IFNγ is a cytokine of innate and adaptative immunity. Its major functions are activation of macrophages, differentiation of Th1 from T cells, inhibition of the Th17 pathway and control of intracellular pathogens [24] . Bermejo-Martin and colleagues found high systemic levels of IFNγ in hospitalized patients with nvA(H1N1) [9] . In contrast, in the present study there were no differences between the control and study groups. The IFNγ level over time in the nvA(H1N1) ARDS group was higher at admission than 3 days later, without significant difference between survivors versus nonsurvivors.