Abraham, David

Significance The intestinal parasite Strongyloides stercoralis infects an estimated 100 million people. This nematode’s unique ability to autoinfect its host enables it to persist for decades undetected and to progress to a potentially fatal hyperinfection that often is induced by glucocorticoid treatment. We report a mouse model, involving the NSG strain, that recapitulates all forms of human strongyloidiasis. Even in severely immunocompromised NSG mice, glucocorticoid treatment was required for autoinfection, raising intriguing questions about the mechanism of glucocorticoid action. Notably, administering a nematode-derived steroid, Δ7-dafachronic acid, which acts through a receptor within S. stercoralis to regulate parasite development, significantly diminished autoinfection in glucocorticoid-treated NSG mice. This opens the possibility of new chemotherapy for hyperinfective strongyloidiasis, targeting the parasite’s own steroid hormone mechanisms.

Abstract Protective immunity to Strongyloides stercoralis infective larvae in mice has been shown to be dependent on IL-5 based on mAb depletion studies. The goal of this study was to determine the functional role of IL-5 during the innate and adaptive immune response to larval S. stercoralis in mice. In these studies, three strains of mice were used: wild-type C57BL/6J (WT), IL-5 knockout (KO), and IL-5 transgenic (TG). Innate responses to the larvae indicated that there was enhanced survival in the KO animals and decreased survival in the TG animals compared with WT. Furthermore, killing of larvae in TG mice was associated with eosinophil infiltration and degranulation. In studying the adaptive immune response, it was observed that immunization of KO mice did not lead to the development of protective immunity. Experiments were then performed to determine whether KO mice reconstituted with Abs or cells could then develop protective immunity. KO mice displayed protective immunity via a granulocyte-dependent mechanism following injection of purified IgM from immune wild-type animals. Immunity in KO mice could also be reconstituted by the injection of eosinophils at the time of immunization. These eosinophils did not participate in actively killing the challenge infection, but rather were responsible for the induction of a protective Ab response. We conclude that IL-5 is required in the protective immune response for the production of eosinophils, and that eosinophils were involved in larval killing during innate immunity and in the induction of protective Abs in the adaptive immune response.

ABSTRACTEosinophils and neutrophils contribute to larval killing during the primary immune response, and neutrophils are effector cells in the secondary response toStrongyloides stercoralisin mice. The objective of this study was to determine the molecular mechanisms used by eosinophils and neutrophils to control infections withS. stercoralis. Using mice deficient in the eosinophil granule products major basic protein (MBP) and eosinophil peroxidase (EPO), it was determined that eosinophils kill the larvae through an MBP-dependent mechanism in the primary immune response if other effector cells are absent. InfectingPHILmice, which are eosinophil deficient, withS. stercoralisresulted in development of primary and secondary immune responses that were similar to those of wild-type mice, suggesting that eosinophils are not an absolute requirement for larval killing or development of secondary immunity. TreatingPHILmice with a neutrophil-depleting antibody resulted in a significant impairment in larval killing. Naïve and immunized mice with neutrophils deficient in myeloperoxidase (MPO) infected withS. stercoralishad significantly decreased larval killing. It was concluded that there is redundancy in the primary immune response, with eosinophils killing the larvae through an MBP-dependent mechanism and neutrophils killing the worms through an MPO-dependent mechanism. Eosinophils are not required for the development or function of secondary immunity, but MPO from neutrophils is required for protective secondary immunity.

AbstractThe heterotrimeric guanine nucleotide-binding protein Gαi2 is involved in regulation of immune responses against microbial and nonmicrobial stimuli. Gαi2−/− mice have a selectively impaired IgM response consistent with a disorder in B cell development yet have augmented T cell effector function associated with increased production of IFN-γ and IL-4. The goal of the present study was to determine if a deficiency in the Gαi2 protein in mice would affect the protective immune response against Strongyloides stercoralis, which is IL-4-, IL-5-, and IgM-dependent. Gαi2−/− and wild-type mice were immunized and challenged with S. stercoralis larvae and analyzed for protective immune responses against infection. Gαi2−/− mice failed to kill the larvae in the challenge infection as compared with wild-type mice despite developing an antigen-specific Th2 response characterized by increased IL-4, IL-5, IgM, and IgG. Transfer of serum collected from immunized Gαi2−/− mice to naïve wild-type mice conferred passive protective immunity against S. stercoralis infection thus confirming the development of a protective antibody response in Gαi2−/− mice. Differential cell analyses and myeloperoxidase assays for quantification of neutrophils showed a significantly reduced recruitment of neutrophils into the microenvironment of the parasites in immunized Gαi2−/− mice. However, cell transfer studies demonstrated that neutrophils from Gαi2−/− mice are competent in killing larvae. These data demonstrate that Gαi2 signaling events are not required for the development of the protective immune responses against S. stercoralis; however, Gαi2 is essential for the recruitment of neutrophils required for host-dependent killing of larvae.

ABSTRACTThe goal of this study was to determine the roles of eosinophils and neutrophils in innate and adaptive protective immunity to larvalStrongyloides stercoralisin mice. The experimental approach used was to treat mice with an anti-CCR3 monoclonal antibody to eliminate eosinophils or to use CXCR2−/−mice, which have a severe neutrophil recruitment defect, and then determine the effect of the reduction or elimination of the particular cell type on larval killing. It was determined that eosinophils killed theS. stercoralislarvae in naïve mice, whereas these cells were not required for the accelerated killing of larvae in immunized mice. Experiments using CXCR2−/−mice demonstrated that the reduction in recruitment of neutrophils resulted in significantly reduced innate and adaptive protective immunity. Protective antibody developed in the immunized CXCR2−/−mice, thereby demonstrating that neutrophils were not required for the induction of the adaptive protective immune response. Moreover, transfer of neutrophil-enriched cell populations recovered from either wild-type or CXCR2−/−mice into diffusion chambers containing larvae demonstrated that larval killing occurred with both cell populations when the diffusion chambers were implanted in immunized wild-type mice. Thus, the defect in the CXCR2−/−mice was a defect in the recruitment of the neutrophils and not a defect in the ability of these cells to kill larvae. This study therefore demonstrated that both eosinophils and neutrophils are required in the protective innate immune response, whereas only neutrophils are necessary for the protective adaptive immune response to larvalS. stercoralisin mice.

ABSTRACTSeveral studies have demonstrated roles for eosinophils during innate and adaptive immune responses to helminth infections. However, evidence that eosinophils are capable of initiating an immune response to parasite antigens is lacking. The goal of the present in vitro study was to investigate the potential of eosinophils to serve as antigen-presenting cells (APC) and initiate an immune response to parasite antigens. Purified eosinophils were exposed to solubleStrongyloides stercoralisantigens, and the expression of various surface markers involved in cell activation was examined. Antigen-exposed eosinophils showed a sixfold increase in expression levels of CD69 and major histocompatibility complex (MHC) class II, a fourfold increase in levels of T-cell costimulatory molecule CD86, and a twofold decrease in levels of CD62L compared to eosinophils cultured in medium containing granulocyte-macrophage colony-stimulating factor. The ability of eosinophils to present antigen to T cells was determined by culturing them with T cells in vitro. Eosinophils pulsed with antigen stimulated antigen-specific primed T cells and CD4+T cells to increase interleukin-5 (IL-5) production. The blocking of MHC class II expression on eosinophils inhibited their ability to induce IL-5 production by CD4+T cells in culture. Antigen-pulsed eosinophils were able to prime naïve T cells and CD4+T cells in culture and polarized them into Th2 cells producing IL-5 similar to that induced by antigen-loaded dendritic cells. These results demonstrate that eosinophils are capable of activating antigen-specific Th2 cells inducing the release of cytokines and assist in the priming of naïve T cells to initiate Th2 responses against infection. This study highlights the potential of eosinophils to actively induce immune responses against infection by amplifying antigen-specific Th2-cell responses.

ABSTRACTMice immunized with irradiatedOnchocerca volvulusthird-stage larvae developed protective immunity. Eosinophil levels were elevated in the parasite microenvironment at the time of larval killing, and measurements of total serum antibody levels revealed an increase in the immunoglobulin E (IgE) level in immunized mice. The goal of the present study was to identify the role of granulocytes and antibodies in the protective immune response to the larval stages ofO. volvulusin mice immunized with irradiated larvae. Immunity did not develop in mice if granulocytes, including both neutrophils and eosinophils, were eliminated, nor did it develop if only eosinophils were eliminated. Moreover, larvae were killed in naïve interleukin-5 transgenic mice, and the killing coincided with an increase in the number of eosinophils and the eosinophil peroxidase (EPO) level in the animals. To determine if EPO was required for protective immunity, mice that were genetically deficient in EPO were immunized, and there were no differences in the rates of parasite recovery in EPO-deficient mice and wild-type mice. Two mouse strains were used to study B-cell function; μMT mice lacked all mature B cells, and Xid mice had deficiencies in the B-1 cell population. Immunity did not develop in the μMT mice but did develop in the Xid mice. Finally, protective immunity was abolished in mice treated to eliminate IgE from the blood. We therefore concluded that IgE and eosinophils are required for adaptive protective immunity to larvalO. volvulusin mice.