A review: the Duffy blood group system K.M. BEATTIE In 1950, two reports described an antibody that had neuraminidase. On the other hand, Fy3, Fy4, and Fy5 been found during the investigation of a hemolytic are not affected. Reactionswith purified trypsin show transfusion reaction in the serum of a 43-year-old man that the Fysup(a) antigen is unaffected and Fy sup(b) is only slightly suffering from hemophilia. 1,2 After the unidentified reduced in strength; Fy3 and Fy6 are slightly enhanced. antibody had been separated from the anti-D, anti-A, The trypsin most commonly used by blood bankers and anti-Bin his serum, it was tested against the blood is a crude preparation that is contaminated with chymo- of 205 unrelated English adults; 64.9 percent were ,agglu- trypsin; therefore, results obtained with that product tinated. With the permission of the patient, the new would approximate those resulting from chymotrypsin blood group system was named Duffy The antigen was treatment. designated as Fysup(a), the gene responsible for it, Fy sup(a), and Inactivation of Fy determinants is such that they are its hypothetical allele, Fysup(b). Anti-Fysup(b) was reported the no longer capable of adsorbing their antithetical anti- following year in the serum of a German woman who bodies. This is not due to the removal of sialic acid but had been pregnant three times but not transfused.sup(3) probably represents proteolytic action on cell membrane Four years later, Fy(a-b-) was reported to be the proteins. Fy(a-b-) red cells are not sialic acid deficient most common phenotype in American blacks.sup(4) and their electrophoretic mobility is normal. 13 Either In 1965, a new allele, Fysup(x), was described,5 but new formaldehyde treatmentor heating the red cells to 56°C antibodies in the system-to Fy3, Fy4, and Fy5—were for 10 minutes denatures the Fy antigens, indicating not reported until 1971 and 1973.sup(6-8) Another 14 years that the receptors are proteins. elapsed before the most recently described antibody- Treatment with 2-aminoethylisothiouronim bromide anti-Fy6, a monoclonal murine antibody, became part affects neither Fysup(a) nor Fysup(b) antigens,sup(14) but Fy sup(b) may be of the Duffy system.sup(9) weakened by 2-hour treatment with chloroquine diphos- This chronology of events must include the 1963 phate. 15 report showing a probable close linkage between the In 'an assay using quantitative immunoferritin micro- Duffy locus and the locus for congenital zonular scopy,sup(16) red cells having a double dose of Fysup(a) antigens cataractsup(10) and five years later the assignment of the were found to have 13,300±3500 sites per cell and Duffy locus to human chromosome 1. 11 Another pro- 6,900 ± 610 sites per cell when only a single dose was foundly significant finding came with report of an present. The latter number was the same for single doses association between the Fysup(a) and Fysup(b) antigens and the of Fy sup(b)antigen, while double doses measured 13,700± invasion of red cells by certain species of malarial 4000 sites per cell. parasites. 12 Duffy antigens appear to be limited to red cells, Fysup(a), Fy sup(b), and Fy3 being absent from leukocytessup(13) and Fysup(a) Biochemical and Serological Characteristics and Fy sup(b) not found on platelets. 17 While the Duffy anti- of the Antigens and Antibodies gens are not natural constituents of body fluids, anti- Duffy antigens genic substances can be shed from red cells into the The Duffy antigens fall into two groups in regard to supernatant when they are stored in a low-pH, low- their sensitivity to enzymes. Fy,sup(a) Fy sup(b), and Fy6 deter- ionic-strength medium. These substances specifically minants are destroyed by proteolytic enzymes such as inhibit their antithetical antibodies—anti-Fysup(a), anti-Fysup(b), ficin, papain, bromelin, and chymotrypsin, but not by or anti-Fy3.sup(18) The investigators reported that these Fysup(a) VOLUME 5, NUMBER 2. 1989 45 K.M. BEATTIE and Fysup(b) structures have a molecular weight of 35-55 of testing, and the anti-Fysup(b) used. kD.sup(19) Other workerssup(20) have reported that the Fyy sup(a) struc- Quantitative hemagglutination assays for Fsup(b) and Fy3 rure has a mobility similar to PAS 2, a band associated antigens on red cells from seven Fysub(x)Fy sub(x) two Fysup(b)Fy sup(x), with MN sialoglycoprotein. This would indicate that and four sup(a)Fy sup(x) persons showed that moderate depres- it is located on or near glycophorin A in the extracellular sion of Fy3 occurs in sup(a)F sup(x) and F Fy sub(b)F sup(x) persons and domain of an integral membrane protein.sup(20,21) marked depression of Fy3 occurs in Fysub(x)Fy sub(x) people.sup(26) Weak reactions with anti-Fy5sup(13) and anti-Fy6sup(9) were also Anti-Fy sup(a) and -Fysup(b) found on testing the cells of Fy sup(x)Fysup(x) individuals. Like the first example of anti-Fysup(a), most Duffy anti- bodies require the antiglobulin test for detection. Saline- Fy3 and anti-Fy3 reactive Duffy antibodies are rarely found. Their reac- An antibody found in the serum of a Fy(a-b-) Cau- tivity is enhanced in a low-ionic-strength medium. Many casian Australian woman reacted with Fy(a+) and Fy(b +) examples of anti-Fysup(a) can be detected in low-ionic hexa- but not Fy(a-b-) red cells. The antibody was shown dimethrine bromide (Polybrene®).sup(22) The antibodies are not to be a mixture of anti-Fysup(a) and -Fysup(b) and also dif- stable at 70°C and are not denatured by 0.1M 2-mer- fered by agglutinating enzyme-treated Fy(a+) or Fy(b+) captoethanol. red cells. The authors of the report6 named the anti- These antibodies react optimally at 37°C and many body anti-Fy3 and speculated that Fy3 might be the activate the complement cascade to bind C3b to antigen- precursor for Fyy sup(a) and Fy sup(b). positive red cells. During a second pregnancy, anti-Fysup(a) and the second Most examples of these antibodies are 7S gamma example of anti-Fy3 were found in the serum of a globulins having a molecular weight of 160,000.IgG1 16-year-old American black woman whose red cells has been found as the only immunoglobulin subclass in typed as Fy(a-b-) Fy: - 3.sup(27) She had received one unit 22 of 25 examples of anti-Fysup(a) and FFy sup(b).sup(23) of Fy(a+ b +) Fy:3 red cells during her first pregnancy. Some examples of anti-Fysup(a) and anti-Fysup(b), when titrated The red cells of her second child typed as Fy(a- b +) against red cells of known phenotype, can distinguish Fy:3, but the direct antiglobulin test was negative at between cells having a single dose of the antigen and birth. those with a double dose. Dosage can be determined A third example was identified in the serum of a Cana- more clearly through antibody-binding techniques such dian Cree Indian woman who had been transfused. She as the enzyme-linked immunosorbent assaysup(24) and produced anti-Fy3 and not anti-Fysup(a), although five of fluorescence-activated flow cytometry.sup(25) her children were Fy(a+).sup(28) Neither her mother nor her maternal aunt, who also had Fy(a-b-) red cells FY sup(x) and had a total of 15 children, produced Duffy anti- The Fysub(x) antigen was detected because of what ap- bodies, suggesting that the risk of immunizationthrough peared to be a discrepancy in inheritance in 20 of 537 pregnancy may be minimal. families tested.sup(5) One or more Fy(a+b-) children were born in nine families where one of the parents tested Fy4 and anti-Fy4 as Fy(a- b+). The silent allele Fy did not account for The suggestion that the Fy(a-b-) phenotype com- the anomaly because in most of these cases the apparent monly observed in blacks represented a null phenotype Fy(a+ b-) person's red cells reacted weakly by anti- was challenged by the report of an antibody found in globulin test with some examples of anti-Fysup(b). a black child who reacted with the red cells of blacks The original investigators felt that Fy sub(x), as they but not whites.' At least in blacks, Fy(a-b-) could not designated the gene, was a new allele to ysup(a), F ysup(b), and be the resultant product of two silent Fy genes. The Fy. However, antibody eluted from Fysub(x) cells had anti- child’s red cells typed as Fy(a+b+),and her serum agglu- Fsup(b) specificity, and efforts to separate an antibody tinated Fy(a-b-) and some Fy(a+b-) or Fy(a-b+) red specific for Fysub(x) from anti-Fysup(b) failed. The difference cells from blacks but did not agglutinate the red cells between Fsup(b) and Fysub(x) may simply be quantitative. The from blacks with the Fy(a+b+)phenotype using anti- distinction between the products of Fy and sup(x) in globulin or enzyme-antiglobulin tests. The reactions were forensic applications depends on the methods, extent weak and some variations were observed by the three 46 I M M U N O H EM AT O L O G Y Duffy system review laboratories studying the serum.