Fluorescence over the lungs of SO rats was significantly lower than that seen in 2CLP animals (Figure 2a ). Intratracheal administration results in little vector uptake in the normal lungs of SO rats, while changes in the intracellular structure occurring during ARDS may be responsible for enhanced viral expression. Similar findings were observed with adenoviruses, and explained by an ARDS-induced exposure/expression of the CAR and integrin receptors that mediate adenoviral entry into the alveolar cells [14] . This mechanism may also apply to the SV40 vector, although different receptors or increased endocytosis may be involved. [39] [40] [41] .