Effects of B7-H3 on the inflammatory response and expression of MMP-9 in mice with pneumococcal meningitis.

B7-H3, a new member of the B7 superfamily, plays a key role in the regulation of T cell-mediated immune responses. Our previous work showed that B7-H3 strongly augmented both LPS- and bacterial lipoprotein-induced NF-κB activation and inflammatory response, and soluble B7-H3 was elevated in CSF and plasma of patients with bacterial meningitis. MMP-9 has been implicated in blood-brain barrier disruption, inflammation, and vasculitis during the pathogenesis of bacterial meningitis. In this study, we report that in a murine model of pneumococcal meningitis, B7-H3 treatment enhances inflammatory response in the meninges, upregulates MMP-9 expression in cerebral parenchyma, and deteriorates clinical disease status indicated by weight loss and impaired movement ability. In vitro results showed that B7-H3 augmented MMP-9 secretion from Streptococcus pneumoniae-stimulated microglia cells. Thus, our data indicate that B7-H3 contributes to the development of pneumococcal meningitis by exaggerating inflammatory responses and upregulating MMP-9 activity in CNS, which ultimately lead to neuronal injury.