AIF1 and amyotrophic lateral sclerosis: Then, to evaluate the origin of Iba1-positive cells of spinal cord in ALS mice, we counted the cell number of Iba1 and YFP double positive cells as BMDCs (Iba1 + YFP +), and that of Iba1 positive and YFP negative cells as resident microglia (Iba1 + YFP −) (Fig. 4b,c).