Cell‐specific expression of alveolar TNFR1

Abstract

Ligation of the cytokine, tumor necrosis factor alpha (TNFα) to TNFα receptor 1 (TNFR1) causes lung inflammation. Therefore, the organization and extent of TNFα‐induced lung inflammation is likely to depend on the distribution and density of TNFR1 in the alveolar epithelium (AE). We addressed this issue by real‐time confocal microscopy of intact alveoli in the isolated, blood‐perfused mouse lung (n=3). To visualize the AE, we microinjected alveoli with the cytosolic marker, calcein green, and with LysoTracker Red (LTR) which localizes to lamellar bodies in alveolar type 2 (AT2) cells. To determine TNFR1 expression, we injected an Alexa‐633‐conjugated anti‐TNFR1 mAb that recognizes an extracellular domain of mouse TNFR1. TNFR1 fluorescence was accepted at ≥50 grey levels. In the imaged region, each alveolus contained 1‐2 AT2 cells, consistent with the understanding that the majority of the alveolar surface area is provided by alveolar type 1 (AT1) cells. TNFR1 expression was spatially heterogeneous, since the receptor fluorescence co‐localized with AT1, but not AT2 cells (P<0.05). Our findings suggest that the primary alveolar inflammatory response to TNFα is driven by TNFR1‐induced signaling in the AT1 cell (HL57556, HL64896).