CD28 and idiopathic pulmonary fibrosis: At the Tregs level, CD45RA+ CD28- CD8+ T cell absolute counts (OR=1.001, 95% CI [1.001-1.002], P=0.044), CD45RA+ CD28- CD8+ T cells (OR=1.001, 95% CI [ 1.00009-1.00219], P=0.033), and CD25 on CD4 Tregs (OR= 1.07, 95% CI [1.005-1.145], P=0.036) were associated with an increased risk of IPF development.