DISORDERS OF THE IMMUNE SYSTEM
A fully functioning immune system is essential for maintaining health but, like all body systems, the immune system itself is subject to many clinical disorders. Immunological disease can occur for one of three reasons. Firstly, immunodeficiency diseases occur in individuals whose immune systems are inadequate, perhaps due to the absence or malfunction of essential components, making them susceptible to infectious disease and even to certain types of cancer. Secondly, autoimmune diseases can occur as a result of the immune system mounting an immune response against ‘self’ components. Finally, immunological hypersensitivity occurs when immune responses, often mounted against seemingly innocuous immunogens, result in tissue damage. Indeed, immunological hypersensitivities are among the commonest of immunological disorders.