Lymphangiogenesis in lymphangioleiomyomatosis: its implication in the progression of lymphangioleiomyomatosis.

Lymphangioleiomyomatosis (LAM) is characterized by the proliferation of abnormal smooth muscle cells (LAM cells) in the lungs, lymph nodes, and/or other organs. We examined lymphangiogenesis using immunohistochemistry for Flt-4 (VEGFR-3), a new specific marker for lymphatic endothelial cells, as well as the expression of vascular endothelial growth factor (VEGF)-C in LAM. Specimens were obtained from 6 autopsy cases, a single lung transplant case, and 8 surgical cases for analyses. We demonstrated that lymphatics were extremely abundant in both pulmonary and extrapulmonary LAM and that lymphatic endothelial cells not only proliferated encompassing LAM foci but also infiltrated the intra-LAM foci, and that in advanced LAM, lymphangiogenesis involved vascular walls and interstitium surrounding the area where LAM cells proliferate. In contrast, angiogenesis, confirmed with CD31 immunostaining, was observed less in the LAM foci. LAM cells demonstrated positive reactivity against anti-VEGF-C antibody at varying intensities. Significant correlation (P < 0.001) was noted between the degree of lymphangiogenesis in LAM or VEGF-C expression on LAM cells and lymphagioleiomyomatosis histologic score (LHS), which represents the histologic severity of pulmonary LAM and has been reported to have prognostic significance. Our study is likely to provide a novel point of view on the pathophysiologic significance of lymphangiogenesis in LAM.