Lymphatics in lymphangioleiomyomatosis and idiopathic pulmonary fibrosis

Abstract

The primary function of the lymphatic system is absorbing and transporting macromolecules and immune cells to the general circulation, thereby regulating fluid, nutrient absorption and immune cell trafficking. Lymphangiogenesis plays an important role in tissue inflammation and tumour cell dissemination. Lymphatic involvement is seen in lymphangioleiomyomatosis (LAM) and idiopathic pulmonary fibrosis (IPF). LAM, a disease primarily affecting females, involves the lung (cystic destruction), kidney (angiomyolipoma) and axial lymphatics (adenopathy and lymphangioleiomyoma). LAM occurs sporadically or in association with tuberous sclerosis complex (TSC). Cystic lung destruction results from proliferation of LAM cells, which are abnormal smooth muscle-like cells with mutations in the TSC1 or TSC2 gene. Lymphatic abnormalities arise from infiltration of LAM cells into the lymphatic wall, leading to damage or obstruction of lymphatic vessels. Benign appearing LAM cells possess metastatic properties and are found in the blood and other body fluids. IPF is a progressive lung disease resulting from fibroblast proliferation and collagen deposition. Lymphangiogenesis is associated with pulmonary destruction and disease severity. A macrophage subset isolated from IPF bronchoalveolar lavage fluid (BALF) express lymphatic endothelial cell markers in vitro, in contrast to the same macrophage subset from normal BALF. Herein, we review lymphatic involvement in LAM and IPF.

Figure 1.

Serum levels of vascular endothelial growth factor (VEGF)-D in lymphangioleiomyomatosis. Serum VEGF-D levels in 111 patients with sporadic lymphangioleiomyomatosis were grouped on the basis of thoracic or abdominal lymphatic involvement (lymphangioleiomyomas and/or adenopathy: presence nequals;77; absence nequals;34) and the presence (nequals;40) or absence (nequals;71) of renal angiomyolipomas (AML). All groups were compared to 40 healthy volunteers. Diamonds: serum measurement of VEGF-D from one patient or healthy volunteer. –––: mean values. ^#: pequals;0.3; ***: p<0.001. Reproduced from [45] with permission from the publisher.

Figure 2.

Mean annual changes in forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁) and diffusing capacity of the lung for carbon monoxide (D_L,CO) before (white) and after sirolimus (grey) therapy in patients with lymphangioleiomyomatosis. Data show sirolimius therapy resulted in an increase in FVC, FEV₁ and D_L,CO. Mixed-effect models were used for statistical analysis. ^#: nequals;18 patients. Reproduced from [76].

Figure 3.

Alveolar lymphangiogenesis is a feature of idiopathic pulmonary fibrosis (IPF). a) Tissue sections reacted with anti-D2-40 (brown) and anti-CD34 (red) antibodies. Lymphatic vessels (D2-40+; black arrows) and blood vessels (CD-34+; red arrows) are visible adjacent to the alveolar spaces (Alv) in early stages of disease. b, c) Presence of hyaluronic acid in IPF lung. Immunofluorescence staining with hyaluronan-binding protein of paraffin-embedded sections of IPF lung tissue shows hyaluronic acid (red) in a representative single confocal microscopy optical section. Fibroblastic areas (*) displaying positive staining for hyaluronic acid are presented as merged images of hyaluronic acid and 4',6-diamidino-2-phenylindole (DAPI; blue) with (b) or without (c) an auto-fluorescence signal (green) and differential influence contrast. Cell nuclei were stained with DAPI. Scale barsequals;50 μm.

Figure 4.

CD11b⁺ alveolar macrophages in idiopathic pulmonary fibrosis (IPF) develop tube-like structures in vitro. CD11b⁺ alveolar macrophages were cultured in Matrigel® for up to 31 days and inspected under white light or after fluorescent-labelling of cytoplasm (CellTracker™ Orange CMTMR; Invitrogen, Carlsbad, CA, USA) and nuclei (Hoechst stain; Invitrogen). Large tube-like structures (150 μm in diameter) were observed when cells from subjects with IPF were cultured in Matrigel® (BD Biosciences, San Jose, CA, USA) for 30 days. A series of confocal images were reconstructed in three-dimensional renderings and representative snapshots of tubular structures are presented as overlaid fluorescence a, b) with or c) without differential influence contrast.