Alteration of gut microbiome in chronic urticaria

Chronic urticaria (CU) is a prevalent chronic inflammatory disease, but the pathogenesis of CU remains elusive. Given the close association between the gut microbiome and immunity, as well as inflammatory conditions across various organs, including skin diseases, this study aimed to evaluate the relationship between gut microbiota and CU. A total of 84 patients with CU and 30 controls were enrolled. The gut microbiota were compared using 16S rRNA gene sequencing of fecal samples. Immunoglobulin (Ig), LL-37, an antimicrobial peptide, and representative bacterial metabolites such as indole-3-acetic acid (IAA), L-kynurenine, deoxycholic acid, cholic acid, and short chain fatty acids were measured in plasma and fecal supernatant using ELISA. The composition of gut microbiome (β-diversity) differed between two groups, although microbial diversity (α-diversity) did not. An increase of the relative abundance of Firmicutes and a decrease in Bacteroidetes were observed. These changes correlated with the severity of CU. Regarding bacterial metabolites, levels of IAA and CA were elevated in the plasma of CU patients. Plasma levels of LL-37 and IgE were also increased in CU patients and showed positive correlation with plasma IAA and CA levels. Patients with CU showed alterations in gut microbiome composition, which were associated with the severity of CU. Plasma levels of some bacterial metabolites and an antimicrobial peptide were altered in CU patients. Thus, the changes in gut microbes might contribute to the pathogenesis of CU.