Jessica C. Jang

Macrophage-derived human resistin is induced in multiple helminth infections and promotes inflammatory monocytes and increased parasite burden.

Parasitic helminth infections can be associated with lifelong morbidity such as immune-mediated organ failure. A better understanding of the host immune response to helminths could provide new avenues to promote parasite clearance and/or alleviate infection-associated morbidity. Murine resistin-like molecules (RELM) exhibit pleiotropic functions following helminth infection including modulating the host immune response; however, the relevance of human RELM proteins in helminth infection is unknown. To examine the function of human resistin (hResistin), we utilized transgenic mice expressing the human resistin gene (hRetnTg+). Following infection with the helminth Nippostrongylus brasiliensis (Nb), hResistin expression was significantly upregulated in infected tissue. Compared to control hRetnTg− mice, hRetnTg+ mice suffered from exacerbated Nb-induced inflammation characterized by weight loss and increased infiltration of inflammatory monocytes in the lung, along with elevated Nb egg burdens and delayed parasite expulsion. Genome-wide transcriptional profiling of the infected tissue revealed that hResistin promoted expression of proinflammatory cytokines and genes downstream of toll-like receptor signaling. Moreover, hResistin preferentially bound lung monocytes, and exogenous treatment of mice with recombinant hResistin promoted monocyte recruitment and proinflammatory cytokine expression. In human studies, increased serum resistin was associated with higher parasite load in individuals infected with soil-transmitted helminths or filarial nematode Wuchereria bancrofti, and was positively correlated with proinflammatory cytokines. Together, these studies identify human resistin as a detrimental factor induced by multiple helminth infections, where it promotes proinflammatory cytokines and impedes parasite clearance. Targeting the resistin/proinflammatory cytokine immune axis may provide new diagnostic or treatment strategies for helminth infection and associated immune-mediated pathology.

Alternatively Activated Macrophages Revisited: New Insights into the Regulation of Immunity, Inflammation and Metabolic Function following Parasite Infection.

The role of macrophages in homeostatic conditions and the immune system range from clearing debris to recognizing and killing pathogens. While classically activated macrophages (CAMacs) are induced by T helper type 1 (Th1) cytokines and exhibit microbicidal properties, Th2 cytokines promote alternative activation of macrophages (AAMacs). AAMacs contribute to the killing of helminth parasites and mediate additional host-protective processes such as regulating inflammation and wound healing. Yet, other parasites susceptible to Th1 type responses can exploit alternative activation of macrophages to diminish Th1 immune responses and prolong infection. In this review, we will delineate the factors that mediate alternative activation (e.g. Th2 cytokines and chitin) and the resulting downstream signaling events (e.g. STAT6 signaling). Next, the specific AAMac-derived factors (e.g. Arginase1) that contribute to resistance or susceptibility to parasitic infections will be summarized. Finally, we will conclude with the discussion of additional AAMac functions beyond immunity to parasites, including the regulation of inflammation, wound healing and the regulation of metabolic disorders.

Comparison of RELMα and RELMβ Single- and Double-Gene-Deficient Mice Reveals that RELMα Expression Dictates Inflammation and Worm Expulsion in Hookworm Infection

ABSTRACT Resistin-like molecules (RELMs) are highly expressed following helminth infection, where they impact both the host and helminth. While RELMα (Retnla) impairs helminth expulsion by inhibiting protective Th2 immunity, RELMβ (Retnlb) can promote its expulsion. We employed Retnla −/− and Retnlb −/− mice to delineate the function of both proteins following infection with Nippostrongylus brasiliensis, a hookworm that infects the lung and intestine. Whereas wild-type (WT) and Retnlb −/− mice exhibited equivalent infection-induced inflammation, Retnla −/− mice suffered a heightened inflammatory response, including increased mortality, weight loss, and lung inflammation. In the intestine, Retnla −/− mice had low parasite egg burdens compared to those of WT mice, while Retnlb −/− mice exhibited high egg burdens, suggesting that RELMα and RELMβ have functionally distinct effects on immunity and inflammation to N. brasiliensis. To test the importance of both proteins, we generated Retnla −/− Retnlb −/− mice. Infected Retnla −/− Retnlb −/− mice exhibited similar responses to Retnla −/− mice, including increased mortality and lung inflammation. This inflammatory response in Retnla −/− Retnlb −/− mice negatively impacted N. brasiliensis fitness, as demonstrated by significantly lower worm ATP levels and decreased intestinal worm burden and fecundity. Lung cytokine analysis revealed that Retnla −/− and Retnla −/− Retnlb −/− mice expressed significantly increased levels of interleukin-4 (IL-4). Finally, we generated Retnla −/− mice on the Rag −/− background and observed that the effects of RELMα were abrogated in the absence of adaptive immunity. Together, these data demonstrate that RELMα but not RELMβ significantly impacts the immune response to N. brasiliensis infection by downregulating the Th2 adaptive immune response in the lung, which protects the host but allows improved parasite fitness.

Human resistin protects against endotoxic shock by blocking LPS–TLR4 interaction

Significance Gram-negative bacterial sepsis is a life-threatening disease that is exacerbated by an uncontrolled immune response to the endotoxin lipopolysaccharide (LPS). Human resistin is a highly expressed cytokine in sepsis, where it is hypothesized to exacerbate inflammation. We identify an unexpected protective role for resistin in endotoxic shock. We use human resistin-expressing transgenic mice and human immune cell assays to show that resistin prevents LPS-induced mortality by blocking LPS binding to its receptor Toll-like receptor 4 (TLR4) and by promoting anti-inflammatory signaling. Helminth infection-induced resistin and treatment with recombinant resistin or resistin N-terminal peptides also inhibited LPS function. These studies report a protective function for resistin and identify the therapeutic potential of resistin-mediated anti-inflammatory pathways or resistin-based reagents in sepsis. Helminths trigger multiple immunomodulatory pathways that can protect from sepsis. Human resistin (hRetn) is an immune cell-derived protein that is highly elevated in helminth infection and sepsis. However, the function of hRetn in sepsis, or whether hRetn influences helminth protection against sepsis, is unknown. Employing hRetn-expressing transgenic mice (hRETNTg+) and recombinant hRetn, we identify a therapeutic function for hRetn in lipopolysaccharide (LPS)-induced septic shock. hRetn promoted helminth-induced immunomodulation, with increased survival of Nippostrongylus brasiliensis (Nb)-infected hRETNTg+ mice after a fatal LPS dose compared with naive mice or Nb-infected hRETNTg− mice. Employing immunoprecipitation assays, hRETNTg+Tlr4−/− mice, and human immune cell culture, we demonstrate that hRetn binds the LPS receptor Toll-like receptor 4 (TLR4) through its N terminal and modulates STAT3 and TBK1 signaling, triggering a switch from proinflammatory to anti-inflammatory responses. Further, we generate hRetn N-terminal peptides that are able to block LPS proinflammatory function. Together, our studies identify a critical role for hRetn in blocking LPS function with important clinical significance in helminth-induced immunomodulation and sepsis.

Polarizing the T helper 17 response in Citrobacter rodentium infection via expression of resistin-like molecule α

Citrobacter rodentium infection is a murine model of pathogenic Escherichia coli infection that allows investigation of the cellular and molecular mechanisms involved in host-protective immunity and bacterial-induced intestinal inflammation. We recently demonstrated that following C. rodentium infection, the absence of Resistin-Like Molecule (RELM) α resulted in attenuated Th17 cell responses and reduced intestinal inflammation with minimal effects on bacterial clearance. In this addendum, we investigated the cytokine modulatory effects of RELMα and RELMα expression in the intestinal mucosa following C. rodentium infection. We show that in addition to promoting Th17 cytokine responses, RELMα inhibits Th2 cytokine expression and Th2-cytokine effector macrophage responses in the C. rodentium-infected colons. Second, utilizing reporter C. rodentium, we examined RELMα expression and macrophage recruitment at the host pathogen interface. We observed infection-induced macrophage infiltration and RELMα expression by intestinal epithelial cells. The influence of infection-induced RELMα on macrophage recruitment in the intestine is discussed.

Host and helminth-derived endocannabinoids are generated during infection with effects on host immunity

Helminths have coevolved with their hosts, resulting in the development of specialized host immune mechanisms and parasite-specific regulatory products. Identification of new pathways that regulate helminth infection could provide a better understanding of host-helminth interaction and may identify new therapeutic targets for helminth infection. ABSTRACT Helminths have coevolved with their hosts, resulting in the development of specialized host immune mechanisms and parasite-specific regulatory products. Identification of new pathways that regulate helminth infection could provide a better understanding of host-helminth interaction and may identify new therapeutic targets for helminth infection. Here we identify the endocannabinoid system as a new mechanism that influences host immunity to helminths. Endocannabinoids are lipid-derived signaling molecules that control important physiologic processes, such as feeding behavior and metabolism. Following murine infection with Nippostrongylus brasiliensis, an intestinal nematode with a life cycle similar to that of hookworms, we observed increased levels of endocannabinoids (2-arachidonoylglycerol [2-AG] or anandamide [AEA]) and the endocannabinoid-like molecule oleoylethanolamine (OEA) in infected lung and intestine. To investigate endocannabinoid function in helminth infection, we employed pharmacological inhibitors of cannabinoid subtype receptors 1 and 2 (CB1R and CB2R). Compared to findings for vehicle-treated mice, inhibition of CB1R but not CB2R resulted in increased N. brasiliensis worm burden and egg output, associated with significantly decreased expression of the T helper type 2 cytokine interleukin 5 (IL-5) in intestinal tissue and splenocyte cultures. Strikingly, bioinformatic analysis of genomic and transcriptome sequencing (RNA-seq) data sets identified putative genes encoding endocannabinoid biosynthetic and degradative enzymes in many parasitic nematodes. To test the novel hypothesis that helminth parasites produce their own endocannabinoids, we measured endocannabinoid levels in N. brasiliensis by mass spectrometry and quantitative PCR and found that N. brasiliensis parasites produced endocannabinoids, especially at the infectious larval stage. To our knowledge, this is the first report of helminth- and host-derived endocannabinoids that promote host immune responses and reduce parasite burden.

Continuous Inhalation Exposure to Fungal Allergen Particulates Induces Lung Inflammation While Reducing Innate Immune Molecule Expression in the Brainstem

Continuous exposure to aerosolized fine (particle size ≤2.5 µm) and ultrafine (particle size ≤0.1 µm) particulates can trigger innate inflammatory responses in the lung and brain depending on particle composition. Most studies of manmade toxicants use inhalation exposure routes, whereas most studies of allergens use soluble solutions administered via intranasal or injection routes. Here, we tested whether continuous inhalation exposure to aerosolized Alternaria alternata particulates (a common fungal allergen associated with asthma) would induce innate inflammatory responses in the lung and brain. By designing a new environmental chamber able to control particle size distribution and mass concentration, we continuously exposed adult mice to aerosolized ultrafine Alternaria particulates for 96 hr. Despite induction of innate immune responses in the lung, induction of innate immune responses in whole brain samples was not detected by quantitative polymerase chain reaction or flow cytometry. However, exposure did trigger decreases in Arginase 1, inducible nitric oxide synthase, and tumor necrosis factor alpha mRNA in the brainstem samples containing the central nervous system respiratory circuit (the dorsal respiratory group, ventral respiratory group, and the pre-Bötzinger and Bötzinger complexes). In addition, a significant decrease in the percentage of Toll-like receptor 2-expressing brainstem microglia was detected by flow cytometry. Histologic analysis revealed a significant decrease in Iba1 but not glial fibrillary acidic protein immunoreactivity in both the brainstem and the hippocampus. Together these data indicate that inhalation exposure to a natural fungal allergen under conditions sufficient to induce lung inflammation surprisingly causes reductions in baseline expression of select innate immune molecules (similar to that observed during endotoxin tolerance) in the region of the central nervous system controlling respiration.

Tissue Remodeling and Repair During Type 2 Inflammation

Tissue remodeling and repair following injury is an active immunologic and tissue regenerative process predicated upon a T helper type 2 (Th2) cell response. While typically associated with immunity to helminths or allergic inflammation, the Th2 response mediates tissue repair, acting to regulate inflammation while promoting the expression of wound healing genes and growth factors involved in tissue regeneration. However, if not appropriately regulated, Th2 responses can drive fibrosis, a pathologic condition where excess extracellular matrix and scar tissue are formed to fill the wound instead of newly regenerated tissue. In this chapter, we review how the Th2 immune responses are generated following injury, and the mechanism by which Th2 cytokines orchestrate wound healing. We focus on the immune cells (e.g., Th2 cells and alternatively activated macrophages) that direct this complex process, and the cytokines (e.g., IL-4 and IL-13) and growth factors (e.g., TGF-β) they secrete to mediate wound healing. Second, we detail the downstream wound healing pathways triggered by these factors notably tissue remodeling, extracellular matrix deposition and tissue regeneration. Finally, we discuss the clinical implications of the Th2 immune response on wound healing and fibrosis, and what key factors can be targeted to regulate the balance between optimal wound healing and detrimental fibrosis.