Pneumocystis jiroveci pneumonia (PcP) increased in non HIV immunocompromised patients. Mortality remains high for those patients with comorbidities (50% for patients with the most severe Pneumocystis pneumonia). Physiopathology, characteristics and outcome of PcP in non-HIV patients remains different from those in HIV patients. Steroids in HIV patients with PcP has been associated with decreased mortality but in non-HIV patients, adjunctive steroids remains controversy. Some retrospective studies in that field did not find any beneficial effects of steroids ((1mg/kg/jour d'Equivalent Prednisone (EP)). However, all the studies were retrospective, non randomised studies including various underlying disease and severity of PcP was variable. Moreover, dosage and delay of steroids were variable leading difficult to interpret all the results.

The investigators want to demonstrate the beneficial effect of steroid during PcP in non-HiV immunocompromised patients with a double blinded randomised clinical trials comparing adjunctive steroids to placebo.

Inclusion Criteria:

• Age ≥ 18 years
• Severe PcP : 1 / interstitial acute pneumonia with possible or typical criteria for PcP and positive specimen for Pneumocystis jirovecii (excluding PCR) ; or interstitial acute pneumonia with typical criteria for PcP and positive PCR in respiratory specimen. 2/ Arterial pression of Oxygen (PaO2) < 60 mmHg on room air need of 3 L/min oxygen for saturation >92% or tachypnea>30min need of mechanical ventilation for acute respiratory failure.
• Treatment for PcP started for less than 7 days.
• Non-HIV immunosuppression : malignant hematological disease, solid tumor cured for less than 5 years, allogenic stem cell transplant, Steroids (>0.3mg/kg equivalent prednisone for more than 3 weeks or > 20mg/days for more than one months) or other immunosuppressive treatment for more than one months or solid organ transplantation.
• Signed inform consent by patient or relatives
• Health insurance

Exclusion Criteria:

• HIV Serology HIV 1 or 2 positive
• Need of steroid ≥1mg/kg/j equivalent prednisone for another pathology (acute Graft versus Host disease (GVH= for example)
• Contra-indication for steroids
• Pregnancy of breath-feeding
• Denied to participate
• No health insurance
• tutelage