LIPOPOLYSACCHARIDE-INDUCED IL-12 EXPRESSION IN THE CENTRAL-NERVOUS-SYSTEM AND CULTURED ASTROCYTES AND MICROGLIA

We examined whether the cytokine IL-12 could be induced locally in the brain or in glial cell cultures following LPS treatment, In the brain , expression of IL-12 p35 mRNA was constitutive and did not alter foll owing i.p. injection of LPS. In contrast, IL-12 p40 mRNA was only dete ctable in the brain of mice given two staggered injections of LPS. Dua l labeling in situ analysis revealed IL-12 p40 RNA-positive cells scat tered throughout the brain parenchyma, with a small number of these ce lls being identified as astrocytes, while the majority of IL-12 p40 RN A-expressing cells appeared to be microglia. in cultured microglia or astrocytes, LPS and to a much lesser degree IL-1 beta, but not IFN-gam ma or TNF-alpha, induced the expression of IL-12 p40 mRNA. Numerous gl ial fibrillary acidic protein-immunopositive cells colabeled for IL-12 p40 RNA, indicating that LPS-stimulated astrocytes expressed IL-12 in vitro, Immunoblot analysis of lysates from LPS-treated astrocytes rev ealed the presence of multiple species of 40, 43, 75, and 120 kDa cont aining the IL-12 p40 protein, Finally, secretion of the IL-12 p75 hete rodimer was detectable by ELISA from astrocytes treated with LPS plus IFN-gamma but not with LPS alone, The findings indicate that IL-12 gen e expression can be activated in the brain, with the resident glial ce lls being a prodigious source of this cytokine, The localized producti on of IL-12 may have a significant impact on the development of cell-m ediated immune responses within the central nervous system.