Neurotoxicity of intrathecal Shiga toxin 2 and protection by intrathecal injection of anti-Shiga toxin 2 antiserum in rabbits

The initial brain lesions in rabbits given intravenous Shiga toxin 2 (Stx2) were noted at 24 h in an area around the third ventricle (Fujii et al., Infect Immun 1996, 64: 5053-60). This result implied that Stx2 is present in the cerebrospinal fluid (CSF) despite the fact that the toxin was administered intravenously. We measured Stx2 activity in CSF by using a Vero cell cytotoxicity assay at various times after an intravenous injection of Stx2. Stx2 was detected from 2 h after the injection, and its concentration in CSF remained at a high level for a further 6 h. Fifty percent lethal doses (LD50) of Stx2 were measured in rabbits after intravenous and intrathecal Stx2 injections; The LD50 after an intrathecal injection of Stx2 was 0.36 mu g/kg, which was 9.2-fold lower than that of an intravenous injection of Stx2 (3.4 mu g/kg). Magnetic resonance images obtained after an intrathecal Stx2 injection (5 mu g/kg) were compared with those obtained after an intravenous Stx2 injection (5 mu g/kg). At 48 h, the cerebellar lesions had spread from the area in contact with the CSF on a T2-weighted image, which suggests that the intrathecal Stx2 may invade the cerebellum directly. We then examined whether anti-Stx2 antiserum injected intrathecally protects rabbits against brain damage. Eighty percent of the rabbits infected with Stx2 at 5 mu g/kg died within 8 days from brain damage. Rabbit anti-Stx2 sera (with titres of x 16 and x 64 by the Ouchterlony precipitation method) were administered into the CSF space through the cisterna magna. All the rabbits (n = 10) survived when they were given an intrathecal injection of rabbit anti-Stx2 antiserum 2 h before the intravenous injection of Stx2. Our results suggest that a leakage of Stx2 into the CSF from the choroid plexus causes brain damage, and that an intrathecal injection of anti-Stx2 antiserum could be a therapy for acute encephalopathy caused by Stx2-producing Escherichia coli. (C) 1998 Academic Press