CD4 and Leigh syndrome: Notably, however, CD4+ T cells from LS patients displayed higher median expression of both receptors (CTLA-4+ 1.8%, PD-1+ 27.8%) compared to non-LS cells (CTLA-4+ 1.4%, PD-1+ 14.6%), indicating an overall downregulation of these receptors in disease, but also that regulatory capacity is retained to a greater extent in LS lungs (Figure 2C; Table 3).