Distribution of type I, III, IV and V collagen in normal and atherosclerotic human arterial wall: immunomorphological characteristics.

35 autopsies--aged 30 to 75 years--were investigated in order to establish trends of collagen localization in various types of arteries depending on age, arterial size and degree of atherosclerosis. Cryostat sections stained with highly specific antibodies to human types I, III, IV or V collagen, or with the antiserum to smooth muscle myosin were examined by the indirect immunofluorescence technique. Localization of type III collagen was very similar to that of type I. Fibrous structures of both type I and type III were then major constituents of the intima, media and adventitia. Sparse fibrils of type I and type III collagens were revealed in the subendothelium of unaffected intima. They gradually became abundant in the deeper intimal layers contrasting with loose fibrillar formations of the media. The content of interstitial collagens was significantly increased in the subendothelium of local intimal thickenings and in a thickened intima of the aged. This fact, considering the thrombogenicity of interstitial collagens, may be relevant to the atherogenesis through the "response-to-injury" mechanism. Type IV and type V collagens are localized to the endothelial basement membrane and basement membranes of smooth muscle cells of the intima and media. Diffusely distributed type V collagen was also observed in the intercellular space of the intima. In lipid streaks, parallel layers of condensed interstitial collagens separated groups of cells and extracellular lipid depositions. In fibrous plaques, types I and III became prevalent structural elements and their densely packed fibers occupied whole regions devoid of any type IV and type V collagen. Heavily thickened type IV collagen structures surrounding individual smooth muscle cells were found in fibrous plaques, but never, in unaffected intima.