IL-33 potentiates histaminergic itch

BACKGROUND

Itch is a common symptom that can greatly diminish quality of life. Histamine is a potent endogenous pruritogen, and while antihistamines are often the first-line treatment for itch, in conditions like chronic spontaneous urticaria (CSU), many patients remain symptomatic while receiving maximal doses. Mechanisms that drive resistance to antihistamines are poorly defined.

OBJECTIVES

Signaling of the alarmin cytokine IL-33 in sensory neurons is postulated to drive chronic itch by inducing neuronal sensitization to pruritogens. Thus, we sought to determine if IL-33 can augment histamine-induced (histaminergic) itch.

METHODS

Itch behavior was assessed in response to histamine after IL-33 or saline administration. Various stimuli and conditional and global knockout mice were utilized to dissect cellular mechanisms. Multiple existing transcriptomic data sets were evaluated, including single-cell RNA sequencing of human and mouse skin, microarrays of isolated mouse mast cells at steady state and after stimulation with IL-33, and microarrays of skin biopsy samples from subjects with CSU and healthy controls.

RESULTS

IL-33 amplifies histaminergic itch independent of IL-33 signaling in sensory neurons. Mast cells are the top expressors of the IL-33 receptor in both human and mouse skin. When stimulated by IL-33, mouse mast cells significantly increase IL-13 levels. Enhancement of histaminergic itch by IL-33 relies on a mast cell- and IL-13-dependent mechanism. IL-33 receptor expression is increased in lesional skin of subjects with CSU compared to healthy controls.

CONCLUSIONS

Our findings suggest that IL-33 signaling may be a key driver of histaminergic itch in mast cell-associated pruritic conditions such as CSU.

A Spatial Examination of COVID-19 Policies among Missouri School Districts

BACKGROUND

As the COVID-19 pandemic spread, school district administrators in the United States were faced with difficult decisions regarding the implementation of virtual or in-person learning to reduce risk of infection throughout student and staff populations. While a coordinated effort with surrounding districts would be most beneficial when encountering a highly infectious respiratory-based infectious disease, the determinants of type of education delivery is unclear.

METHODS

Data from the Missouri Department of Elementary and Secondary Education assessing education delivery method at each school district across the state of Missouri (n = 514) from August 2020 were used. This cross-sectional study, using results from a school district-level survey, local COVID-19 rates, and community-level sociodemographic characteristics, conducted a spatially adjusted analysis of variance (ANOVA) to determine associations between education delivery type and geographic-level sociogeographic characteristics.

RESULTS

Among Missouri school districts, 172 (33.4%) reported starting the 2020-2021 academic year with an in-person policy, 52 (10.1%) with a distant/virtual policy, 242 (47.1%) in-person with a distance option, and 48 (9.3%) with a blended policy. This study found districts with lower household income levels were less likely to offer students any virtual learning options. Additionally, community COVID-19 infection rates were not associated with the selection of virtual or in-person education delivery.

CONCLUSIONS

These findings suggest the presence of a specific school policy was spatially random in regard to neighboring community policies, even when accounting for community characteristics. The efficacy of policy is likely to benefit upon application of a spatial framework when addressing a crisis fundamentally tied to location. Future planning that highlights and focuses on regional coordination for community resilience in the face of a pandemic should incorporate data sources that inform decisions made for families, students, and communities.

IL-33 signaling in sensory neurons promotes dry skin itch

BACKGROUND

Chronic pruritus, or itch, is common and debilitating, but the neuroimmune mechanisms that drive chronic itch are only starting to be elucidated. Recent studies demonstrate that the IL-33 receptor (IL-33R) is expressed by sensory neurons. However, whether sensory neuron-restricted activity of IL-33 is necessary for chronic itch remains poorly understood.

OBJECTIVES

We sought to determine if IL-33 signaling in sensory neurons is critical for the development of chronic itch in 2 divergent pruritic disease models.

METHODS

Plasma levels of IL-33 were assessed in patients with atopic dermatitis (AD) and chronic pruritus of unknown origin (CPUO). Mice were generated to conditionally delete IL-33R from sensory neurons. The contribution of neuronal IL-33R signaling to chronic itch development was tested in mouse models that recapitulate key pathologic features of AD and CPUO, respectively.

RESULTS

IL-33 was elevated in both AD and CPUO as well as their respective mouse models. While neuron-restricted IL-33R signaling was dispensable for itch in AD-like disease, it was required for the development of dry skin itch in a mouse model that mirrors key aspects of CPUO pathology.

CONCLUSIONS

These data highlight how IL-33 may be a predominant mediator of itch in certain contexts, depending on the tissue microenvironment. Further, this study provides insight into future therapeutic strategies targeting the IL-33 pathway for chronic itch.