Development of Lymphatic Capillary Network Along the Alveolar Walls of Autopsied Human Lungs with Pneumonia.

BACKGROUND: Limited information is available regarding the lymphatic vasculature during pneumonia.

OBJECTIVE: To characterize lymphatic vasculatures in autopsied cadavers with pneumonia.

METHODS: Paraffin-embedded lung tissues obtained from 20 autopsied cadavers with complicated pneumonia and 10 control cadavers without pneumonia were used for immunohistochemical analyses using primary antibodies against podoplanin, vascular endothelial growth factor receptor-3 (VEGFR-3), CD34, vascular endothelial growth factor (VEGF)-C, VEGF-D, CD73, and CD163.

RESULTS: There was no difference in the vascular density of podoplanin+ usual lymphatics between the individuals with and without pneumonia. In half of the cadavers with pneumonia, however, a network of podoplanin+ cells lying together in a side-by-side bead-like arrangement appeared along the alveolar septa; however, this was absent in the control cadavers. The podoplanin+ cells in the network were characterized by a weaker expression of podoplanin, relative to usual lymphatics, and the occasional presence of ductal structures. Although podoplanin+ cells were not coexpressed with VEGFR-3, a part of the network was connected to CD73+ afferent lymphatics. The network showed an intertwined relationship with CD34+ capillaries, suggesting that the network represents lymphatic capillaries. The number of CD163+ macrophages was significantly increased in individuals with the network than those without the network, while a significant decrease in neutrophils was observed. VEGF-C expressed in CD163+ macrophages and type II epithelial cells was observed in the cadavers with the network.

CONCLUSION: The development of lymphatic capillary networks along the alveolar septa rather than the usual lymphangiogenesis was noted in autopsied individuals with pneumonia.