Interactions between gut-associated lymphoid tissue and colonization levels of indigenous, segmented, filamentous bacteria in the small intestine of mice

Unlike most other indigenous bacteria, segmented filamentous bacteria (SFB) are potent activators of the mucosal immune system. SFB are strongly ancho red to the epithelial cells of the small intestine where they have a prefer ence for mucosal lymphoid epithelium. Since SFB are only present in high nu mbers shortly after weaning, it was investigated whether an SFB-induced imm une reaction results in the removal of these bacteria from the small intest ine. A correlation was found between age and colonization levels in the sma ll intestines of SFB monoassociated Swiss mice. Five-week-old athymic BALB/ c (nu/nu) mice showed lower colonization levels than their heterozygous lit termates, but the opposite was found at the age of 12 weeks. However, SFB i noculation of germfree Swiss mice resulted in higher colonization levels in 5-week-old mice when compared with 4-month-old mice. We conclude that SFB colonization levels in the small intestine are Likely influenced by the act ivity of the mucosal immune system. However, an additional age-dependent fa ctor that modulates SFB colonization levels cannot be excluded.