Q. An otherwise healthy 3-year-old male child is brought to the emergency department because of shortness of breath (dyspnea). His mother mentions that the patient is up to date with his vaccinations. Vital signs are remarkable for fever and tachypnea. Upon examination, chest auscultations reveal right basal coarse crepitations. Chest x-ray confirms the diagnosis of lobar pneumonia. Which of the following is directly responsible for the patient's elevated temperature?