found between HIV susceptibility and the expression of the Duffy antigen. The absence of the DARC receptor appears to increase the susceptibility to infection by HIV. However once established, the absence of the DARC receptor appears to slow down the progression of the disease. HIV-1 appears to be able to attach to erythrocytes via DARC. The association between the Duffy antigen and HIV infection appears to be complex. Leukopenia (a low total white cell count) is associated with relatively poor survival in HIV infection and this association is more marked in whites than in people of Black African descent, despite the (on average) lower white cell counts found in black Africans. This difference appears to correlate with a particular genotype (-46C/C) associated with the absence of the Duffy antigen. This genotype has only been found in black Africans and their descendants. The strength of this association increases inversely with the total white cell count. The basis for this association is probably related to the role of the Duffy antigen in cytokine binding but this has yet to be verified. A study of 142 black South African high-risk female sex workers over 2 years revealed a seroconversion rate of 19.0%. Risk of seroconversion appeared to be correlated with Duffy-null-associated low neutrophil counts. Inflammation An association with the levels monocyte chemoattractant protein-1 has been reported. In the Sardinian population, an association of several variants in the DARC gene (coding and non-coding) correlates with increased serum levels of monocyte chemoattractant protein (MCP -1). A new variant in this population, consisting of the amino acid substitution of arginine for a cysteine at position 89 of the protein diminishes the ability to bind chemokines. DARC has also been linked to rheumatoid arthritis (RA), possibly displaying chemokines such as CXCL5 on the surface of endothelial cells within the synovium, increasing the recruitment of neutrophils in the disease state. Lung transplantation The Duffy antigen has been implicated in lung transplantation rejection. Multiple myeloma An increased incidence of Duffy antigen has been reported in patients with multiple myeloma compared with healthy controls. Pneumonia The Duffy antigen is present in the normal pulmonary vascular bed. Its expression is increased in the vascular beds and alveolar septa of the lung parenchyma during suppurative pneumonia. Pregnancy Duffy antigen has been implicated in haemolytic disease of the newborn. Prostate cancer Experimental work has suggested that DARC expression inhibits prostate tumor growth. Men