Age-dependent loss of TM in pulmonary vascular cells during endotoxemia. Immunohistochemical analysis of TM was performed on lung sections from young (4 months) and aged (24 months) mice that were sacrificed 12 hours after LPS injection (2.5 mg/kg, intraperitoneal). Strong positive immunostaining for TM is seen in young control (A), aged control (B), and young mice with LPS (C), but not in aged mice with LPS (D). Control mice received no LPS. TM-positive cells in capillaries and large vessels (V) are indicated by arrowheads and arrows, respectively (original magnification ×400).