IL-33 is known to play an important role in Th2 immunity. In this study, we investigated the effect of IL-33 pretreatment on anti-fungal response using an acute Candida albicans peritoneal infection model. IL-33 pretreatment induced a rapid fungal clearance and markedly reduced the C. albicans infection-associated mortality. The priming effect of IL-33 occurred during multiple steps of the neutrophil-mediated anti-fungal response. First, the anti-fungal effect occurred due to the rapid and massive recruitment of neutrophils to the site of infection as a result of the release of CXCR2 chemokines by peritoneal macrophages and by reversal of the TLR-induced reduction of CXCR2 expression in neutrophils during IL-33 priming. Second, conditioning of neutrophils by IL-33 activated the TLR and dectin-1 signaling pathways, leading to the upregulation of complement receptor 3 expression induced by C. albicans. Upregulated CR3 in turn increased the phagocytosis of opsonized C. albicans and resulted in the production of high levels of reactive oxygen species and the subsequent enhanced killing activity of neutrophils. Taken together, our results suggest that IL-33 can regulate the anti-fungal activity of neutrophils by collaborative modulation of the signaling pathways of different classes of innate immune receptors.

Pseudomonas aeruginosa is among the most formidable antibiotic-resistant pathogens and is a leading cause of hospital-associated infections. With dwindling options for antibiotic-resistant infections, a new paradigm for treatment and disease resolution is required. MEDI3902, a bispecific antibody targeting the P. aeruginosa type III secretion (T3S) protein PcrV and Psl exopolysaccharide, was previously shown to mediate potent protective activity in murine infection models. With the current challenges associated with the clinical development of narrow-spectrum agents, robust preclinical efficacy data in multiple animal species are desirable. Here, we sought to develop a rabbit P. aeruginosa acute pneumonia model to further evaluate the activity of MEDI3902 intervention. In the rabbit model of acute pneumonia, prophylaxis with MEDI3902 exhibited potent dose-dependent protection, whereas those receiving control IgG developed fatal hemorrhagic necrotizing pneumonia between 12 and 54 h after infection. Blood biomarkers (e.g., partial pressure of oxygen [pO2], partial pressure of carbon dioxide [pCO2], base excess, lactate, and creatinine) were grossly deranged for the vast majority of control IgG-treated animals but remained within normal limits for MEDI3902-treated animals. In addition, MEDI3902-treated animals exhibited a profound reduction in P. aeruginosa organ burden and a marked reduction in the expression of proinflammatory mediators from lung tissue, which correlated with reduced lung histopathology. These results confirm that targeting PcrV and Psl via MEDI3902 is a promising candidate for immunotherapy against P. aeruginosa pneumonia.

IL-33 has been implicated in the pathogenesis of asthma, atopic allergy, anaphylaxis, and other inflammatory diseases by promoting the production of proinflammatory cytokines and chemokines or Th2 immune responses. In this study, we analyzed the in vivo effect of IL-33 administration. IL-33 markedly promoted myelopoiesis in the bone marrow and myeloid cell emigration. Concomitantly, IL-33 induced hematopoietic stem and progenitor cell (HSPC) mobilization and extramedullary hematopoiesis. HSPC mobilization was mediated mainly through increased levels of CCL7 produced by vascular endothelial cells in response to IL-33. In vivo treatment of IL-33 rapidly induced phosphorylation of ERK, JNK, and p38, and inhibition of these signaling molecules completely blocked the production of CCL7 induced by IL-33. Consistently, inhibitor of CCR2 markedly reduced IL-33–mediated HSPC mobilization in vivo and migration of HSPCs in response to CCL7 in vitro. IL-33–mobilized HSPCs were capable of homing to, and of long-term reconstitution in, the bone marrow of irradiated recipients. Immune cells derived from these recipients had normal antifungal activity. The ability of IL-33 to promote migration of HSPCs and myeloid cells into the periphery and to regulate their antifungal activity represents a previously unrecognized role of IL-33 in innate immunity. These properties of IL-33 have clinical implications in hematopoietic stem cell transplantation.

Staphylococcus aureus is a common pathogen causing infections in humans with various degrees of severity, with pneumonia being one of the most severe infections. In as much as staphylococcal pneumonia is a disease driven in large part by α-hemolysin (Hla) and Panton-Valentine leukocidin (PVL), we evaluated whether active immunization with attenuated forms of Hla (HlaH35L/H48L) alone, PVL components (LukS-PVT28F/K97A/S209A and LukF-PVK102A) alone, or combination of all 3 toxoids could prevent lethal challenge in a rabbit model of necrotizing pneumonia caused by the USA300 community-associated methicillin-resistant S. aureus (MRSA). Rabbits vaccinated with Hla toxoid alone or PVL components alone were only partially protected against lethal pneumonia, whereas those vaccinated with all 3 toxoids had 100% protection against lethality. Vaccine-mediated protection correlated with induction of polyclonal antibody response that neutralized not only α-hemolysin and PVL, but also other related toxins, produced by USA300 and other epidemic MRSA clones.

The role broad-spectrum antibiotics play in the spread of antimicrobial resistance, coupled with their effect on the healthy microbiome, has led to advances in pathogen-specific approaches for the prevention or treatment of serious bacterial infections. One approach in clinical testing is passive immunization with a monoclonal antibody (MAb) targeting alpha toxin for the prevention or treatment of Staphylococcus aureus pneumonia. Passive immunization with the human anti-alpha toxin MAb, MEDI4893*, has been shown to improve disease outcome in murine S. aureus pneumonia models. The species specificity of some S. aureus toxins necessitates testing anti-S. aureus therapeutics in alternate species. We developed a necrotizing pneumonia model in ferrets and utilized an existing rabbit pneumonia model to characterize MEDI4893* protective activity in species other than mice. MEDI4893* prophylaxis reduced disease severity in ferret and rabbit pneumonia models against both community-associated methicillin-resistant S. aureus (MRSA) and hospital-associated MRSA strains. In addition, adjunctive treatment of MEDI4893* with either vancomycin or linezolid provided enhanced protection in rabbits relative to the antibiotics alone. These results confirm that MEDI4893 is a promising candidate for immunotherapy against S. aureus pneumonia.

Susceptibility to systemic Candida albicans infection is determined by immune resistance, as well as by the ability to control Candida-induced immunopathologies. We showed previously that exogenous IL-33 can increase resistance to peritoneal C. albicans infection by regulating multiple steps of the neutrophil anti-Candida response. In this study, using a mouse model of systemic candidiasis, we observed that IL-33 administration limited fungal burden and inflammation and increased survival. In kidneys, IL-33 seemed to directly act on neutrophils and CD4+ T cells: IL-33 administration enhanced fungal clearance by increasing neutrophil phagocytic activity without which Candida proliferation was uncontrollable. In contrast, IL-33 stimulated CD4+ T cells to produce IL-13, which, in turn, drove the polarization of macrophages toward the M2 type. Furthermore, the absence of IL-13 abolished IL-33–mediated polarization of M2 macrophages and renal functional recovery. In addition, IL-33 and IL-13 acted synergistically to increase M2 macrophage polarization and its phagocytic activity. Overall, this study identifies IL-33 as a cytokine that is able to induce resistance and tolerance and suggests that targeting resistance and tolerance simultaneously with therapeutic IL-33 may benefit patients with systemic candidiasis.

Pseudomonas aeruginosa is a challenge for clinicians due to increasing drug resistance and dwindling treatment options. We report on the activity of MEDI3902, an antibody targeting type 3 secretion protein PcrV and Psl exopolysaccharide, in rabbit bloodstream and lung infection models. MEDI3902 prophylaxis or treatment was protective in both acute models and exhibited enhanced activity when combined with a subtherapeutic dose of meropenem. These findings further support MEDI3902 for the prevention or treatment of serious P. aeruginosa infections.

Staphylococcus aureus is a major human pathogen that causes a wide range of infections by producing an arsenal of cytotoxins. We found that passive immunization with either a monoclonal antibody (MAb) neutralizing alpha-hemolysin or a broadly cross-reactive MAb neutralizing Panton-Valentine leukocidin, leukocidin ED, and gamma-hemolysins HlgAB and HlgCB conferred only partial protection, whereas the combination of those two MAbs conferred significant protection in a rabbit model of necrotizing pneumonia caused by the USA300 methicillin-resistant S. aureus epidemic clone.