How are Duffy-negative red blood cells related to resistance to Plasmodium knowlesi infection?

Duffy-negative red blood cells are resistant to infection by Plasmodium knowlesi because they lack the specific Duffy antigens that the parasite uses as receptors to bind to and enter the cells.12

In the Duffy blood group system, the Duffy antigens (specifically Fy${}^a$ and Fy${}^b$) function as necessary entry points for certain malarial parasites, including P. knowlesi and P. vivax. Individuals with the Fy${}^{a-b-}$ phenotype—often referred to as Duffy-negative—do not express these antigens on the surface of their red blood cells. Without these receptors, the parasite is unable to successfully attach to and invade the host's red blood cells, thereby providing a degree of protection against the infection. This biological mechanism is a significant example of how natural selection has influenced the distribution of blood phenotypes in populations where malaria is endemic.12