The INDIVIDUALIST

A Wiki about biochemical individuality

Polymorphism

See Also

FY Gene locus - FY

Introduction

In 1950, the Duffy blood group was named for the multiply transfused hemophiliac whose serum contained the first example of anti-Fya. In 1951, the antibody to the antithetical antigen, Fyb, was discovered in the serum of a woman who had been pregnant three times. Using these antibodies three common phenotypes were defined: Fy(a+b+), Fy(a+b-), and Fy(a-b+). Differences in the racial distribution of the Duffy antigens were discovered four years later when it was reported that the majority of Blacks had the erythrocyte phenotype Fy(a-b-). This phenotype is exceedingly rare in Whites. The frequency of the Fy(a-b-) phenotype is 68 percent in American Blacks and 88-100 percent in African Blacks.

The Duffy system of blood groups is genetically simple, being controlled by four allelic genes at one locus, of which only three are sufficiently common to be of anthropological and medical significance. Since the letter D is used for the principal gene of the Rh system the last two letters of the name Duffy are used in the gene symbols, Fya, Fyb , and Fy4. The Fy4 gene is very rare outside Africa and very common within that continent. Not only is it therefore an important anthropological marker, but, it provides one of the few cases where we think we know, in terms of natural selection, why one population differs from another in their blood-group frequencies.(1)

The Duffy genes, located on chromosome one at position 1922-23, have recently been cloned and sequenced. The difference between Fya and Fyb is a change in the amino acid at position 43 from aspartic acid (Fya) to glycine (Fyb). Studies have shown that blacks whose erythrocytes express Fyb antigen also have the antigen on the cells of their kidney, heart, muscle, brain and placenta. The Duffy gene codes for a protein known as a chemokine receptor, which is important in the inflammatory process. Accordingly, the Fy protein is also known as DARC (Duffy Antigen Receptor for Chenokines).

The molecular basis for the Fy(c-b-) phenotype is the result of a point mutation in the erythroid specific promoter. The absence of Duffy antigens on erythrocytes results in their resistance to invasion by two malaria parasites, Plasmodium vivax and Plasmodium knowlesi. This racial variation in distribution of the Duffy system antigens provides one of the few known examples of selective advantage conferred by a blood group phenotype.

Sanger discovered that a high percentage of African Negroes are of the phenotype Fy (a- b-), which is apparently a third gene termed Fyx which does not react with anti-Fya or anti -Fyb. In 1975 Miller was able to show that this type is probably specifically resistant to Vivax malaria, to which Africans have long been known to be resistant.

Molecular biology

Duffy has been found to act as a multispecific receptor for chemokines of both the C-C and C-X-C families, including: MGSA, regulated upon activation normal T expressed and secreted (RANTES; CCL5), monocyte chemotatic protein-1 (MCP-1; CCL2) and the angiogenic CXC chemokines interleukin-8 (IL-8, CXCL8), growth related gene alpha (GRO-α, CXCL1), neutrophil activating peptide-2 (NAP-2, CXCL7) and ENA-78 (CXCL5). Consequently the Fy protein is also known as DARC (Duffy Antigen Receptor for Chenokines).

Tissue distribution

While Duffy is expressed on erythrocytes the Duffy antigen is found on some epithelial cells (kidney collecting ducts), Purkinje cells of the cerebellum, endothelial cells of thyroid capillaries, the post-capillary venules of some organs and the large lung alveoli.

Disease association

On erythrocytes the Duffy antigen acts as a receptor for invasion by the human malarial parasites Plasmodium vivax and Plasmodium knowlesi; Duffy negative individuals whose erythrocytes do not express the receptor are resistant to infection. This antigen may also play a role in erythrocyte invasion in the rodent malarial parasite Plasmodium yoelii.

gp-Fy plays a role in inflammation and in malaria infection. It is a member of the super-family of chemokine receptors and the receptor for the human malarial parasite Plasmodium vivax and the simian malarial parasite Plasmodium knowlesi. The parasite-specific binding site, the binding site for chemokines and the major antigenic domains are located in overlapping regions at the exocellular N-terminal terminus.

In DARC-transfected cells, DARC is internalized following ligand binding and this led to the hypothesis that expression of DARC on the surface of erythocytes, endothelial, neuronal cells and epithelial cells may act as a sponge and provide a mechanism by which inflammatory chemokines may be removed from circulation as well as their concentration modified in the local environment. This hypothesis has also been questioned after knock out mice were created. These animals appeared healthy and had normal responses to infection.

Homozygous Duffy-deleted mice (Dfy-/-) are indistinguishable from their wild-type in size, health, embryonic development and neurological behavior.The only difference noted is a diminution of neutrophil trafficking in the mutant mice (to be published). The human equivalents of the Dfy-/- mice are also healthy; they are individuals whose phenotype is Fy(a-b-) and who lack gp-Fy on erythrocytes; its level of expression on non-erythroid cells is not known. This phenotype or the absence of the protein on the erythrocyte surface, appears to be protective against malaria Plasmodium vivax parasite.

About the alleles

The antigenic determinants reside in an acidic glycoprotein (gp-Fy), which spans the membrane seven times and has an exocellular N-Terminal domain and an endocellular C-terminal domain.

The system is defined by three common alleles: FYA and FYB encode two antithetical antigens, Fya and Fyb; FYBES (ES stands for erythroid silent) is the major allele in African American and Blacks and occurs rarely in other populations; a mutation in the promoter region abolishes expression of gp-Fy in erythroid but not in non-erythroid cells. This phenotype, or the absence of the protein on the erythrocyte surface appears to be protective against malaria vivax.

So far, the molecular basis has been documented for only a few types of rare alleles, FYBWK (WK stands for "weak") and FYAO or FYBO. FYBWK is characterized by a Fy (a-,b+wk) phenotype exhibiting a weak reaction with anti-Fyb. The ability of the Fy (a-,b+wk) erythrocytes to bind to all anti-Fy antibodies, as well as chemokines, albeit weakly, indicates that the overall structure of the Fy protein is not grossly altered but rather that its amount is markedly reduced. FYAO and FYBO are very rare alleles whose products do not appear at the surface of the erythocytes and thus result in Duffy (Fy) null phenotypes. A few cases of apparently healthy, non Black, Duffy-negative individuals (other than those having the FYBES alleles) have been documented and the molecular bases established for the absence of the reactive antigens. The allelic frequency of FYBWK for Caucasians or Blacks is ~ 0.02.

In the list of alleles the cDNA and translation changes are numbered from the codon for the initiator Met; note the following problem in the number assignements of amino acids: two kinds of Duffy mRNA have been described; a less abundant splicoform that encodes a protein of 338 residues was discovered first and used for cloning (acc. no UO1839, seq. MASSGYVLQAELS...) and the more abundant form, that encodes a protein of 336 residues (not in GenBank, ref. Iwamoto et al., seq. MGNCLHRAELS...). FYB, sequence acc. no. U01839 is taken as reference. Genomic sequence acc. no. X85785 can be used to visualize the sites of mutations in the list of alleles. (Coding sequence starts at nt. 979.)

Abstracts

The Duffy antigen/receptor for chemokines (DARC) regulates prostate tumor growth

FASEB J. 2006 Jan;20(1):59-64. Shen H, Schuster R, Stringer KF, Waltz SE, Lentsch AB.

  • The Duffy antigen/receptor for chemokines (DARC) is a promiscuous chemokine receptor that binds to members of the CXC chemokine family possessing angiogenic properties. The DARC is expressed on erythrocytes and endothelial cells and is required for Plasmodium vivax infection of erythrocytes. Approximately 70% of African-Americans lack erythrocyte expression of the DARC as a genetic mechanism of protection against malaria infection. African-American men have a 60% greater incidence of prostate cancer and a 2-fold higher mortality rate than Caucasian men. Using a transgenic model of prostate cancer with DARC-deficient mice, we tested the hypothesis that lack of DARC expression on erythrocytes contributes to enhanced prostate tumor growth. In vitro, erythrocytes from wild-type mice but not DARC-deficient mice cleared angiogenic chemokines produced by prostate cancer cells and reduced endothelial cell chemotaxis. In vivo, tumors from DARC-deficient mice had higher intra-tumor concentrations of angiogenic chemokines, increased tumor vessel density, and greatly augmented prostate tumor growth. The data suggest that the DARC functions to clear angiogenic CXC chemokines from the prostate tumor microcirculation and that the lack of erythroid DARC, as occurs in the majority of African-Americans, may be a contributing factor to the increased mortality to prostate cancer in this population.
Contribution of Duffy antigen to chemokine function

Cytokine Growth Factor Rev. 2005 Dec;16(6):687-94. Epub 2005 Jul 27.

Rot A.

  • In addition to classical G protein-coupled receptors (GPCRs), a group of alternative, "silent" chemokine receptors has recently been identified. These serpentine molecules are not coupled to G proteins and subsequent signaling cascades, but can efficiently internalize their cognate chemokine ligands, thus act as "interceptors" (internalizing receptors). Here we discuss a mechanism by which a member of this family, Duffy antigen (DARC), contributes to chemokine-induced leukocyte emigration. Cumulative experimental evidence suggests that DARC on venular endothelium mediates chemokine internalization at the abluminal surface followed by transcytosis and transfer of the chemokine cargo onto the luminal surface. DARC is also expressed on the erythrocyte surface of DARC positive individuals. Erythrocyte DARC binds plasma chemokines which results, on one hand, in impediment of the chemokines loss from the circulation and, on the other hand, in neutralization of chemokines in the blood. This leads to leukocyte protection from inadvertent "desensitization" and enhancement of leukocyte recruitment.
A structural model of a seven-transmembrane helix receptor: the Duffy antigen/receptor for chemokine (DARC)

Biochim Biophys Acta. 2005 Aug 5;1724(3):288-306.

de Brevern AG, Wong H, Tournamille C, Colin Y, Le Van Kim C, Etchebest C.

  • The Duffy antigen/receptor for chemokine (DARC) is an erythrocyte receptor for malaria parasites (Plasmodium vivax and Plasmodium knowlesi) and for chemokines. In contrast to other chemokine receptors, DARC is a promiscuous receptor that binds chemokines of both CC and CXC classes. The four extracellular domains (ECDs) of DARC are essential for its interaction with chemokines, whilst the first (ECD1) is sufficient for the interaction with malaria erythrocyte-binding protein. In this study, we elaborate and analyze structural models of the DARC. The construction of the 3D models is based on a comparative modeling process and on the use of many procedures to predict transmembrane segments and to detect far homologous proteins with known structures. Threading, ab initio, secondary structure and Protein Blocks approaches are used to build a very large number of models. The conformational exploration of the ECDs is performed with simulated annealing. The second and fourth ECDs are strongly constrained. On the contrary, the ECD1 is highly flexible, but seems composed of three consecutive regions: a small beta-sheet, a linker region and a structured loop. The chosen structural models encompass most of the biochemical features and reflect the known experimental data. They may be used to analyze functional interaction properties.
The human Duffy antigen binds selected inflammatory but not homeostatic chemokines

Biochem Biophys Res Commun. 2004 Aug 20;321(2):306-12. Gardner L, Patterson AM, Ashton BA, Stone MA, Middleton J.

  • The aim of the study was to compare the ability of the human Duffy antigen to bind homeostatic and inflammatory chemokines. Homeostatic chemokines did not bind to the Duffy antigen on erythrocytes with high affinity. In contrast, 60% of inflammatory chemokines bound strongly to Duffy, with no obvious preference for CXC or CC classes. It was investigated if this binding profile was reflected in the binding pattern of endothelial cells. Two examples of homeostatic (125I-CXCL12 and 125I-CCL21) and inflammatory (125I-CXCL8 and 125I-CCL5) chemokines were incubated with human synovia. In agreement with the erythrocyte binding data, intense specific signals for CXCL8 and CCL5 binding were found on endothelial cells, whereas CXCL12 and CCL21 showed only weak binding to these cells. Our study provides evidence that the human Duffy antigen binds selected inflammatory, but not homeostatic, chemokines and that this binding pattern is reflected by endothelial cells within inflamed and non-inflamed tissue.

Links

Attribution

References


1. Mourant, AE. Blood Relations, Blood Groups and Anthropology. Oxford University Press, Oxford, UK 1983.

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