In chronic spontaneous urticaria, increased Galectin‐9 expression on basophils and eosinophils is linked to high disease activity, endotype‐specific markers, and response to omalizumab treatment

Background Galectin‐9 (Gal‐9) has been implicated in allergic and autoimmune diseases, but its role and relevance in chronic spontaneous urticaria (CSU) are unclear. Objectives To characterize the role and relevance of Gal‐9 in the pathogenesis of CSU. Methods We assessed 60 CSU patients for their expression of Gal‐9 on circulating eosinophils and basophils as well as T cell expression of the Gal‐9 receptor TIM‐3, compared them with 26 healthy controls (HCs), and explored possible links with disease features including disease activity (urticaria activity score, UAS), total IgE, basophil activation test (BAT), and response to omalizumab treatment. We also investigated potential drivers of Gal‐9 expression by eosinophils and basophils. Results Our CSU patients had markedly increased rates of circulating Gal‐9 + eosinophils and basophils and high numbers of lesional Gal‐9 + cells. High rates of blood Gal‐9 + eosinophils/basophils were linked to high disease activity, IgE levels, and BAT negativity. Serum levels of TNF‐α were positively correlated with circulating Gal‐9 + eosinophils/basophils, and TNF‐α markedly upregulated Gal‐9 on eosinophils. CSU patients who responded to omalizumab treatment had more Gal‐9 + eosinophils/basophils than non‐responders, and omalizumab reduced blood levels of Gal‐9 + eosinophils/basophils in responders. Gal‐9 + eosinophils/basophils were negatively correlated with TIM‐3 + T H 17 cells. Conclusion Our findings demonstrate a previously unrecognized involvement of the Gal‐9/TIM‐3 pathway in the pathogenesis CSU and call for studies that explore its relevance.