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CR1) Polymorphisms in West Africa

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CR1) Polymorphisms in West Africa Genes and Immunity (2000) 1, 325–329 2000 Macmillan Publishers Ltd All rights reserved 1466-4879/00 $15.00 www.nature.com/gene Identification of complement receptor one (CR1) polymorphisms in West Africa JM Moulds1, L Kassambara2, JJ Middleton1, M Baby2, I Sagara2, A Guindo2, S Coulibaly2, D Yalcouye2, DA Diallo2, L Miller3 and O Doumbo2 1University of Texas-Houston Medical School, Houston, TX, USA; 2University of Mali, Bamako, Mali, W. Africa; 3National Institute of Allergy and Infectious Disease, NIH, Bethesda, MD, USA Complement receptor one (CR1) is a ligand for the rosetting of Plasmodium falciparum infected red cells with uninfected cells. Since CR1 exhibits three known polymorphisms, we studied European-Americans (n = 112) and African-Americans (n = 330) and Malians (n = 158) to determine if genetic differences existed in an area endemic for malaria that could offer a survival advantage. The frequencies of Knops blood group phenotypes McC(b+) and Sl(a−) were greatly increased in Africans vs Europeans. Although the frequency of McC(b+) was similar between Africans from the USA or Mali, the Sl(a−) phenotype was significantly higher in Mali (39% vs 65%, respectively). There was an increased frequency of the largest size (250 kD) of CR1 in Mali, but this did not differ significantly from the USA (P = 0.09). Both cohorts of Africans had higher expression of red cell CR1 than European-Americans but this showed little difference between the USA and Mali groups. Thus, the most important CR1 polymorphism relevant to rosetting of malaria infected cells appears to be the Knops blood group. Genes and Immunity (2000) 1, 325–329. Keywords: malaria; blood groups; complement receptors Introduction found in a study of African-Americans.5 Although there appears to be genetic regulation of E-CR1, low CR1 copy Complement receptor one (CR1) is a glycoprotein found numbers can also be an acquired phenomenon in malig- on most peripheral blood cells including red blood cells. nant and inflammatory disorders.6–8 Its major function is the adherence to and removal of In 1991, two groups independently identified the immune complexes, however, it also has complement Knops blood group system on CR1.9,10 It has been shown 1 regulatory activity. Human CR1 exhibits three known to be independent from the other known CR1 polymor- polymorphisms including: molecular weight (structural), phisms, ie, molecular weight or red cell expression. The level of red cell expression, and the Knops blood group. Knops blood group system began with the description There are four molecular weight variants that differ in of anti-Knops (Kna), in a transfused Caucasian woman.11 size by approximately 30 kD yet possess similar Factor I Presently it consists of seven antigens including the 2 co-factor activity. The molecular weights for these vari- allelic pairs Kna/Knb (Knops), McCa/McCb (McCoy), ants determined by SDS-PAGE using non-reduced con- Sla/Vil (Swain-Langley/Villien) and Yka (York). McCb = = = ditions are: CR1*1 190 kD, CR1*2 220 kD, CR1*3 and Vil have not been officially recognized by the Inter- = 3 160 kD and CR*4 250 kD. Holers et al showed that the national Society of Blood Transfusion12 as they lack com- difference in molecular weight was due to differing sizes plete biochemical and genetic studies for inclusion in the of mRNA and not post-translational processing. The CR1 system. To date, none have been identified at the molecu- size polymorphism is not unique to red cells but also lar level. The serological null phenotype is known as the exists on other cells such as neutrophils and eosinophils. ‘Helgeson phenotype’ which results from very low CR1 The number of CR1 copies on erythrocytes (E-CR1) can copy numbers on the red cell.13 vary as much as ten-fold between individuals. In Euro- The importance of CR1 in malaria became evident pean-Americans, a Hind II RFLP has been identified when Rowe et al14 reported that CR1 was a ligand to which correlates with high (H allele) or low (L allele) which the parasite receptor, ie, PfEMP-1, bound when 4 expression. However, a similar correlation was not Plasmodium falciparum infected red cells rosetted with uninfected cells. Red cells with low CR1 copy numbers did not rosette or rosetted poorly. In addition, red cells Correspondence: Joann M Moulds, Department of Microbiology and that typed as Sl(a−) formed fewer rosettes than Sl(a+) red Immunology, MCP Hahnemann University School of Medicine, 2900 cells. In an earlier study,15 the Sl(a−) phenotype was Queen Lane, Room G44, Philadelphia, PA 19129–1096, USA. found with an increased frequency among African- E-mail: [email protected] Americans compared to European-Americans. Since This research was supported by grants from the National Institutes rosetting had previously been correlated with severity of of Health RO1 AI 42367 (JMM) and the National Blood Foun- 16 14 a dation (JMM). disease, Rowe et al suggested that the Sl mutation Received 20 December 1999; revised 25 January 2000; accepted 8 might protect against severe malaria in African derived February 2000 populations. Thus, we studied a population in West CR1 polymorphisms in West Africa JM Moulds et al 326 Table 1 Gene frequencies for CR1 structural variants. Correspond- Table 2 Comparison of E-CR1 copy numbers between European- ing molecular weight of the protein is noted in parenthesis Americans and Africans Gene frequency CR1*1 CR1*2 CR1*3 CR1*4 European-Americans African-Americans Malians (190 kD) (220 kD) (160 kD) (240 kD) (n=65) (n=60) (n=158) Tienequebougou Average 284 389 410 (n = 46) 0.76 0.16 0.06 0.02 Std. Dev. 130 125 173 Bamako Median 311 362 382 (n = 40) 0.81 0.14 0.03 0.03 Bancoumana (n = 53) 0.84 0.08 0.06 0.02 Total Mali = derived groups, the average levels of E-CR1 were higher (n 139) 0.80 0.13 0.05 0.02 than in White subjects (Table 2). The Mali data had a African-Americans = (n = 330)a 0.84 0.12 0.04 Ͻ0.01 somewhat broader range of values (s.d. 173) when com- European- pared to the other two groups (s.d. = 125 and 130). Americans (n = 112)a 0.87 0.11 0.02 Ͻ0.01 Knops blood group The results for the Knops blood grouping are shown in aReported in Moulds et al.20 Table 3. Although the McCb antigen is rare among European-Americans it was found in ෂ40% of both Africa to determine whether any of the CR1 polymor- African-Americans and West Africans from Mali. Of the phisms were more frequent in Africans as compared to 11 families studied, three were informative for the African or European-Americans. McCoy locus (Figure 2). In families three and 20 the mother carries the McC(b+) haplotype which is passed to the child while in family eight the paternal haplotype is Results McC(b+). These families provide evidence that McCb is CR1 molecular weight The gene frequencies for the four molecular weight vari- Table 3 Phenotype frequencies of the Knops blood group antigens in unrelated European-Americans and Africans ants of CR1 are shown in Table 1. The gene frequencies for CR1*1, CR1*2 and CR1*3 occurred with the same fre- Phenotype Kn(a+) McC(a+) McC(b+) Sl(a−) quency in Africa as in the USA. Of note, the CR1*3 allele (160 kD) has been found more often in African- 17 Tienequebougou Americans than any other population tested. The larg- (n = 46) 99% 95% 44% 72% est size of CR1 (250 kD, CR1*4) was found in 4.6% of Bamako Malians as compared to 1% of African-Americans (P = (n = 40) 100% 93% 53% 72% 0.09). We also noted that not all CR1 structural variants Bancoumana = were equally expressed (Figure 1) but this differential (n 53) 100% 82% 56% 68% expression did not correlate with any particular CR1 Total Mali (n = 139) 100% 89% 49% 70% size allele. African-Americans (n = 150) 99% 90% 44% 39% E-CR1 expression European-Americans E-CR1 was quantified in 65 European-Americans, 60 (n = 112) 98% 98% 1% 1% African-Americans and 158 Malians. In both African- Figure 1 Differential expression of CR1 structural alleles is noted using equal amounts of sample in all lanes. Lane 1 shows low expression of the CR1*4 allele. Lane 3 is a donor with the Helgeson phenotype that is the result of low E-CR1. This allele is inherited from the mother shown in lane 2. Lanes 4–8 are unrelated Malian donors having normal expression of E-CR1. Genes and Immunity CR1 polymorphisms in West Africa JM Moulds et al 327 the allele to McCa and is inherited in a Mendelian domi- nant manner. Of greater interest perhaps, is the incidence of Sla. The Sl(a−) phenotype is rare in European-Americans (Ͻ1%) but found in ෂ39% of African-Americans. However, all three sites in West Africa had a high frequency of the Sl(a−) phenotype ranging from 68–72% suggesting that this mutation may have a survival advantage. The Helge- son or null phenotype occurred in 2% of the Mali donors which is similar to other populations. Red cells having the Helgeson phenotype type as negative for all of the Knops antigens and possess low E-CR1 numbers. Discussion The different CR1 molecular weight variants are the pro- ducts of four different mRNA rather than varying glycos- ylation.3 It had been proposed that they arose through the duplication and deletion of long homologous regions of a primordial CR1 gene.
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