SOD1 and amyotrophic lateral sclerosis: To determine whether misfolded SOD1 proteins induced an increase in surface P2X4 of macrophages during ALS, we performed biotinylation assays and western blot to measure P2X4 surface/total ratio from peritoneal macrophages of the different mouse lines used in this study at different time points (Figs. 5 and S7).