Distinct Gut Microbiome Signatures of Complete Responders to Omalizumab in Chronic Spontaneous Urticaria

The gut microbiota composition of patients with chronic spontaneous urticaria (CSU) has been shown to be different from that of healthy controls. However, whether the gut microbiome is different between CSU patients with different treatment responses to omalizumab is seldom examined and is largely unknown. Antihistamine-refractory CSU patients were enrolled to receive three injections of omalizumab. The patients were divided into two groups based on their treatment responses to omalizumab determined using the weekly urticarial activity score. Demographic data, blood samples and faecal specimens were collected before, during and after omalizumab treatment. Faecal specimens underwent bacterial 16S ribosomal RNA sequencing to determine the gut bacterial microbiome. Serum biomarkers were examined using enzyme-linked immunosorbent assay. Fourteen patients were enrolled and were divided into two groups: complete responders (CRs) and non-complete responders (NCRs). At baseline, the α-diversity indices of the CR group were higher than those of the NCR group. The bacterial microbiota composition was different between the groups, but these differences became less obvious after omalizumab treatment. At baseline, the genera Bacteroides, Lactobacillus, Prevotella_9, Butyricimonas, Dialister, Megasphaera and Ruminococcaceae_UCG-002 were more abundant in the CR group. In addition, the changes in the IL-33 and IL-17 levels after omalizumab treatment were correlated with the changes in the relative abundances of Dialister (r = 0.929, p = 0.003) and Ruminococcaceae-UCG-002 (r = -0.828, p = 0.022), respectively. In conclusion, the CR patients' distinct and characteristic gut bacterial microbiota profile before treatment may contribute to their better responses to omalizumab.