IgA determines bacterial composition in the gut

Abstract

Abstract Background: Classically IgA in the gut prevents the invasion of microorganisms to systemic organs through the process of neutralization and immune exclusion. Interestingly, recent reports suggest that IgA might help in biofilm formation and promote bacterial growth inside the intestine. Method and Results: In this study, we asked whether quality and quantity of IgA can select for bacterial persistence in the gut. We found that members of Proteobacteria are preferentially coated by IgA in WT mice and that there are no significant differences in the frequency of bacteria coated with IgA in mice that lack T-dependent IgA responses (TCRb-/-) mice as compared to WT mice. However, CBA/N mice that make poor T-independent IgA, had a lower frequency of IgA-coated bacteria and reduced Proteobacteria in the gut. Further, Rag-/- mice that lack all antibodies, had a severe reduction in Proteobacteria and were resistant to DSS induced colitis, suggesting that secretory IgA might be essential for differential retention of these taxa in the mouse gut. Rag-/- littermates in the F2 generation generated from (B6 x Rag-/-) F1 mice acquired Proteobacteria through vertical transmission of flora and died soon after weaning possibly due to the acquired flora. Additionally, continued exposure of Rag-/- mice to B6 flora by cohousing mice led to the acquisition of Proteobacteria and to mortality. Conclusion: Together, our results indicate that host survival in the complete absence of an IgA response necessitates the exclusion of certain bacterial taxa from the gut microbiome.