Using bicistronic IL-4 reporter mice to identify IL-4 expressing cells following immunisation with aluminium adjuvant

Expression Efficiency of Multiple Il9 Reporter Alleles Is Determined by Cell Lineage

Generation of allelic gene reporter mice has provided a powerful tool to study gene function in vivo. In conjunction with imaging technologies, reporter mouse models facilitate studies of cell lineage tracing, live cell imaging, and gene expression in the context of diseases. Although there are several advantages to using reporter mice, caution is important to ensure the fidelity of the reporter protein representing the gene of interest. In this study, we compared the efficiency of two Il9 reporter strains Il9^citrine and Il9^GFP in representing IL-9-producing CD4⁺ T_H9 cells. Although both alleles show high specificity in IL-9-expressing populations, we observed that the Il9^GFP allele visualized a much larger proportion of the IL-9-producing cells in culture than the Il9^citrine reporter allele. In defining the mechanistic basis for these differences, chromatin immunoprecipitation and chromatin accessibility assay showed that the Il9^citrine allele was transcriptionally less active in T_H9 cells compared with the wild-type allele. The Il9^citrine allele also only captured a fraction of IL-9-expressing bone marrow-derived mast cells. In contrast, the Il9 ^citrine reporter detected Il9 expression in type 2 innate lymphoid cells at a greater percentage than could be identified by IL-9 intracellular cytokine staining. Taken together, our findings demonstrate that the accuracy of IL-9 reporter mouse models may vary with the cell type being examined. These studies demonstrate the importance of choosing appropriate reporter mouse models that are optimal for detecting the cell type of interest as well as the accuracy of conclusions.

Cyclic AMP concentrations in dendritic cells induce and regulate Th2 immunity and allergic asthma

The inductive role of dendritic cells (DC) in Th2 differentiation has not been fully defined. We addressed this gap in knowledge by focusing on signaling events mediated by the heterotrimeric GTP binding proteins Gαs, and Gαi, which respectively stimulate and inhibit the activation of adenylyl cyclases and the synthesis of cAMP. We show here that deletion of Gnas, the gene that encodes Gαs in mouse CD11c(+) cells (Gnas(ΔCD11c) mice), and the accompanying decrease in cAMP provoke Th2 polarization and yields a prominent allergic phenotype, whereas increases in cAMP inhibit these responses. The effects of cAMP on DC can be demonstrated in vitro and in vivo and are mediated via PKA. Certain gene products made by Gnas(ΔCD11c) DC affect the Th2 bias. These findings imply that G protein-coupled receptors, the physiological regulators of Gαs and Gαi activation and cAMP formation, act via PKA to regulate Th bias in DC and in turn, Th2-mediated immunopathologies.

Neither T-helper type 2 nor Foxp3+ regulatory T cells are necessary for therapeutic benefit of atorvastatin in treatment of central nervous system autoimmunity

Oral atorvastatin has prevented or reversed paralysis in the multiple sclerosis (MS) model experimental autoimmune encephalomyelitis (EAE), and reduced development of new MS lesions in clinical trials. Besides inhibiting development of encephalitogenic T cells, atorvastatin treatment of EAE has been associated with an induction of anti-inflammatory myelin-reactive T-helper type (Th)-2 cells. To investigate the clinical significance of atorvastatin-mediated Th2 differentiation, we first evaluated atorvastatin treatment in interleukin (IL)-4 green fluorescent protein-enhanced transcript (4-GET) reporter mice. Atorvastatin treatment failed to induce IL-4-producing Th2 cells in vivo; however, when T cells from atorvastatin-treated 4-GET mice were reactivated in vitro, T cells preferentially differentiated into Th2 cells, while antigen-specific T-cell proliferation and secretion of proinflammatory cytokines (interferon gamma, IL-17, tumor necrosis factor and IL-12) were reduced. Oral atorvastatin also prevented or reversed EAE in signal transducer and activator of transcription 6-deficient (STAT6^−/−) mice, which cannot generate IL-4-producing Th2 cells. Further, atorvastatin treatment did not induce or expand Foxp3⁺ regulatory T cells in either wild-type or STAT6^−/− mice. In vivo proliferation of T cells, as measured by incorporation of bromodeoxyuridine, was inhibited in atorvastatin-treated wild-type and STAT6^−/− mice. These data imply that atorvastatin ameliorates central nervous system autoimmune disease primarily by inhibiting proliferation of proinflammatory encephalitogenic T cells, and not simply through induction of anti-inflammatory Th2 cells. This cytostatic effect may be a relevant mechanism of action when considering use of statins in MS and other inflammatory conditions.

Alum induces innate immune responses through macrophage and mast cell sensors, but these sensors are not required for alum to act as an adjuvant for specific immunity

To understand more about how the body recognizes alum we characterized the early innate and adaptive responses in mice injected with the adjuvant. Within hours of exposure, alum induces a type 2 innate response characterized by an influx of eosinophils, monocytes, neutrophils, DCs, NK cells and NKT cells. In addition, at least 13 cytokines and chemokines are produced within 4 h of injection including IL-1beta and IL-5. Optimal production of some of these, including IL-1beta, depends upon both macrophages and mast cells, whereas production of others, such as IL-5, depends on mast cells only, suggesting that both of these cell types can detect alum. Alum induces eosinophil accumulation partly through the production of mast cell derived IL-5 and histamine. Alum greatly enhances priming of endogenous CD4 and CD8 T cells independently of mast cells, macrophages, and of eosinophils. In addition, Ab levels and Th2 bias was similar in the absence of these cells. We found that the inflammation induced by alum was unchanged in caspase-1-deficient mice, which cannot produce IL-1beta. Furthermore, endogenous CD4 and CD8 T cell responses, Ab responses and the Th2 bias were also not impacted by the absence of caspase-1 or NLRP3. These data suggest that activation of the inflammasome and the type 2 innate response orchestrated by macrophages and mast cells in vivo are not required for adjuvant effect of alum on endogenous T and B cell responses.

T-helper 1 and T-helper 2 adjuvants induce distinct differences in the magnitude, quality and kinetics of the early inflammatory response at the site of injection

Vaccine adjuvants activate the innate immune system and thus influence subsequent adaptive T-cell responses. However, little is known about the initial immune mechanisms preceding the adjuvant-induced differentiation of T-helper (Th) cells. The effect of a T-helper 1 (Th1) adjuvant, dimethyldioctadecylammonium liposomes with monophosphoryl lipid-A (DDA/MPL), and a T-helper 2 adjuvant, aluminium hydroxide [Al(OH)(3)], on early, innate chemotactic signals and inflammatory cell influx at the site of injection was therefore investigated. Injection of the adjuvants into the peritoneal cavity of mice demonstrated distinct differences in the magnitude, quality and kinetics of the response. The inflammatory response to DDA/MPL was prominent, inducing high local levels of pro-inflammatory cytokines, chemokines and a pronounced inflammatory exudate consisting of neutrophils, monocytes/macrophages and activated natural killer cells. This was in contrast to the response induced by Al(OH)(3), which, although sharing some of the early chemokine signals, was more moderate and consisted almost exclusively of neutrophils and eosinophils. Notably, Al(OH)(3) specifically induced the release of a significant amount of interleukin (IL)-5, whereas DDA/MPL induced high amounts of tumour necrosis factor-alpha (TNF-alpha), IL-1alpha and IL-6. Finally, a microarray analysis confirmed that the effect of DDA/MPL was broader with more than five times as many genes being specifically up-regulated after injection of DDA/MPL compared with Al(OH)(3). Thus, the adjuvants induced qualitatively distinct local inflammatory signals early after injection.

Alternative activation of macrophages: an immunologic functional perspective

Macrophages are innate immune cells with well-established roles in the primary response to pathogens, but also in tissue homeostasis, coordination of the adaptive immune response, inflammation, resolution, and repair. These cells recognize danger signals through receptors capable of inducing specialized activation programs. The classically known macrophage activation is induced by IFN-gamma, which triggers a harsh proinflammatory response that is required to kill intracellular pathogens. Macrophages also undergo alternative activation by IL-4 and IL-13, which trigger a different phenotype that is important for the immune response to parasites. Here we review the cellular sources of these cytokines, receptor signaling pathways, and induced markers and gene signatures. We draw attention to discrepancies found between mouse and human models of alternative activation. The evidence for in vivo alternative activation of macrophages is also analyzed, with nematode infection as prototypic disease. Finally, we revisit the concept of macrophage activation in the context of the immune response.

Gr1+IL-4-producing innate cells are induced in response to Th2 stimuli and suppress Th1-dependent antibody responses

Alum is used as a vaccine adjuvant and induces T(h)2 responses and T(h)2-driven antibody isotype production against co-injected antigens. Alum also promotes the appearance in the spleen of Gr1+IL-4+ innate cells that, via IL-4 production, induce MHC II-mediated signaling in B cells. To investigate whether these Gr1+ cells accumulate in the spleen in response to other T(h)2-inducing stimuli and to understand some of their functions, the effects of injection of alum and eggs from the helminth, Schistosoma mansoni, were compared. Like alum, schistosome eggs induced the appearance of Gr1+IL-4+ cells in spleen and promoted MHC II-mediated signaling in B cells. Unlike alum, however, schistosome eggs did not promote CD4 T cell responses against co-injected antigens, suggesting that the effects of alum or schistosome eggs on splenic B cells cannot by themselves explain the T cell adjuvant properties of alum. Accordingly, depletion of IL-4 or Gr1+ cells in alum-injected mice had no effect on the ability of alum to improve expansion of primary CD4 T cells. However, Gr1+ cells and IL-4 played some role in the effects of alum, since depletion of either resulted in antibody responses to antigen that included not only the normal T(h)2-driven isotypes, like IgG1, but also a T(h)1-driven isotype, IgG2c. These data suggest that alum affects the immune response in at least two ways: one, independent of Gr1+ cells and IL-4, that promotes CD4 T cell proliferation and another, via Gr1+IL-4+ cells, that participates in the polarization of the response.