Genetic variants related to disease susceptibility and immunotolerance in the Duffy antigen receptor for chemokines (DARC, Fy) gene in the black lion tamarin (Leontopithecus chrysopygus, primates).

The DARC (Duffy antigen receptor for chemokines) gene encodes the DARC protein, which serves multiple roles in the immune system, as a binding site for the malarial parasites Plasmodium vivax and Plasmodium knowlesi, a promiscuous chemokine receptor and a blood group antigen. Variation in DARC may play particularly significant roles in innate immunity, immunotolerance and pathogen entry in callitrichines, such as the black lion tamarin (Leontopithecus chrysopygus). We compared amino acid sequences of DARC in the black lion tamarin (BLT) to non-human Haplorhine primates and Homo sapiens. Consistent with prior studies in other Haplorhines, we observed that the chemokine receptor experiences two opposing selection forces: (1) positive selection on the Plasmodium binding site and (2) purifying selection. We observed also that D21N, F22L, and V25L differentiated BLT from humans at a critical site for P. vivax and P. knowlesi binding. One amino acid residue, F22L, was subject to both positive selection and fixation in New World monkeys, suggesting a beneficial role as an adaptive barrier to Plasmodium entry. Unlike in humans, we observed no variation in DARC among BLTs, suggesting that the protein does not play a role in immunotolerance. In addition, lion tamarins differed from humans at the blood compatibility Fy(a)/Fy(b) antigen-binding site 44, as well as at the putative destabilizing residues A61, T68, A187, and L215, further supporting a difference in the functional role of DARC in these primates compared with humans. Further research is needed to determine whether changes in the Plasmodium and Fy(a)/Fy(b) antigen-binding sites disrupt DARC function in callitrichines.