Mast cells are key promoters of contact allergy that mediate the adjuvant effects of haptens.

A prominent feature of sensitizing environmental compounds that cause allergic contact dermatitis is the rapid induction of an innate inflammatory response that seems to provide danger signals for efficient T cell priming. We generated mouse models of mast cell deficiency, mast cell-specific gene inactivation, and mast cell reporter mice for intravital imaging and showed that these adjuvant effects of contact allergens are mediated by mast cells and histamine. Mast cell deficiency resulted in impaired emigration of skin DCs to the lymph node and contact hypersensitivity was dramatically reduced in the absence of mast cells. In addition, mast cell-specific inactivation of the Il10 gene did not reveal any role for mast cell-derived IL-10 in the regulation of contact allergy. Collectively, we demonstrate that mast cells are essential promoters of contact hypersensitivity, thereby highlighting their potential to promote immune responses to antigens entering via the skin.

Lack of Trex1 Causes Systemic Autoimmunity despite the Presence of Antiretroviral Drugs.

Biallelic mutations of three prime repair exonuclease 1 (TREX1) cause the lupus-like disease Aicardi-Goutières syndrome in which accumulation of a yet unknown endogenous DNA substrate of TREX1 triggers a cyclic GMP-AMP synthase-dependent type I IFN response and systemic autoimmunity. Products of reverse transcription originating from endogenous retroelements have been suggested to be a major substrate for TREX1, and reverse transcriptase inhibitors (RTIs) were proposed as a therapeutic option in autoimmunity ensuing from defects of TREX1. In this study, we treated Trex1-/- mice with RTIs. The serum RTI levels reached were sufficient to block retrotransposition of endogenous retroelements. However, the treatment did not reduce the spontaneous type I IFN response and did not ameliorate lethal inflammation. Furthermore, long interspersed nuclear elements 1 retrotransposition was not enhanced in the absence of Trex1. Our data do not support the concept of retroelement-derived cDNA as key triggers of systemic autoimmunity in Trex1-deficient humans and mice and motivate the continuing search for the pathogenic IFN-inducing Trex1 substrate.

Loss of Trex1 in Dendritic Cells Is Sufficient To Trigger Systemic Autoimmunity.

Defects of the intracellular enzyme 3' repair exonuclease 1 (Trex1) cause the rare autoimmune condition Aicardi-Goutières syndrome and are associated with systemic lupus erythematosus. Trex1(-/-) mice develop type I IFN-driven autoimmunity, resulting from activation of the cytoplasmic DNA sensor cyclic GMP-AMP synthase by a nucleic acid substrate of Trex1 that remains unknown. To identify cell types responsible for initiation of autoimmunity, we generated conditional Trex1 knockout mice. Loss of Trex1 in dendritic cells was sufficient to cause IFN release and autoimmunity, whereas Trex1-deficient keratinocytes and microglia produced IFN but did not induce inflammation. In contrast, B cells, cardiomyocytes, neurons, and astrocytes did not show any detectable response to the inactivation of Trex1. Thus, individual cell types differentially respond to the loss of Trex1, and Trex1 expression in dendritic cells is essential to prevent breakdown of self-tolerance ensuing from aberrant detection of endogenous DNA.

A20-deficient mast cells exacerbate inflammatory responses in vivo.

Mast cells are implicated in the pathogenesis of inflammatory and autoimmune diseases. However, this notion based on studies in mast cell-deficient mice is controversial. We therefore established an in vivo model for hyperactive mast cells by specifically ablating the NF-κB negative feedback regulator A20. While A20 deficiency did not affect mast cell degranulation, it resulted in amplified pro-inflammatory responses downstream of IgE/FcεRI, TLRs, IL-1R, and IL-33R. As a consequence house dust mite- and IL-33-driven lung inflammation, late phase cutaneous anaphylaxis, and collagen-induced arthritis were aggravated, in contrast to experimental autoimmune encephalomyelitis and immediate anaphylaxis. Our results provide in vivo evidence that hyperactive mast cells can exacerbate inflammatory disorders and define diseases that might benefit from therapeutic intervention with mast cell function.

Mast cell hyperplasia, B-cell malignancy, and intestinal inflammation in mice with conditional expression of a constitutively active kit.

Signaling through the receptor tyrosine kinase kit controls proliferation and differentiation of hematopoietic precursor cells and mast cells. Somatic point mutations of the receptor that constitutively activate kit signaling are associated with mastocytosis and various hematopoietic malignancies. We generated a Cre/loxP-based bacterial artificial chromosome transgenic mouse model that allows conditional expression of a kit gene carrying the kitD814V mutation (the murine homolog of the most common mutation in human mastocytosis, kitD816V) driven by the kit promoter. Expression of the mutant kit in cells of adult mice, including hematopoietic precursors, caused severe mastocytosis with 100% penetrance at young age frequently associated with additional hematopoietic (mostly B lineage-derived) neoplasms and focal colitis. Restriction of transgene expression to mature mast cells resulted in a similar mast cell disease developing with slower kinetics. Embryonic expression led to a hyperproliferative dysregulation of the erythroid lineage with a high rate of perinatal lethality. In addition, most adult animals developed colitis associated with mucosal mast cell accumulation. Our findings demonstrate that the effects of constitutive kit signaling critically depend on the developmental stage and the state of differentiation of the cell hit by the gain-of-function mutation.

Establishment of low-cost laboratory automation processes using AutoIt and 4-axis robots.

In most small laboratories, many processes are not yet automated because existing laboratory automation solutions are usually expensive and inflexible to use. Examples of this are autosamplers that are only compatible with one specific laboratory instrument or larger liquid handling stations that are expensive and usually self-contained. A flexible and inexpensive way to automate laboratory processes would be to automate existing laboratory equipment with the help of suitable robotic arms. In this study, we investigate the feasibility of such a strategy based on a low-cost 4-axis robot and freely available software. We used the scripting language AutoIt that automates any Windows-based instrument control software. Using these tools, we automated three fundamentally different laboratory processes: a pipetting process, a use as an autosampler for an atomic absorption spectroscopy instrument, and a more complex process involving the inoculation of bacterial cultures. We also integrated a conventional webcam for 2D barcode recognition. Compared to a trained professional who performed all experiments manually, all setups showed no significant differences in accuracy and precision. In summary, the tested system consisting of a 4-axis robot and freely available software is suitable for flexible automation and has potential for even more complex laboratory processes. Limitations such as a lack of collaboration and speed will be addressed in follow-up studies. The system thus represents a well-suited flexible laboratory automation system for both research and teaching purposes.

Cre/loxP-based mouse models of mast cell deficiency and mast cell-specific gene inactivation.

Over the past decades, research on in vivo functions of mast cells has largely relied on kit-mutant mouse strains. Recently, new mouse models for investigation of mast cell functions based on the Cre/loxP recombination system have been published and results in these new models challenged findings of previous studies in kit-mutant mice. Herein we describe procedures central to mast cell-specific gene inactivation and the generation of mast cell-deficient mice based on the mouse strain Mcpt5-Cre, which expresses Cre recombinase selectively in connective tissue mast cells.

IκB kinase 2 is essential for IgE-induced mast cell de novo cytokine production but not for degranulation.

The immunoglobulin E (IgE)-mediated mast cell (MC) response is central to the pathogenesis of type I allergy and asthma. IκB kinase 2 (IKK2) was reported to couple IgE-induced signals to MC degranulation by phosphorylating the SNARE protein SNAP23. We investigated MC responses in mice with MC-specific inactivation of IKK2 or NF-κB essential modulator (NEMO), or animals with MC-specific expression of a mutant, constitutively active IKK2. We show that the IgE-induced late-phase cytokine response is reduced in mice lacking IKK2 or NEMO in MCs. However, anaphylactic in vivo responses of these animals are not different from those of control mice, and in vitro IKK2-deficient MCs readily phosphorylate SNAP23 and degranulate similarly to control cells in response to allergen or calcium ionophore. Constitutive overactivation of the NF-κB pathway has only slight effects on allergen-triggered MC responses. Thus, IKK2 is dispensable for MC degranulation, and the important question how IgE-induced signals trigger MC vesicle fusion remains open.

Effects of the selective glucocorticoid receptor modulator compound A on bone metabolism and inflammation in male mice with collagen-induced arthritis.

Glucocorticoids (GCs) are potent drugs to treat rheumatoid arthritis but exert adverse skeletal effects. Compound A (CpdA) is a selective GC receptor modulator with an improved risk/benefit profile in mouse models of inflammation and bone loss. Here we tested whether CpdA also exerts bone-sparing effects under proinflammatory circumstances using the collagen-induced arthritis model, a murine model of rheumatoid arthritis. CpdA decreased disease activity, paw swelling, and the paw temperature by 43%, 12%, and 7%, respectively, but was less potent than dexamethasone (DEX), which reduced these parameters by 72%, 22%, and 10%, respectively. Moreover, T cells isolated from CpdA- and DEX-treated animals were less active based on proliferation rates after challenge with type II collagen and produced smaller amounts of interferon-γ and TNF as compared with T cells from PBS-treated mice. Histological assessment of the joints confirmed the weaker potency of CpdA as compared with DEX in preventing infiltration of inflammatory cells, induction of osteoclastogenesis, and destruction of articular cartilage. Due to the lack of GC-susceptible arthritis models, we were not able to fully address the bone-sparing potential of CpdA in inflammatory conditions. Nevertheless, the bone formation marker procollagen type 1 N-terminal peptide, a surrogate marker for GC-mediated suppression of bone formation, was significantly decreased by DEX in arthritic mice but not by CpdA. Our data indicate that CpdA moderately suppresses inflammation, whereas the concurrent effects on bone remain unknown. In light of its narrow therapeutic range, CpdA may be more useful as a molecular tool for dissecting GC actions rather than a therapeutic agent.

Mouse SAMHD1 has antiretroviral activity and suppresses a spontaneous cell-intrinsic antiviral response.

Aicardi-Goutières syndrome (AGS), a hereditary autoimmune disease, clinically and biochemically overlaps with systemic lupus erythematosus (SLE) and, like SLE, is characterized by spontaneous type I interferon (IFN) production. The finding that defects of intracellular nucleases cause AGS led to the concept that intracellular accumulation of nucleic acids triggers inappropriate production of type I IFN and autoimmunity. AGS can also be caused by defects of SAMHD1, a 3' exonuclease and deoxynucleotide (dNTP) triphosphohydrolase. Human SAMHD1 is an HIV-1 restriction factor that hydrolyzes dNTPs and decreases their concentration below the levels required for retroviral reverse transcription. We show in gene-targeted mice that also mouse SAMHD1 reduces cellular dNTP concentrations and restricts retroviral replication in lymphocytes, macrophages, and dendritic cells. Importantly, the absence of SAMHD1 triggered IFN-ß-dependent transcriptional upregulation of type I IFN-inducible genes in various cell types indicative of spontaneous IFN production. SAMHD1-deficient mice may be instrumental for elucidating the mechanisms that trigger pathogenic type I IFN responses in AGS and SLE.