CD38 and pulmonary fibrosis: Cluster of differentiation 38 (CD38), a cardinal nicotinamide adenine dinucleotide (NAD) hydrolase, is a marker of senescent cells and is highly expressed in the AEC2s of patients with pulmonary fibrosis, which serves as a potential therapeutic target.[233] Researchers have discovered that CD38 AECs are negatively associated with the pulmonary functions of patients.[234] Similarly, increased expression of CD38 in the AECs of fibrotic lungs was detected in young mice and further strengthened in aged mice.