Pro-tolerogenic gut microbiota induce rapid and distinct gut metabolic changes after cardiac allografting

Abstract Desulfovibrio desulfuricans (Desulfo) induces pro-inflammatory effects, while Bifidobacterium pseudolongum (Bifido) induces pro-tolerant effects. Bifido results in decreased cardiac allograft inflammation and fibrosis compared to Desulfo. Lymph node (LN) laminins α4 and α5 are differentially regulated in transplant tolerance (α4>α5) and immunity (α4<α5). We investigated whether specific microbiota alter LN architecture, immune cell content, and gut metabolites. B6 mice received antibiotics followed by bacteria gavage (Bifido, Desulfo, or PBS control), BALB/c heart transplants, and daily tacrolimus. LNs were assessed by immunohistochemistry. Stool metabolome profiling used capillary electrophoresis-mass spectrometry with partial least square-discriminant analyses. Desulfodecreased LN laminin α4:α5 ratios and Foxp3+ regulatory T cells (Tregs) after 7 days. After 14 days, Desulfotreated animals had greater allograft fibrosis while Bifidoincreased LN laminin α4:α5 ratios and Tregs. Gut metabolomes demonstrated highly distinct clustering between groups after 7 days. Bifidotreatment enriched compounds related to polyamine metabolism (spermine, spermidine, and putrescine), as well as by pathway analysis (arginine and proline plus spermidine and spermine metabolism) compared to Desulfoand control. Overall, Desulfoinduced rapid pro-inflammatory changes (decreased LN laminin ratios and Tregs, increased graft fibrosis), while Bifidoinduced rapid pro-tolerant changes (increased LN laminin ratios and Tregs). Bifidomodulated distinct polyamine pathway metabolites, compounds critical for T cell reprogramming. These results suggest polyamines as mediators of Bifidopro-tolerogenic effects. This work is supported by grants from NIH (R01HL148672, U01AI170050, and T32AI95190-10).