The proliferation of microglia, one of the hallmarks of neurodegenerative diseases, is triggered by an increase in the expression of components of the CSF1R pro-mitogenic pathway (Gomez-Nicola et al., 2013, Olmos-Alonso, 2015), so here we investigated if the disruption in PD-1 could have an impact on the expression of Csf1r and its ligands Csf1 and Il-34 in the brain. Here, IL34 is linked to neurodegenerative disease.