PECAM1 and myeloid sarcoma: In comparison to normal white matter (NWM) from non-neurological controls, PECAM-1 expression was more than 5-fold increased in initial (pre-phagocytic) white matter MS lesions (IniL), while it was only slightly upregulated in the periplaque white matter (PPWM) and unchanged in active demyelinating lesions (ActL).