IL-4 selectively enhances FcgammaRIII expression and signaling on mouse mast cells

Orally desensitized mast cells form a regulatory network with Treg cells for the control of food allergy

Oral immunotherapy (OIT) is an effective approach to controlling food allergy. Although the detailed molecular and cellular mechanisms of OIT are unknown currently, they must be understood to advance the treatment of allergic diseases in general. To elucidate the mechanisms of OIT, especially during the immunological transition from desensitization to allergy regulation, we generated a clinical OIT murine model and used it to examine immunological events of OIT. We found that in mice that completed OIT successfully, desensitized mast cells (MCs) showed functionally beneficial alterations, such as increased induction of regulatory cytokines and enhanced expansion of regulatory T cells. Importantly, these regulatory-T-cell-mediated inhibitions of allergic responses were dramatically decreased in mice lacking OIT-induced desensitized MC. Collectively, these findings show that the desensitization process modulates the activation of MCs, leading directly to enhanced induction of regulatory-T-cell expansion and promotion of clinical allergic unresponsiveness. Our results suggest that efficiently inducing regulatory MCs is a novel strategy for the treatment of allergic disease.

Controlling Mast Cell Activation and Homeostasis: Work Influenced by Bill Paul That Continues Today

Mast cells are tissue resident, innate immune cells with heterogenous phenotypes tuned by cytokines and other microenvironmental stimuli. Playing a protective role in parasitic, bacterial, and viral infections, mast cells are also known for their role in the pathogenesis of allergy, asthma, and autoimmune diseases. Here, we review factors controlling mast cell activation, with a focus on receptor signaling and potential therapies for allergic disease. Specifically, we will discuss our work with FcεRI and FγR signaling, IL-4, IL-10, and TGF-β1 treatment, and Stat5. We conclude with potential therapeutics for allergic disease. Much of these efforts have been influenced by the work of Bill Paul. With many mechanistic targets for mast cell activation and different classes of therapeutics being studied, there is reason to be hopeful for continued clinical progress in this area.

Recipient mucosal-associated invariant T cells control GVHD within the colon

Mucosal-associated invariant T (MAIT) cells are a unique innate-like T cell subset that responds to a wide array of bacteria and yeast through recognition of riboflavin metabolites presented by the MHC class I-like molecule MR1. Here, we demonstrate using MR1 tetramers that recipient MAIT cells are present in small but definable numbers in graft-versus-host disease (GVHD) target organs and protect from acute GVHD in the colon following bone marrow transplantation (BMT). Consistent with their preferential juxtaposition to microbial signals in the colon, recipient MAIT cells generate large amounts of IL-17A, promote gastrointestinal tract integrity, and limit the donor alloantigen presentation that in turn drives donor Th1 and Th17 expansion specifically in the colon after BMT. Allogeneic BMT recipients deficient in IL-17A also develop accelerated GVHD, suggesting MAIT cells likely regulate GVHD, at least in part, by the generation of this cytokine. Indeed, analysis of stool microbiota and colon tissue from IL-17A-/- and MR1-/- mice identified analogous shifts in microbiome operational taxonomic units (OTU) and mediators of barrier integrity that appear to represent pathways controlled by similar, IL-17A-dependent mechanisms. Thus, MAIT cells act to control barrier function to attenuate pathogenic T cell responses in the colon and, given their very high frequency in humans, likely represent an important population in clinical BMT.

Mast cell production and response to IL-4 and IL-13

IL-4 was identified as the first cytokine to be produced by mast cells and is responsible for promoting mast cell IL-13 production. IL-4 and IL-13 play a prominent role in stimulating and maintaining the allergic response. As closely related genes, IL-4 and IL-13 share a common receptor subunit, IL-4Rα, necessary for signaling. Here we summarize the literature on mast cell activation associated with IL-4 and IL-13 production, including downstream signaling. We also describe the positive and negative roles each cytokine plays in mast cell immunity and detail the differences that exist between mouse and human mast cell responses to IL-4 and IL-13.

Interleukin-10 from T cells, but not macrophages and granulocytes, is required for chronic disease in Leishmania mexicana infection

Chronic cutaneous disease of mice caused by the protozoan parasite Leishmania mexicana requires interleukin-10 (IL-10) and FcγRIII (an activating IgG receptor). Macrophages readily secrete IL-10 in response to IgG-coated amastigotes, making macrophages a prime candidate as the critical source of IL-10. However, indirect evidence suggested that macrophage IL-10 is not essential for chronic disease. I now show directly that mice lacking IL-10 from macrophages and granulocytes still have chronic disease, like wild-type C57BL/6 mice. However, T cell-derived IL-10 is required for chronic disease. CD4-cre IL-10flox/flox mice lack IL-10 from T cells (both CD4+ and CD8+) and heal their L. mexicana lesions, with parasite control. I had previously shown that depletion of CD25+ T cells had no effect on chronic disease, and thus, T cells other than CD25+ regulatory T (Treg) cells should be the important source of IL-10. Given that conventional T cells do not express FcγRs, there is likely to be an indirect pathway by which FcγRIII on some other cell engaged by IgG1-amastigote immune complexes induces IL-10 from T cells. Further work is needed to delineate these pathways.

Apoptosis of mouse mast cells is reciprocally regulated by the IgG receptors FcγRIIB and FcγRIIIA

BACKGROUND

Mast cells are important effector cells in allergy. They usually have a long life span and resist cell death induction. Fcγ receptor- and IgG immune complex-mediated apoptosis has been demonstrated in B-lineage cells, but not in mast cells. The aim of the current study was to investigate whether mast cells could respond to apoptosis induction by IgG immune complex aggregation of Fcγ receptors. It is known that mouse mast cells express the low-affinity Fcγ receptors FcγRIIB and FcγRIIIA, which bind IgG especially in the form of antigen-IgG immune complexes.

METHODS

Mouse bone marrow-derived cultured mast cells were examined for surface expression of FcγRIIB and FcγRIIIA. Apoptosis of such cells from wild-type, FcγRIIB(-/-) or FcγRIIIA(-/-) mice was measured following receptor aggregation by IgG immune complexes.

RESULTS

Our data demonstrate that aggregation of either FcγRIIB or FcγRIIIA by IgG immune complexes induced apoptosis of mouse bone marrow-derived cultured mast cells. However, mast cells expressing both FcγRIIB and FcγRIIIA were able to resist cell death induction by IgG immune complexes.

CONCLUSION

Our findings reveal a fine-tuning system for regulating mast cell apoptosis through aggregating Fcγ receptors by IgG immune complexes. Such apoptosis regulation may have a substantial impact on mast cell homeostasis during allergic inflammation.

Apoptosis of mouse mast cells is reciprocally regulated by the IgG receptors FcγRIIB and FcγRIIIA

BACKGROUND

Mast cells are important effector cells in allergy. They usually have a long life span and resist cell death induction. Fcγ receptor- and IgG immune complex-mediated apoptosis has been demonstrated in B-lineage cells, but not in mast cells. The aim of the current study was to investigate whether mast cells could respond to apoptosis induction by IgG immune complex aggregation of Fcγ receptors. It is known that mouse mast cells express the low-affinity Fcγ receptors FcγRIIB and FcγRIIIA, which bind IgG especially in the form of antigen-IgG immune complexes.

METHODS

Mouse bone marrow-derived cultured mast cells were examined for surface expression of FcγRIIB and FcγRIIIA. Apoptosis of such cells from wild-type, FcγRIIB(-/-) or FcγRIIIA(-/-) mice was measured following receptor aggregation by IgG immune complexes.

RESULTS

Our data demonstrate that aggregation of either FcγRIIB or FcγRIIIA by IgG immune complexes induced apoptosis of mouse bone marrow-derived cultured mast cells. However, mast cells expressing both FcγRIIB and FcγRIIIA were able to resist cell death induction by IgG immune complexes.

CONCLUSION

Our findings reveal a fine-tuning system for regulating mast cell apoptosis through aggregating Fcγ receptors by IgG immune complexes. Such apoptosis regulation may have a substantial impact on mast cell homeostasis during allergic inflammation.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

Mast cell-derived interleukin 10 limits skin pathology in contact dermatitis and chronic irradiation with ultraviolet B

Allergic contact dermatitis, such as in response to poison ivy or poison oak, and chronic low-dose ultraviolet B irradiation can damage the skin. Mast cells produce proinflammatory mediators that are thought to exacerbate these prevalent acquired immune or innate responses. Here we found that, unexpectedly, mast cells substantially limited the pathology associated with these responses, including infiltrates of leukocytes, epidermal hyperplasia and epidermal necrosis. Production of interleukin 10 by mast cells contributed to the anti-inflammatory or immunosuppressive effects of mast cells in these conditions. Our findings identify a previously unrecognized function for mast cells and mast cell-derived interleukin 10 in limiting leukocyte infiltration, inflammation and tissue damage associated with immunological or innate responses that can injure the skin.

Fc gamma RIIa, not Fc gamma RIIb, is constitutively and functionally expressed on skin-derived human mast cells

The expression of FcgammaR by human skin-derived mast cells of the MC(TC) type was determined in the current study. Expression of mRNA was analyzed with microarray gene chips and RT-PCR; protein by Western blotting and flow cytometry; function by release of beta-hexosaminidase, PGD(2), leukotriene C(4) (LTC(4)), IL-5, IL-6, IL-13, GM-CSF, and TNF-alpha. FcgammaRIIa was consistently detected along with FcepsilonRI at the mRNA and protein levels; FcgammaRIIc was sometimes detected only by RT-PCR; but FcgammaRIIb, FcgammaRI, and FcgammaRIII mRNA and protein were not detected. FcgammaRIIa-specific mAb caused skin MC(TC) cells to degranulate and secrete PGD(2), LTC(4), GM-CSF, IL-5, IL-6, IL-13, and TNF-alpha in a dose-dependent fashion. FcepsilonRI-specific mAb caused similar amounts of each mediator to be released with the exception of LTC(4), which was not released by this agonist. Simultaneous but independent cross-linking of FcepsilonRI and FcgammaRIIa did not substantially alter mediator release above or below levels observed with each agent alone. Skin MC(TC) cells sensitized with dust-mite-specific IgE and IgG, when coaggregated by Der p2, exhibited enhanced degranulation compared with sensitization with either IgE or IgG alone. These results extend the known capabilities of human skin mast cells to respond to IgG as well as IgE-mediated signals.

Gene expression in splenic CD4 and CD8 cells from BALB/c mice immunized with Porphyromonas gingivalis

BACKGROUND

T cells are fundamental in the pathogenesis of periodontal disease. Suppression of cell-mediated responses is associated with disease progression together with the concomitant increase in plaque pathogens including Porphyromonas gingivalis. The aim of the present study was to examine gene expression in T cells in response to P. gingivalis in mice.

METHODS

BALB/c mice were given weekly intraperitoneal injections of P. gingivalis outer-membrane antigens with Freund's incomplete adjuvant for 3 weeks, whereas control mice received phosphate buffered saline (PBS) and adjuvant only. Splenic CD4 and CD8 subpopulations were isolated by magnetic cell separation and their responses investigated using microarray analysis.

RESULTS

Most genes coded for enzymes concerned with metabolic pathways. Only five and 28 genes, respectively, were upregulated in CD4 and CD8 cells extracted from P. gingivalis-immunized mice, including immunoglobulin (Ig) heavy-chain genes for IgG1 and IgG2a in CD4 cells. In contrast, 1,141 and 1,175 genes, respectively, were downregulated. A total of 60 and 65 genes, respectively, coded for immune response proteins or those relevant to periodontal disease pathogenesis. The overlap of genes in the two subsets was 21%. One of the major effects, apart from T-cell function suppression, was the shift away from Th1 responses, although there was also a downregulation of two genes and upregulation of one Th2-response gene. Genes downregulated included those encoding cytokines, proteins involved in Ig binding, antigen presentation, innate immunity, extracellular matrix, and cell adhesion molecules that could result in dysregulation in the progressive periodontal lesion.

CONCLUSIONS

Early findings in humans demonstrated that periodontopathic bacteria induce immunosuppressive effects on T cells. The present study has shown that P. gingivalis had a predominant downregulatory effect on gene expression in CD4 and CD8 T cells in mice.

Integrated signalling pathways for mast-cell activation

Mast-cell activation mediated by the high-affinity receptor for IgE (FcepsilonRI) is considered to be a key event in the allergic inflammatory response. However, in a physiological setting, other receptors, such as KIT, might also markedly influence the release of mediators by mast cells. Recent studies have provided evidence that FcepsilonRI-dependent degranulation is regulated by two complementary signalling pathways, one of which activates phospholipase Cgamma and the other of which activates phosphatidylinositol 3-kinase, using specific transmembrane and cytosolic adaptor molecules. In this Review, we discuss the evidence for these interacting pathways and describe how the capacity of KIT, and other receptors, to influence FcepsilonRI-dependent mast-cell-mediator release might be a function of the relative abilities of these receptors to activate these alternative pathways.

Local IL-13 gene transfer prior to immune-complex arthritis inhibits chondrocyte death and matrix-metalloproteinase-mediated cartilage matrix degradation despite enhanced joint inflammation

During immune-complex-mediated arthritis (ICA), severe cartilage destruction is mediated by Fcgamma receptors (FcgammaRs) (mainly FcgammaRI), cytokines (e.g. IL-1), and enzymes (matrix metalloproteinases (MMPs)). IL-13, a T helper 2 (Th2) cytokine abundantly found in synovial fluid of patients with rheumatoid arthritis, has been shown to reduce joint inflammation and bone destruction during experimental arthritis. However, the effect on severe cartilage destruction has not been studied in detail. We have now investigated the role of IL-13 in chondrocyte death and MMP-mediated cartilage damage during ICA. IL-13 was locally overexpressed in knee joints after injection of an adenovirus encoding IL-13 (AxCAhIL-13), 1 day before the onset of arthritis; injection of AxCANI (an empty adenoviral construct) was used as a control. IL-13 significantly increased the amount of inflammatory cells in the synovial lining and the joint cavity, by 30% to 60% at day 3 after the onset of ICA. Despite the enhanced inflammatory response, chondrocyte death was diminished by two-thirds at days 3 and 7. The mRNA level of FcgammaRI, a receptor shown to be crucial in the induction of chondrocyte death, was significantly down-regulated in synovium. Furthermore, MMP-mediated cartilage damage, measured as neoepitope (VDIPEN) expression using immunolocalization, was halved. In contrast, mRNA levels of MMP-3, -9, -12, and -13 were significantly higher and IL-1 protein, which induces production of latent MMPs, was increased fivefold by IL-13. This study demonstrates that IL-13 overexpression during ICA diminished both chondrocyte death and MMP-mediated VDIPEN expression, even though joint inflammation was enhanced.

Fcgamma receptors on mast cells: activatory and inhibitory regulation of mediator release

Mast cell activation and subsequent release of proinflammatory mediators are primarily a consequence of aggregation of the high affinity receptors for IgE (FcepsilonRI) on the mast cell surface following antigen-dependent ligation of FcepsilonRI-bound IgE. However, data obtained from rodent and human mast cells have revealed that IgG receptors (FcgammaR) can both promote and inhibit mast cell activation. These responses appear to be species and/or mast cell phenotype dependent. In CD34+-derived human mast cells exposed to interferon-gamma, FcgammaRI is upregulated, FcgammaRII is expressed but not upregulated, and FcgammaRIII is not expressed. In contrast, in mouse mast cells, FcgammaRII and FcgammaRIII receptors are expressed, whereas FcgammaRI is not. Aggregation of FcgammaRI on human mast cells promotes mediator release in a manner generally similar to that observed following FcepsilonRI aggregation. Aggregation of FcgammaRIIb in mouse mast cells fails to influence cellular processes; however, when coligated with FcepsilonRI, signaling events thus activated downregulate antigen-dependent mediator release. These divergent responses are a consequence of different motifs contained within the cytosolic tails of the signaling subunits of these receptors and the specific signaling molecules recruited by these receptors following ligation. The studies described imply that data obtained in rodent models regarding the influence of FcgammaRs on mast cells may not be directly translatable to the human. The exploitation of FcgammaRs for a potential therapy for the treatment of allergic disorders is discussed in this context.

IL-10 Inhibits FcεRI Expression in Mouse Mast Cells

FcepsilonRI expression and function is a central aspect of allergic disease. Using bone marrow-derived mouse mast cell populations, we have previously shown that the Th2 cytokine IL-4 inhibits FcepsilonRI expression and function. In the current study we show that the Th2 cytokine IL-10 has similar regulatory properties, and that it augments the inhibitory effects of IL-4. FcepsilonRI down-regulation was functionally significant, as it diminished inflammatory cytokine production and IgE-mediated FcepsilonRI up-regulation. IL-10 and IL-4 reduced FcepsilonRI beta protein expression without altering the alpha or gamma subunits. The ability of IL-4 and IL-10 to alter FcepsilonRI expression by targeting the beta-chain, a critical receptor subunit known to modulate receptor expression and signaling, suggests the presence of a Th2 cytokine-mediated homeostatic network that could serve to both initiate and limit mast cell effector function.