Which of the following is a cause of bronchospasm?

Bronchospasm is a condition characterized by the constriction of the smooth muscles surrounding the airways, leading to narrowed air passages, increased airway resistance, and difficulty in breathing. One of the primary causes of bronchospasm is allergic reactions. This occurs when an individual is exposed to an allergen, which triggers an immune response, often releasing histamines and other inflammatory mediators. These substances can induce bronchial smooth muscle contraction and increase mucus production, resulting in the typical symptoms of bronchospasm, such as wheezing, cough, and shortness of breath.

In the context of the other choices, while atelectasis, pneumonia, and sepsis can all lead to respiratory symptoms, they do not directly cause bronchospasm in the manner that allergic reactions do. Atelectasis involves the collapse of lung tissue, affecting ventilation but not necessarily inducing bronchospasm. Pneumonia is an infection that causes inflammation in the lungs but may lead to bronchial hyperreactivity in some cases rather than direct bronchospasm, and sepsis is a systemic inflammatory response that may impact lung function without primarily causing bronchospasm. Thus, allergic reactions stand out as a specific and direct trigger for bronchospasm.