In addition, Dsg3‐specific Tfh cells were detected using I‐Ab tetramer with Dsg3 (516–530 aa) peptide highly expressed ICOS, and ICOS blockade reduced anti‐Dsg3 antibody production in the model, demonstrating pivotal roles of Dsg3‐specific ICOS+CXCR5+PD‐1+ Tfh cells in the pemphigus mouse model. Here, ICOS is linked to pemphigus.