Signaling through Galphai2 protein is required for recruitment of neutrophils for antibody-mediated elimination of larval Strongyloides stercoralis in mice.

The heterotrimeric guanine nucleotide-binding protein Galphai2 is involved in regulation of immune responses against microbial and nonmicrobial stimuli. Galphai2-/- 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-gamma and IL-4. The goal of the present study was to determine if a deficiency in the Galphai2 protein in mice would affect the protective immune response against Strongyloides stercoralis, which is IL-4-, IL-5-, and IgM-dependent. Galphai2-/- and wild-type mice were immunized and challenged with S. stercoralis larvae and analyzed for protective immune responses against infection. Galphai2-/- 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 Galphai2-/- mice to naïve wild-type mice conferred passive protective immunity against S. stercoralis infection thus confirming the development of a protective antibody response in Galphai2-/- 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 Galphai2-/- mice. However, cell transfer studies demonstrated that neutrophils from Galphai2-/- mice are competent in killing larvae. These data demonstrate that Galphai2 signaling events are not required for the development of the protective immune responses against S. stercoralis; however, Galphai2 is essential for the recruitment of neutrophils required for host-dependent killing of larvae

CD40-CD40 Ligand Costimulation Is Not Required for Initiation and Maintenance of a Th1-Type Response to Leishmania major Infection

Although previous studies demonstrated a requirement for CD40-CD40 ligand (CD40L) interaction in the development of resistance to Leishmania infection, we recently showed that mice lacking the gene for CD40L (CD40L(−/−) mice) can control Leishmania major infection when they are infected with reduced numbers of parasites. In this study, we examine the cytokine pattern in healing versus nonhealing CD40L(−/−) mice and investigated whether CD40 activation is required for resistance to reinfection. We observed that CD4(+) cells in healed CD40L(−/−) mice produce high levels of gamma interferon compared to cells from nonhealing, high-dose-inoculated mice. In addition, we observed a higher frequency of interleukin-12 (IL-12)- producing cells and a reduced number of IL-4-producing cells in mice infected with reduced numbers of parasites. Importantly, we found that healed CD40L(−/−) mice are highly resistant to reinfection with a large parasite inoculum. In addition, by comparing the cytokine patterns at an early and late stage of infection in nonhealing CD40L(−/−) mice, we demonstrated that nonhealing CD40L(−/−) mice produce a weak Th1-type response during the early stage of infection, but this response wanes as a Th2-type response emerges during late stages of infection. Anti-IL-4 antibody treatment, starting either at the beginning of infection or at week 4 postinfection enabled CD40L(−/−) mice to control a high-dose infection. Together, these results show that CD40-CD40L interaction, although important for IL-12 production in high-dose infections, is not required for either the development or maintenance of resistance in mice infected with reduced numbers of parasites

The Development of a Th1-Type Response and Resistance to <i>Leishmania major</i> Infection in the Absence of CD40-CD40L Costimulation

Abstract CD40-CD40L interactions have been shown to be essential for the production of IL-12 and IFN-γ and control of L. major infection. In contrast, C57BL/6 mice deficient in CD28 develop a dominant Th1-type response and heal infection. In this study, we investigate the effects of a deficiency in both CD40L and CD28 molecules on the immune response and the course of L. major infection. We compared infection in mice genetically lacking CD40L (CD40L−/−), CD28 (CD28−/−), or both (CD40L−/−CD28−/−), and in C57BL/6 mice, all on a resistant background. Although CD40L−/− mice failed to control infection, CD28−/− and CD40L−/−CD28−/− mice, as well as C57BL/6 mice, spontaneously resolved their infections. Healing mice had reduced numbers of lesion parasites compared with nonhealing CD40L−/− mice. At wk 9 of infection, we detected similar levels of IL-4, IFN-γ, IL-12p40, and IL-12Rβ2 mRNA in draining lymph nodes of healing C57BL/6, CD28−/−, and CD40L−/−CD28−/− mice, whereas CD40L−/− mice had increased mRNA levels for IL-4 but reduced levels for IFN-γ, IL-12p40, and IL-12Rβ2. In a separate experiment, blocking of the CD40-CD40L pathway using Ab to CD40L led to an exacerbation of infection in C57BL/6 mice, but had little or no effect on infection in CD28−/− mice. Together, these results demonstrate that in the absence of CD28 costimulation, CD40-CD40L interaction is not required for the development of a protective Th1-type response. The expression of IL-12p40, IL-12Rβ2, and IFN-γ in CD40L−/−CD28−/− mice further suggests the presence of an additional stimulus capable of regulating IL-12 and its receptors in absence of CD40-CD40L interactions.</jats:p

Eosinophils Can Function as Antigen-Presenting Cells To Induce Primary and Secondary Immune Responses to Strongyloides stercoralis

Several 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 soluble Strongyloides stercoralis antigens, 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