ABSTRACT
The immune system is a multicomponent defence system that recognizes and protects the host against microorganisms, toxins, mutant host cells or transplanted tissues that can potentially damage tissues or organs. It is composed of (1) macromolecules (proteins) found in the extra-cellular fluid compartment and in blood, and which make these inhospitable to pathogens, and (2) specialized cells that can recognize and destroy various pathogens or harmful substances. The innate immune system is made up of three components: physicochemical barriers, humoral and cellular defence mechanisms. The physicochemical barriers that prevent micro-organisms from gaining access to the body include the skin and mucous membranes, mucus, cilia and hydrochloric acid produced in the stomach. The humoral components of the innate immune system include complement, acute-phase proteins and proteolytic enzymes. The complement system must be activated before it can function. Lysozyme is a bactericidal enzyme secreted in saliva, tears and mucus of the respiratory and gastrointestinal tract.
