The immunopathology of acute experimental allergic encephalomyelitis. V. A light microscopic and ultrastructural immunohistochemical analysis of fibronectin and fibrinogen.

Cellular expression and extracellular deposition of fibronectin and fibrin/fibrinogen in experimental allergic encephalomyelitis (EAE) in guinea pigs (GP) were studied by light and electron microscopic immunohistochemistry of the central nervous system (CNS). Normal GPs had few fibronectin+ and fibrin/fibrinogen+ CNS vessels. Positively stained vessels were more numberous in sensitized GPs prior to and after onset of EAE, and there were extracellular deposits of these molecules in inflammatory foci. Staining was greater in EAE-susceptible strain 13 GPs than in sensitized EAE-resistant strain 2 GP. On ultrastructural analysis both molecules were localized on endothelial cell luminal surfaces and on intravascular mononuclear cells. Fibronectin and the macrophage fibronectin receptor (A6F10) were found on mononuclear cells in parenchyma. Endothelial cell luminal surface fibronectin and fibrin/fibrinogen may mark and/or contribute to early immune events in EAE, including mononuclear cell margination and emigration in inflammatory sites. Genetic factors, cytokines, and components of coagulation may regulate these interactions in vivo.