Immunology is the branch of biomedical science that deals with the response of an organism to antigenic challenge and its recognition of what is self and what is not. It deals with the defence mechanisms including all physical, chemical and biological properties of the organism that help it to combat its susceptibility to foreign organisms, material, etc.

Innate and adaptive immune systems

The immune system is divided into those which are static, or innate to the organism, and those which are responsive, or adaptive to a potential pathogen or foreign substance.

The innate system of immunity is on evolutionary terms, the older system that forms the first line of defence. It is non-specific and the resistance is static (it does not improve with repeated exposure and there is no memory on subsequent exposures). This includes physical defences such as skin & epithelial surfaces, cilia, commensual flora, acidic gastric contents, fever etc. Others are biochemical defences such as soluble - lysosyme, acute phase reactants and complement, fibronectin, interferons. Cellular components include natural killer cells, RES phagocytes.

The adaptive system is the second line of defence and is activated once the innate system has been overwhelmed. It is specific to the infective agent and can store the information about the invader as memory to show an enhanced response to subsequent challenge.

What is immunology?

Immunology deals with physiological functioning of the immune system in states of both health and disease as well as malfunctions of the immune system in immunological disorders like allergies, hypersensitivities, immune deficiency, transplant rejection and autoimmune disorders.

Immunology deals with physical, chemical and physiological characteristics of the components of the immune system in vitro, in situ, and in vivo. Immunology has a vast array of uses in several disciplines of science and medical science.

Origin of the word immunity

The word immunity was derived from the Lain word “immunis” meaning exempt.

Key lymphoid organs of the immune system

The key primary lymphoid organs of the immune system are thymus and bone marrow, and secondary lymphatic tissues such as spleen, tonsils, lymph vessels, lymph nodes, adenoids, and skin.

In good health thymus, spleen, portions of bone marrow, lymph nodes and secondary lymphatic tissues can be surgically removed without much harm to humans.

The actual components of the immune system are cellular in nature and not associated with any specific organ. They are widely present in circulation throughout the body.