Clinical presentation of patients after severe injury such as a severe infection, trauma or extensive burns is characterized by the simultaneous occurrence of dysregulation of the initial inflammatory response and immunosuppression associating quantitative and functional alterations of innate and adaptive immune cells. These acquired immune dysfunctions have been associated with an increased susceptibility to nosocomial infections, foremost among which are ventilator-associated pneumonia (VAP). Despite the implementation of a set of preventive measures, the incidence of these VAP remains high in intensive care, with rates in Europe of 1.5% per day of ventilation. Post-aggressive immunosuppression is characterized by the decrease in the expression of HLA-DR (belonging to the type II major histocompatibility complex, MHC-II) on the surface of monocytes (mHLA-DR). The administration of interferon gamma (IFNγ) can restore the level of mHLA-DR and may possibly improve the prognosis as an adjuvant therapy associated to antibiotics. However, the level of proof of this therapeutic strategy is low, limited to small cohorts of patients, or clinical studies without prior immunodepression assessment. The objective of this study is to conduct a randomized, double-blind, placebo-controlled superiority trial to assess the effect of IFNγ administration on the duration of mechanical ventilation following the first episode of VAP in patients having an HLA-DR \< 8000 AB/C All reported data about recombinant human IFNγ 1b for the control of secondary infections in patients with septic shock used the dose of 100 micrograms per day by subcutaneous route for 3 to 5 days . At this dose, no retrospective study has reported any serious adverse effects and recombinant human IFNγ 1b allows an increase in monocyte membrane expression of mHLA-DR.