CCR2 ⁺ Inflammatory Monocytes Are Recruited to Yersinia pseudotuberculosis Pyogranulomas and Dictate Adaptive Responses at the Expense of Innate Immunity during Oral Infection

Abstract

Murine Ly6C inflammatory monocytes (IMs) require CCR2 to leave the bone marrow and enter mesenteric lymph nodes (MLNs) and other organs in response to infection. We are investigating how IMs, which can differentiate into CD11c dendritic cells (DCs), contribute to innate and adaptive immunity to Previously, we obtained evidence that IMs are important for a dominant CD8 T cell response to the epitope YopE and host survival using intravenous infections with attenuated Here we challenged CCR2 or CCR2 mice orally with wild-type to investigate how IMs contribute to immune responses during intestinal infection. Unexpectedly, CCR2 mice did not have reduced survival but retained body weight better and their MLNs cleared faster and with reduced lymphadenopathy compared to controls. Enhanced bacterial clearance in CCR2 mice correlated with reduced numbers of IMs in spleens and increased numbers of neutrophils in livers. imaging of MLNs and spleens from CCR2-GFP mice showed that green fluorescent protein-positive (GFP) IMs accumulated at the periphery of neutrophil-rich containing pyogranulomas. GFP IMs colocalized with CD11c cells and YopE-specific CD8 T cells in MLNs, suggesting that IM-derived DCs prime adaptive responses in pyogranulomas. Consistently, CCR2 mice had reduced numbers of splenic DCs, YopE-specific CD8 T cells, CD4 T cells, and B cells in organs and lower levels of serum antibodies to antigens. Our data suggest that IMs differentiate into DCs in MLN pyogranulomas and direct adaptive responses in T cells at the expense of innate immunity during oral infection.

All Yersinia Are Not Created Equal: Phenotypic Adaptation to Distinct Niches Within Mammalian Tissues

“…Neutrophils directly interact with clustered centers of extracellular Y. pseudotuberculosis , and additional phagocytes are maintained at a distance relative to the bacterial centers (Figure 1 ). The layer of NO-producing cells likely contains a mixed population of monocytes, macrophages, and dendritic cells, and is adjacent to an apoptotic cell layer likely composed of monocytes (Davis et al, 2015 ; Peterson et al, 2017 ; Zhang et al, 2018 ). In the spleen, only the bacteria at the periphery of replicating centers respond to NO, and detoxify NO to prevent further diffusion into the microcolony, thus protecting interior bacteria (Davis et al, 2015 ).…”

“…NO was detoxified by Hmp, which was expressed in response to the Nos2 gene product, inducible nitric oxide synthase, indicating hmp expression was a specific response to NO. This example of cooperative behavior likely also exists within mesenteric LNs, based on the recruitment of NO-producing cells, and the similarities in these microcolony or pyogranuloma structures (Zhang et al, 2018 ). Peripheral Y. pseudotuberculosis cells also respond to neutrophil contact in the spleen by expressing heightened levels of the T3SS (Pettersson et al, 1996 ; Davis et al, 2015 ).…”

“…Yersinia replicate extracellularly within host tissue sites to form clonal bacterial clusters (Simonet et al, 1990 ; Logsdon and Mecsas, 2006 ; Oellerich et al, 2007 ; Crimmins et al, 2012 ; Davis et al, 2015 ). The sites of Y. pseudotuberculosis replication have been termed lesions, microcolonies, and recently, pyogranulomas, but each term refers to the same structure, described in Figure 1 (Davis et al, 2015 ; Peterson et al, 2017 ; Zhang et al, 2018 ). This review will first describe disease progression in mammalian hosts, to introduce the different tissues Yersinia replicates within, and then discuss similarities and differences in the inflammatory lesions that form during Yersinia infection, with a focus on how interactions with distinct immune cell subsets may alter the gene expression profile of individual Yersinia cells within a replicating population.…”

Iron-sulfur cluster repair contributes to Y. pseudotuberculosis survival within deep tissues

“…Following bloodstream access, Y. pseudotuberculosis colonizes deep tissue sites where individual bacteria replicate to form clonal microcolonies (29–31). Neutrophils, monocytes, and macrophages are recruited to sites of bacterial replication, which are kept at bay by Yersinia , primarily via substrates of the bacterial type III secretion system (32–34). Recruited monocytes and macrophages produce NO, which diffuses across a layer of neutrophils and is inactivated at the periphery of the microcolony by bacteria expressing Hmp, preventing diffusion of NO into the interior of the microcolony (31).…”

The pyrin inflammasome and the Yersinia effector interaction

“…This target cell specificity is due in part to the fact that neutrophils and inflammatory monocytes are recruited in large numbers to sites of Yersinia infection and make direct contact with the bacteria 39,40 . This cellular recruitment results in the formation of granuloma‐like structures, variously characterized histopathologically as microabscesses, necrotic lesions, or pyogranulomas 42,43 . The injectisome components of the T3SS (the YscF needle, LcrV tip protein, YopB, and YopD translocators) mediate translocation of the seven Yop effectors 44 .…”