Blood-borne cells involved in arterial repair upon experimental incision injury

Summary. We had previously shown that microscopically detectable infiltration of dendritic cells and expression of Hsp47 in tissue lysates occur during repair upon experimental arterial injury. We have further analysed here the cell types involved in the repair process by histology, electron microscopy and immunofluorescence. Rat carotid arteries were subjected to brief crushing and full thickness incision and were analysed up to 21 d thereafter. Adhesion and activation of platelets occurred 3 h after surgery. A neointima had formed 7 d after surgery, where immature cells entered from the lumen and gave rise to cells rich in organelles of the secretory pathway and endowed with bundles of phalloidin-binding microfilaments. Alpha smooth muscle-positive, secretory and contractile smooth muscle cells were found in the neointima 14 and 21 d after injury. Seven to 21 d after surgery, endothelial cells appeared immature and the newly formed tissue contained MHC-II positive, CD43 positive dendritic cells which clustered with lymphocytes, a few macrophages containing apoptotic remnants and cells labelled for Hsp47. Thin elastic fibrils appeared in the neointima 21 d after injury. The results suggest that the response to acute arterial incision injury is mediated by blood borne cells which differentiate along multiple pathways; the process evolves without reaching stabilization within the observed time lapse; the secretion of extracellular matrix is marked by the expression of Hsp47; and the constant presence of dendritic cells clustered with lymphocytes makes these cells candidate to a pivotal role in the tissue response to injury.