Chitinase 3-Like 1 Contributes to Food Allergy via M2 Macrophage Polarization

Purpose: Food allergy is a hypersensitive immune response to specific food proteins. Chitinase 3-like 1 (CHI3L1, also known as YKL-40 in humans or BRP-39 in mice) is associated with various chronic diseases, such as cancer, rheumatoid arthritis, and allergic disease. CHI3L1 is involved in allergen sensitization and type 2 helper T (Th2) inflammation, but the role of CHI3L1 in food allergy remains unclear. In this study, we sought to investigate the role of CHI3L1 in the development of food allergy. Methods: We measured serum levels of CHI3L1 in food allergic patients. Food allergy was induced in wild-type (WT) and CHI3L1 null mutant (CHI3L1−/−) BALB/c mice with ovalbumin (OVA). We investigated Th2 immune responses, M2 macrophage polarization, and mitogen-activated protein kinase (MAPK)/phosphoinositide 3-kinase (PI3K) signaling pathways, and also performed transcriptome analysis. Results: Serum levels of CHI3L1 were significantly higher in children with food allergy compared with those in healthy controls. Furthermore, CHI3L1 expression levels were elevated in WT mice after OVA treatment. Food allergy symptoms, immunoglobulin E levels, Th2 cytokine production, and histological injury were attenuated in food allergy-induced CHI3L1−/− mice compared with those in food allergy-induced WT mice. CHI3L1 expression was increased in OVA-treated WT intestinal macrophages and caused M2 macrophage polarization. Furthermore, CHI3L1 was involved in the extracellular signal-regulated kinases (ERK) and AKT signaling pathways and was associated with immune response and lipid metabolism as determined through transcriptome analysis. Conclusions: CHI3L1 plays a pivotal role in Th2 inflammation and M2 macrophage polarization through MAPK/ERK and PI3K/AKT phosphorylation in food allergy.