Moreover, the perforin and granzyme B productions (Figure 1B) of the CD4+CD28null lymphocytes could conceivably account for infiltrates of cytotoxic granule-laden lymphocytes that are present in IPF lungs [40] (Figure 6), and are believed to contribute to the pulmonary epithelial apoptosis of this disease [35]. This evidence concerns the gene PRF1 and idiopathic pulmonary fibrosis.