Nerve regeneration in silicone tubes: distribution of macrophages and interleukin-1β in the formed fibrin matrix

Macrophages have been regarded as important sources for different growth stimulating factors in nerve regeneration. The distribution of macrophages in the fibrin matrix, which is formed between the proximal and distal nerve stumps in silicone tubes [29], was investigated in rats. The sciatic nerves of rats were transected and the stumps were introduced into a silicone tube. After 3, 6, 14 or 28 days, the distribution of macrophages (ED1 and ED2), the cytokine Interleukin-1β (IL-1β), fibrin/fibrinogen, fibronec-tin, neurofilament and 5-100 protein was investigated using immunocytochemistry. The pattern of fibrin/fibrinogen, fibronectin, neurofilament and 5-100 protein was similar to previously published data [29]. The matrices at 3 and 6 days, as well as the later regenerate, contained both ED 1 and ED2 positive macrophages which was one of the cell types present. These cells were evenly distributed along the fibrin fibers or migrating cell columns. At the proximal and distal nerve stumps, macrophages were more abundant in the perineurial tissue which was close to the silicone tube, except for more macrophages in the distal part. IL-1β was also present, especially at 3 and 6 days and evenly distributed in the matrix, but the intensity of the staining decreased later. There was however no specific relation of ED1 or ED2 macrophage to the detected IL-1β. It is concluded that macrophages are trapped and present in the fibrin matrix formed between the proximal and distal nerve stumps at an early stage of the regeneration process and one of their products, IL-1β, was distributed in the matrix.