Involved in countering the first line of host defense mechanisms. Specifically inhibits the response of human neutrophils and monocytes to complement anaphylatoxin C5a and formylated peptides, like N-formyl-methionyl-leucyl-phenylalanine (fMLP). Acts by binding directly to the C5a receptor (C5aR) and formylated peptide receptor (FPR), thereby blocking the C5a- and fMLP-induced calcium responses. Prevents phagocytosis of the bacterium (By similarity).