While the weak association between RhD-positive blood types and HIV susceptibility is thought to result from residual confounding, other studies indicated lower rates of HIV infection among RhD-negative individuals. Therefore, the researchers believe that there could be a degree of protection offered by the absence of the RhD antigen or that the RhD antigen in RhD-positive blood types could potentially be offering viral receptor sites to HIV, increasing the susceptibility to HIV infections. Source: https://www.news-medical.net/news/20230428/Is-there-an-association-between-ABO-and-RhD-blood-groups-and-risk-of-HIV-infection.aspx