Immunology finds a wide variety of uses in understanding, diagnosis and treatment of diseases in medicine today.

Advent of immunology in clinical medicine

Immunology began as a branch of microbiology. It was initially understood to be related to infectious diseases alone. The study of infectious disease and the body’s response to them has a major role for the development of immunology and its study. This began with the concept of germ theory.

Edward Jenner first studied the response of the body to foreign substances. He observed that dairy maids who had naturally contracted a mild infection called cowpox seemed to be protected against smallpox that killed and disfigured millions at that time.

In 1796, Jenner inoculated an eight year-old boy with fluid from cowpox blisters on the hand of a dairymaid. The boy contracted cowpox. Then two month later Jenner inoculated him with fluid from a small pox blister, the boy only developed a small sore at the site of inoculation. This was the first vaccine used and Jenner proposed that the boy’s exposure to the mild disease cowpox had made him immune to the small pox infection.

In 1879, gonococcus, was isolated by Neisser. In 1883, Klebs and Loeffler isolated diphtheria bacilli which led to the production of the first defined antigen, diphtheria toxin, by Roux and Yersin in 1888. In 1888, the first antibodies, serum bactericidins, were reported by Nuttal and Pasteur. Thereafter in 1890, von Behring and Kitasato discovered antitoxins that led to development of toxoids for diphtheria and tetanus. In 1900, Land Steiner discovered the blood group antigens and their corresponding antibodies and this was a major leap in blood transfusion without provoking reactions.

What does clinical immunology involve?

Clinical immunology is thus the study of:-

• Diseases caused by disorders of the immune system – this could be due to failure (under-activity), abnormal activation or malignant or cancerous growth of the cellular elements of the system.
• Pathology of other disorders where immune reactions play a part.
• Medications and drugs that modify or modulate the immune system for example those used in transplant rejections.
• Vaccines and other agents that modify immune reaction to specific pathogens.

Disorders of the immune system

The diseases caused by disorders of the immune system fall into broad categories:-

• Immunodeficiency – this occurs if the immune system fails to provide an adequate response to pathogens. This may be seen as a response to a long term disease condition like diabetes, chronic granulomatous disease or due to an infection such as HIV AIDS (Human Immunodeficiency virus causing Acquired Immunodeficiency syndrome).
• Autoimmunity – this occurs when the immune system attacks its own host's body. Some examples include systemic lupus erythematosus, rheumatoid arthritis, Hashimoto's disease and myasthenia gravis.
• Hypersensitivities and allergic reactions are also a part of immune system disorders. Here the system responds inappropriately to harmless compounds for example in asthma and allergies or may respond too aggressively for example in anaphylaxis reactions.