ABSTRACT
Immunology is a discipline in the biomedical sciences dealing with the mechanisms and structures in a living organism (including man) for protection against infectious diseases. The evolution of living organisms on earth has resulted in the development of various self-defense systems to prevent the proliferation of microorganisms such as bacteria, fungi, protozoa, and viruses which constantly search for hosts to infect. Without this immunity, it would be impossible for higher organisms to exist on earth. The self-defense system has evolved into a complicated infrastructure (immune system) in vertebrates, which not only acts to prevent infections but occasionally can cause various diseases itself (immunopathology).
