Stromal Cell-Derived CXCL12 and CCL8 Cooperate To Support Increased Development of Regulatory Dendritic Cells Following Leishmania Infection

In the immune system, stromal cells provide specialized niches that control hematopoiesis by coordinating the production of chemokines, adhesion molecules, and growth factors. Stromal cells also have anti-inflammatory effects, including support for the differentiation of hematopoietic progenitors into dendritic cells (DCs) with immune regulatory properties. Together, these observations suggest that the alterations in hematopoiesis commonly seen in infectious disease models, such as experimental visceral leishmaniasis in mice, might result from altered stromal cell function. We report in this study that the stromal cell-derived chemokines CXCL12 and CCL8 cooperate to attract hematopoietic progenitors with the potential to differentiate into regulatory DCs. We also show that infection of murine bone marrow stromal cells by Leishmania donovani enhanced their capacity to support the development of regulatory DCs, as well as their capacity to produce CCL8. Likewise, in experimental visceral leishmaniasis, CCL8 production was induced in splenic stromal cells, leading to an enhanced capacity to attract hematopoietic progenitor cells. Thus, intracellular parasitism of stromal cells modifies their capacity to recruit and support hematopoietic progenitor differentiation into regulatory DCs, and aberrant expression of CCL8 by diseased stromal tissue may be involved in the switch from resolving to persistent infection.