Toxin B ofClostridium difficileactivates human VIP submucosal neurons, in part via an IL-1β-dependent pathway

Abstract

This study investigated whether toxin B of Clostridium difficile can activate human submucosal neurons and the involved pathways. Isolated segments of human colon were placed in organ culture for 3 h in the presence of toxin B or IL-1β. Whole mounts of internal submucosal plexus were stained with antibodies against c-Fos, neuron-specific enolase (NSE), vasoactive intestinal polypeptide (VIP), and substance P (SP). The membrane potential (Vm) response of submucosal neurons to local application of toxin B and IL-1β was determined by a multisite optical recording technique. Toxin B (0.1 to 10 ng/ml) increased the proportion of c-Fos-positive neurons dose dependently compared with the control. In the presence of toxin B (10 ng/ml), most c-Fos-positive neurons were immunoreactive for VIP (79.8 ± 22.5%) but only 19.4 ± 14.0% for SP. Toxin B induced a rapid rise in IL-1β mRNA level and a sixfold increase in IL-1β protein in supernatant after 3 h of incubation. c-Fos expression induced by toxin B was reduced dose dependently by IL-1 receptor antagonist (0.1-10 ng/ml). IL-1β significantly increased c-Fos expression in submucosal neurons compared with the control (34.2 ± 10.1 vs. 5.1 ± 1.3% of NSE neurons). Microejection of toxin B had no effect on the Vmof enteric neurons. Evidence of a direct excitatory effect of IL-1β on Vmwas detected in a minority of enteric neurons. Therefore, toxin B of C. difficile activates VIP-positive submucosal neurons, at least in part, via an indirect IL-1β-dependent pathway.