Clinical pulmonary autograft valves: Pathologic evidence of adaptive remodeling in the aortic site

Morphologic features and collagenous architecture of PAVs. A, Three distinct layers are present in normal pulmonary valve (PV; a-b): the fibrosa (f), with an abundance of collagen (yellow); the spongiosa (s), with glycosaminoglycans (blue-green); and the ventricularis (v), with elastin (black). Both early and late pulmonary autografts (PAV; c-f) showed near-normal 3-layered structure and intact elastin, usual outflow surface corrugations, and well-preserved collagen microstructure detected with picrosirius red. This was similar to that seen in normal aortic valves (AV; g-h). Homograft valves (i-j) showed loss of interlayer demarcations, flattening of the normal outflow surface corrugations, and structural deterioration of the ECM revealed with picrosirius red staining under polarized light, which demonstrated that collagen fibers were almost undetectable and had lower birefringence than those in normal valves. (Original magnification of all panels 100×.) *Pannus formation. B, Valve thickness and interstitial cell density in PAVs compared with those in normal aortic valves (AV) and pulmonary valves (PV). *Significant differences between all combinations of pulmonary valves and early PAVs versus late PAVs and aortic valves (P < .05); †significant differences in cell density between all sets of valves (P < .05); no difference was found between pulmonary valves and aortic valves. C, Collagen accumulation in PAVs compared with that in normal aortic valves (AV), pulmonary valves (PV), and homograft valves (H). *Statistically significant decrease in collagen content in homograft valves compared with that in PAVs and normal valves.

Arterial wall of pulmonary autografts. A, Movat pentachrome stain shows overall morphologic features of a normal pulmonary valve compared with that of a PAV and associated arterial wall (top). (Original magnification 40×.) The middle panel demonstrates loss of elastin (black) and accumulation of collagen (yellow), suggesting scarring formation in late PAVs. (Original magnification 400×.) Immunohistochemistry for α-SMA shows loss of medial smooth muscle cells (bottom) in late PAVs. (Original magnification 400×; bar = 50 μm.) B, Late PAV walls showed lower collagen birefringence compared with that seen in normal valve wall (arrows). (Original magnification 40×.)

Comparative morphologic features of autografts and homografts obtained from the same patients. Autograft valves had near-normal structure and cellular population (a, c, and e). In contrast, homografts from the same patients (b, d, and f) had progressive collagen hyalinization and loss of cellularity. (Original magnification 400×; bar = 50 μm.)

Immunophenotypes of interstitial cells of normal pulmonary valves and autograft explants. A, In normal pulmonary valves (PV) fibroblast-like interstitial cells expressed predominantly vimentin but not α-SMA (a-c). Cells that stained positive for α-SMA were localized immediately below the endothelium. *Pannus formation in early PAVs (d). In early PAVs a large population of cells in the spongiosa and the ventricularis expressed both vimentin and α-SMA, suggesting modulation to myofibroblasts in early PAVs (d-f). In late PAVs the subendothelial distribution of α-SMA⁺/vimentin-positive myofibroblasts among the interstitial cells resembled the quiescent fibroblast-like cell population of the normal valves (g-i). (original magnification: a, d, and g, 100×; b, c, e, f, h, and i, 400×.) B, An initial increase in the number of α-SMA⁺ cells in early PAVs eventually normalized to aortic valve (AV) levels in late PAVs. *Difference between early PAVs and all other valve combinations (P < .01). PV, Pulmonary valve.

Proteolytic enzyme expression in pulmonary autografts compared with that seen in normal valves. A, Interstitial cells in the early PAVs expressed higher levels of MMP-13 than normal valves. In late PAVs only a few superficial cells showed weak expression of MMP-13, suggesting cuspal intimal proliferative lesion formation. (Original magnification 400×; bar = 50 μm.) PV, Pulmonary valve. B, An initial increase in the number of interstitial cells expressing MMP-13 in early PAVs decreases to aortic valve (AV) and pulmonary valve (PV) levels in late PAVs. *Significant difference in MMP-13 expression in early PAVs compared with that seen in late PAVs and normal valves.

Immunophenotype of endothelial cells of normal valves and autograft explants. A, EphrinB2 was detected in normal aortic valve (AV) but not pulmonary valve (PV) endothelium (top panels). Endothelial cells of early PAVs had patchy expression of EphrinB2 (arrow, middle panels), whereas an increased population of endothelial cells expressed the CD31⁺/EphrinB2⁺ phenotype in late PAVs (bottom). (Original magnification 400×.) B, Progressive increase of EphrinB2 expression in PAVs toward levels of a normal aortic valve (AV). *Significant differences between late PAVs and aortic valves versus pulmonary valves (PVs) and early PAVs (P < .01).