TNF immunoreactivity after focal cerebral ischemia
The appearance of TNF immunoreactivity (TNF IR) within the densely ischemic core (A), and adjacent hypoperfused penumbra (B) at 6 hr after permanent MCA occlusion; the contralateral side revealed a virtual lack of TNF IR (C). High-magnification photomicrographs (D—H) illustrate a qualitatively different appearance of cell-associated TNF IR. The most abundant type, punctate and filamentous, was observed 6–24 hr after the onset of ischemia (E). Cytoplasmic expression of TNF IR also occurred (F). TNF IR reaction product at the cell surface presumably reflects membrane-associated 26-kD TNF (G). TNF expression was visualized within activated microglial cells adjacent to TNF-positive neurons (D) and within transformed, macrophage-like microglia (H).