CXCL12-abundant Reticular Cells are the Major Source of IL-6 Upon LPS-stimulation and Thereby Regulate Hematopoiesis.

Abstract

Hematopoiesis is maintained by hematopoietic stem and progenitor cells (HSPCs) that are located in the bone marrow (BM) where they are embedded within a complex supportive microenvironment, consisting of a multitude of various non-hematopoietic and hematopoietic cell types. The BM microenvironment not only regulates steady-state hematopoiesis by provision of growth factors, cytokines and cell-cell contact but is also an emerging key player during the adaptation to infectious and inflammatory insults (emergency hematopoiesis). Through a combination of gene expression analyses in prospectively isolated non-hematopoietic BM cell populations and various mouse models we have revealed that BM CXCL12-abundant reticular (CAR) cells are a major source of systemic and local BM IL-6 levels during emergency hematopoiesis following lipopolysaccharide (LPS) stimulation. Importantly, while IL-6 is dispensable during the initial phase of LPS-induced emergency hematopoiesis, it is required to sustain an adequate hematopoietic output during chronic-repetitive inflammation. Our data highlight the essential role of the non-hematopoietic BM microenvironment for the sensing and integration of pathogen-derived signals into sustained demand-adapted hematopoietic responses.