Human body is continuously exposed to various micro-organisms which can cause disease. Ability of human body to defend against diseases caused by micro-organisms and other agents is known as immunity and the system of this defense is known as immune system. Immunity is of 2 types: innate (non-specific) or inborn and acquired (specific) or one which develops after birth. Innate immunity is represented by various natural barriers such as skin, acidic environment (sweat and gastric fluid), fever (raised temperature), release of chemicals such as histamine at the site of inflammation (red hot swelling) and cellular responses. Cells such as macrophages engulf and destroy microbes. Human body has natural killer cells too. Acquired immunity can be passive (mother-to-child, passive immunization) or active (active immunization or contracting a disease).

White cells in our blood are responsible for acquired immunity. White cells are of 5 different types. Monocytes and neutrophils form the initial lines of defense. Eosinophils and basophils are involved in allergic responses. Lymphocytes are cells of acquired immunity. T lymphocytes form cell-mediated immune system which defends the body against micro-organisms and tumor cells. B lymphocytes are mainstay of humoral immune system which comprises of antibodies directed against micro-organisms and other non-self elements. T cells are thus soldiers of this battle whereas antibodies produced by B cells are the weapons. Acquired immune mechanism has specific ability to recognize and differentiate vast variety of foreign molecules and save this ability as memory cells for ever.
Antigens are substances that are foreign to our body and can be toxins, micro-organisms, cancer cells or cells of transplanted organs. An antigen elicits immune response which includes formation of antibodies by B cells. Antigen and antibody interlock with each other to form antigen-antibody complex which helps in detoxification and removal of the antigen.
Our immune system can also differentiate between our own cells or tissues and foreign particles or invaders. Recognizing self and avoiding response to own tissues is known as autoimmunity. This inertness is also known as immune tolerance. Failure of immune tolerance can result in one or more of over 100 autoimmune diseases. Regulatory systems fail and autoantibodies are formed which attack normal cells. The damage thus caused is known as autoimmune disease. The situation here is like war between Kaurvas and Pandavas – members of the same house fighting with each other. Biting by your own dog is also a similar example. Many rheumatologic diseases such as Systemic Lupus Erythematosus, scleroderma, Sjogren’s syndrome and rheumatoid arthritis are classified as systemic autoimmune diseases. They affect many systems of our body at the same time.
Autoimmune diseases affect women more frequently than men and are known to run in families. Various environmental factors, micro-organisms and physical or psychological stress are implicated in triggering autoimmune reactions in these diseases. Diagnosis is often delayed and management requires specialized rheumatology care. Some drugs suppress immune system, control disease and preserve organ function. Many new high-end drugs are now available as a result of continuous research in this field. These drugs control diseases well but do not cure them. Treatment must, therefore, continue throughout life. A healthy life style, balanced nutritious diet, regular physical exercise, enough rest, reduction of stress and quitting of smoking are all important in management of these diseases.