Pneumocystis jirovecii pneumonia (PJP) is an invasive fungal infection (IFI) that occurs mostly in immunocompromised patients, especially in HIV-positive patients with a CD4+ lymphocyte count lower than 200 cells/mm3, solid organ transplant recipients and patients with hematologic malignancies or rheumatic conditions receiving prolonged doses of steroids or lymphocyte-depleting agents [1,2,3]. This evidence concerns the gene CD4 and pneumocystosis.