Biology subjects

Roncaioli, J. L.

Publications and source records attributed to Roncaioli, J. L..

5 recordsLinked to original sources

bioRxiv2025

Innate detection of Salmonella replication triggers caspase-8-dependent apoptosis via TLR-driven TNF signaling and NLRC4-mediated sensing of the SPI-2 Type III secretion system

Salmonella enterica comprises over 2500 serovars that are responsible for over 90 million annual infections and 100,000 deaths worldwide. Despite this diversity, our understanding of innate immune responses to Salmonella is based on extensive study of a few serovars, primarily Typhimurium, including strains that cannot replicate within primary murine macrophages. Non-replicating Salmonella trigger caspase-1 and -11-dependent pyroptosis. Whether the innate immune system distinguishes between replicating and non-replicating intracellular Salmonella is poorly defined. Here we demonstrate that replicating Salmonella enterica induce a distinct pathway of TNF- and caspase-8-driven apoptosis via host TLR4 and Salmonella Pathogenicity Island-2 activity. This pathway is independent of gasdermin D and involves the apoptotic pore protein Pannexin-1. Combined loss of Pannexin-1 and gasdermin D resulted in defective control of systemic Salmonella, indicating that these pathways function together to promote anti-Salmonella host defense. Altogether, our findings uncover a previously unappreciated pathway by which macrophages sense intracellular replicating bacteria.

microbiology↗

bioRxiv2025

Macrophages orchestrate elimination of Shigella from the intestinal epithelial cell niche via TLR-induced IL-12 and IFN-γ

Bacteria of the genus Shigella replicate in intestinal epithelial cells and cause shigellosis, a severe diarrheal disease that resolves spontaneously in most healthy individuals. During shigellosis, neutrophils are abundantly recruited to the gut, and have long been thought to be central to Shigella control and pathogenesis. However, how shigellosis resolves remains poorly understood due to the longstanding lack of a tractable and physiological animal model. Here, using our newly developed Nlrc4-/-Casp11-/- mouse model of shigellosis, we unexpectedly find no major role for neutrophils in limiting Shigella or in disease pathogenesis. Instead, we uncover an essential role for macrophages in the host control of Shigella. Macrophages respond to Shigella via TLRs to produce IL-12, which then induces IFN-{gamma}, a cytokine that is essential to control Shigella replication in intestinal epithelial cells. Collectively, our findings reshape our understanding of the innate immune response to Shigella.

immunology↗

bioRxiv2023

Analysis of intestinal epithelial cell responses to Cryptosporidium highlights the temporal effects of IFN-gamma on parasite restriction

The production of IFN-{gamma} is crucial for control of multiple enteric infections, but its impact on intestinal epithelial cells (IEC) is not well understood. Cryptosporidium parasites exclusively infect epithelial cells and the ability of interferons to activate the transcription factor STAT1 in IEC is required for parasite clearance. The use of single cell RNA sequencing to profile IEC during infection revealed induction of IFN-{gamma}-dependent gene signatures that was comparable between uninfected and infected cells, and IEC expression of the IFN-{gamma} receptor was required for parasite control. Unexpectedly, treatment of Ifng-/- mice with IFN-{gamma} demonstrated the IEC response to this cytokine correlates with a delayed reduction in parasite burden but did not affect parasite development. These data sets provide insight into the impact of IFN-{gamma} on IEC and suggest a model in which IFN-{gamma}-mediated bystander activation of uninfected enterocytes is important for control of Cryptosporidium. AUTHOR SUMMARYThe cytokine interferon-gamma (IFN-{gamma}) plays an important role in the control of intracellular infections by a wide variety of bacteria, viruses and parasites. While the impact of IFN-{gamma} on immune cells has been a major research focus, how it impacts intestinal epithelial cells remains poorly understood. Cryptosporidium parasites are an important cause of morbidity in a variety of epidemiological settings and exclusively infect intestinal epithelial cells (IEC). Recent advances in the ability to genetically modify and study Cryptosporidium in wild-type hosts provides a useful model to investigate IEC-intrinsic mechanisms of pathogen control. In this study, single cell RNA-sequencing was used to analyze the IEC response to infection and IFN-{gamma} signalling. We demonstrate broad changes in the epithelial compartment during infection that include the induction of an IEC population with robust induction of IFN-{gamma}-stimulated genes. In addition, we show that infected IEC remain responsive to IFN-{gamma} signalling, and that this cytokine causes a delayed reduction in parasite burden that correlates with the kinetics of IEC responsiveness to IFN-{gamma} stimulation. Together, our work uncovers how Cryptosporidium infection impacts the IEC compartment and helps define the relationship between the kinetics of IFN-{gamma} responsiveness and pathogen control in IEC.

immunology↗

bioRxiv2022

A hierarchy of cell death pathways confers layered resistance to shigellosis in mice

Bacteria of the genus Shigella cause shigellosis, a severe gastrointestinal disease driven by bacterial colonization of colonic intestinal epithelial cells. Vertebrates have evolved programmed cell death pathways that sense invasive enteric pathogens and eliminate their intracellular niche. Previously we reported that genetic removal of one such pathway, the NAIP-NLRC4 inflammasome, is sufficient to convert mice from resistant to susceptible to oral Shigella flexneri challenge (Mitchell, Roncaioli et al., 2020). Here, we investigate the protective role of additional cell death pathways during oral mouse Shigella infection. We find that the Caspase-11 inflammasome, which senses Shigella LPS, restricts Shigella colonization of the intestinal epithelium in the absence of NAIP-NLRC4. However, this protection is limited when Shigella expresses OspC3, an effector that antagonizes Caspase-11 activity. TNF, a cytokine that activates Caspase-8-dependent apoptosis, also provides protection from Shigella colonization of the intestinal epithelium, but only in the absence of both NAIP- NLRC4 and Caspase-11. The combined genetic removal of Caspases-1,-11, and -8 renders mice hyper-susceptible to oral Shigella infection. Our findings uncover a layered hierarchy of cell death pathways that limit the ability of an invasive gastrointestinal pathogen to cause disease.

immunology↗

bioRxiv2020

NAIP-NLRC4-deficient mice are susceptible to shigellosis

Bacteria of the genus Shigella cause shigellosis, a severe gastrointestinal disease that is a major cause of diarrhea-associated mortality in humans. Shigellosis develops upon oral ingestion of as few as 100 bacteria, but million-fold higher doses fail to cause disease in mice. The lack of a physiologically relevant mouse model of shigellosis has impeded our understanding of this important human disease, but why mice are resistant is unknown. Here we show that in human cells, but not in mice, Shigella evades detection by the NAIP-NLRC4 inflammasome, an immune sensor present in intestinal epithelial cells (IECs). We find that NAIP-NLRC4-deficient mice are highly susceptible to oral Shigella infection and recapitulate the clinical features of human shigellosis, including bacterial replication in IECs and neutrophilic inflammation of the colon. Confirming a role for bacterial replication in IECs in our new model, a Shigella mutant lacking IcsA, a factor required for cell-to-cell spread among IECs, is attenuated in otherwise susceptible NAIP-NLRC4-deficient mice. Although inflammasome-mediated cell death is widely held to promote Shigella infection and pathogenesis, we instead demonstrate that IEC-specific NAIP-NLRC4-induced cell death is sufficient to protect the host from shigellosis. Thus, NAIP-NLRC4-deficient mice are a physiologically relevant and experimentally tractable model for shigellosis. More broadly, our results suggest that the lack of an inflammasome response in IECs may help explain the extreme susceptibility of humans to shigellosis.

microbiology↗