Differential Activation of Eosinophils by ‘Probiotic’ Bifidobacterium bifidum and ‘Pathogenic’ Clostridium difficile

Abstract

Background: Recent studies suggest that probiotics alleviate pathophysiological processes of allergic diseases and inflammatory bowel diseases, whereas ‘non-probiotic’ microflora has negative effects. However, the underlying mechanisms are not well known, especially in relation to eosinophils, the major effector cells of these inflammatory diseases. Objective: To investigate the effects of probiotic Bifidobacterium bifidum (BB) on human eosinophil functions compared with pathogenic Clostridium difficile (CD). Methods: Peripheral human eosinophils were cultured with heat-killed BB or CD. FISH-labeled CD and BB were incubated with eosinophils visualized by confocal laser scanning microscopy. Superoxide generation and degranulation of eosinophils were measured with the cytochrome c reduction method and the eosinophil-derived neurotoxin (EDN) release assay, respectively. Results: Confocal microscopy revealed that Cy3-labeled CD and BB were apparently ingested by eosinophils. Both bacteria induced minimal superoxide generation. However, CD elicited significantly higher EDN release than BB. GM-CSF significantly enhanced EDN release by CD but not by BB. Bacterial-induced EDN release was calcium dependent. Conclusion: The beneficial effect of probiotic BB might be explained, at least in part, by its ability to decrease EDN release from eosinophils compared with ‘pathogenic’ CD.