“…The innate immune system includes barriers such as the skin, mucous membranes, and nasal hairs. Areas of turbulent airflow, temperature and pH extremes, and debris removal systems, such as the gastrointestinal tract and the mucociliary elevator, also are functional barriers (1,7). The innate immune system also includes infection-fighting cells, such as natural killer (NK) cells and phagocytes, and proteins such as tumor necrosis factor, cytokines, and complement factor (1,8).…”