Immunohistology of the subfornical organ (SFO) during EAE. During EAE, MECA-32+ capillaries within the SFO stain positive for ICAM-1 and VCAM-1 (left panels). A large number of CD45+ cells preferentially localized in close vicinity to the microvessels can be detected within the SFO (second column top panel). Whereas expression of MHC class I is upregulated throughout the SFO parenchyma seen as diffuse staining, MHC class II is solely induced on perivascular cells (second column middle and lower panel). The majority of CD45+ cells within the SFO during EAE are macrophages/microglial cells as determined by positive immunostaining for the β2-integrin Mac-1 and for F4/80 (third column top and middle panel). Note, whereas staining for Mac-1 can be detected on round and ramified cells throughout the SFO, staining for F4/80 remains restricted to perivascular cells. Besides macrophages, a low number of CD3+ T lymphocytes of the CD4 and CD8 (data not shown) subclass and B220+ B cells can be detected (right panels). Most of the immune cells present within the SFO stain positive for LFA-1, but negative for α4-integrins (not shown). Immunoperoxidase, hematoxylin counterstain. Bar = 100 μm. This result was observed in at least 10 individual stainings.