Interleukin-1beta expression in the pineal gland of the rat

Increasing evidence of the neuroimmunomodulatory role of the pineal gland prompted the present study of pineal gland expression of the immunoregulatory cytokine, interleukin (IL)-1beta. IL-1beta was constitutively expressed in the adult gland, with mRNA levels higher in glands collected during the photophase than in those collected during the scotophase of the light:dark cycle. IL-1beta was up-regulated in pineal cultures, after treatment with either norepinephrine (NE) or interferon (IFN)/lipopolysaccharide (LPS). Although both astrocytes and microglia expressed IL-1beta, important differences were found in the cellular expression of this cytokine under in vivo and in vitro conditions. Increased IL-1beta expression by NE ex vivo and the decline in IL-1 expression at night, when NE levels are elevated, can be explained by immunocytochemical data showing that astrocytes are the predominant cell type expressing this cytokine in vivo, whereas IL-1beta-positive cells are predominantly microglia in pineal explants and dispersed cell cultures. These results are consistent with the hypothesis that cytokines secreted by pineal glia (astrocytes and microglia) may have an important regulatory role in the pineal gland.