Conversely, C5a signaling through C5aR2 (also known as C5L2) protects against oxazolone-induced allergic contact dermatitis, as it is thought to prevent aberrant activation of the C5aR1 (50), possibly via inhibition of C5aR1/β-arrestin–mediated initiation of the ERK1/2 signaling cascade (51). Here, C5AR1 is linked to allergic contact dermatitis.