Fibronectin in delayed-type hypersensitivity skin reactions: associations with vessel permeability and endothelial cell activation.

Abstract

Fibronectin, a 440,000-m.w. glycoprotein found in connective tissue matrix and basement membranes of blood vessels, circulates in the plasma and associates with fibrin upon activation of the clotting system. This study reveals the participation of fibronectin in vivo in cell-mediated hypersensitivity reactions, which typically show local fibrin deposition and endothelial cell activation. Fibronectin deposits were marked in classic delayed hypersensitivity (DH) skin reactions elicited with PPD in guinea pigs, but not in cutaneous basophil hypersensitivity reactions elicited with KLH. By radioisotopic and immunofluorescence techniques, fibronectin accumulated in DH reactions in 2 distinct sites with different time courses. In 1- and 2-day-old DH reactions, the dermal extravascular space showed a coarse reticular pattern of staining with fluorescein-conjugated F(ab’)2 anti-fibronectin. The pattern and time course were similar to those of fibrin. By 3 days, a marked reduction in extravascular fibronectin and fibrin was apparent. At this time, fibronectin was detected in the dermal vessels in a brilliant homogeneous linear pattern; no fibrin was found within the vessels. Over the next several days, the intensity of the vessel staining for fibronectin slowly diminished and became more granular. Accumulation of circulating 125l-fibronectin into DH skin sites peaked and exceeded 131l-albumin accumulation between 16 to 40 hr after PPD challenge and then dropped dramatically. Maximal accumulation of 125l-fibronectin occurred just subsequent to the time (16 hr) of maximal vessel permeability and paralleled the deposition of fibronectin in the dermal extravascular space observed by immunofluorescence. In contrast, vessel wall fibronectin peaked when the accumulation of exogenous 125l-fibronectin was minimal and when endothelial activation and mitosis occurred in 1-μ sections. These and other data indicate that the microvasculature modulates the accumulation of fibronectin in DH reactions both by increased vascular permeability with extravasation of plasma fibronectin and by local synthesis in the vessel wall associated with endothelial cell proliferation. Both events occur in a number of other biologically important inflammatory responses, and we hypothesize that the fibronectin provides a provisional matrix that influences cell migration and macrophage activation.