Cerebral endothelial cells release TNF-alpha after stimulation with cell walls of Streptococcus pneumoniae and regulate inducible nitric oxide synthase and ICAM-1 expression via autocrine loops

TNF-alpha, inducible NO synthase (iNOS), and ICAM-1 are considered to be ke y proteins in the inflammatory response of most tissues. We tested the hypo thesis that cell walls of Streptococcus pneumoniae (PCW), the most common c ause of adult bacterial meningitis, induce TNF-alpha, iNOS, and ICAM-1 expr ession in rat primary brain microvascular endothelial cell cultures, We det ected TNF-alpha mRNA by RT-PCR already 1 h after stimulation with PCW, whil e TNF-alpha protein peaked at 4 h (9.4 +/- 3.6 vs 0.1 +/- 0.1 pg/mu g prote in). PCW induced iNOS mRNA 2 h after stimulation, followed by an increase o f the NO degradation product nitrite (18.1 +/- 4 vs 5.5 +/- 1.8 at 12 h; 18 .1 +/- 4 vs 5.8 +/- 1.8 pmul/mu g protein at 72 h), The addition of TNF-alp ha Ab significantly reduced nitrite production to 62.2 +/- 14.4% compared w ith PCW-stimulated brain microvascular endothelial cells (100%). PCW induce d the expression of ICAM-1 (measured by FAGS), which was completely blocked by TNF-alpha Ab (1 12 +/- 18.6 vs 97.5 +/- 12.4%; 100% unstimulated brain microvascular endothelial cells), Cerebral endothelial cells express TNF-al pha mRNA as well as iNOS mRNA and release the bioactive proteins in respons e to PCW, PCW-induced NO production is mediated in part by an autocrine pat hway involving TNF-alpha, whereas ICAM-1 expression is completely mediated by this autocrine loop. By these mechanisms, cerebral endothelial cells may regulate critical steps in inflammatory blood-brain-barrier disruption of bacterial meningitis.