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Project 6 of the NCCR 'Neural Plasticity and Repair' focuses on mechanisms of immunity and tissue damage in autoimmune and infectious diseases of the central nervous system (CNS). In one of the subprojects, the influence of transforming growth factor-beta (TGF-beta) on the immune reactivity of the CNS was investigated. In mice with Streptococcus pneumoniae-induced meningitis, a deletion of TGF-beta receptor II on leukocytes is found to enhance recruitment of neutrophils to the site of infection and to promote bacterial clearance. The improved host defense against S. pneumoniae was associated with an almost complete prevention of meningitis-induced vasculitis, a major intracranial complication leading to brain damage. The data show that endogenous TGF-beta suppresses host defense against bacterial infection in the CNS. This contrasts with findings from other body compartments that suggested that TGF-beta is a powerful chemotactic cytokine and increases microbial clearance.

In bacterial meningitis, chemokines lead to recruitment of polymorphonuclear leucocytes (PMN) into the CNS. At the site of infection in the subarachnoid space, PMN release reactive oxygen species, reactive nitrogen intermediates (RNI) and interleukin-1beta (IL-1beta). Although these immune factors assist in clearance of bacteria, they also result in neuronal injury associated with meningitis. Transforming growth factor beta (TGFbeta) is a potent deactivator of PMN and macrophages since TGFbeta suppresses the production of ROI, RNI and IL-1. Here, we report that the deletion of the TGFbeta receptor II gene in PMN enhances PMN recruitment into the CNS of mice with Streptococcus pneumoniae meningitis. This was associated with more efficient clearance of bacteria, and almost complete prevention of intracerebral necrotizing vasculitis. Differences in PMN in the CNS of infected control mice and mice lacking TGFbeta receptor II were not explained by altered expression of chemokines acting on PMN. Instead, TGFbeta was found to impair the expression of L (leucocyte)-selectin on PMN from control mice but not from mice lacking TGFbeta receptor II. L-selectin is known to be essential for PMN recruitment in bacterial meningitis. We conclude that defective TGFbeta signalling in PMN is beneficial in bacterial meningitis by ameliorating migration of PMN and bacterial clearance.

This study investigated whether the 21-aminosteroid U74389F, an inhibitor of lipid peroxidation, attenuates pathophysiologic changes in experimental pneumococcal meningitis. Infected rats injected intravenously with vehicle and U74389F developed increases in regional cerebral blood flow (rCBF), intracranial pressure (ICP), brain water content, and white blood cells (WBC) in cerebrospinal fluid (CSF) within 8 h after intracisternal challenge. Pretreatment with or administration of U74389F 4 h after infection significantly reduced the increase in ICP but had no effect on rCBF increase. Moreover, U74389F pretreatment significantly reduced brain water content and CSF WBC count. In vitro, U74389F inhibited iron-dependent lipid peroxidation of astrocyte cultures and the production of tumor necrosis factor-a, interleukin-6, and nitric oxide by stimulated macrophages. These data suggest that U74389F modulates early pathophysiologic alterations in experimental pneumococcal meningitis