Expression and localization of p80 interleukin-1 receptor protein in the rat spinal cord

The biological effects of interleukin (IL)-1 are mediated by two distinct receptors, the p80 or type I (ILARI) and p68 or type II (IL-1RII) receptors. Because IL-1RII has a short, 29-amino acid cytoplasmic domain which may not be sufficient for signaling, there is considerable evidence indicating that IL-1 may signal exclusively through the ILARI receptor. Here, we report the expression, distribution, and cellular localization of the ILARI protein in the adult rat spinal cord in vivo and embryonic spinal cord in vitro. We found that IL-1RI was expressed in both the gray and white matter throughout the entire length of the spinal cord and was localized in neurons of the anterior horn, astrocytes, oligodendrocytes, and central canal ependymal cells. Interestingly, resting microglia were negative for IL-1RI. In primary cultures obtained from the embryonic day (E) 15 rats, ILARI was expressed in neurons, astrocytes, and oligodendrocytes as well as microglia. These data provide both in vivo and in vitro evidence that neurons and glial cells express the IL-1 RI proteins. The differential expression of IL-1RI in the developing, but not mature, microglia may indicate the difference of these cells in response to IL-1 stimuli during maturation. The distribution and cellular localization of IL-1RI proteins in the spinal cord provide a molecular basis for understanding the reciprocal interaction between the immune and the central nervous systems.