Ans. (c) P. VivaxRef: Microbiology by Ananthanarayan and Paniker 8th ed. 1694* Duffy antigen/chemokine receptor (DARC) also known as CD234, is a protein that in humans is encoded by DARC gene.* The Duffy antigen is located on the surface of red blood cells.* The Duffy antigen protein is also the receptor for the human malarial parasites Plasmodium vivax.* Polymorphisms in this gene are the basis of the Duffy blood group system.Clinical Significance of Duffy Antigen* Asthma: There appears to be a correlation with both total IgE levels and asthma and mutations in the Dufly antigen.* Malaria: On erythrocytes the Duffy antigen acts as a receptor for invasion by the human malarial parasites P. vivax and P. knowles.* Duffy negative individuals whose erythrocytes do not express the receptor are believed to be resistant to merozoite invasion.* HIV infection: The absence of the DARC receptor appears to increase the susceptibility to infection by HIV. HIV-1 appears to be able to attach to erythrocytes via DARC* 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.* Prostate cancer: Experimental work has suggested that DARC expression inhibits prostate tumor growth. The reasons for this increased risk are not known.* Sickle cell anemia: Duffy antigen-negative individuals with sickle cell anaemia tend to suffer from more severe organ damage than do those with the Duffy antigen.