Summary A most unusual combination of serological findings in a healthy blood donor is described. His blood group is A1, and his red cells are weakly H positive; they are type MN, both the M and N antigens being of normal strength. His saliva contains A and H substances. His serum shows weak anti‐H and anti‐N activity which is best demonstrated at 12° to 16°, but is hardly detectable at 37°. This dual specificity, according to the results of agglutination tests and absorption experiments, appears to be due to two distinct antibodies, both of natural origin. The anti‐H is neutralized by the donor's own saliva. The donor presents no clinical or serological signs of auto‐immunization. Résumé Les auteurs décrivent une combinaison absolument inhabituelle des résultats sérologiques obtenus avec le sang d'un donneur de sang en bonne santé. Le groupe sanguin de ce donneur est A1, ses érythrocytes sont faiblement H positif; ils sont du type MN, les deux antigènes M et N étant de force normale. La salive de ce donneur contient des substances A et H. Son sérum présente une faible activité anti‐H et anti‐N, dont l'optimum thermique de réaction se situe de 12 à 16° C, mais qui est difficilement décelable à 37° C. Cette double spécificité, mise en évidence par les tests d'agglutination et confirmée par les épreuves d'absorption semble être due à deux anticorps distincts, tous deux d'origine naturelle. L'anti‐H est inhibé par la salive du donneur lui‐même. Ce donneur ne présente aucun des signes cliniques ou sérologiques d'un processus d'auto‐immunisation. Zusammenfassung Eine äußerst ungewöhnliche Kombination von serologischen Befunden bei einem gesunden Blutspender wird beschrieben. Seine Blutgruppe ist A,; seine Erythrozyten sind schwach H‐positiv. Er zeigt die Faktorenkombination MN; die Antigene M und N sind normal ausgeprägt. Sein Speichel enthält A‐ und H‐Substanz. Sein Serum zeigt eine schwache Anti‐H‐ und Anti‐N‐Aktivität, welche am besten bei Temperaturen von 12–16°C zur Darstellung gelangt. Bei 37°C ist sie kaum nachzuweisen. Auf Grund der Agglutinations‐ und Absorptionsversuche erscheint die Annahme am naheliegendsten, daß diese Doppelspezifität auf zwei verschiedene natürliche Antikörper zurückzuführen ist. Der Anti‐H‐Antikörper wird durch den Speichel des Spenders inaktiviert. Der Spender zeigte weder klinische noch serologische Zeichen einer Autoimmunisierung.
M and N are the two common ("normal") alleles at the MN locus of the MNSs blood group system. The antigens M and N that they determine are located within the amino-terminal region of glycophorin A. In the serologically active and glycosylated (*) fragment of glycophorin AN the sequence is Leu-Ser*-Thr*-Thr*-Glu-, and in that of glycophorin AM it is Ser-Ser*-Thr*-Thr*-Gly-. Mg and Mc are very rare ("variant") alleles of M and N; as to the corresponding antigens, Mg is serologically quite distinct from M and N, while Mc is a compound of both. Erythrocytes of genotypes MgN, MgM, Mg~g, and MCM, which were the object ofthe present study, contain normal amounts ofglycophorin A in their membrane. In glycophorin AM" the amino-terminal sequence is related to that of glycophorin AN by substitution of asparagine for threonine in position 4, and it is nonglycosylated: LeuSer-Thr-Asn-Glu-. The corresponding structure of glycophorin AM, is Ser-Ser*-Thr*-Thr*-Glu-it is thus closely related to that of glycophorin AN and AM, by substitution of the amino acids in positions 1 or 5, respectively. All ofthese substitutions can be explained by single base changes. The distinctions in chemical structure not only confirm the location of M and N in this region of glycophorin A, because they are the only differences observed, but also indicate, because they are correlated with the distinctions in antigenic specificity, that M andN are structural genes coding for amino acid sequences. The finding that Mc contains structural features ofboth M and N suggests that these two forms of glycophorin A have evolved from a common ancestral gene by single base substitutions at sites in the genome coding for amino acids in positions 1 and 5 of the sequence. Carbohydrate structures, however, are also necessary for full expression of antigens M and N. Glycosylation during biosynthesis of residues within the polypeptide appears to depend on a particular protein structure.The MN blood group antigens were described over 50 years ago by Landsteiner and Levine (1), who immunized rabbits with human erythrocytes in a deliberate attempt to find antigenic differences independent ofthe ABO blood groups. It has been recognized since that these antigens are situated on the integral membrane protein glycophorin A (2-4). The complex antigenic structure is located within the amino-terminal five amino acids ofthe sequence, three ofthese residues being glycosylated. The amino acid sequence of glycophorin A is different in positions 1 and 5 for molecules isolated from erythrocyte membranes ofindividuals homozygous for M or N, but no differences in carbohydrate structure or sites ofglycosylation (*) are apparent for the two forms (5, §): AN Leu-Ser-Thr-Thr-Glu- Glycophorin A was isolated from 100-400 ml of blood by methods outlined elsewhere (8). Briefly, after preparation of hemoglobin-free membranes the lyophilized ghosts were extracted with lithium diiodosalicylate and the sialoglycoprotein fraction was recovered from the aqueous phase after phenol partitioni...
Because of an apparent exclusion of paternity of the type father M/child N, and of the father's insistent denial of this exclusion, a thorough investigation of the MNSs groups of a Chinese family was carried out. The 'cxctusion' was proved false by the demonstration of Mk in the persons involved. It is the first time that this rare gene comes to notice through disputed paternity, and this is the first example of M k in Chinese. The family also had several members possessing Ms"', a gene complex which produces M, s, and the antigens characteristic of Cell Class I11 in the Miltenberger suh-system. Three sibs of the propo situs had the very rare genotype Ms"'/M". The medico-legal and serological aspects of the case adiscussed.
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