C5AR1 and Sepsis: However, recent studies found that C5aR2 acts as a functional receptor in sepsis, as C5aR2 hindered the release of high mobility group box 1 (HMGB1) protein from macrophages; moreover, the blockage of C5aR2 along with C5aR1 improved survival in sepsis compared to the blockage of either receptor alone [256].