ICOS and idiopathic interstitial pneumonia: The median proportion of PD-1+ICOS+ Tfh cells to total Tfh cells in the IPF patients (5.2% [IQR, 2.5–9.4%]) was also significantly higher than that of the healthy controls (2.1% [IQR, 1.6–3.6%], p = 0.004; Fig. 2).