In PD patients the CD4 population seems to be altered (Fiszer et al., 1994; Saunders et al., 2012; Stevens et al., 2012) and they seem to be more prone to apoptosis, and differ in their activation state, which could suggest that a failure of the CD4 cells response might be happening in PD (Romero-Ramos et al., 2014). Here, CD4 is linked to Parkinson disease.