Sections from the dorsolateral prefrontal cortex of individuals who either did (n = 4) or did not (n = 3) fulfill a pathologic diagnosis for Alzheimer’s disease (see Supplementary Data 9 for subject characteristics) were stained for the presence of ISG15, CD83, CD74, or PCNA and were co-labeled with anti-IBA1 or anti-CD45 antibodies (general markers of myeloid cells in the brain). Here, ISG15 is linked to Alzheimer disease.