Background: Activation of the complement system is one component of the inflammatory response. Various components of the complement system participate in killing foreign organisms, recruiting immune cells, enhancing edema, and stimulating cytokine formation. Complement-mediated enhancement of the inflammation surrounding surgical incisions may increase pain.
Methods: In these studies, the authors used a murine hind paw incisional model to study the role of the complement C5a receptor in supporting incisional inflammation. At baseline and at various time points after incision, they measured the effects of a highly selective C5a receptor antagonist on nociceptive thresholds, edema formation, and cytokine production in the skin surrounding the incision. They also measured changes in C5a receptor expression near the incisions.
Results: The once-daily injection of the C5a receptor antagonist AcF-[OPdChaWR] reduced mechanical allodynia and edema in the incised hind paw. A multiplexed cytokine assay revealed that 8 of the 18 cytokines examined showed significant increases in skin tissue abundance after incision. Distinct time courses for the patterns of elevation were seen, though some degree of resolution occurred for all cytokines within 96 h. For 7 of these 8 cytokines, the C5a receptor antagonist reduced the enhancement of expression. In addition, the authors found that the C5a receptor messenger RNA level increased 15-fold in the skin surrounding the incisions within 24 h and then slowly declined.
Conclusions: The tissue directly surrounding incisions in mouse hind paws undergoes large changes in the content of specific cytokines in addition to demonstrating edema and nociceptive sensitization. By blocking the receptor for one component of the complement system, C5a, all of these changes can be reduced. Complement receptor inhibitors may constitute a novel group of compounds useful in reducing the pain and swelling of surgical incisions.