A history of allergies doubles the risk of vulvodynia—a chronic pain condition of unknown etiology often accompanied by increases in numbers of vulvar mast cells. We previously established the biological plausibility of this relationship in mouse models where repeated exposures to the allergens oxazolone or dinitrofluorobenzene on the labiar skin or inside the vaginal canal of ND4 Swiss Webster outbred mice led to persistent tactile sensitivity and local increases in mast cells. In these models, depletion of mast cells alleviated pain. While exposure to cleaning chemicals has been connected to elevated vulvodynia risk, no single agent has been linked to adverse outcomes. We sensitized female mice to methylisothiazolinone (MI)—a biocide preservative ubiquitous in cosmetics and cleaners—dissolved in saline on their flanks, and subsequently challenged them with MI or saline for ten consecutive days in the vaginal canal. MI-challenged mice developed persistent tactile sensitivity, increased vaginal mast cells and eosinophils, and had higher serum Immunoglobulin E. Therapeutic and preventive intra-vaginal administration of Δ9-tetrahydrocannabinol reduced mast cell accumulation and tactile sensitivity. MI is known to cause skin and airway irritation in humans, and here we provide the first pre-clinical evidence that repeated MI exposures can also provoke allergy-driven genital pain.

Occupational exposure to toxic chemicals increases the risk of developing localized provoked vulvodynia—a prevalent, yet poorly understood, chronic condition characterized by sensitivity to touch and pressure, and accumulation of mast cells in painful tissues. Here, we topically sensitized female ND4 Swiss mice to the common household and industrial preservative methylisothiazolinone (MI) and subsequently challenged them daily with MI or acetone and olive oil vehicle on the labiar skin. MI-challenged mice developed significant, persistent tactile sensitivity and long-lasting local accumulation of mast cells alongside early, transient increases in CD4 + and CD8 + T cells, eosinophils, neutrophils, and increases in pro-inflammatory cytokines. Therapeutic administration of imatinib, a c-Kit inhibitor known to inhibit mast cell survival, led to reduced mast cell accumulation and alleviated tactile genital pain. We provide the first pre-clinical evidence of dermal MI-induced mast-cell dependent pain and lay the groundwork for detailed understanding of these intersections between MI-driven immunomodulation and chronic pain.

We are building novel outbred mouse models of a poorly understood yet prevalent vulvar pain condition – localized, provoked vulvodynia – that affects a substantial proportion of 18–60 year old women. Epidemiologic studies have shown a surprising and increased risk for developing this condition in women with a history of skin and airway allergies. We show that repeated exposures to low doses of the common contact irritant haptens oxazolone or dinitrofluorobenzene on the genital skin of mice produce sustained painful sensitivity to touch as well as a non-normative accumulation of mast cells and an overgrowth of cutaneous nerves in the affected tissue – changes that are also seen in vulvar biopsies taken from women diagnosed with vulvodynia providing the first evidence of biological plausibility for the immunological underpinnings of this chronic pain condition. In addition to laboratory haptens, we show that the hapten methylisothiazolinone (a common cosmetic preservative found in soaps, shampoos, and feminine hygiene products) can induce these responses suggesting that this ubiquitous environmental exposure might be a possible immunological trigger of hitherto unexplained genital pain conditions that affect many women. We have further characterized infiltrating T cells at the allergic site to show that FoxP3+ regulatory CD4 T cells and CD103+ resident memory CD8 T accumulate at these sites as well. Our mouse models provide new tools to both dissect allergy driven pain conditions as well as test novel therapies targeting immune cells and mechanisms for the management and treatment of these debilitating disorders.