The lungs of spontaneously breathing B6 and lpr mice showed normal architecture (Figure 4 ). The lungs of B6 mice exposed to MV + LPS showed thickening of the alveolar walls, intra-alveolar neutrophilic infiltrates, and intra-alveolar fibrin strand deposition. In contrast, the lungs of lpr mice exposed to MV + LPS retained their normal architecture. The LPS was administered with inert colloidal carbon, which on the tissue sections was taken up by macrophages and appears as black granulate material in the cytoplasm. This indicates that the Figure 1 Inflammatory response. C57BL/6 (B6) and Fas-deficient lpr mice received intratracheal installations of either PBS followed by four hours of spontaneous breathing (SB), or E. coli LPS, 15 ng/kg, followed by 4 hrs of mechanical ventilation (MV) with tidal volumes of 10 mL per kilogram, FiO 2 of 0.21, PEEP = 3 and respiratory rate = 150 breaths per minute. In response to the combination of MV and LPS, the B6 mice showed significantly more total neutrophils (PMN) in the BAL fluid than the lpr mice (A). A similar pattern was seen for the lung MPO activity, which is a measure of the total neutrophil content in the lung (B). MV + LPS was associated with increases in the lung homogenate concentrations of the cytokinesTNF-α, MIP-2, and KC, and these similar in the B6 and the lpr mice; MV + LPS had no effect on IL-1β (C-F). n = at least 6/group. sections depicted were all exposed to instillate -an important point as intratracheal instillations are patchy and normal tissue can simply reflect a non-instilled area.