Increased expression of chemokines (MCP-1, MIP-1 alpha, RANTES) after peripheral nerve transection

After nerve injury, recruitment of circulating macrophages into the endoneu rium is essential for degeneration and subsequently for successful regenera tion. However, the factors leading to macrophage recruitment are not known in detail. Chemokines are one of many possible factors influencing recruitm ent. In this study we wanted to examine, immunohistochemically, the express ion of MCP-1, MIP-1 alpha and RANTES from 6 hours up to 4 weeks after trans ection of rat sciatic nerve. An increased expression of MCP-1 was noted alr eady 6 hours after transection, mainly in Schwann cells. Later, the MCP-1 p ositive staining was seen also in macrophages, fibroblast-like cells and en dothelial cells. An increased number of MIP-1 alpha positive cells could be noticed after 24 hours, the maximum expression in Schwann cells was noted at the 5-day timepoint. Later, part of the positive cells appeared to be ma crophages. RANTES was mainly expressed in inflammatory cells. Endothelial c ells in the epi- and endoneurium showed positive staining for every chemoki ne studied after transection. The contralateral non-operated nerves showed an increased number of positive cells for MCP-1 and MIP-1 alpha. in the con trol nerves MCP-1 and MIP-1 alpha positive cells were scattered throughout the endoneurium. This study shows that increased expression of chemokines t akes place within endoneurium after peripheral nerve transection. Thus, it is probable that chemokines can take part in the recruitment of macrophages . It further shows that there is an increased expression of the studied che mokines in the non-operated contralateral nerves. Even in normal conditions chemokines are needed, probably to keep resident macrophages within endone urium.