Immune System - The system of biological structures and processes that protects the body from foreign substances, including pathogens.⏎
Infectious Disease - A type of illness caused by a pathogenic agent, including viruses, bacteria, fungi, protozoa, parasites, or abnormal proteins known as prions.⏎
Mucous Membrane - The moist linings of body passages and internal cavities involved with absorption and secretion of substances.⏎
Infection - The entry, establishment, and replication of pathogens inside a host organism.⏎