CD4 and idiopathic pulmonary fibrosis: The increased percentage of [CD4 + CTLA4 +], [CD4 + CTLA4 + CD28 +], [CD8 + PD-1 +], [CD8 + CTLA +] and [CD8 + CTLA4 + CD28 +] indicate that there is substantial downregulation in immune response in IPF patients [72].