CD28 and idiopathic pulmonary fibrosis: Serum biomarkers cluster of differentiation 28 (CD28), inducible T-cell co-stimulator (ICOS), LCK- protooncogene (LCK), IL-2 inducible T-cell kinase (ITK) as part of a 52-gene RNA signature [88], a composite score of OPN, periostin, MMP-7 and intercellular adhesion molecule 1 (ICAM-1) [89], and the Total-to-Background Ratio (TBR) calculated from 18F-FDG-PET imaging [90] have been reported to effectively differentiate low from high risk patients with IPF.