However, the total level of Iba1 and OX-42, which also serves as a marker of microglial levels, was not significantly different between patients with PD and age-matched controls (Fig. 1c), even though there was a significant increase in tumor necrosis factor-alpha (TNF-α) as a neurotoxic inflammatory cytokine, which could be produced by activated microglia, in the SN of patients with PD compared with age-matched controls (Extended data Fig. 1). Here, AIF1 is linked to Parkinson disease.