Fig. 3. Cytokine levels in lung tissue homogenate. Mechanical ventilation significantly increased levels of interleukin (IL)-1α, IL-1β, tumor necrosis factor (TNF)-α, IL-6, IL-10, and keratinocyte-derived chemokine (KC) in lung tissue homogenate compared with unventilated animals (group C). When animals were allowed to recover for 2 days (group R), all lung tissue cytokine levels were found to be lower when compared with levels found in animals killed immediately after 240 min of ventilation (group 240). IL-1α and KC levels in group R animals were higher compared with group C animals. In leukocyte-depleted animals (group D), mechanical ventilation resulted in significantly higher levels of lung tissue IL-1α, IL-6, IL-10, and KC compared with group C animals. IL-1β, TNF-α, and KC levels were lower compared with the levels found after 240 min of mechanical ventilation in healthy animals (group 240). Data are expressed as  box (median, 25th and 75th percentiles) and  whiskers (range). *  P < 0.05 compared with control. +  P < 0.05 compared with group 240 (= 240 min of ventilation). −= Lower detection limit; 30, 60, 120, 240 = minutes of ventilation in healthy mice; C = control group (unventilated, healthy mice); D = leukocyte-depleted group (these animals were leukocyte depleted before 240 min of mechanical ventilation and were killed immediately thereafter); R = recovery group (these animals were ventilated for 240 min and analyzed after 2 days of recovery).