene, at first regarded
as an amorph and so named Fy. It is now known that two distinct genes have is the past been confused under this term. One,
Fyx with a frequency of approximately 1-6 per cent in Europeans, gives a product which is negative with anti-Fya but which reacts feebly with anti-Fy6 (Chown et al., 1972). The other, almost universal in Africans, gives a product which completely fails to react with either of these antibodies, but is not a true amorph, for Behzad et al. (1973) have shown its product to react specifically with an antibody which they call anti-Fy4; the gene should presumably be called
Fy4. Miller et al. (1975) have shown that the homozygote of this type is probably specifically resistant to
vivax malaria to which to which Africans have been known on be resistant.
THE P BLOOD-GROUP SYSTEM
See also: P (P1, P2) Blood Groups
The P blood groups were discovered by Landsteiner and Levine (1927) in the course of the same investigations defined the MN groups. It was at first thought that only one antigen, P, was involved, determined by a gene
P, the allele p being an amorph, the two genes having each a frequency of about 50 per cent in European populations. Further investigation has disclosed a system of considerable complexity, one feature of which will be described here. The antigen Tja found by Levine et al. (1951) was at first regarded as product of a gene present in nearly all human beings, extremely rare allele being an amorph, with the homozygous usually having a strong anti-Tja antibody. Sanger (1955) showed that Tja was part of the P system, with three alleles,
P1 (formerly P), P2 (formerly p), and the new
p (formally regarded as the amorph allele of Tja). These relationships are similar to those existing between
A1, A2, and O of ABO system. P2 bloods sometimes show anti-P1, in the plasma usually with a very low titer, but the rare
p bloods always have a high titer of anti-P+anti-P1. The P1 antigen is present in hydatid cyst fluid (Cameron and Stavalky, 1957) and in a considerable variety of worms, both parasitic and free living. It is likely that the anti-P1 not infrequently found in the plasma Of P2 individuals and in that of several species of mammals is a response to worm infestation, but so work appears to have been done on possible association between the P groups and such infestation.
Women of genotype pp, who always have anti-P+anti-P1 in their plasma, are particularly subject to abortion, apparently resulting from the action of the antibody upon the almost invariably P-positive fetus.
Paroxysmal cold hemoglobinuria is due to the presence in the patient's plasma of a cold reacting auto-antibody. It was shown by Levine in 1963 that this usually has anti-P specificity.