Background & Aims Gastric dendritic cells (DCs) control the adaptive response to infection with Helicobacter pylori , a major risk factor for peptic ulcer disease and gastric cancer. We hypothesize that DC interactions with the gastric epithelium position gastric DCs for uptake of luminal H pylori and promote DC responses to epithelial-derived mediators. The aim of this study was to determine whether the gastric epithelium actively recruits DCs using a novel co-culture model of human gastric epithelial spheroids and monocyte-derived DCs. Methods Spheroid cultures of primary gastric epithelial cells were infected with H pylori by microinjection. Co-cultures were established by adding human monocyte-derived DCs to the spheroid cultures and were analyzed for DC recruitment and antigen uptake by confocal microscopy. Protein array, gene expression polymerase chain reaction array, and chemotaxis assays were used to identify epithelial-derived chemotactic factors that attract DCs. Data from the co-culture model were confirmed using human gastric tissue samples. Results Human monocyte-derived DCs co-cultured with gastric spheroids spontaneously migrated to the gastric epithelium, established tight interactions with the epithelial cells, and phagocytosed luminally applied H pylori . DC recruitment was increased upon H pylori infection of the spheroids and involved the activity of multiple chemokines including CXCL1, CXCL16, CXCL17, and CCL20. Enhanced chemokine expression and DC recruitment to the gastric epithelium also was observed in H pylori –infected human gastric tissue samples. Conclusions Our results indicate that the gastric epithelium actively recruits DCs for immunosurveillance and pathogen sampling through chemokine-dependent mechanisms, with increased recruitment upon active H pylori infection.

Influenza A viruses (IAVs) have multiple mechanisms for altering the host immune response to aid in virus survival and propagation. While both type I and II interferons (IFNs) have been associated with increased bacterial superinfection (BSI) susceptibility, we found that in some cases type I IFNs can be beneficial for BSI outcome. Specifically, we have shown that antagonism of the type I IFN response during infection by some IAVs can lead to the development of deadly BSI. The nonstructural protein 1 (NS1) from IAV is well known for manipulating host type I IFN responses, but the viral proteins mediating BSI severity remain unknown. In this study, we demonstrate that the PDZ-binding motif (PDZ-bm) of the NS1 C-terminal region from mouse-adapted A/Puerto Rico/8/34-H1N1 (PR8) IAV dictates BSI susceptibility through regulation of IFN-a/b production. Deletion of the NS1 PDZ-bm from PR8 IAV (PR8-TRUNC) resulted in 100% survival and decreased bacterial burden in superinfected mice compared with 0% survival in mice superinfected after PR8 infection. This reduction in BSI susceptibility after infection with PR8-TRUNC was due to the presence of IFN-b, as protection from BSI was lost in Ifn-b-/mice, resembling BSI during PR8 infection. PDZ-bm in PR8-infected mice inhibited the production of IFN-b posttranscriptionally, and both delayed and reduced expression of the tunable interferon-stimulated genes. Finally, a similar lack of BSI susceptibility, due to the presence of IFN-b on day 7 post-IAV infection, was also observed after infection of mice with A/TX98-H3N2 virus that naturally lacks a PDZ-bm in NS1, indicating that this mechanism of BSI regulation by NS1 PDZ-bm may not be restricted to PR8 IAV. These results demonstrate that the NS1 C-terminal PDZ-bm, like the one present in PR8 IAV, is involved in controlling susceptibility to BSI through the regulation of IFN-b, providing new mechanisms for NS1-mediated manipulation of host immunity and BSI severity.

Three million people globally suffer from infections caused by Aspergillus fumigatus (Af). Over 300,000 of these cases are due to invasive pulmonary aspergillosis (IPA) in patients with suppressed immune systems. The recent increase of aspergillosis in influenza-infected patients suggests that influenza infection creates transiently suppressed immune environments permissive to fungal infection. Consistent with this, we found that influenza infected WT mice had increased Af lung fungal burden and cellular damage compared to Af-only infected mice. We recently discovered that type I interferon (IFN) signaling, via IFNAR2 of the IFNAR1/2 receptor, regulates susceptibility to and damage from influenza. A main factor contributing to IPA pathology and outcome is the level of damage the host incurs. Importantly, we found that IFNAR2 deficiency (Ifnar2−/− mice) resulted in increased cellular damage and morbidity at 24 hrs post-Af compared to WT and Ifnar1−/− mice. Interestingly, Ifnar2−/− mice cleared spores more efficiently than both WT and Ifnar1−/− mice but were unable to control invasive disease and maintain pulmonary architecture, evidenced by hyphal growth and fibrosis-like tissue at 48 hrs post-Af. Although cellular recruitment was unaltered, the levels of inflammatory cytokines in Ifnar2−/− mice was two-fold higher than WT and Ifnar1−/− mice, and Ifnar2−/− neutrophils produced more external ROS in response to Af suggesting altered effector cell function may be involved in the IFNAR2 regulated damage response. Together, our results begin to establish a role for IFNAR2 in regulation of the host damage response to Af and suggest that aberrant type I IFN signaling creates a permissive environment allowing for Af infection to occur.

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