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Background While delivery of supplemental oxygen is a life-saving therapy, exposure to high oxygen, called hyperoxia, leads to increased intensive care unit mortality. Hyperoxia induces oxidant-mediated acute lung injury (ALI) and pulmonary cell death, called hyperoxic ALI (HALI). Elucidating molecular mechanisms in HALI could identify therapeutic targets in ALI. Methods In the current study, we examined in vivo effects of HALI on Beclin-1 (BCN1), which regulates autophagy, and modulation of BCN1 by epidermal growth factor receptor (EGFR). Effects of HALI on BCN1 and autophagy were examined in mice with genetically decreased EGFR (EGFR Wa5/+ ). Wildtype (WT) and EGFR Wa5/+ mice were exposed to 100% oxygen for 24–72 hours along with normoxia controls (eight groups; n=4–6/group), and analysis of pulmonary BCN1 and autophagy was completed. Results In WT, HALI led to increased BCN1 (59% increased total BCN1/β-Actin; p<0.01) in lung and alveolar epithelium (484% increased H-score; p<0.001). HALI led to decreased microtubule-associated protein 1B-light chain (LC3B)-II/-I ratios (43% decrease; p<0.05) and increased p62 (93% increase; p<0.05), suggesting reduced autophagic flux. In human alveolar type-II cells derived from induced pluripotent stem cells (AT2s iPSC ), HALI caused increased LDH release (130% increase; p<0.0001) and decreased LC3B-II/-I ratios (32% decrease; p<0.05). We previously showed that EGFR Wa5/+ mice are protected in HALI. In the current study, EGFR Wa5/+ mice showed increased pulmonary BCN1 (122% increase; p<0.05), reduced phosphorylated-(p-)/total BCN1 (47% decrease; p<0.05) and decreased LC3B-II/-I ratios (70% decrease; p<0.01) in HALI compared with WT. In addition, wortmannin (1 mg/kg), which decreases BCN1-mediated autophagy, increased mortality in HALI compared with vehicle control (n=10/group; 18% decreased hours survived; p<0.001). Conclusions These data delineate a novel cell death pathway in HALI involving BCN1 and EGFR with therapeutic potential.

Abstract Bacterial superantigens (BSAg) are produced by Staphylococcus aureus and Streptococcus pyogenes. BSAg bind directly to the MHC class II molecules without undergoing any processing and subsequently activate T cells in an antigen non-specific manner by interacting with the TCR Vβ region. BSAg have been implicated primarily in acute diseases such as food poisoning, toxic shock syndrome, etc. Since carrier strains of S. aureus and S. pyogenes can elaborate superantigens, there is a distinct possibility of chronic exposure to low doses of BSAg and it is imperative to study its outcome. As BSAg bind more avidly to human (HLA) than to murine (H-2) MHC class II, we delivered low concentrations (total of 10 μg/mouse) of BSAg to HLA-DR3 [staphylococcal enterotoxin (SE) B] or HLA-DQ8 [streptococcal pyrogenic exotoxin (SPE) A] transgenic mice through subcutaneously implanted miniosmotic pumps for 7 days. Continuous exposure to low concentrations of BSAg resulted in a significant protracted expansion of CD4+ T cells expressing TCR Vβ8 (for SEB); Vβ8 and Vβ14 (for SPEA) with a concomitant decrease in percentage of CD8+ T cells expressing these TCR. T cells bearing TCR Vβ6 showed an inverse correlation (slight decrease in CD4+ and increase in CD8+ compartments with SEB and SPEA). Histological examinations of major organs showed intense perivascular infiltration in lungs, kidneys and liver along with inflammatory infiltrates in the cardiac valvular endothelium in mice bearing pumps delivering BSAg but not PBS. In conclusion, we have shown the immunological outcome of chronic exposure to low levels of BSAg using the HLA class II transgenic mouse model.

Abstract Staphylococcal Enterotoxin B (SEB) is a superantigen made by S. aureus. SEB can cause food poisoning and shock and its stability and ease of preparation make it a potential agent of bioterrorism. SEB-mediated activation induces T cell proliferation and secretion of cytokines. Antibodies that block the interaction between SEB and MHC or SEB and TCR, can neutralize the activating effects of SEB and provide protection against its debilitating effects. Human IVIG, a therapy for SEB intoxication is of low potency and sometimes, short supply. To surmount we have derived of mouse monoclonal antibodies that block the binding of SEB to MHC at separate and distinct sites. Combinations of these antibodies synergistically neutralize SEB mediated T cell activation. Genes encoding the VL and VH genes of synergistically neutralizing pairs of cell lines were cloned and grafted onto genes encoding either the constant region of human IgH or Igκ and transfected into SP2/0 cells. Chimeric human-mouse antibodies expressed by the transfectants were purified. Tests of these chimeric antibodies demonstrated that they were neutralizing and in combination with each other, still capable of synergistic neutralization of SEB. Supported by NIH grant # AI057652

Abstract TCR interactions with agonist pMHCs induce a conformational change in the tails of the associated CD3 complex (CD3Δc) that contributes to efficient TCR/CD3 triggering and productive T cell responses. In contrast, TCR engagement by antagonistic pMHCs does not induce either CD3Δc or full TCR/CD3 signaling in mature T cells. Here, we have used a monovalent Fab fragment (Mono-Fab) specific for the murine CD3 complex to provide induction of CD3Δc to mature T cells engaging pMHC ligands. This Mono-Fab does not interfere with TCR capacity to bind pMHC and fails to elicit signaling in the absence of TCR/MHC interactions. Using OT-I Tg T cells and a collection of altered peptide ligands derived of the agonist peptide OVA, we show that addition of CD3Δc to OT-I T cells using Mono-Fab enables T cell responses to antagonist ligands that fail to induce CD3Δc on their own. Moreover, using a mouse model of metastatic melanoma, we show that Mono-Fab promotes in vivo T cell dependent anti-melanoma responses that are antigen-specific. This Mono-Fab can also be combined with established therapies targeting signals 2 and 3 involved in T cell activation for a synergistic effect. Our data suggests that in-trans CD3Δc provision decreases the activation threshold of T cells. We propose that targeting the CD3 complex for the induction of CD3Δc could be exploited to achieve efficient TCR/CD3 triggering by poorly immunogenic antigens in the context of vaccination against cancer and infectious diseases.

Abstract CD4 and CD8 coreceptors play an important role in the development and maturation of αβ TCR+ T cells. However, T cells lacking CD4 and CD8 (double negative T or DNT cells) are present in the periphery and are significantly expanded in systemic lupus erythematosus (SLE) and Sjogren’s syndrome. The antigens that cause expansion of these DNT cells are unknown. As T cell activation by superantigens does not require coreceptors, we hypothesized that superantigens could activate DNT cells and contribute to autoimmunity. HLA-DQ8 and HLA-DR3 transgenic mice lacking both CD4 and CD8 were generated by intercrossing CD4 and CD8 single knockout mice. The CD4.CD8 double knockout (DKO) mice harbored a diverse repertoire of DNT cells in the periphery, albeit at reduced numbers compared to wild type (WT) mice. DNT cells from DKO mice responded robustly to the superantigen, staphylococcal enterotoxin B, but not to HLA restricted conventional antigens. Implantation of mini-osmotic pumps delivering 10 or 50 μg of SEB continuously over 7 or 28 days induced a lupus-like disease in WT as well as DKO DR3 and DQ8 mice. However, the immunopathology was significantly more pronounced in DKO mice. Immunostaining revealed extensive infiltration of multiple organs including lungs, liver and kidneys with CD3+ T cells in DKO mice. Overall, our study unraveled the role of CD4 and CD8 coreceptors in T cell development/function and the role of superantigens and DNT cells in the pathogenesis of lupus.

Abstract Menstrual or non-menstrual toxic shock syndrome (TSS), caused by the superantigen exotoxins of Staphylococcus aureus or Streptococcus pyogenes, is characterized by a robust activation of the immune system, systemic cytokine/chemokine storm, multiple organ failure and possibly death, if not treated promptly. We tested whether increasing the numbers of Treg in vivo by administration of IL-2-anti-IL-2 complexes (IL2C) could be beneficial in TSS. Administration of IL2C [prepared by incubating 1µg of IL-2 (Peprotech) and 5µg anti-IL-2 (eBioscience, clone-JES6-1A12) in a total 200 µl at 37oC for 30 min] on days 0, 1 and 2, caused a 3 to 4-fold increase in CD4+CD25+FoxP3+ Treg numbers in the spleens of HLA-DR3 transgenic mice by day 5. However, upon challenge with staphylococcal enterotoxin B (SEB, 50µg), compared to untreated HLA-DR3 transgenic mice, IL2C-treated mice produced significantly higher levels of IFN-γ (1714±1365 versus 6642±2253 pg/ml), MIP-1α (782±23 versus 2305±376 pg/ml,), MIP-1β, RANTES and TNF-α. SEB-induced mortality was also significantly increased in the IL2C treated group. While only 1/5 mice died in untreated group, 6/11 mice died in the IL2C treated group. In conclusion, even though administration of IL2C significantly increased the Treg numbers, such a treatment also increased their susceptibility to TSS. Hence, the benefits of T reg-promoting IL-2-anti-IL-2 complexes in TSS or related conditions need more stringent evaluation.

Abstract Bacterial superantigen-induced toxic shock syndrome (TSS) and sepsis are characterized by a profound systemic inflammatory response. Given the important role of NF¿B pathway in inflammation, we investigated whether a clinically approved proteasome inhibitor, Bortezomib, capable of inhibiting NF¿B pathway, be of therapeutic use in such conditions using HLA class II transgenic mice. Bortezomib significantly blocked staphylococcal enterotoxin B (SEB)-induced T cell activation and cytokine production in vitro. In SEB-induced TSS, in vivo administration of Bortezomib significantly reduced serum levels of several pro-inflammatory cytokines and chemokines. Nevertheless, 100% of SEB challenged mice treated with Bortezomib succumbed to TSS, and Bortezomib sensitized mice to TSS at concentrations of SEB which are otherwise non-lethal (i.e., as low as 2 μg/mouse), even when administered 24 hours after exposure to SEB. Sensitization to TSS by Bortezomib was not due to the pro-apoptotic effects of Bortezomib. Serum biochemical parameters and histopathological findings suggested acute liver failure as the possible cause of mortality. In sepsis model, whereas LPS alone (10 μg/mouse) was seldom lethal, it was uniformly lethal when administered along with Bortezomib. In conclusion, Bortezomib sensitizes mice to certain acute systemic inflammatory diseases. Supported by R01AI068741 and AI 72211

To understand the role of regulatory T cells in staphylococcal enterotoxin B‐induced toxic shock syndrome (TSS), we performed gene expression profiling in HLA‐DR3 transgenic mice using microarrays. We observed that at 3 hours after systemic exposure to SEB (10 μg), the splenic expression of FoxP3, a hall mark of regulatory T cells, was increased by 5 folds (p<0.005). In addition, other genes that regulate FoxP3 + Tregs were also significantly modulated by SEB. These include IL‐2R (27‐fold), IL‐2 (234‐fold), IL‐6 (689‐fold), IL‐21 (21‐fold), TGF‐B1 (0.7‐fold), IL‐17 (5.5‐fold) and IL‐22 (98‐fold). To further characterize the homeostasis of Tregs cells during superantigen‐induced TSS in vivo, HLA‐DR3 transgenic mice were first challenged with SEB and were administered BrdU in drinking water for 3 days. Mice were killed 3 days later and splenocytes analyzed by flow cytometry. We observed that in addition to FoxP3‐TCR Vβ8 + T cells, FoxP3 + TCR Vβ8 + T cells also significantly expanded in vivo as evident from their BrdU staining patterns. This indicated that SEB is able to activate Tregs as well. Depletion of Tregs using anti‐CD25 antibodies (clone PC‐61, 500 ug/mouse) 2 days prior to SEB challenge did not significantly alter serum cytokine levels as compared to control mice treated with rat IgG and SEB. Thus, T regulatory cells have a minimal role in SEB‐induced TSS.

AbstractStaphylococcal enterotoxin B (SEB), which is produced by the major human pathogen, Staphylococcus aureus, represents a powerful superantigenic toxin and is considered a bioweapon. However, the contribution of SEB to S. aureus pathogenesis has never been directly demonstrated with genetically defined mutants in clinically relevant strains. Many isolates of the predominant Asian community-associated methicillin-resistant S. aureus lineage sequence type (ST) 59 harbor seb, implying a significant role of SEB in the observed hypervirulence of this lineage. We created an isogenic seb mutant in a representative ST59 isolate and assessed its virulence potential in mouse infection models. We detected a significant contribution of seb to systemic ST59 infection that was associated with a cytokine storm. Our results directly demonstrate that seb contributes to S. aureus pathogenesis, suggesting the value of including SEB as a target in multipronged antistaphylococcal drug development strategies. Furthermore, they indicate that seb contributes to fatal exacerbation of community-associated methicillin-resistant S. aureus infection.

Abstract TNF-related apoptosis-inducing ligand (TRAIL) was initially described to induce apoptosis of tumor cells and/or virally infected cells, although sparing normal cells, and has been implicated in the pathogenesis of HIV disease. We previously identified TRAILshort, a TRAIL splice variant, in HIV-infected patients and characterized it as being a dominant negative ligand to subvert TRAIL-mediated killing. Herein, using single-cell genomics we demonstrate that TRAILshort is produced by HIV-infected cells, as well as by uninfected bystander cells, and that the dominant stimulus which induces TRAILshort production are type I IFNs and TLR7, TLR8, and TLR9 agonists. TRAILshort has a short t1/2 by virtue of containing a PEST domain, which targets the protein toward the ubiquitin proteasome pathway for degradation. Further we show that TRAILshort binds preferentially to TRAIL receptors 1 and 2 with significantly reduced interaction with the decoy TRAIL receptors 3 and 4. Recombinant TRAILshort is sufficient to protect cells against TRAIL-induced killing, whereas immunodepletion of TRAILshort with a specific Ab restores TRAIL sensitivity. Importantly we show that TRAILshort is shed in microvesicles into the cellular microenvironment and therefore confers TRAIL resistance not only on the cell which produces it, but also upon neighboring bystander cells. These results establish a novel paradigm for understanding and overcoming TRAIL resistance, in particular how HIV-infected cells escape immune elimination by the TRAIL:TRAILshort receptor axis.