Nickel (Ni) has been shown to be one of the most frequent
metal allergens. We have already reported a murine
metal allergy model with
pathogen-associated molecular patterns (
PAMPs) as adjuvants.
Interleukin (IL)-1β plays a critical role in our mouse model. Because nonimmune cells, including fibroblasts, play important roles in local allergic
inflammation, we investigated whether Ni induces inflammatory responses in mouse dermal fibroblasts (
MDF). We also analyzed the synergistic effects between Ni,
PAMPs, and IL-1β.
MDF stimulated with Ni produced a significantly higher amount of
nitric oxide (NO) in a dose-dependent manner. NO production was augmented by costimulation with IL-1β but not with
PAMPs. On the other hand, IL-1β or
PAMPs induced a significantly higher amount of
IL-6 production by
MDF, but no augmentation was detected in the presence of Ni. A specific inhibitor for
inducible nitric oxide synthase (iNOS) inhibited Ni-induced NO production. iNOS
mRNA expression was significantly higher in
MDF stimulated with Ni, IL-1β, or both. A specific inhibitor for
hypoxia-inducible factor (HIF)-2α, but not HIF-1α, inhibited NO production. Another frequent
metal allergen,
cobalt, also induced iNOS expression and NO production by
MDF via the HIF-2α-dependent pathway. The inhibitor for iNOS augmented ear swelling in Ni
allergy mouse model. On the other hand, HIF-2α inhibitor attenuates allergic
inflammation. These results indicate that
metal allergens induce NO production in
MDF via the HIF-2α-dependent pathway and IL-1β augments NO production, which suggests that the NO induced by
metal allergens plays a pathological role in
metal allergies.