CD28 and idiopathic pulmonary fibrosis: Also, the proportion of CD8+HLA-DR+ (i.e., cytotoxic activated cells) and CD8+CD28− T cells (i.e., cytotoxic exhausted, mainly of effector and memory effector phenotype) was higher in IPF patients than in controls, whereas that of naive CD8+ T cells was lower (Figure 1b and Table S3).