 Ventilator-associated pneumonia VAP typically refers to nosocomial pneumonia developing 48 hours later from endotracheal intubation and mechanical ventilation.ICU patients who receive mechanical ventilation have 4-fold higher risk of developing pneumonia with a rate of 3 per day after day 7 in the intensive care unit. Several risk factors have been reported to be associated with VAP, including the duration of mechanical ventilation, the presence of chronic pulmonary disease, sepsis, acute respiratory distress syndrome ARDS, neurological disease and trauma. The immune system defends the host against infection. Protective immunity can be divided into innate and adaptive immunity. The innate immune response evolves as a first defence barrier in the host and mounts an immediate, but nonspecific, immune response to rapidly destroy or limit the invaders. The innate defense mechanisms are the external epithelia, the mucosal surfaces, the cells NK cells, phagocytes and the complement system. 