Figure 2

Lymphoid aggregates (LAs) have extensive interfaces with the alveolar lumen and peripheral lymphatic vessels. (A) Quantitative data showing that in all study groups the majority of LAs had an alveolar lumen–LA interface, irrespective of anatomical localisation. Values are given as mean±SEM. (B) Quantification of the total length of alveolar–LA interfaces. Statistical analysis was performed using the Kruskal–Wallis non-parametric test followed by Dunn's multiple comparison post test. Horizontal lines indicate medians for each group. *p<0.05. (C) Photomicrograph of a typical bronchiolar-associated lymphoid tissue (BRALT) with its interface with the alveolar lumen (asterisk) and podoplanin⁺/α-smooth muscle actin⁺ lymphatic vessels (arrowheads; brown). α-Smooth muscle actin⁺ cells are shown in red. Arrow indicates alveolar macrophages and ‘Ep’ the bronchiolar epithelium. Black endogenous pigment depositions are also visible. Epithelial basal cells and pneumocytes showed a weak immunoreactivity for podoplanin. Cell nuclei were counterstained with Mayer's haematoxylin (blue stain). (D) Photomicrograph of a similarly stained vascular-associated lymphoid tissue (VALT) with its direct interface with the alveolar lumen and extensive connection to podoplanin⁺/α-smooth muscle actin⁺ lymphatic vessel (arrowheads). (E) Three-dimensional rendering of an image stack with 40 (4 μm thick) serial sections revealed an intricate relationship between immunostained lymphatic vessels and peripheral lung LA. White: LA; blue: lymphatic vessels. (F) The relative proportion of anatomic structures along the LA perimeters, divided into alveolar interface, lymphatic vessel borders and remaining firm tissue (ie, airway wall tissue, adventitial tissue of pulmonary vessels, or parenchymal tissue). Values are given as mean±SEM. Scale bars: (C–E) 100 µm.