Heterogeneous Characteristics of Lymphatic Microvasculatures Associated with Pulmonary Sarcoid Granulomas

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Abstract

Rationale:

Pulmonary sarcoidosis is a disorder characterized by noncaseating epithelioid granulomas that are anatomically distributed along lymphogenous routes. Currently, limited information is available about lymphangiogenesis in pulmonary sarcoidosis.

Objective:

To clarify the characteristics of lymphangiogenesis in pulmonary sarcoidosis.

Methods:

The concentrations of vascular endothelial growth factor (VEGF), VEGF-C, and VEGF-D in serum and bronchoalveolar lavage fluid from 65 patients with pulmonary sarcoidosis, 10 with idiopathic pulmonary fibrosis, and 29 healthy volunteers were measured by ELISA. Paraffin-embedded lung tissues obtained from 19 patients were used for immunohistochemical analyses, using primary antibodies against VEGF, VEGF-C, VEGF-D, podoplanin, VEGF receptor (VEGFR)-2, VEGFR-3, and CD73.

Results:

The serum and bronchoalveolar lavage fluid concentrations of VEGF and VEGF-C were significantly increased in patients with pulmonary sarcoidosis. Immunohistochemical analysis showed that VEGF and VEGF-C were expressed in sarcoid granulomas. Immunostaining with anti-podoplanin antibody for the detection of lymphatic vasculatures showed the presence of usual lymphatics and atypical tubular structures around sarcoid granulomas. Atypical tubular structures were characterized by a thin membrane, with weak expression of podoplanin and a membrane deficit in a part of the borderline. The structures were observed in around 58.6% of the total of 193 granulomas, whereas usual lymphatics were limited in 15.6%. Atypical tubular structures were coexpressed with VEGFR-2, but not VEGFR-3, whereas VEGFR-3 was expressed in usual lymphatics. Part of the tubular structures was connected to CD73+ afferent lymphatics.

Conclusion:

These results indicate the presence and the importance of heterogeneous lymphatic microvasculature around sarcoid granulomas in pulmonary sarcoidosis.

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