Journal of Clinical Apheresis 7:158-162 (1992)
Basic Principles of the ABO and Rh Blood Group Systems for Hemapheresis Practitioners Janice M. Sigmon Therapeutic Plasma Exchange Program, Nephrology Service, Walter Reed Army Medical Center, Washington, D.C. Since 1901, more than 20 distinct blood group systems have been identified and characterized. Yet, the ABO System. the first described, remains the most clinically significant in blood transfusion and organ transplantation medicine. The ABO antigens are the only cellular antigens which consistently produce a potent, naturally occurring antithetical antibody which circulates in the plasma of healthy individuals. ABO antigens are expressed on most blood cells. organs, and tissues and in most body fluids. Expression of the antigens results from thc interaction of several separate, but closely related genes: ABO, H , and Secretor (Se). Blood group specificity depends upon the inheritance of the ABO and H genes, and the subsequent expression of these antigens on the red blood cells. The “D” or Rho antigen is the most clinically significant blood group antigen next to the ABO antigens. The D antigen belongs to the Rh System, which consists of a trio of genes that are so closely linked that they are inherited as a package. The antigens are an integral part of the red blood cell membrane. They lend stability to the membrane structure when they are normal. but result in decreased red cell survival when abscnt. Rh antibodics are immune antibodies requiring a stimulus and can cause significant transfusion and childbearing complications 0 1992 Wiley-Liss, Inc. if present.
Key words: blood group genetics, blood group biochemistry, blood group systems, ABO antigens, Rh antigens
THE ABO SYSTEM
The ABO antigens were first defined and characterized in 1901 by Karl Landsteiner, an immigrant physician working in a New York laboratory because he was not licensed to establish a medical practice in the United States. He described the reactions which occurred when the red cells of one individual were mixed with the plasma of another individual. The categorical testing and documentation of the reactions of hundreds of blood and plasma samples resulted in the identification of 4 basic blood groups and their consistently present antithetical plasma antibodies (Table I). Frequency of ABO phenotypes is shown in Table 11. The ABO antigens are known to be present on all tissues and organs of the body. It is an expected fact of nature that within the first 6 months of life, healthy individuals develop circulating plasma antibodies specific for those ABO blood group antigens which are not present on their red blood cells. These antibodies are very potent and pose a major threat to life if an ABO incompatible transfusion or solid organ transplantation occurs. Herein lies the clinical significance of the ABO system.
lar circulation. They are IgM immunoglobulins capable of complement activation and intravascular hemolysis. ABO antibodies are very potent, often demonstrating hemolysis when serially diluted (titers of 1 : 256 or greater). An ABO incompatible transfusion can activate the classical pathway of the complement cascade and result in rapid hemolysis of the donor’s incompatible red cells [ 11. The release of hemoglobin and fragments of the ruptured red cell membranes into the plasma can be toxic to the kidneys, causing blocked glomeruli and subsequent renal failure. Therefore, every consideration must be given to these antigens and their antithetical antibodies when blood component and/or transplantation therapy are required (Table 111). Frequent transfusion of moderate quantities (>I50 cc/ transfusion) of ABO incompatible plasma with platelets and cryoprecipitate may result in the attachment of plasma antibodies to the patient’s red cells and tissues. This passively transfused antibody may result in the development of a positive direct antiglobulin test (DAT) and may cause a delayed transfusion reaction [2]. Al-
Nature of the ABO Antibodies
Address reprint rquests to Janice M . Sigmon, M . A . , MT(ASCP)SBB, Nephrology Service, Bldg 2 , Room 4903, Walter Reed Army Medical Center, Washington, D.C. 20307-5001.
The ABo antibodies between birth and months as the infant’s immune system develops. These antibodies are naturally occurring within the intravascu-
The opinions and assertions contained herein are the private views of the author and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.
0 1992 Wiley-Liss, Inc.
dntigens
the plasma
A B 0 AB
Anti-B Anti-A Anti-A and Anti-B None
&+ Genotype A 0 Phenotype A
F p Genotype BO Phenotype. B
TABLE 111. ABO Compatible Blood Components Patient Antigens on
red cells A B 0
AB
Compatible donor
Antibodies in the plasma
Red cells from group
Plasma from group
Anti-B Anti-A Anti-A and Anti-B None
A. 0 B. 0
0
A. AB B , AB A, B. 0, AB
A , B. 0 , AB
AB
though shortened survival of the patient’s own red blood cells is not always the result, a positive DAT discovered in a recently transfused patient will often require an extensive antibody workup prior to subsequent transfusions. While ABO compatibility is not an essential required for bone marrow transplantation [ 31, ABO compatible blood components must be transfused during the transition phase and until engraftment of the new bone marrow has occurred [4]. This may require multiple transfusions and time-consuming testing for a period of 10-14 days or even longer. It is interesting to note that after engraftment of a marrow from an ABO incompatible donor, the recipient’s tissue antigens may not be affected by the incompatible ABO antibodies produced by the new marrow I S ] . Genetics of the ABO Antigens
The genes which determine an individual’s blood group are located on Chromosome 9. The genes code for the production of an enzyme, a transferase, which will attach a blood group specific sugar to a precursor oligosaccharide chain. Each parent conveys one gene to the
child. The genotype is the actual genetic makeup, while the phenotype is the expression of the gene as seen in laboratory testing. The A and B genes are codurninanr alleles, meaning different forms of a gene, but both having equal strength of expression. When both alleles are conveyed (one from each parent), both are expressed as in group AB. Therefore, a group AB individual is herernzygous. The 0 antigen is recessive. It will not be evident unless inherited in the homozygous form (00).If an A or B gene is inherited with an 0 gene ( A 0 or BO), only the A or B gene is expressed. The 0 gene product is masked. Therefore, a group A or group B individual may be either homozygous (AA or BB) or heterozygous ( A 0 or BO). The only way to differentiate zygosity is to perform family studies and to predict the individual’s pedigree (Fig. 1). Biochemistry of ABO
Expression of the ABO antigens depends on the interaction of 3 separate and independent genetic systems: ABO, H, and Secretor (Se). The ABO genes code for the production of a transferase, which will attach a blood group specific sugar to a precursor oligosaccharide chain attached to the red cell membrane (Fig. 2). The precursor chain for all blood groups is the same: glucose, galactose, N-acetylglucosamine, and galactose. The H gene is required to transfer an L-fucose to the second galactose so that the ABO sugar can attach. The terminal sugar will then convey the specificity of the blood group. The attachment of N-acetylgalactosamine as the terminal sugar will convey blood group A specificity, while the attachment of D-galactose will convey group B specificity. Both N-acetylgalactosamine and D-galactose terminal sugar chains are found on the red cells of group AB
160
Sigmon
T h e ‘Precursor’ Chain (Bombay, oh)
T h e ’H’ Antigen Chain (also T h e ‘0’ Antigen)
T h e ‘A’ Antigen Chain
a
Glucose
0
Galactose
6
N-Acetylglucosarnine
L-Fucose
-
N Ac e t y Ig a1ac tosarn ine
T h e ’B’ Antigen Chain
Fig. 2.
T h e ‘A’ and ‘B’ Antigen Chains
+
D-Galactose
Different blood group antigens attached to the red blood cell membrane.
individuals. Group AB red cells often have quantitatively more group A antigens than group B antigens. The genes of a Group 0 individual do not code for the production of a transferase and the attachment of another sugar to the precursor chain. The “lack of” the additional terminal sugar is considered an “amorphic” phenomenon, and the blood group is interpreted as “missing,” thus group 0. Subsequently, the terminal sugar of group 0 individuals is the L-fucose of the H antigen, and group 0 red cells have quantitatively more H antigens than A, B, or AB red cells, which must compete with the H antigen for the limited antigen sites on the red cell membrane. is a rare blood group exThe Bombay genotype (0\,) pression. I t was identified in a small population of residents of Bombay in 1952 (61. These individuals do not inherit the dominant H gene. Instead, they inherit the recessive h gene from each parent, making them homozygous (hh). Although they inherit functional ABO genes, the transferase to attach the L-fucose is not produced, and the genetic blood group sugars (A or B) cannot attach to the precursor chain. Their blood type appears to be group 0. But these individuals do not have the H antigen, and they produce a naturally occurring, hemolytic anti-H as well as anti-A and anti-B, which circulate in their plasma. Bombay (0,) patients can receive red cell transfusions only from another Bombay (0,)individual; however, they can safely receive plasma
or plasma components from an individual of any blood group. The expression of ABO antigens in body fluids is dependent on the presence of the Secretor (Se) gene. Eighty percent of the general population carry at least one Se gene which is dominant over the se gene. The secretor status of an individual is of little importance in transfusion and transplantation medicine, but plays a major role in forensic science. THE Rh SYSTEM
In 1939, a student of Landsteiner, Philip Levine, published an obstetrical report of a case of hydrops fetalis in which he suggested the causative agent to be maternal blood group antibodies stimulated from an earlier pregnancy 17). In 1940, another student of Landsteiner, Alexander Wiener, reported the description of a new blood group system identified in Rhesus monkeys, Rh IS]. The antibodies produced in both cases demonstrated the same characteristics and thus were named anti-Rh. Several years later the 2 antibodies were shown to be of different specificities, but by that time several different nomenclatures had developed, further complicating the study of this clinically significant blood group system. The Rh antigens are found only on red blood cells. The Rh System consists of more than 40 distinguishable Rh antigens. The Rh, antigen, commonly known as D,
ABO/Rh for the HP
161
TABLE IV. Frequencies of Rh Phenotypes* Phenotype
White
Black
Oriental
D Positive D Negative
8S%
92% X% 28Ti 235% 98%. 99%
954’ 5%
15% 70%
c
E
307~ 80% 98%
c e
~~
~
~
*Composite ot figures from listed refcrcnces
rc
Chromosome #1
D Positive
D Positive Genotype ccDdEe PhenOtyDe cDEe
Genotype C c D d e e Phenotype CcDe
cde /
CDE
D Positive Genotype: CcDDEe Phenotype: CcDEe
Fig. 4. The Rh antigens are an integrated part of the red cell membrane, lending support to thc cellular structurc.
d ~ ecde D Positive Genotype: CcDdee Phenotype. CcDe
I CDE
cde
D Positive Genotype: ccDdEe P h e n o t y p e cDEe
cde /cde D Negative Genotype: ccddee Phenotype: c-d’e
Fig. 3. Schematic of predicted Rh genotypes and phenotypes from heterozygous Rh,, (D) positive parents. The trio of Rh antigens which comprise the Rh complex is so closely linked that they are inherited as a single genetic unit.
is the most immunogenic red blood cell antigen and thus plays a significant role in transfusion medicine. A single exposure to the D antigen will stimulate an antibody (anti-D) in more than 80% of the D negative population [ 9 ] . The Rh, (D) antibody may be stimulated in pregnancy, through transfusion, or by deliberate immunization. The Rho Antigen
The Rh, gene codes for the antigen D. The D is missing in approximately 15% of the general population. There is no actual d allele that can be tested for in the laboratory. However, for ease, the notation “d” is used for the missing gene product. An individual is reported as being Rho (D) positive or Rh, (D) negative. The D gene is dominant over the amorphic allele d. Therefore. the inheritance of a single D gene from either parent will make the individual Rh,, positive. Conversely, the Rh,, negative individual would have to be homozygous for d. The Rh Complex
The Rh complex is located on Chromosome 1. It is comprised of 3 genes located so close together that they
are inherited as a single genetic package. In addition to the D locus, there is the C locus with its alleles C and c, and the E locus with its alleles E and e. Frequencies of Rh phenotypes are shown in Table IV. The alleles at the C and E loci are codominant. Therefore an individual inherits a package of 3 genes (D, C , and E) from each parent for a total of 6 possible alleles (Fig. 3). If the allele is present, the allele is expressed (except d). If the allele is not seen in testing, the individual has probably inherited a double dose of the related allele (homozygous) . The Rh System is made more complicated by the infrequent appearance of uncommon allelic variations, i.e., Cw,D”, Rh:32, ce, f, etc. However, these are usually identified only if a patient has a transfusion complication. Transfusion is delayed due to the time required to identify the problem and to locate phenotypically similar blood to meet the transfusion needs of these patients. Biochemistry of the Rh System
The Rh antigens are made of glycoproteins, which are an integral part of the red cell membrane (Fig. 4). They play a key role in maintaining the red cell structure. Individuals who have aberrant Rh antigens, i.e.. Rh,,,, or Rh,,,,,(,, demonstrate shortened red cell survival and frequently have a compensated anemia [ 10,l I ] . The Nature of Rh Antibodies
Rh antibodies do not occur naturally. They are immune or acquired antibodies stimulated after exposure, sometimes requiring up to 6 months to develop. They are IgG immunoglobulins which can cross the placenta and cause fetal distress during pregnancy and problems at birth. They do not activate complement and cause immediate reactions. However, they are capable of causing delayed hemolytic transfusion reactions and shortened red cell survival. For this reason and because only 15% of the population is Rh,, (D) negative, national transfusion medicine policy is to make every reasonable
162
Sigmon
effort to transfuse Rho negative patients, especially women within childbearing age, with Rho negative blood.
REFERENCES 1 . Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, p 416. 2. Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V. Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks. 1990, p 315. 3. Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengclen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, p 262. 4. Kasprisin C A , Snyder EL: “Bone Marrow Transplantation: A Nursing Perspective.” Arlington, VA: American Association of Blood Banks. 1990, p 39. 5 . Kasprisin C A , Snyder EL: “Bone Marrow Transplantation: A Nursing Perspective.” Arlington. VA: American Association of Blood Banka, 1990, p 7. 6. Harmening D, Calhoun L, Polesky HF: “Modern Blood Banking and Transfusion Practices,” 2d ed. Philadelphia: F. A. Davis, 1989, p 87.
7. Lcvinc P, Stetson RE: An unusual case of intragroup agglutination. JAMA 113:126-127, 1939. 8 . Wiener AS, Peters HR: Hemolytic reactions following transfusions of blood of the homologous group, with three cases in which the same agglutinogen was responsible. Ann Intern Med 13:2306-2322, 1940. 9. Walker RH. Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, p 198. 10. lssitt PD: Biochemistry of the Rh blood group system 1988: eight new antigens in nine years and some observations on the biochemistry and genetics of the system. Transfus Med Rev 3: 1- 12. 1989. 1 1 . Walker RH, Hoppe PA. Judd WJ. Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington. VA: American Association of Blood Banks. 1990, p 21 I .
SELECTED READINGS Harmening D, Calhoun L, Polesky HF: “Modern Blood Banking and Transfusion Practices,” 2nd ed. Philadelphia: F.A. Davis, 1989, pp 24-42, 78-1 19, 366-378. Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF. Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, pp 159-223, 249-267.
Basic Principles of the ABO and Rh Blood Group Systems for Hemapheresis Practitioners Janice M. Sigmon Therapeutic Plasma Exchange Program, Nephrology Service, Walter Reed Army Medical Center, Washington, D.C. Since 1901, more than 20 distinct blood group systems have been identified and characterized. Yet, the ABO System. the first described, remains the most clinically significant in blood transfusion and organ transplantation medicine. The ABO antigens are the only cellular antigens which consistently produce a potent, naturally occurring antithetical antibody which circulates in the plasma of healthy individuals. ABO antigens are expressed on most blood cells. organs, and tissues and in most body fluids. Expression of the antigens results from thc interaction of several separate, but closely related genes: ABO, H , and Secretor (Se). Blood group specificity depends upon the inheritance of the ABO and H genes, and the subsequent expression of these antigens on the red blood cells. The “D” or Rho antigen is the most clinically significant blood group antigen next to the ABO antigens. The D antigen belongs to the Rh System, which consists of a trio of genes that are so closely linked that they are inherited as a package. The antigens are an integral part of the red blood cell membrane. They lend stability to the membrane structure when they are normal. but result in decreased red cell survival when abscnt. Rh antibodics are immune antibodies requiring a stimulus and can cause significant transfusion and childbearing complications 0 1992 Wiley-Liss, Inc. if present.
Key words: blood group genetics, blood group biochemistry, blood group systems, ABO antigens, Rh antigens
THE ABO SYSTEM
The ABO antigens were first defined and characterized in 1901 by Karl Landsteiner, an immigrant physician working in a New York laboratory because he was not licensed to establish a medical practice in the United States. He described the reactions which occurred when the red cells of one individual were mixed with the plasma of another individual. The categorical testing and documentation of the reactions of hundreds of blood and plasma samples resulted in the identification of 4 basic blood groups and their consistently present antithetical plasma antibodies (Table I). Frequency of ABO phenotypes is shown in Table 11. The ABO antigens are known to be present on all tissues and organs of the body. It is an expected fact of nature that within the first 6 months of life, healthy individuals develop circulating plasma antibodies specific for those ABO blood group antigens which are not present on their red blood cells. These antibodies are very potent and pose a major threat to life if an ABO incompatible transfusion or solid organ transplantation occurs. Herein lies the clinical significance of the ABO system.
lar circulation. They are IgM immunoglobulins capable of complement activation and intravascular hemolysis. ABO antibodies are very potent, often demonstrating hemolysis when serially diluted (titers of 1 : 256 or greater). An ABO incompatible transfusion can activate the classical pathway of the complement cascade and result in rapid hemolysis of the donor’s incompatible red cells [ 11. The release of hemoglobin and fragments of the ruptured red cell membranes into the plasma can be toxic to the kidneys, causing blocked glomeruli and subsequent renal failure. Therefore, every consideration must be given to these antigens and their antithetical antibodies when blood component and/or transplantation therapy are required (Table 111). Frequent transfusion of moderate quantities (>I50 cc/ transfusion) of ABO incompatible plasma with platelets and cryoprecipitate may result in the attachment of plasma antibodies to the patient’s red cells and tissues. This passively transfused antibody may result in the development of a positive direct antiglobulin test (DAT) and may cause a delayed transfusion reaction [2]. Al-
Nature of the ABO Antibodies
Address reprint rquests to Janice M . Sigmon, M . A . , MT(ASCP)SBB, Nephrology Service, Bldg 2 , Room 4903, Walter Reed Army Medical Center, Washington, D.C. 20307-5001.
The ABo antibodies between birth and months as the infant’s immune system develops. These antibodies are naturally occurring within the intravascu-
The opinions and assertions contained herein are the private views of the author and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.
0 1992 Wiley-Liss, Inc.
dntigens
the plasma
A B 0 AB
Anti-B Anti-A Anti-A and Anti-B None
&+ Genotype A 0 Phenotype A
F p Genotype BO Phenotype. B
TABLE 111. ABO Compatible Blood Components Patient Antigens on
red cells A B 0
AB
Compatible donor
Antibodies in the plasma
Red cells from group
Plasma from group
Anti-B Anti-A Anti-A and Anti-B None
A. 0 B. 0
0
A. AB B , AB A, B. 0, AB
A , B. 0 , AB
AB
though shortened survival of the patient’s own red blood cells is not always the result, a positive DAT discovered in a recently transfused patient will often require an extensive antibody workup prior to subsequent transfusions. While ABO compatibility is not an essential required for bone marrow transplantation [ 31, ABO compatible blood components must be transfused during the transition phase and until engraftment of the new bone marrow has occurred [4]. This may require multiple transfusions and time-consuming testing for a period of 10-14 days or even longer. It is interesting to note that after engraftment of a marrow from an ABO incompatible donor, the recipient’s tissue antigens may not be affected by the incompatible ABO antibodies produced by the new marrow I S ] . Genetics of the ABO Antigens
The genes which determine an individual’s blood group are located on Chromosome 9. The genes code for the production of an enzyme, a transferase, which will attach a blood group specific sugar to a precursor oligosaccharide chain. Each parent conveys one gene to the
child. The genotype is the actual genetic makeup, while the phenotype is the expression of the gene as seen in laboratory testing. The A and B genes are codurninanr alleles, meaning different forms of a gene, but both having equal strength of expression. When both alleles are conveyed (one from each parent), both are expressed as in group AB. Therefore, a group AB individual is herernzygous. The 0 antigen is recessive. It will not be evident unless inherited in the homozygous form (00).If an A or B gene is inherited with an 0 gene ( A 0 or BO), only the A or B gene is expressed. The 0 gene product is masked. Therefore, a group A or group B individual may be either homozygous (AA or BB) or heterozygous ( A 0 or BO). The only way to differentiate zygosity is to perform family studies and to predict the individual’s pedigree (Fig. 1). Biochemistry of ABO
Expression of the ABO antigens depends on the interaction of 3 separate and independent genetic systems: ABO, H, and Secretor (Se). The ABO genes code for the production of a transferase, which will attach a blood group specific sugar to a precursor oligosaccharide chain attached to the red cell membrane (Fig. 2). The precursor chain for all blood groups is the same: glucose, galactose, N-acetylglucosamine, and galactose. The H gene is required to transfer an L-fucose to the second galactose so that the ABO sugar can attach. The terminal sugar will then convey the specificity of the blood group. The attachment of N-acetylgalactosamine as the terminal sugar will convey blood group A specificity, while the attachment of D-galactose will convey group B specificity. Both N-acetylgalactosamine and D-galactose terminal sugar chains are found on the red cells of group AB
160
Sigmon
T h e ‘Precursor’ Chain (Bombay, oh)
T h e ’H’ Antigen Chain (also T h e ‘0’ Antigen)
T h e ‘A’ Antigen Chain
a
Glucose
0
Galactose
6
N-Acetylglucosarnine
L-Fucose
-
N Ac e t y Ig a1ac tosarn ine
T h e ’B’ Antigen Chain
Fig. 2.
T h e ‘A’ and ‘B’ Antigen Chains
+
D-Galactose
Different blood group antigens attached to the red blood cell membrane.
individuals. Group AB red cells often have quantitatively more group A antigens than group B antigens. The genes of a Group 0 individual do not code for the production of a transferase and the attachment of another sugar to the precursor chain. The “lack of” the additional terminal sugar is considered an “amorphic” phenomenon, and the blood group is interpreted as “missing,” thus group 0. Subsequently, the terminal sugar of group 0 individuals is the L-fucose of the H antigen, and group 0 red cells have quantitatively more H antigens than A, B, or AB red cells, which must compete with the H antigen for the limited antigen sites on the red cell membrane. is a rare blood group exThe Bombay genotype (0\,) pression. I t was identified in a small population of residents of Bombay in 1952 (61. These individuals do not inherit the dominant H gene. Instead, they inherit the recessive h gene from each parent, making them homozygous (hh). Although they inherit functional ABO genes, the transferase to attach the L-fucose is not produced, and the genetic blood group sugars (A or B) cannot attach to the precursor chain. Their blood type appears to be group 0. But these individuals do not have the H antigen, and they produce a naturally occurring, hemolytic anti-H as well as anti-A and anti-B, which circulate in their plasma. Bombay (0,) patients can receive red cell transfusions only from another Bombay (0,)individual; however, they can safely receive plasma
or plasma components from an individual of any blood group. The expression of ABO antigens in body fluids is dependent on the presence of the Secretor (Se) gene. Eighty percent of the general population carry at least one Se gene which is dominant over the se gene. The secretor status of an individual is of little importance in transfusion and transplantation medicine, but plays a major role in forensic science. THE Rh SYSTEM
In 1939, a student of Landsteiner, Philip Levine, published an obstetrical report of a case of hydrops fetalis in which he suggested the causative agent to be maternal blood group antibodies stimulated from an earlier pregnancy 17). In 1940, another student of Landsteiner, Alexander Wiener, reported the description of a new blood group system identified in Rhesus monkeys, Rh IS]. The antibodies produced in both cases demonstrated the same characteristics and thus were named anti-Rh. Several years later the 2 antibodies were shown to be of different specificities, but by that time several different nomenclatures had developed, further complicating the study of this clinically significant blood group system. The Rh antigens are found only on red blood cells. The Rh System consists of more than 40 distinguishable Rh antigens. The Rh, antigen, commonly known as D,
ABO/Rh for the HP
161
TABLE IV. Frequencies of Rh Phenotypes* Phenotype
White
Black
Oriental
D Positive D Negative
8S%
92% X% 28Ti 235% 98%. 99%
954’ 5%
15% 70%
c
E
307~ 80% 98%
c e
~~
~
~
*Composite ot figures from listed refcrcnces
rc
Chromosome #1
D Positive
D Positive Genotype ccDdEe PhenOtyDe cDEe
Genotype C c D d e e Phenotype CcDe
cde /
CDE
D Positive Genotype: CcDDEe Phenotype: CcDEe
Fig. 4. The Rh antigens are an integrated part of the red cell membrane, lending support to thc cellular structurc.
d ~ ecde D Positive Genotype: CcDdee Phenotype. CcDe
I CDE
cde
D Positive Genotype: ccDdEe P h e n o t y p e cDEe
cde /cde D Negative Genotype: ccddee Phenotype: c-d’e
Fig. 3. Schematic of predicted Rh genotypes and phenotypes from heterozygous Rh,, (D) positive parents. The trio of Rh antigens which comprise the Rh complex is so closely linked that they are inherited as a single genetic unit.
is the most immunogenic red blood cell antigen and thus plays a significant role in transfusion medicine. A single exposure to the D antigen will stimulate an antibody (anti-D) in more than 80% of the D negative population [ 9 ] . The Rh, (D) antibody may be stimulated in pregnancy, through transfusion, or by deliberate immunization. The Rho Antigen
The Rh, gene codes for the antigen D. The D is missing in approximately 15% of the general population. There is no actual d allele that can be tested for in the laboratory. However, for ease, the notation “d” is used for the missing gene product. An individual is reported as being Rho (D) positive or Rh, (D) negative. The D gene is dominant over the amorphic allele d. Therefore. the inheritance of a single D gene from either parent will make the individual Rh,, positive. Conversely, the Rh,, negative individual would have to be homozygous for d. The Rh Complex
The Rh complex is located on Chromosome 1. It is comprised of 3 genes located so close together that they
are inherited as a single genetic package. In addition to the D locus, there is the C locus with its alleles C and c, and the E locus with its alleles E and e. Frequencies of Rh phenotypes are shown in Table IV. The alleles at the C and E loci are codominant. Therefore an individual inherits a package of 3 genes (D, C , and E) from each parent for a total of 6 possible alleles (Fig. 3). If the allele is present, the allele is expressed (except d). If the allele is not seen in testing, the individual has probably inherited a double dose of the related allele (homozygous) . The Rh System is made more complicated by the infrequent appearance of uncommon allelic variations, i.e., Cw,D”, Rh:32, ce, f, etc. However, these are usually identified only if a patient has a transfusion complication. Transfusion is delayed due to the time required to identify the problem and to locate phenotypically similar blood to meet the transfusion needs of these patients. Biochemistry of the Rh System
The Rh antigens are made of glycoproteins, which are an integral part of the red cell membrane (Fig. 4). They play a key role in maintaining the red cell structure. Individuals who have aberrant Rh antigens, i.e.. Rh,,,, or Rh,,,,,(,, demonstrate shortened red cell survival and frequently have a compensated anemia [ 10,l I ] . The Nature of Rh Antibodies
Rh antibodies do not occur naturally. They are immune or acquired antibodies stimulated after exposure, sometimes requiring up to 6 months to develop. They are IgG immunoglobulins which can cross the placenta and cause fetal distress during pregnancy and problems at birth. They do not activate complement and cause immediate reactions. However, they are capable of causing delayed hemolytic transfusion reactions and shortened red cell survival. For this reason and because only 15% of the population is Rh,, (D) negative, national transfusion medicine policy is to make every reasonable
162
Sigmon
effort to transfuse Rho negative patients, especially women within childbearing age, with Rho negative blood.
REFERENCES 1 . Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, p 416. 2. Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V. Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks. 1990, p 315. 3. Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengclen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, p 262. 4. Kasprisin C A , Snyder EL: “Bone Marrow Transplantation: A Nursing Perspective.” Arlington, VA: American Association of Blood Banks. 1990, p 39. 5 . Kasprisin C A , Snyder EL: “Bone Marrow Transplantation: A Nursing Perspective.” Arlington. VA: American Association of Blood Banka, 1990, p 7. 6. Harmening D, Calhoun L, Polesky HF: “Modern Blood Banking and Transfusion Practices,” 2d ed. Philadelphia: F. A. Davis, 1989, p 87.
7. Lcvinc P, Stetson RE: An unusual case of intragroup agglutination. JAMA 113:126-127, 1939. 8 . Wiener AS, Peters HR: Hemolytic reactions following transfusions of blood of the homologous group, with three cases in which the same agglutinogen was responsible. Ann Intern Med 13:2306-2322, 1940. 9. Walker RH. Hoppe PA, Judd WJ, Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, p 198. 10. lssitt PD: Biochemistry of the Rh blood group system 1988: eight new antigens in nine years and some observations on the biochemistry and genetics of the system. Transfus Med Rev 3: 1- 12. 1989. 1 1 . Walker RH, Hoppe PA. Judd WJ. Ness P, Polesky HF, Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington. VA: American Association of Blood Banks. 1990, p 21 I .
SELECTED READINGS Harmening D, Calhoun L, Polesky HF: “Modern Blood Banking and Transfusion Practices,” 2nd ed. Philadelphia: F.A. Davis, 1989, pp 24-42, 78-1 19, 366-378. Walker RH, Hoppe PA, Judd WJ, Ness P, Polesky HF. Rolih SD, Snyder EL, Vengelen-Tyler V, Ward M: “Technical Manual,” 10th ed. Arlington, VA: American Association of Blood Banks, 1990, pp 159-223, 249-267.
