Complement peptide 5a (C5a) (the parent molecule of CPDI-02 [26]) and its cleavage product C5a des-Arg [25] increase protection against bacterial pathogens at the site of infection by increasing activation of neutrophils and macrophages, acting as chemoattractants for neutrophils, monocytes, macrophages, and eosinophils, and inducing acute inflammation through local activation of mast cells, neutrophils, and endothelial cells [47]. This evidence concerns the gene C5AR1 and infection.