A cytokine storm is a potentially fatal immune reaction that results from an uncontrolled positive feedback loop between immune cells and cytokines, proteins that facilitate intercellular communication. During an immune response, cytokines prompt immune cells to travel to the site of infection as well as stimulate the production of more cytokines. The body regulates this process, but in some cases it becomes inappropriately elevated. What are the primary symptoms of a cytokine storm?