The failure of normal subjects to acquire acute bacterial pneumonia is due to the efficient defense barriers of the lower respiratory tract.

• 正常人获得急性细菌性肺炎的障碍是由于下呼吸道的有效防御屏障。正常人之所以不会患急性细菌性肺炎是由于下呼吸道的有效防御屏障。