This last finding suggeststhe possibility that microglia activation could be a surrogate marker for early PD pathology asup-regulation of HLA-DR expression appears to be an early pathological event in the disease process.Another activation marker up-regulated in the brains of PD patients and widely used in animal modelsof PD is the phagocytic receptor CD68, also known as macrosialin, which upon microglia activation isoften found in cytoplasmic vesicles (Banati et al., 1998;Croisier et al., 2005). Here, CD68 is linked to Parkinson disease.