Human intestinal mast cells produce IL‐5 in vitro upon IgE receptor cross‐linking and in vivo in the course of intestinal inflammatory disease

IL-5, known to be produced by T lymphocytes and eosinophils, is a key regulator of intestinal diseases such as parasitosis or eosinophilic gastroenteritis. Here we examined if mast cells contribute to the IL-5 production in human intestinal mucosa. The number of IL-5-positive lamina propria cells was substantially higher in patients with intestinal inflammatory diseases (5.3 ± 4.6 %, n = 17) compared to healthy controls (0.5 ± 0.9 %, n = 8, p < 0.01). In patients, the IL-5-positive cells were eosinophils (70 ± 13  %) and mast cells (29 ± 14 %), whereas in controls all IL-5-positive cells were eosinophils. IL-5-positive T cells were not detected, likely because they do not store IL-5. In vitro: studies with isolated human intestinal mast cells and eosinophils showed that mast cells do not produce IL-5 constitutively, but release high amounts of IL-5 (315 ± 115 pg/106 cells) following IgE receptor cross-linking, compared to activated eosinophils (24 ± 5 pg/106 cells). Inhibitor studies suggest a regulation of IL-5 production at the transcriptional level. In conclusion our data demonstrate that activated mast cells are a potent source of IL-5 in the human intestinal mucosa.