Signaling through Gαi2 protein is required for recruitment of neutrophils for antibody-mediated elimination of larvalStrongyloides stercoralisin mice

Abstract

The 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.

Extracellular traps are associated with human and mouse neutrophil and macrophage mediated killing of larval Strongyloides stercoralis

“…Diffusion chambers containing larvae alone had small visible clots that stained positive for extracellular DNA indicating that ETs entered through the pores of the diffusion chamber. Chemotactic studies have demonstrated that a soluble extract of larval S. stercoralis directly recruits neutrophils in a CXCR2 [26] and Gαi2 [25] dependent manner. Neutrophils may have been attracted to soluble parasite material that diffused out of the diffusion chamber and in response underwent ETosis giving rise to ETs that entered the diffusion chamber.…”

“…Neutrophils, eosinophils and macrophages are found in the parasite microenvironment in high numbers in naïve mice [24]. Neutrophils and eosinophils are directly recruited to the parasite microenvironment [25–27], with neutrophils recruited in a CXCR2 [26] and Gαi2 [25] dependent manner. MPO from neutrophils is required for larval killing during innate and adaptive immune responses [24,28].…”

Human and Mouse Macrophages Collaborate with Neutrophils To Kill Larval Strongyloides stercoralis

“…In mice, several components of protective primary and secondary immunity to the parasite have been described (17). Molecules from larval S. stercoralis directly recruit granulocytes to the parasite microenvironment (18)(19)(20), where they kill the parasite in collaboration with complement component C3 (21), eosinophil major basic protein, and neutrophil-derived myeloperoxidase (22,23). The cellular composition of the parasite microenvironment in naive mice consists of high numbers of neutrophils, eosinophils, and macrophages (22).…”

Major Basic Protein from Eosinophils and Myeloperoxidase from Neutrophils Are Required for Protective Immunity to Strongyloides stercoralis in Mice

“…If neutrophil recruitment in mice was blocked, because of a defect either in G␣i2 signaling (52) or in the expression of CXCR2 (21), the capacity of naïve and immunized mice to kill S. stercoralis larvae is significantly decreased. Adding neutrophils isolated from CXCR2 Ϫ/Ϫ mice directly into the larval microenvironment in recipient CXCR2 Ϫ/Ϫ mice restores larval killing (21).…”