Crosstalk between murine marginal zone B cells, macrophages and CD8alpha+ dendritic cells promotes Listeria monocytogenes infection

Type 1 CD8α+ conventional dendritic cells (cDC1s) harbor and transport Listeria monocytogenes (LM) within the spleen and thereby promote infection; cDC1s are also required for CD8+ T cell priming. To test the role of the second lineage of splenic cDC in regulating infection or adaptive immunity to LM we used Dock8-deficient mice, which have impaired 33D1+ type 2 cDC (cDC2) function. We found reduced CD8+ T cell activation in Dock8-deficient mice, but this was not due to impaired cDC2 function but rather resistance to LM infection. Bacterial resistance was due to loss of marginal zone B (MZB) cells. We showed that IL-10 production by MZB cells did not alter antigen handling pathways in dendritic cells (DCs), including ones relevant for cross-priming or Listeria survival. Instead, IL-10 increased intracellular LM in macrophages in the marginal zone, which transfer bacteria to cDC1s. Bacteria-harboring cDC1s then traffic into the splenic white pulp where protection from sterilizing phagocytes promotes LM expansion. This work uncovers a unique crosstalk between the innate immune cells in the marginal zone, facilitated by IL-10, that promotes both infection but also CD8+ T cell activation. RNA-seq of murine splenic CD8a+ DCs incubated for 4 hours with or without IL10