Plasmodium falciparum RIFIN is a novel ligand for inhibitory immune receptor LILRB2.

Plasmodium falciparum causes the most severe form of malaria. Acquired immunity against P. falciparum provides insufficient protection even after repeated infections. Therefore, P. falciparum parasites might exploit inhibitory receptors for immune evasion. P. falciparum RIFINs are products of a multigene family consisting of 150-200 genes. Previously, we demonstrated that some RIFINs downregulate the immune response through the leukocyte immunoglobulin-like receptor (LILR) family inhibitory receptor, LILRB1, and leukocyte-associated immunoglobulin-like receptor 1, LAIR1. In this study, we further analyzed the expression of inhibitory receptor ligands on P. falciparum-infected erythrocytes and found that P. falciparum-infected erythrocytes expressed ligands for another LILR family inhibitory receptor, LILRB2, that recognizes HLA class I molecules as a host ligand. Furthermore, we identified that a specific RIFIN was a ligand for LILRB2 by using a newly developed RIFIN expression library. In addition, the domain 3 of LILRB2 was involved in RIFIN binding, whereas the domains 1 and 2 of LILRB2 were involved in the binding to HLA class I molecules. These results suggest that inhibitory receptor LILRB2 is also targeted by RIFIN for immune evasion of P. falciparum similar to LILRB1 and LAIR1.