Key Question 1. What are the causative microorganisms of community-acquired bacterial meningitis in specific groups (neonates, children, adults and immunocompromised patients)?

CXCL13 shows high sensitivity and specificity for acute, untreated LNB. This novel marker appears to be helpful in clinically atypical cases and, in particular, in early stages of the disease when the B burgdorferi AI is (still) negative.

Pneumococcal meningitis is the most common and severe form of bacterial meningitis. Fatality rates are substantial, and long-term sequelae develop in about half of survivors. Disease outcome has been related to the severity of the proinflammatory response in the subarachnoid space. The complement system, which mediates key inflammatory processes, has been implicated as a modulator of pneumococcal meningitis disease severity in animal studies. Additionally, SNPs in genes encoding complement pathway proteins have been linked to susceptibility to pneumococcal infection, although no associations with disease severity or outcome have been established. Here, we have performed a robust prospective nationwide genetic association study in patients with bacterial meningitis and found that a common nonsynonymous complement component 5 (C5) SNP (rs17611) is associated with unfavorable disease outcome. C5 fragment levels in cerebrospinal fluid (CSF) of patients with bacterial meningitis correlated with several clinical indicators of poor prognosis. Consistent with these human data, C5a receptor-deficient mice with pneumococcal meningitis had lower CSF wbc counts and decreased brain damage compared with WT mice. Adjuvant treatment with C5-specific monoclonal antibodies prevented death in all mice with pneumococcal meningitis. Thus, our results suggest C5-specific monoclonal antibodies could be a promising new antiinflammatory adjuvant therapy for pneumococcal meningitis.

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BAFF and APRIL, which control B-cell homeostasis, are therapeutic targets in autoimmune diseases. TACI-Fc (atacicept), a soluble fusion protein containing the extracellular domain of the BAFF-APRIL-receptor TACI, was applied in clinical trials. However disease activity in multiple sclerosis (MS) unexpectedly increased, whereas in systemic lupus erythematosus (SLE) atacicept was beneficial. Here, we show that an endogenous soluble form of TACI exists in vivo. TACI proteolysis involved shedding by ADAM10 releasing sTACI from activated B cells. The membrane-bound stub was subsequently cleaved by γ-secretase reducing ligand-independent signaling of the remaining C-terminal fragment. The shed ectodomain assembled ligand-independently in a homotypic way. It functioned as a decoy receptor inhibiting BAFF- and APRIL-mediated B-cell survival and NFκB-activation. We determined sTACI levels in autoimmune diseases with established hyper-activation of the BAFF-APRIL system. sTACI levels were elevated both in the cerebrospinal fluid (CSF) of the brain-restricted autoimmune disease MS correlating with intrathecal IgG production, as well as in the serum of the systemic autoimmune disease SLE correlating with disease activity. Together, we show that TACI is sequentially processed by ADAM10 and γ-secretase. The released sTACI is an immunoregulator that shares decoy functions with atacicept. Itreflectssystemic and compartmentalized B-cell accumulation and activation.