CD4 and cystic fibrosis: Finally, a recent study showed that overexpression of PD-L1 in monocytes with CF mutations, was associated with P. aeruginosa infections in patients with CF [182]; furthermore, not only PD-L1 was increased in the CF monocytes, but also the levels of sPD-L1 were increased in the plasma of these patients, as well as PD-1 in both CD4+ and CD8+ T cells [182].