Differential Activation of Eosinophils by ‘Probiotic’ <i>Bifidobacterium bifidum</i> and ‘Pathogenic’ <i>Clostridium difficile</i>

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.To investigate the effects of probiotic Bifidobacterium bifidum (BB) on human eosinophil functions compared with pathogenic Clostridium difficile (CD).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.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.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.