In this study, we ask whether the Fas/FasL system plays a role in the amplification of inflammatory responses that occur early in the course of mechanical ventilation. The specific hypothesis to be tested is that the Fas/FasL system is required for the development of lung injury in mechanically ventilated mice exposed to LPS. To test this hypothesis, we investigate whether the combination of a non-injurious mechanical ventilation strategy with a minimal dose of intratracheal LPS results in an acute lung injury, and whether this injury is attenuated in Fas-deficient lpr mice. We further investigate whether the development of injury is associated with formation and deposition of anti-KC:KC immune complexes.