Proc. Nat. Acad. Sci. USAVol. 70, No. 5, pp. 1303-1307, May 1973

Genetic Model for the Rh Blood-Group System(conjugated operons/repressors/quantitative blood typing)

RICHARD E. ROSENFIELD*, FRED H. ALLEN, JR.t, AND PABLO RUBINSTEIN*t

*Department of Pathology, Mount Sinai School of Medicine, 5th Ave. and 100th Street, New York, N.Y. 10029;tNew York Blood Center, 310 East 67th Street, New York, N.Y. 10021

Communicated by P. Levine, February 26, 1173

ABSTRACT Inherited quantitative aspects of the Rhblood-group system and susceptibility of Rh to the effectsof independently segregating suppressor genes can beaccounted for with a conjugated operon model. Thisassumes the existence of four operator or promotor (con-trol) genes for these functions, while closely linked struc-tural regions determine the qualitative characteristics ofRh antigens. Observed restriction of antigenic crossre-activity to the products of adjacent genetic regions anddata from blood typing of nonhuman primates bothsuggest that Rh complexity arose from a series of geneduplications and independent mutations.

The 33 qualitatively different antigenic specificities of the Rhblood-group system (1, 2) have become extraordinarily dif-ficult to organize systematically. Each allele at the Rh locusdetermines a variable number of different antigens (3, 4), andrecombination has been observed in just one family (5). Inaddition, quantitative differences in the expression of Rh anti-gens are also under the control of Rh genes (6). Accommoda-tion of quantitative data by genetic theories devised to ac-count only for qualitative alloantigenic variants (3, 4, 7, 8)results in a vast increase in an already overwhelmingly largenumber of complex alleles.

In this report, Rh data have been arranged in a manner thatdistinguishes qualitative from quantitative information. Fromthis arrangement, a consistent genetic model emerges that mayprovide a biologically sounder conceptual basis for this com-plex system.

In the Rh system (see Table 1 for glossary of terms) Rh: wl(Rh or DU) was the first quantitative variant found (9).A most interesting situation was shown to involve allelicinteraction, with the R-",2 -3 (r' or dCe) gene being suppres-sive of RI alleles (R or D) in trans position (10). Quantitativevariants of RI were documented quantitatively by Silber etal. (11) and Masouredis (12), but Gibbs and Rosenfield (6)found that the quantitative "degree of expression" was underthe strict genetic control of Rh genes and so was the inter-allelic depressive effect of R-1"2 -3. Within an extensive pedi-gree, identical genotypes were quantitatively identical forfour different Rh antigens, whereas qualitatively similar geno-types in the general population varied over a significant range(6). Using a different method, Berkman et al. (13) con-firmed these observations and extended the findings to theother blood groups.

Studies of the chemistry of secreted human blood-groupsubstances have provided detailed insight into the chemicalgenetics of ABO, H, and Lewis antigens (14, 15), while evalua-tion of N-acetyl-galactosaminyl transferases established boththe nature and the mechanism of production of quantitativevariants of the A antigen through the Km value of the specifictransferase (16).

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No such studies have been possible with membrane anti-gens, perhaps because their actual isolation from lipid mem-brane constituents might cause serious degradation (17).Recent studies of the microstructure of human erythrocytemembranes revealed moveable protein particles embedded inthe lipid phase (18); they were associated with blood-group Aactivity (18) and with receptors for both phytohemagglutininand influenza virus (19). The number of these particles wasestimated to be 4200 (18)-4500 (19) per /Am2 of the surface oferythrocyte ghosts or about 6 X 105 for an average intactcell.Membrane protein particles are likely to consist of several

polypeptides, some of which may be wholely or partly re-sponsible for the expression of blood-group antigens. If such apolypeptide were directly determined by a single blood-groupgene, alloantigenic variation could be the result of singleamino-acid substitutions similar to the situation for Gml ofIgG heavy chains (20). However, tertiary structures arisingfrom interaction between a polypeptide and either other poly-peptides or other membrane structures could also give rise toblood-group antigens. For instance, Rh antigenic activity waslost when ghosts were extracted with lipid solvents, but Rh

TABLE 1. Glossary of Rh terminology*(refs. 26 and 27, text)

I - Rho or D

2 - rhI or C

3 - rh" or E

4 a hr ' or c

5 - hr" or e

6 a hr or f or cis ce

7 - hr1 or cis Ce

8 - rhWl or CW

9 - rhX or CX

10 = hrt or V or eS

11 - rht or Ew

12 - rhG or G 23 - Dw

13 a RhA

14 - RhB15 - RhC

16 n Rh017 a Hr018 a Hr

19 a hrs

20 a VS

21 a CG22 a cia CE

24 w ET

26 a Deal

27 - cis cE

28 - hrH

29 - 'total Rh'

30 u Goa31 - hrB32 a determined by RN33 - determined by R0 Har

34 a Bas.

* Antigens shown as "Rh" followed by corresponding number.Phenotypes shown as "Rh: " followed by numbered antigensseparated by commas for which tests were performed. Negativeor weak result of test shown by minus (-) or "w," respectively,preceding number. Alleles shown by R with antigens producedor not produced given as for phenotype but in superscript. Rh25(LW) is the main antigen shared by human and rhesus eryth-rocytes. In man Rh25 is determined by genes that segregateindependently of the Rh locus. Rh34 has been assigned to thespecificity of the total immune response of Mrs. Bas (32).

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activity of ghosts treated with n-butanol was restored byaddition of "nonspecific" phosphatidyl choline (21). In-terestingly, F. A. Green found that Rh.,,1 cells reported inref. 22 were neither deficient in "restorative" phosphatidylcholine nor could their ghosts be rendered Rh-antigenic byaddition of n-butanol extracts of normal cells (personal com-munication to R.E.R.). Tertiary structure interactions appearto underly the HI and AI determinants (3) and may explain(see Rh25 of Table 1) the phenotypic association between Rhand LW (3, 23).

Strongly suggestive evidence that Rh is protein in nature(24) includes its reversible inactivation by p-chloromercuri-benzoate (25), inactivation by N-ethylmaleimide (25), de-struction by heating to 56' (26), susceptibility to proteolyticdigestion (27), and denaturation by urea (25, 28) or exposureto pH 3.0 (29). The role of phosphatidyl choline and the highlability of Rh indicate that the tertiary structure of a protein-lipid complex is essential to the formation, orientation, and/orstabilization of the expression of Rh determinants.

Table 1 gives the 33 antigenic specificities described in theRh system. The genetics of Rh, however, is far more com-plicated because the qualitative combination of antigenswithin each allotype and the degree to which each antigen isexpressed are both under the control of the Rh locus. In fact,to account for the thousands of resulting Rh allotypes, no lessthan four conjugated and coordinated systems, or operons(30), appear to be needed on chromosome 1 (31). This is shownin Fig. 1.A main point of regulation, although not an absolute neces-

sity, clearly indicates how all of Rh is susceptible to suppres-sion, especially by independently segregating, partially reces-sive genes. The known independent suppressors are calledX~r (33) and XQ (34) although neither is associated with theX chromosome. Both have profound effects when homo-zygous: X~r/X~r produces Rhnull (33) in which no Rh anti-

gens are expressed, while XQ/XQ depresses slightly less andproduces "pseudo rhG" (34). Furthermore, all known ex-amples of either blood type are associated with congenitalhemolytic anemia characterized by cup-shaped erythrocytes(stomatocytes) rather than normal discoid erythrocytes (35,36). Rhnull also arises from the homozygous state of "amor-phic" Rh genes (r or -) (37), and this, too, is associated withstomatocytic hemolytic anemia (38). Thus, one adequatelyfunctioning Rh gene appears to be needed for production ofnormal erythrocyte membranes. Whether the erythrocytechanges associated with RhnuiI and "pseudo rhG" are a directconsequence of the altered expression of Rh antigens or theresult of an epistatic effect of Rh genes is as yet unknown.The expression of all Rh antigens from one Rh gene can be

depressed by certain paired genes, especially those determin-ing Rh2 (rh' or C) (6). This effect, too, is more readily com-prehensible when a main point of regulation is assumed.The main regulatory locus of Rh may display allelic alterna-

tives. If R29 is considered the "normal" allele, R-29 can beassumed for cis Rhnun1 and RI' can be used for an abnormalexpression of all structurally specified antigens with coinciden-tal emergence of a rare and otherwise unobserved antigen,Rh33 (39). These allelic possibilities, however, are not obliga-tory because similar effects would obtain with selected cisconditions at other regions of the Rh system. These and otherproblems relating to the main point of regulation will be con-sidered later.The serology of the Rh blood-group system can be divided

into two parts, one concerning Rhl (Rh. or D) and the othernon-Rhl antigenic specificities. Indeed, this is the basis ofWiener's Rh-Hr terminology (4). However, Rhl is not likelyto be a discrete antigenic determinant but, rather, a series ofdistinct antigens inherited en bloc and all determined by"normal" RI genes. Rare R' genes lack one or more of theseantigens, and people who are type Rh:1 (Rh- or D-positive)

0 = Operator orpromotor; LII = Structural gene; - = Direction of control

IMPORTANT R933 RWI R(v),23 R32 R-4,21 pW3 R-3,5ALLELES R29 Rp ,(V),30 qP17 also -518 also

AT p(I,-) R4,±26 R-34 R3,tll,±24EACH R\ih/) R21,t2,tB9 p3or5 R5,±10,28LOCUS RI(')

Suppressors Ironsof R29 (x°x0)(1?21 )

CROSSREACTIVITIES Cis PRODUCTSSPECIFICITY CROSSREACTION ANTIGEN ALLELE

RhI2 Rhl/Rh2I Rh6 R4,5 or weokly, R-3,4hr- Rh 3 / Rh4 Rh7 R2 45

hrjr Rh2I/Rh 5 Rh 22 P2,3Rh2O RhlO/ Rh28 Rh27 34

FIG. 1. Proposed genetic model for the Rh blood-group system. Figure represents some described relationships of different portionsof the Rh system and does not purport molecular assumptions in terms of mechanisms whereby, for example, R17 regulates both the Rh4or 21 structural region and the control locus for the Rh3 or 5 region. Likewise, it does not attempt to discriminate as to whether thecontrol region for the entire Rh system is a complete operon or merely an operator or promotor. Numbers used refer to recognized sero-logical specificities as defined in refs. 1 and 2, text, and Table 1. Roman numerals for categories of Rhl positivity (23) have been used inplace of ill-defined combinations of R13, R14, R15, R16, and possibly others.

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by virtue of such "incomplete" genes can become immunizedby, what are for them, foreign components. A study of thespecificity of different sources of anti-Rhl revealed strong re-semblances between antibodies made by many Rh: -1 personsand the immune response of a person carrying an "incom-plete" Rh:1 phenotype (40). Furthermore, the unusual im-munogenicity of Rhl (3, 4), in comparison with other non-ABO antigens, may well be due to its being a cluster of dif-ferent antigens that provide the Rh:1 recipient with a spec-trum of antigens toward which to respond.There is no evidence to suggest the simultaneous existence

of both Rhl as a discrete antigen and of component Rhi-likeantigens. Alternatively, the Rh phenotype in reference to Rhlcan be considered to be conditioned by a structural geneticregion that specifies component antigens under control of aclosely linked regulatory gene. Such a control gene, as shownin Fig. 1, can be designated RI because its effects fit exactlythe operational definition of the Rhl antigen. RI switches"on" the structural region for components, but alleles at theRI locus switch "on" with variable efficiency, giving rise togenetically controlled quantitative differences in "expression"of Rhl. At very weak levels of "on," RI can be called Rel (Ror DU) because the majority of these people show depressionof all studied components. The R-1 allele (r or d) provides"off" to explain the Rh: -1 (Rh-negative) status. Further-more, as a regulatory gene, R-' could not have an antigenicstructural product, d. There is no way to determine at presentwhether this closely linked control locus acts as "operator" or"promotor." For the purposes of this discussion, alleles atsuch regulatory loci will be referred to as control genes.

Tippett (23) resolved Rhl component polymorphism intosix categories, whereas Wiener (4) described four "factors,"RhAB.CD. A more precise definition of this structural regionis needed, but Tippett's classification accommodates all ob-servations efficiently, including the very important discoveriesthat Class IV phenotypes have Rh3O (Goa) (41) and thatpersons in Class V have Rh23 (DW) (42). Neither Rh3O norRh23 is observed under other conditions. Thus, we can assumethe existence, under the control of R', of structural allelesR R(), R~ t R(i) 0, R(M23,2R(), and R(), with R(°)designating absence of a class and thereby presence of allcomponents (Fig. 1).The "non-Rhl" part of Rh includes structural genes for

either Rh4 or Rh2l, and for either Rh3 or Rh5. It appears toconsist of two conjugated operons, but one control gene com-mands both operons and is defined (Fig. 1) by the rare "off"allele, R-'7 (R0 or D-) (3, 4). The homozygote R-1-'17/R- '-7 (43) could also produce cis Rhull, hypotheticallyindistinguishable from what would be produced by R-29/R-29.Another rare alternative of R-17, R32 (RN) (44), depresses

both Rh2l and Rh5 and leads to the expression, perhaps as adirect consequence, of the rare antigen, Rh32 (45). The allo-type designated D(C)-, carries partially depressed Rh2l andfully suppressed Rh5 without appearance of Rh32 (23), but isotherwise quite similar. Rare allotypes, Ad, rL, and rt (3),could arise from other alleles at this control locus.The common alleles of R-'7, collectively termed R17, regulate

directly the degree of expression of the Rh4 or 21 structuralregion in which several alternative antigenic characteristicsare known (1, 2). Data are insufficient to further resolve thisstructural region. In Fig. 1, R4 produces Rh4 with or without

mines Rh2l (C') with or without Rh2. Rh: - 2,21 has beencalled rh' (46). R21 alleles also may (18R21) or may not produceRh8, and may (R9,21) or may not produce Rh9.The Rh3 or 5 region in Fig. 1, in addition to being under

control of both R29 and R17, has its own control gene as evi-denced by the rare R-8' - allotypes, DCP'- and Dc- (3), whicharise from the "off" alternative. The "on" alleles control thedegree of expression of Rh3 or 5 antigens in "normal" allo-types while additional alleles at this control locus determineRh: w3 (EU) (3) and both the Shabalala-Santiago (2, 47) andBastiaan (2, 32) types. The latter two alternatives are des-ignated, respectively, R-18 and R-"4. Rh34 has been assignedto the specificity of the total immune response of Mrs. Bas(32).The Rh3 or 5 structural region in Fig. 1 also cannot be re-

solved beyond treating its genes as a series of alternatives(1, 2,32). Thus, RI produces Rh3 with (R1? ) or without Rhil,and with (RI 24) or without Rh24. R5, the most inclusive alleleof R3, may produce Rh5 with (R5 10) or without RhlO, andwith (R5,21) or without Rh28 (48). Two antigens, Rhl9 andRh3l, are expressed by R5 alleles except when control genes

are R-1'8-34, R-18, or R-34.Ascribing control functions to genetic determinants of anti-

genic specificities such as Rh29, Rhl7, Rhi8, and Rh34 is notnecessarily contradictory. Such antigens could be propertiesof structural products arising in consequence of each and all"on"l alleles at corresponding control loci. A new symbology isnot needed immediately merely to denote this relationship.

Separate antigenic determinants interact in various ways.

(1) Some antigens alter the serological expression of others.Thus in Fig. 1, R21 in trans position partially represses theproducts of all three structural regions (6). In cis position,however, R21 augments the expression of Rh3 while Rhl ap-

pears depressed when compared to its expression in Rh: 1,-21phenotypes (3). Another example is RhlO from R45'60,, whichis often associated with reduced cis Rh6 (13). (2) Antigensmay crossreact and thereby create additional specificities, as

shown in Fig. 1. These include Rhl2 representing either Rhlor Rh2l; "hri" (43) representing either Rh3 or Rh4; "hr-."representing either Rh2l or Rh5; and Rh2O representing eitherRhlO or Rh28 (47). (3) As shown in Fig. 1, antigenic deter-minants may arise as cis products (1-3) of different structuralregions: Rh6 from R4,5 or, weakly, from R-3'4' 5 (cD-); Rh7from R2'-4'5; Rh22 from R2'3; and Rh27 from R834. (4) Rhantigens may be essential for the expression of other blood-group genes. Thus, all examples of Rhull are LW-negativeand show depressed S, s, and U (49). The mechanism of thisinteraction is unknown but since LW-positive persons may

become phenotypically negative temporarily (50), it can bepostulated that the corresponding structure (polypeptide?) is

antigenic only when bound to Rh. This bond could be lostreversibly enabling such people to make anti-LW even thoughLW antigenicity eventually reappears (50).

Assignation of control and structural Rh functions to sepa-

rate loci may be considered as merely an updating of Fisher'sCDE proposal (7, 8). The model now proposed, however, more

closely resembles the four conjugated operons responsible forstructural protein synthesis by A phage (51). Rh also appears

to be part of an important membrane protein. In both Rh andX phage a main control locus commands three structural re-

Rh26. The most inclusive alternative to R4 is R21, which deter-

Genetic Model for Rh 1305

gions, each of which has its own control gene. Further, in both

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systems one of these secondary control genes influences twodistinct structural regions.The existence of specific control genes that determine

"degree of expression" while structural genes generate qual-itative differences has already been proposed for mammals:X-linked testicular feminization in the mouse is very likelythe result of a noninducible regulatory mutation of the Jacob-Monod type (52).

Hughes-Jones et al. (53) found evidence suggesting that thetotal number of antigenic sites per cell, as determined by thethree structural regions of both chromosomes, may be con-stant for most Rh: 29 phenotypes. According to the model nowproposed, such a quantitative limitation could easily be im-posed by a structural product of the main control (R29) region(e.g., RNA polymerase) on all conjugated genes.Although conjugated systems are not characterized by high

crossover rates, and only one Rh recombination has actuallybeen detected (5), some complex Rh alleles may have resultedfrom unequal crossing over. R-',2 -3 4,5,6 -7,21,28 (r'") and thevery similar R1,w2,3,4,5,6,7,w21'28 (GU) are prime suspects(1, 54). The difference between these alleles is likely to residewith R17 control genes for the "non-Rhl" part of Rh, some be-ing more depressive of the Rh4 or 21 region than others. Thesame sort of variation could underly the difference betweenR-1,2, -3, -4,5, -6,7,21, -28 (r') and R-1,w2, -3, -4,5, 6, -7,21, -28 (rG).From these examples, Rh7 is clearly a product of R2 -4,5 inwhich Rh2 must be reasonably well expressed.The products of adjacent structural regions, as proposed,

exhibit several important crossreactions. This finding suggeststhat these structural loci may have appeared during evolu-tion by a series of gene duplications resembling the evolutionof Hp2 from Hp"F plus HplS (55). Serological crossreactionsare the result of stereochemical similarities more likely to existbetween products of closely related genes than between prod-ucts of genes separated by more mutational events. There-fore, the Rh4 or 21 region should occupy a central positionbecause its antigens crossreact with antigens of both the Rhland the Rh3 or 5 regions and probably its first duplication,through mutation, evolved into Rhl components. The dupli-cation that gave rise to Rh3 or 5 is likely to be more recentsince many more crossreactions involve its products with thoseof Rh4 or 21. Crossreactions between Rhl and Rh3 have notbeen observed.The phylogeny of Rh shows a parallel increase in com-

plexity. All gibbons tested (56) had only Rh4, while chim-panzees, gorillas, and orangutans possessed both Rh4 andRhl (56). Neither Rh3 nor Rh5 determinants were found innonhuman primates (56), and hence this region's appearancein man may have occurred later in evolution. The main pointof control (R29) either coexisted with an original Rh4 operonor it arose from a duplication of the R17 control gene. The factthat the Rh3 or 5 operon is under the control of both R29 andR'7 as well as R3 or further supports the idea of its morerecent divergence from Rh4 or 21.The status of Rh4 as the oldest Rh antigen may also explain

the interesting finding that, when present, Rh4 is associatedwith more antigenic sites per cell than any other Rh antigen(53). 8 X 104 Rh4 sites per cell were found in the homozygote,very close to the value of 105 for Rhl sites on Rh:17 (Rh. orD-) cells (53) in which there is no competitive production of"non-Rhl" antigens.Other blood-group systems may be explained on the basis of

similar models, but there is insufficient data as yet to attemptthis. Two systems in which we require more quantitative datafor such consideration are Kell and Lutheran. Both havecomplex alleles, each of which determines multiple antigens.However, some of these alloantigens appear to be allelic toothers in the sense that they segregate as alternatives, and nogene complex carrying more than one has been observed (3).Rare amorphic genes at both the Kell and Lutheran locidetermine "null" types when homozygous (3). Lutheran genesare additionally subject to the repressive effect of a rare dom-inant gene at an unmapped locus causing a "null"-like type(3). Kell genes, too, are repressed by what appear to be rarerecessive genes at an independent locus (3), apparently re-lated to the X chromosome (57). When hemizygous, this isassociated with "McLeod," a very weak Kell phenotype, andoften with X-linked chronic granulomatous disease (57).

This genetic model for membrane structural polypeptidesthat have not been isolated is, admittedly, entirely specula-tive. It does, however, provide a rational conceptual frame-work with which to view the complexity of Rh in its entirety.The model arose as a consequence of finding the strict geneticcontrol exerted by the Rh locus on the quantitative expressionof all Rh antigens, and it should be subject to critical studyfrom quantitative considerations. Human kinships involvinglarge sibships and three generations should be assayed quan-titatively in search for crossover data involving control genes.These loci, rather than those for qualitative structural data,may provide new and significant information concerning thestructure of genes that control the expression of Rh antigens.

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36. Chown, B., Lewis, M., Kaita, H. & Lowen, B. (1971) "Anew cause of haemolytic anaemia?" Lancet i, 396.

37. Ishimori, I. & Hasekura, H. (1967) "A Japanese with nodetectable Rh blood group antigens due to silent Rh allelesor deleted chromosome," Transfusion 7, 84-87.

38. Hasekura, H., Ishimori, T., Furusawa, S., Kawaguchi, H.,Kawada, K., Shishido, H., Komiya, M., Fukuoka, Y. &Miwa, S. (1971) "Hematological observations on the Ph(---/---) propositus, the homozygote of amorphic Rhblood group genes," Proc. Jap. Acad. 47, 579-583.

39. Giles, C. M., Crossland, J. D., Haggas, W. K. & Longster,G. (1971) "An Rh gene complex which results in a 'new'antigen detectable by a specific antibody, anti-Rh33,"Vox Sang. 21, 289-301.

40. Rosenfield, R. E., Haber, G. & Gibbel, N. (1958) in "Anew Rh variant," Proc. 6th (1956) Congr. Int. Soc. BloodTrans. (Karger, Basel), pp. 90-95.

41. Lewis, M., Chown, B., Kaita, H., Hahn, D., Kangelos,M., Shepeard, W. L. & Shackelton, K. (1967) "Blood groupantigen Goa and the Rh system," Transfusion 7, 440-441.

42. Chown, B., Lewis, M. & Kaita, H. (1962) "A new Rhantigen and antibody," Transfusion 2, 150-154.

43. Rosenfield, R. E. (1960) "The complexity of Rh antigens,"Proc. of the 7th (1958) Cong. Int. Soc. of Blood Transf.(Karger, Basel), pp. 557-563.

44. Rosenfield, R. E., Haber, G., Schroeder, R. & BallardR. (1960) "Problems in Rh typing as revealed by a singleNegro family," Amer. J. Hum. Genet. 12, 147-159.

45. Chown, B., Lewis, M. & Kaita, H. (1971) "The Rh system.An anomaly of inheritance, probably due to mutation,"Vox Sang. 21, 385-396.

46. Levine, P., Rosenfield, R. E. & White, J. (1961) "The firstexample of the phenotype rG rG," Amer. J. Hum. Genet. 13,299-305.

47. Shapiro, M. (1960) "Serology and genetics of a new bloodfactor: hrs," J. Forensic Med., 7, 96-105.

48. Shapiro, M., (1964) "Serology and genetics of a 'new' bloodfactor: hrH," J. Forensic Med. 11, 52-66.

49. Levine, P., Celano, M., Vos. G. H. & Morrison, J. (1962)"The first human blood, ---/---, which lacks the "D-like"antigen," Nature 194, 304-305.

50. Chown, B., Kaita, H., Lowen, B. & Lewis, Al. (1971) "Tran-sient production of anti-LW by LW-positive people,"Transfusion 11, 220-222.

51. Watson, J. D. (1970) in Molecular Biology of the Gene (W.A. Benjamin, New York), 2nd ed., pp. 487-490.

52. Ohno, S. & Lyon, M. F. (1970) "X-Linked testicular femini-zation in the mouse as a non-inducible regulatory mutationof the Jacob-Monod type," Clin. Genet. 1, 121-127.

53. Hughes-Jones, N. C., Gardner, B. & Lincoln, P. J. (1971)"Observations of the number of available c, D, and Eantigen sites on red cells," Vox Sang. 21, 210-216.

54. Beattie, K. M\., Neitzer, G. M\., Zanardi, V. & Zuelzer, W. W.(1971) "Gu, a variant of G," Transfusion 11, 152-156.

55. Smithies, 0. (1964) "Chromosomal rearrangements andprotein structure," Cold Spring Harbor Symp. Quant. Biol.29, 309-319.

56. Wiener, A. S., Moor-Jankowski, J. & Gordon, E. B. (1964)"Blood groups of apes and monkeys. IV. The Rh-Hr bloodtypes of anthropoid apes," Amer. J. Hum. Genet. 16, 246-253.

57. Gibblet, E. R., Klebanoff, S. J., Pincus, S. H., Swanson, J.,Park, B. H. & McCullough, J. (1971) "Kell phenotypes inchronic granulomatous disease: A potential transfusionhazard," Lancet, i, 1235-1236.

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