F2R and chronic obstructive pulmonary disease: Immunofluorescent PAR-1 immunoreactivity was demonstrated in central airways: (1) inactive receptor (H111 Ab) (green colors), mainly localized in the cell membrane, and total receptor (ATAP2 Ab) (red colors) in the cytoplasm of epithelial cells of HC; (2) inactive receptor (H111 ab) (green colors), localized in the cell membrane (low levels of intensity) and total receptor (ATAP2 Ab) (red colors), in both the cell membrane and cytoplasm (high levels of intensity), with a specific localization in the apical pole of the columnar epithelial cells from COPD patients.