The Past, the Present, and the Future of Periostin in Allergy.

Periostin is a matricellular protein that binds to its receptors, which include several integrin molecules but mainly αvβ3 integrin on cell surfaces, thereby transducing its signals into cells. Almost 20 years have passed since we found that periostin is involved in the pathogenesis of asthma, which marked the first evidence of its involvement in allergic diseases. Over the past 2 decades, cumulative evidence has demonstrated that periostin plays important roles in the onset or progress of many allergic diseases such as chronic rhinitis with nasal polyp, atopic dermatitis (AD), allergic conjunctivitis, eosinophilic esophagitis, eosinophilic otitis media, allergic rhinitis, and eosinophilic granulomatosis with polyangiitis. Starting from the observation of highly expressed periostin in the lesions of these diseases, periostin studies have expanded to include how periostin contributes to the generation of allergic phenotypes, how measurement of periostin is useful as a biomarker for allergic diseases, and recently how periostin inhibitors can improve allergic diseases. Periostin contributes to the generation of allergic phenotypes by acting as a matricellular protein on many cells, including both non-immune and immune cells. Based on the characteristics of periostin as a surrogate biomarker of interleukin-13, a signature cytokine of type 2 inflammation, serum periostin has been used as a biomarker for stratifying endotypes, estimating disease severity, predicting or monitoring the efficacy of therapeutic drugs, and predicting disease relapse or recurrence. Moreover, a lot of attention is now being paid to periostin in body fluids such as tears and sputum as a biomarker directly reflecting type 2 inflammation. Since it has been shown that periostin evokes itch in AD, we hope to see the development of a novel therapeutic agent for AD targeting periostin/αvβ3 integrin. Here we summarize the discovery and characteristics of periostin, as well as questions and/or problems regarding periostin that remain to be resolved.