The median proportions of Tfh cells per total CD4+ T cells and of PD-1+ICOS+ proportion of Tfh cells per total Tfh cells was significantly more in the IPF patients (20.4 and 5.2%, respectively) compared with healthy controls (15.4 and 2.1%, respectively; p = 0.042 and p = 0.004, respectively). Here, ICOS is linked to idiopathic interstitial pneumonia.