Leigh Maher

T cell-intrinsic S1PR1 regulates endogenous effector T-cell egress dynamics from lymph nodes during infection

Significance The control of a microbial infection by effector T cells is intrinsically linked to their migration. However, little is known about the mechanisms that control effector T-cell egress after infection. Sphingosine-1-phosphate receptor-1 (S1PR1) is a G-coupled protein receptor that plays an important role in naive T-cell egress from lymph nodes. However, less is known about its role in regulating effector T-cell trafficking during infection. Here, we used an inducible mouse model with temporally disrupted S1PR1 signaling exclusively in endogenous effector CD8 T cells to demonstrate that, after infection, even in the absence of retention signals such as CC chemokine receptor 7 (CCR7), intrinsic S1PR1 signaling is the overriding factor that regulates effector T-cell egress kinetics from the draining lymph node. Viral clearance requires effector T-cell egress from the draining lymph node (dLN). The mechanisms that regulate the complex process of effector T-cell egress from the dLN after infection are poorly understood. Here, we visualized endogenous pathogen-specific effector T-cell migration within, and from, the dLN. We used an inducible mouse model with a temporally disrupted sphingosine-1-phosphate receptor-1 (S1PR1) gene specifically in endogenous effector T cells. Early after infection, WT and S1PR1−/− effector T cells localized exclusively within the paracortex. This localization in the paracortex by CD8 T cells was followed by intranodal migration by both WT and S1PR1−/− T cells to positions adjacent to both cortical and medullary lymphatic sinuses where the T cells exhibited intense probing behavior. However, in contrast to WT, S1PR1−/− effector T cells failed to enter the sinuses. We demonstrate that, even when LN retention signals such as CC chemokine receptor 7 (CCR7) are down-regulated, T cell intrinsic S1PR1 is the master regulator of effector T-cell emigration from the dLN.

CD169+ macrophages orchestrate innate immune responses by regulating bacterial localization in the spleen

CD169+ macrophages in the spleen play an essential role in the clearance of Listeria monocytogenes. Positioning sentinels Immune cells in the marginal zone of the spleen, particularly marginal zone macrophages, play a critical role in detecting and capturing blood-borne pathogens. Here, Perez et al. have examined the role of CD169+ splenic marginal zone macrophages in priming antibacterial responses. Selective deletion of CD169+ macrophages using a diphtheria toxin–based depletion system severely impaired the ability of mice to clear Listeria monocytogenes. By tracking L. monocytogenes and immune cells, they show that CD169+ macrophages cooperate with splenic dendritic cells to transport bacteria from the marginal zone to the T cell zone to prime immune responses to Listeria. The study illustrates the importance of splenic architecture in containing initial pathogen dissemination and in shaping antimicrobial responses. The spleen is an important site for generating protective immune responses against pathogens. After infection, immune cells undergo rapid reorganization to initiate and maintain localized inflammatory responses; however, the mechanisms governing this spatial and temporal cellular reorganization remain unclear. We show that the strategic position of splenic marginal zone CD169+ macrophages is vital for rapid initiation of antibacterial responses. In addition to controlling initial bacterial growth, CD169+ macrophages orchestrate a second phase of innate protection by mediating the transport of bacteria to splenic T cell zones. This compartmentalization of bacteria within the spleen was essential for driving the reorganization of innate immune cells into hierarchical clusters and for local interferon-γ production near sites of bacterial replication foci. Our results show that both phases of the antimicrobial innate immune response were dependent on CD169+ macrophages, and, in their absence, the series of events needed for pathogen clearance and subsequent survival of the host was disrupted. Our study provides insight into how lymphoid organ structure and function are related at a fundamental level.

Pregnane X Receptor Regulates Pathogen-Induced Inflammation and Host Defense against an Intracellular Bacterial Infection through Toll-like Receptor 4

The nuclear pregnane X receptor (PXR) plays a central role in regulating xenobiotic metabolism. We now report a novel role for PXR as a critical negative regulator of innate immunity after infection. Pxr−/− mice exhibited remarkably elevated pro-inflammatory cytokine and chemokine production following infection with Listeria monocytogenes (Lm). Despite the more robust innate immune response, Pxr−/− mice were highly susceptible to Lm infection. Surprisingly, disruption of the Toll-like receptor 4 (TLR4) but not TLR2 signaling restored the inflammation to normal levels and the ability to clear Lm in Pxr−/− mice. Mechanistically, the heightened inflammation in Pxr−/− mice resulted in the death of inflammatory monocytes that led to the enhanced susceptibility to Lm infection. These data demonstrated that PXR regulated pathogen-induced inflammation and host defense against Lm infection through modulating the TLR4 pathway. In summary, we discovered an apical role for PXR in regulating innate immunity. In addition, we uncovered a remarkable negative impact of the TLR4 pathway in controlling the quality of the inflammatory response and host defense against a gram-positive bacterial infection.

Targeting the PXR-TLR4 signaling pathway to reduce intestinal inflammation in an experimental model of necrotizing enterocolitis

BackgroundThere is substantial evidence that signaling through Toll-like receptor 4 (TLR4) contributes to the pathogenesis of necrotizing enterocolitis (NEC). Pregnane X receptor (PXR), a xenobiotic sensor and signaling intermediate for certain host-bacterial metabolites, has been shown to negatively regulate TLR4 signaling. Here we investigated the relationship between PXR and TLR4 in the developing murine intestine and explored the capacity of PXR to modulate inflammatory pathways involved in experimental NEC.MethodsWild-type and PXR−/− mice were studied at various time points of development in an experimental model of NEC. In addition, we studied the ability of the secondary bile acid lithocholic acid (LCA), a known PXR agonist in liver, to activate intestinal PXR and reduce NEC-related intestinal inflammation.ResultsWe found a reciprocal relationship between the developmental expression of PXR and TLR4 in wild-type murine intestine, with PXR acting to reduce TLR4 expression by decreasing TLR4 mRNA stability. In addition, PXR−/− mice exhibited a remarkably heightened severity of disease in experimental NEC. Moreover, LCA attenuated intestinal proinflammatory responses in the early stages of experimental NEC.ConclusionThese findings provide proactive insights into the regulation of TLR4 in the developing intestine. Targeting PXR may be a novel approach for NEC prevention.