TABLE OF CONTENTS Immunity describes the body defence mechanisms against harmful substances. These include bacteria, viruses, parasites and malignant cells. The word immunity is derived from the Latin immunitas , which means free from disease. The immune response can be divided into three parts; recognition, activation and removal. These functions are achieved by cellular, humoral and innate immune systems.
Innate immunity is the part of the immune system that is present in an individual from birth; it is also referred to as non-specific immunity. Innate immunity does not require previous exposure to an antigen to be effective and does not result in specificity. The innate immune system is the first line of defence against microorganisms and a major component is the physical barrier provided by intact skin or mucous membranes (see Section 13.2). Sebum is a skin secretion that has a low pH (3 5) and inhibits microorganism growth, whereas mucous on membranes traps pathogens. Tears, mucous secretions and saliva all act to wash away organisms or have bactericidal properties e.g. lysozyme in tears. Soluble factors such as interferon, complement and acute phase proteins are also important in the innate immune system. Interferon is released by virus-infected cells and helps provide protection against the virus to surrounding cells. Various microbial proteins can activate the alternative complement pathway resulting in cell lysis, recruitment of phagocytic cells and opsonisation. Acute phase proteins include C-reactive protein (CRP) and antitrypsin, and serve to enhance the immune response (CRP) or to limit...
