Introduction: 
Pneumonia is an infection of the lungs caused by bacteria, viruses, fungi, and parasites that impose significant costs for the health care system and exhibit the most common reason for the death of infectious origin1. In this disease, polymorphonuclear neutrophils and macrophages fight with microorganisms by using reactive oxygen species (ROSs) and lysosomal enzymes2. As a consequence of pulmonary defense mechanism in inflammatory diseases such as pneumonia and asthma, Oxidative stress (OS) at the systemic level may have a central role with adverse clinical outcomes of these diseases, such as the endothelial dysfunction (ED), exacerbation of inflammation, and shortness of breath, and ultimately acute respiratory distress syndrome (ARDS), and death 3-5.
ED causes pulmonary edema due to an increase in endothelial permeability. The activated endothelium mediates leukocyte binding to express the adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule 1  (ICAM-1) that mediate leukocyte binding. Upon leukocyte binding, these adhesion molecules activate endothelial cell signal transduction and then alter endothelial cell shape for the opening of passageways, through which leukocytes can migrate 6-7.
Characterized by chronic inflammation in the airway wall, asthma is the most common chronic respiratory disease in children, which is prevalent in developing countries. Although it cannot be considered a direct cause of pneumonia, children with asthma are more prone to develop pneumonia due to previous lung damage. As a result, a child with asthma may have more severe symptoms and complications from pneumonia. Asthma may exacerbate the clinical consequences of pneumonia, such as ED8-11.
We are not aware of any studies on assessing the changes in OS, inflammation, and ED biomarkers in children with asthma and pneumonia together compared with children with pneumonia only. Therefore, the current study assessed the alterations in OS, TNF-α, and ED biomarkers in children with asthma and pneumonia, children with pneumonia only, and healthy children.