Immunohistochemical expression and distribution of alpha2beta1, alpha6beta1, alpha5beta1 integrins and their extracellular ligands, type IV collagen, laminin and fibronectin in palmar fibromatosis.

Palmar fibromatosis is characterized by changes in the expression of extracellular matrix (ECM) proteins and re-organization of the interactions between cellular and extracellular compartments. We compared the expression and distribution of alpha2beta1, alpha6beta1, alpha5beta1 integrins and their corresponding extracellular ligands, type IV collagen, laminin and fibronectin in palmar fibromatosis nodules from 24 patients. Depending on the degree of cellularity and fibrosis, three different histologic phases were identified: proliferative, involutional, and residual. Immunohistochemistry revealed that only stromal cells of the highly cellular areas of both proliferative and involutional phases were myofibroblasts, as demonstrated by their cytoplasmic positivity for alpha-smooth-muscle actin. The ECM, surrounding these cells, was strongly and diffusely positive to type IV collagen, laminin and fibronectin, whereas no immunoreactivity was found in the ECM of the fibrotic and hypocellular areas of both involutional and residual phases. Immunostaining for alpha2beta1, alpha6beta1 and alpha5beta1 integrins revealed that alpha5beta1 integrin was expressed and restricted to the myofibroblast-rich cellular areas, whereas no expression was detected for alpha2beta1 and alpha6beta1 integrins. By examining serial sections, a co-localization of alpha5beta1 integrin and fibronectin was observed in the myofibroblast-rich cellular areas, indicating that, in palmar fibromatosis, a co-ordinate expression between cellular and extracellular ligand is detected only for the alpha5beta1 integrin/fibronectin complex. These findings suggest that the alpha5beta1 integrin/fibronectin complex may be involved in regulating the interactions between myofibroblasts and ECM in palmar fibromatosis.