 At the first day, in each patient samples of blood, bronchoalveolar lavage BAL and tracheobronchial aspirate TBA will be taken. Bronchoscopy is a technique of visualizing the inside of the airways for diagnostic and therapeutic purposes. A bronchoscope is inserted into the airways, usually through the nose or mouth, or occasionally through a tracheostomy. This allows the practitioner to examine the patients airways for abnormalities such as foreign bodies, bleeding, tumors, or inflammation. Specimens may be taken from inside the lungs: biopsies, fluid bronchoalveolar lavage, or endobronchial brushing. BAL is typically performed to diagnose lung disease. In particular, BAL is commonly used to diagnose infections in people with immune system problems, pneumonia in people on ventilators and some types of lung cancer. BAL is often used in immunological research as a means of sampling cells or pathogen levels in the lung T-cell populations. Specimens may be taken again in 48 hours from the diagnosis of VAP. BAL will be placed in 10FBS-RPMIc and centrifuges at 400g, 5 min, and then will be added RPMI-1640 and 10 FBS. The number and the type of the cells will be defined by Μay-Grunwald-Giemsa staining, and the subpopulations with flow cytometry. 