T cell-derived IL-10 determines leishmaniasis disease outcome and is suppressed by a dendritic cell based vaccine

In the murine model of Leishmania major infection, resistance or susceptibility to the parasite has been associated with the development of a Th1 or Th2 type of immune response. Recently, however, the immunosuppressive effects of IL-10 have been ascribed a crucial role in the development of the different clinical correlates of Leishmania infection in humans. Since T cells and professional APC are important cellular sources of IL-10, we compared leishmaniasis disease progression in T cell-specific, macrophage/neutrophil-specific and complete IL-10-deficient C57BL/6 as well as T cell-specific and complete IL-10-deficient BALB/c mice. As early as two weeks after infection of these mice with L. major, T cell-specific and complete IL-10-deficient animals showed significantly increased lesion development accompanied by a markedly elevated secretion of IFN-γ or IFN-γ and IL-4 in the lymph nodes draining the lesions of the C57BL/6 or BALB/c mutants, respectively. In contrast, macrophage/neutrophil-specific IL-10-deficient C57BL/6 mice did not show any altered phenotype. During the further course of disease, the T cell-specific as well as the complete IL-10-deficient BALB/c mice were able to control the infection. Furthermore, a dendritic cell-based vaccination against leishmaniasis efficiently suppresses the early secretion of IL-10, thus contributing to the control of parasite spread. Taken together, IL-10 secretion by T cells has an influence on immune activation early after infection and is sufficient to render BALB/c mice susceptible to an uncontrolled Leishmania major infection.

The clinical symptoms caused by infections with Leishmania parasites range from self-healing cutaneous to uncontrolled visceral disease and depend not only on the parasite species but also on the type of the host's immune response. It is estimated that 350 million people worldwide are at risk, with a global incidence of 1–1.5 million cases of cutaneous and 500,000 cases of visceral leishmaniasis. Murine leishmaniasis is the best-characterized model to elucidate the mechanisms underlying resistance or susceptibility to Leishmania major parasites in vivo. Using T cell-specific and macrophage-specific mutant mice, we demonstrate that abrogating the secretion of the immunosuppressive cytokine IL-10 by T cells is sufficient to render otherwise susceptible mice resistant to an infection with the pathogen. The healing phenotype is accompanied by an elevated specific inflammatory immune response very early after infection. We further show that dendritic cell-based vaccination against leishmaniasis suppresses the early secretion of IL-10 following challenge infection. Thus, our study unravels a molecular mechanism critical for host immune defense, aiding in the development of an effective vaccine against leishmaniasis.

Accelerated wound closure in mice deficient for interleukin-10

The impact of the local inflammatory response on the process of wound healing has been debated for decades. In particular, the question whether infiltrating macrophages and granulocytes promote or impede tissue repair has received much attention. In the present study, we show that wound healing is accelerated in mice deficient for the anti-inflammatory cytokine interleukin (IL)-10. IL-10-/- mice closed excisional wounds significantly earlier compared with IL-10-competent control littermates. This effect was attributable to accelerated epithelialization as well as enhanced contraction of the wound tissue in the mutant animals. Increased alpha-smooth muscle actin expression in IL-10-deficient mice suggests that augmented myofibroblast differentiation is responsible for the enhanced contraction of wounds in mutant mice. The number of macrophages infiltrating the wound tissue was significantly increased in IL-10-/- mice compared with control littermates suggesting that this cell type mediates the accelerated tissue repair. These results show for the first time that IL-10 can impede wound repair.

Interleukin-10 derived from macrophages and/or neutrophils regulates the inflammatory response to LPS but not the response to CpG DNA

Interleukin-10 (IL-10) is an important regulator of immune responses secreted by different cell types. We have previously shown that mice with selective inactivation of the IL-10 gene in T cells suffer from deregulated T cell responses similar to those observed in IL-10(-/-) animals. Unlike IL-10(-/-) mice, however, T cell-specific mutants do not mount an enhanced innate immune response to LPS, which must, therefore, be subject to control by IL-10 from non-T cells. Herein we show that subcutaneous injection of LPS, which causes moderate local inflammation in WT and T cell-specific IL-10 mutant mice, results in augmented inflammatory infiltration and extensive tissue necrosis in mice with deficiency for IL-10 in macrophages and neutrophils. Correspondingly, we observed an enhanced sensitivity of the macrophage/neutrophil-specific IL-10 mutants to systemic LPS exposure when compared with WT animals. In contrast, the inflammatory response of these mutants to CpG oligodeoxynucleotides was not different from that of WT mice. While IL-10(-/-) mice developed massive inflammation, necrosis and increased serum cytokine levels after subcutaneous CpG injection, only moderate responses were observed in macrophage/neutrophil-specific IL-10 mutant and WT mice. These results show that different innate immune responses can be subject to control by IL-10 from different cellular sources.

Integrin alpha2beta1 deficiency does not affect contact hypersensitivity

Collagens in the extracellular matrix are thought to play an important role in regulating inflammatory responses by affecting cell adhesion and migration. The contact between collagens and cells is established mainly by alpha1beta1, alpha2beta1 and alpha11beta1integrin receptors. Here, we analyzed the contact hypersensitivity (CHS) reaction in mice that were genetically deficient in the collagen receptor alpha2beta1. Integrin alpha2beta1 is widely expressed and has been suggested to play an important role in mediating inflammatory responses. CHS was induced by applying dinitrofluorobenzene to abdominal skin and challenging with the same reagent on ear skin. Macroscopically and histologically, ear swelling in alpha2beta1-deficient mice did not differ from that in wild-type control mice. Immunohistological detection of infiltrated T lymphocytes, neutrophils and mast cells in inflamed ear skin revealed similar numbers in controls and integrin alpha2beta1-deficient animals. Our results suggest that the adhesive functions of integrin alpha2beta1 are dispensable for the CHS response; they may be compensated for by the collagen receptor alpha1beta1 or other collagen receptors.

T cell-specific inactivation of the interleukin 10 gene in mice results in enhanced T cell responses but normal innate responses to lipopolysaccharide or skin irritation

Interleukin (IL)-10 is a regulator of inflammatory responses and is secreted by a variety of different cell types including T cells. T regulatory cells have been shown to suppress immune responses by IL-10-dependent, but also IL-10-independent, mechanisms. Herein, we address the role of T cell-derived IL-10 in mice with an inactivation of the IL-10 gene restricted to T cells generated by Cre/loxP-mediated targeting of the IL-10 gene. Splenocytes from this T cell-specific mutant secrete increased amounts of proinflammatory cytokines after activation in vitro compared with show enhanced contact hypersensitivity reactions, and succumb to severe immunopathology upon infection with Toxoplasma gondii. Despite intact IL-10 genes in other cell types, the dysregulation of T cell responses observed in the T cell-specific IL-10 mutant closely resembles the phenotype in complete IL-10 deficiency. However, in contrast to complete IL-10 deficiency, sensitivity to endotoxic shock and irritant responses of the skin are not enhanced in the T cell-specific IL-10 mutant. Our data highlight the importance of T cell-derived IL-10 in the regulation of T cell responses and demonstrate that endotoxic shock and the irritant response of the skin are controlled by IL-10 from other cell types.