IL-8 RELEASE AND NEUTROPHIL ACTIVATION BY CLOSTRIDIUM-DIFFICILE TOXIN-EXPOSED HUMAN MONOCYTES

Neutrophil infiltration is central to the pathogenesis of Clostridium difficile toxin A-induced enterocolitis. This study examines whether m onocyte activation by C. difficile toxins is instrumental in initiatin g neutrophil activation and recruitment. Human monocytes were exposed to low concentrations of highly purified C. difficile toxins, and the conditioned media were harvested for cytokine and functional assays. M onocytes exposed to C. difficile toxin A (10(-10) M) or toxin B (10(-1 2) M) released 100 and 20 times basal levels, respectively, of the neu trophil chemoattractant interleukin-8 (IL-8). Reverse trans criptase-p olymerase chain reaction demonstrated a marked increase in IL-8 mRNA e xpression by monocytes 3 h after toxin exposure. Conditioned media fro m toxin A-and toxin B-treated monocytes stimulated neutrophil migratio n (324 and 245% of control, respectively). This effect was completely blocked by IL-8 antiserum. These media also upregulated neutrophil CD1 1b/CD18 and endothelial cell intercellular adhesion molecule-1 express ion. C. difficile toxins, at low concentrations, potently activate mon ocytes to release factors, including IL-8, that facilitate neutrophil extravasation and tissue infiltration. Our findings indicate a major r ole for toxin-mediated monocyte and macrophage activation in C. diffic ile colitis.