Akkermansia Muciniphila induces chronic extramedullary hematopoiesis through cooperative IL-1R and TLR signals

Bacterial infections can activate and mobilize hematopoietic stem and progenitor cells (HSPCs) from the bone marrow (BM) to spleen, which is termed as extramedullary hematopoiesis (EMH). Recent studies suggest that commensal bacteria, particularly the microbiota, regulates not only the host immune system but also hematopoietic homeostasis. However, the impact of gut microbial species on hematopoietic pathology remains largely unknown. Here we found that systemic injection of Akkermansia muciniphila (A. m.), a mucin-degrading bacterium abundantly existing in the human gut rapidly activates BM myelopoiesis, and induces a slow but long-lasting hepato-splenomegaly, characterized by the expansion and differentiation of functional HSPCs, which we termed chronic EMH. Genetic deletion of Toll-like receptor-2 and -4 (TLR2/4) partially diminished A. m.-induced chronic EMH, while additional pharmacological inhibition of the interleukin-1 receptor (IL-1R) completely alleviated splenomegaly and EMH. Our results demonstrate that cooperative IL-1R- and TLR-mediated innate immune signals regulate commensal bacteria-driven EMH, which might be relevant for certain autoimmune disorders. Article SummaryThe aim of our study is to understand how Akkermansia muciniphila (A.m.), one of the major mucin-degrading microbial species in the human gut activate the immune and hematopoietic systems in a mouse model. We found that a single injection of the A.m. membrane fraction can induce long-lasting hepatosplenomegaly with splenic EMH through cooperative IL-1R- and TLR-mediated innate immune signals.