CD46, a negative regulator of the classical and lectin pathways, aids in the dissemination of bacteria (N. meningitidis) (Johansson et al., 2003, 2005) and viruses [Measles virus (Rall et al., 1997; Manchester et al., 1999; Oldstone et al., 1999; Evlashev et al., 2000) and HHV-6 (Cassiani-Ingoni et al., 2005)] into the CNS, leading to meningitis and encephalitis, respectively. The gene discussed is CD46; the disease is infectious meningitis.