Abrogation of anti-retinal autoimmunity in IL-10 transgenic mice due to reduced T cell priming and inhibition of disease effector mechanisms.

Experimental autoimmune uveitis (EAU) induced by immunization of animals with retinal Ags is a model for human uveitis. The immunosuppressive cytokine IL-10 regulates EAU susceptibility and may be a factor in genetic resistance to EAU. To further elucidate the regulatory role of endogenous IL-10 in the mouse model of EAU, we examined transgenic (Tg) mice expressing IL-10 either in activated T cells (inducible) or in macrophages (constitutive). These IL-10-Tg mice and non-Tg wild-type controls were immunized with a uveitogenic regimen of the retinal Ag interphotoreceptor retinoid-binding protein. Constitutive expression of IL-10 in macrophages abrogated disease and reduced Ag-specific immunological responses. These mice had detectable levels of IL-10 in sera and in ocular extracts. In contrast, expression of IL-10 in activated T cells only partially protected from EAU and marginally reduced Ag-specific responses. All IL-10-Tg lines showed suppression of Ag-specific effector cytokines. APC from Tg mice constitutively expressing IL-10 in macrophages exhibited decreased ability to prime naive T cells, however, Ag presentation to already primed T cells was not compromised. Importantly, IL-10-Tg mice that received interphotoreceptor retinoid-binding protein-specific uveitogenic T cells from wild-type donors were protected from EAU. We suggest that constitutively produced endogenous IL-10 ameliorates the development of EAU by suppressing de novo priming of Ag-specific T cells and inhibiting the recruitment and/or function of inflammatory leukocytes, rather than by inhibiting local Ag presentation within the eye.

General nature of the STAT3-activated anti-inflammatory response.

Although many cytokine receptors generate their signals via the STAT3 pathway, the IL-10R appears unique in promoting a potent anti-inflammatory response (AIR) via STAT3 to antagonize proinflammatory signals that activate the innate immune response. We found that heterologous cytokine receptor systems that activate STAT3 but are naturally refractory (the IL-22R), or engineered to be refractory (the IL-6, leptin, and erythropoietin receptors), to suppressor of cytokine signaling-3-mediated inhibition activate an AIR indistinguishable from IL-10. We conclude that the AIR is a generic cytokine signaling pathway dependent on STAT3 but not unique to the IL-10R.

WASP- mice exhibit defective immune responses to influenza A virus, Streptococcus pneumoniae, and Mycobacterium bovis BCG.

OBJECTIVE: To quantify the immune response of WASP- mice to three different pathogens: influenza A virus, Streptococcus pneumoniae, and Mycobacterium bovis. METHODS: Primary and secondary T-cell responses to influenza A virus were quantified via tetramer assays. Viral clearance from lung was also measured. Lethality of intranasal inoculation with luminescent S. pneumoniae was assessed by dose escalation and direct luminescence imaging. After intravenous inoculation with M. bovis, residual mycobacteria in lung, liver, and spleen were measured by standard culture methods. RESULTS: The reduced secondary T-cell response to influenza A virus correlates with a relative but not absolute loss of splenic T and B cells similar to that seen in clinical Wiskott-Aldrich Syndrome (WAS), and slower clearance of virus from lung. The reduced magnitude of the secondary T-cell response correlates with a progressive loss of influenza-specific T cells after primary inoculation. WASP- mice show an increased susceptibility to lethal pneumonia after intranasal inoculation with S. pneumoniae, which is among the most frequent causes of clinical complications in WAS patients. WASP- mice clear M. bovis bacille Calmette-Guerin (BCG) more slowly from lung, liver, and spleen. Bone marrow-derived macrophages, however, show normal ex vivo cytokine secretion in response to M. bovis. CONCLUSIONS: These results demonstrate that WASP- mice are functionally immunodeficient in regard to three different pathogens, and provide relevant end points for the study of treatment modalities in this model. They also suggest a specific physiologic mechanism, failure to accumulate memory T cells, for at least one of the defective immune responses.

Enhancer-mediated control of macrophage-specific arginase I expression.

Arginase I expression in the liver must remain constant throughout life to eliminate excess nitrogen via the urea cycle. In contrast, arginase I expression in macrophages is silent until signals from Th2 cytokines such as IL-4 and IL-13 are received and the mRNA is then induced four to five orders of magnitude. Arginase I is hypothesized to play a regulatory and potentially pathogenic role in diseases such as asthma, parasitic, bacterial, and worm infections by modulating NO levels and promoting fibrosis. We show that Th2-inducible arginase I expression in mouse macrophages is controlled by an enhancer that lies -3 kb from the basal promoter. PU.1, IL-4-induced STAT6, and C/EBPbeta assemble at the enhancer and await the effect of another STAT6-regulated protein(s) that must be synthesized de novo. Identification of a powerful extrahepatic regulatory enhancer for arginase I provides potential to manipulate arginase I activity in immune cells while sparing liver urea cycle function.

SOCS3 regulates the plasticity of gp130 signaling.

Suppressor of cytokine signaling (SOCS) proteins are feedback inhibitors of the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) signaling pathway. SOCS3 is upregulated by several signals in macrophages and has been implicated as a regulator of various signaling pathways. Here we show that phosphorylation of STAT3 is prolonged in mouse Socs3-deficient macrophages after stimulation with interleukin-6 (IL-6) but not IL-10, indicating that SOCS3 specifically affects signaling mediated by IL-6 and gp130. IL-6 induces a wider transcriptional response in Socs3-deficient macrophages than in wild-type cells; this response is dominated by interferon (IFN)-regulated genes owing to an excess of STAT1 phosphorylation. Thus, SOCS3 functions to control the quality of the response to IL-6 and prevents the activation of an IFN-induced program of gene expression.

Shaping gene expression in activated and resting primary macrophages by IL-10.

IL-10 regulates inflammation by reducing cytokine and chemokine production from activated macrophages. We performed microarray experiments to identify possible effector molecules of IL-10 and to investigate the global effect of IL-10 on the transcriptional response induced in LPS-activated macrophages. To exclude background effects of endogenous IL-10, macrophages from IL-10-deficient mice were used. IL-10 up-regulated expression of a small number of genes (26 and 37 after 45 min and 3 h, respectively), including newly identified and previously documented targets such as suppressor of cytokine signaling-3 and IL-1 receptor antagonist. However, the activation program triggered by LPS was profoundly affected by IL-10. IL-10 repressed 62 and further increased 15 of 259 LPS-induced genes. For all genes examined, the effects of IL-10 were determined to be STAT3-dependent. These results suggest that IL-10 regulates STAT3-dependent pathways that selectively target a broad component of LPS-induced genes at the mRNA level.

Autocrine deactivation of macrophages in transgenic mice constitutively overexpressing IL-10 under control of the human CD68 promoter.

IL-10 plays an essential role in blocking cytokine production by activated macrophages. To analyze the consequences of enforced expression of IL-10 by macrophages on innate and adaptive immune responses, we generated transgenic mice (macIL-10tg mice) expressing an epitope-tagged IL-10 (Flag-IL-10) under control of the human CD68 promoter. Expression of Flag-IL-10 was constitutive and restricted to macrophages, as shown by sorting splenocyte cell populations and intracellular staining for IL-10. Transgenic macrophages displayed suppressed production of TNF-alpha and IL-12 upon stimulation with LPS. When macIL-10tg mice were challenged with LPS, serum levels of proinflammatory cytokines were attenuated compared with controls. Infection with Mycobacterium bovis bacille Calmette-Guérin resulted in approximately 10-fold-higher bacterial loads than in wild-type mice. Normal T and B cell responses were observed in macIL-10tg mice, suggesting that macrophage-specific overexpression of IL-10 predominantly acts in an autocrine/paracrine manner, resulting in chronically deactivated macrophages that manifest an impaired ability to control pathogens.