Mast cells are often regarded through the lens of IgE-dependent reactions as a cell specialized only for anti-parasitic and type I hypersensitive responses. However, recently many researchers have begun to appreciate the expansive repertoire of stimuli that mast cells can respond to. After the characterization of the interleukin (IL)-33/suppression of tumorigenicity 2 (ST2) axis of mast cell activation—a pathway that is independent of the adaptive immune system—researchers are revisiting other stimuli to induce mast cell activation and/or subsequent degranulation independent of IgE. This discovery also underscores that mast cells act as important mediators in maintaining body wide homeostasis, especially through barrier defense, and can thus be the source of disease as well. Particularly in the gut, inflammatory bowel diseases (Crohn’s disease, ulcerative colitis, etc.) are characterized with enhanced mast cell activity in the context of autoimmune disease. Mast cells show phenotypic differences based on tissue residency, which could manifest as different receptor expression profiles, allowing for unique mast cell responses (both IgE and non-IgE mediated) across varying tissues as well. This variety in receptor expression suggests mast cells respond differently, such as in the gut where immunosuppressive IL-10 stimulates the development of food allergy or in the lungs where transforming growth factor-β1 (TGF-β1) can enhance mast cell IL-6 production. Such differences in receptor expression illustrate the truly diverse effector capabilities of mast cells, and careful consideration must be given toward the phenotype of mast cells observed in vitro. Given mast cells’ ubiquitous tissue presence and their capability to respond to a broad spectrum of non-IgE stimuli, it is expected that mast cells may also contribute to the progression of autoimmune disorders and other disease states such as metastatic cancer through promoting chronic inflammation in the local tissue microenvironment and ultimately polarizing toward a unique T_h17 immune response. Furthermore, these interconnected, atypical activation pathways may crosstalk with IgE-mediated signaling differently across disorders such as parasitism, food allergies, and autoimmune disorders of the gut. In this review, we summarize recent research into familiar and novel pathways of mast cells activation and draw connections to clinical human disease.

There is evidence that berberine (BBR), a clinically relevant plant compound, ameliorates clinically apparent collagen-induced arthritis (CIA) in vivo. However, to date, there are no studies involving the use of BBR which explore its prophylactic potential in this model of rheumatoid arthritis (RA). The aim of this study was to determine if prophylactic BBR use during the preclinical phase of collagen-induced arthritis would delay arthritic symptom onset, and to characterize the cellular mechanism underlying such an effect. DBA/1J mice were injected with an emulsion of bovine type II collagen (CII) and complete Freund’s adjuvant (day 0) and a booster injection of CII in incomplete Freund’s adjuvant (day 18) to induce arthritis. Mice were then given i.p. injections of 1 mg/kg/day of BBR or PBS (vehicle with 0.01% DMSO) from days 0 to 28, were left untreated (CIA control), or were in a non-arthritic control group (n = 15 per group). Incidence of arthritis in BBR-treated mice was 50%, compared to 90% in both the CIA and PBS controls. Populations of B and T cells from the spleens and draining lymph nodes of mice were examined on day 14 (n = 5 per group) and day 28 (n = 10 per group). BBR-treated mice had significantly reduced populations of CD4⁺T_h and CD4⁺CXCR5⁺ T_fh cells, and an increased proportion of Foxp3⁺ T_reg at days 14 and 28, as well as reduced expression of co-stimulatory molecules CD28 and CD154 at both endpoints. The effect seen on T cell populations and co-stimulatory molecule expression in BBR-treated mice was not mirrored in CD19⁺ B cells. Additionally, BBR-treated mice experienced reduced anti-CII IgG2a and anti-CII total IgG serum concentrations. These results indicate a potential role for BBR as a prophylactic supplement for RA, and that its effect may be mediated specifically through T cell suppression. However, the cellular effector involved raises concern for BBR prophylactic use in the context of vaccine efficacy and other primary adaptive immune responses.

For immune cells transforming growth factor beta-1 (TGF-β1) can enhance or repress effector functions. Here, we characterize the effects of TGF-β1 on IgE-mediated and IL-33-mediated activation of primary murine mast cells derived from hematopoietic stem cells (bone marrow derived mast cells; BMMC). We also investigated potential interactions between TGF-β1 and stem cell factor (SCF). We conclude TGF-β1 plays a selectively stimulatory role for mast cell cultures in vitro. BMMCs from C57BL/6 mice were differentiated with IL-3 and then treated with TGF-β1. BMMCs were exposed to TGF-β1, primed with IgE, activated with antigen, and then IL-6 and IL-13 cytokine release was quantified using ELISA. Additionally, the effects of TGF-β1 on both IgE and IL-33-mediated short term activation were observed via flow cytometric analysis of both surface LAMP-1 expression and intracellular IL-6. Receptor colocalization was visualized using fluorescence confocal microscopy and individual receptor expression levels were also quantified. Resting IL-6 production increased with TGF-β1 but significance was lost following BMMC activation via IgE receptor (FcεRI) crosslinking. This was similar to a comparison effect due to SCF treatment alone, which also enhanced resting levels of IL-6. TGF-β1 treatment enhanced release of IL-13 only with FcεRI-IgE-mediated activation. TGF-β1 suppressed mobilization of IL-6 with short-term BMMC activation when stimulated with IL-33. Lastly, colocalization patterns of the SCF receptor (CD117) and FcεRI with IgE crosslinking were unaffected by TGF-β1 treatment, but individual expression levels for FcεRI, CD117, and TGFβRII were all reduced following either IgE activation or TGF-β1 treatment; this reduction was partially recovered in BMMCs that were both activated by IgE and treated with TGF-β1. These data reveal a novel positive effect of soluble TGF-β1 on mast cell activation in vitro, suggesting mast cells may be activated through a non-canonical pathway by TGF-β1. Understanding this interaction will provide insight into the potential role of mast cells in settings where TGF-β1 is produced in an aberrant manner, such as in and around high grade tumors.

Formative assessments have been shown to improve student success; however, the format in which these assessments are implemented has not been well researched. In this study, individual Anatomy and Physiology lab sections were administered formative assessments composed of either a projected (i.e. ‘shared-display’) quiz presentation or a pen-and-paper quiz presentation. Students’ performance, as well as their answer-changing behaviours, were recorded to compare the effect of these two assessment formats. We found no significant difference in mean quiz grade between shared-display and pen-and-paper assessments, nor did answer-changing frequency differ by treatment. Student answer-changing success rate – a measure of how often a student changed an answer and their new response was correct – was found to have a weak but significant positive correlation with mean quiz grade. Our findings suggest that the assessment presentation format does not significantly affect student performance and that, given the population sampled, answer-changing tended to benefit students’ final quiz grade. Therefore, projecting images for use in formative assessments provides an alternative to traditional pen-and-paper administration with no apparent detriment or advantage to student success.

Mast cell (MC) contributions to solid cancer microenvironments are controversial and seem tissue dependent. TGFβ is a potent MC chemokine abundantly expressed by high-grade cancers. Previous work reported that TGFβ alone induces biologically relevant expression of IL-6 from MC, which is potentially important for reciprocal paracrine interactions with cancer cells and other leukocytes. Therefore, the objective of the present study was to examine MC in an immunocompetent, high-grade model of breast cancer. Using the 4T1 system in BALB/c mice, we compared mast cell infiltration into primary tumors of wild-type versus 4T1 cell-specific knockouts of IL-6. We also hypothesized that TGFβ institutes a training effect on MC like other metabolically driven mechanisms involving the NLRP3 inflammasome. Using a mixture of flow cytometric and qPCR assays we explored potential MC training in the context of TGFβ. Results: Contrary to our prediction, MC infiltration into IL-6KO tumors was significantly increased compared to WT. Studies of classic intracellular training mechanisms in response to TGFβ were mixed. Glucose uptake, glycolytic capacity, mitochondrial potential, and ASC speck formation were unaffected by TGFβ, but IL-6 expression increased as previously seen. Additionally, we were unable to detect substantive NLRP3 expression in MC regardless of condition. Despite these results, we were surprised to observe robust increases in expression of IL-1β, IL-18, and caspase-1 with TGFβ stimulus. We conclude that MC are actively recruited to 4T1 tumors dependent on IL-6 (and TGFβ), MC produce select cytokines in response to TGFβ, yet the mechanism explaining this does not involve the NLRP3 inflammasome and remains unresolved.