Interleukin-1\beta affects the macrophage recruitment and proliferation in the injured brain of 6-day-old rat

Six-day-old male rats received a mechanical lesion in the left cerebral hemisphere. Thereafter, a single dose of either 5, 50 or 500 units (U) of recombinant rat interleukin-1 beta (IL-1 beta) was injected into the lesion cavity. One or 2 days after the injury, the rats were injected with H-3-thymidine. Brain sections were subjected to BSI-B4 lectin histochemistry and autoradiography to visualise proliferating and non-proliferating macrophages located within the region of injury. A mitogenic effect of IL-1 beta on macrophages was observed on day 2 in brains injected with the lowest 5 U dose of cytokine. Following administration of higher 50 U and 500 U doses, infiltration of the injured tissue by macrophages was significantly intensified on day 1. However, on day 2, dose-dependent reductions of the total number of macrophages as well as their proliferative activity were recorded. The findings suggest that the higher the initial quantity of macrophages,the sooner they disappeared from the injury site. It may therefore be hypothesised that IL-1 beta-induced increase in macrophage recruitment at the beginning of the inflammatory response speeded the removal of tissue debris and, therefore, accelerated healing of the injured nervous tissue