Allergy and auto-immunity

Allergy is an exaggerated response of the immune system to certain antigens in the environment. The substances that trigger it are allergens, and the antibodies made against them are of the IgE type.

Common allergens: mites in dust, pollen and animal dander. They differ from place to place, which is why symptoms can start in a new place and vanish on leaving it.

Symptoms are sneezing, watery eyes, running nose and difficulty in breathing. They come from chemicals such as histamine and serotonin released by mast cells.

To find the cause, doctors expose the patient to tiny doses of suspected allergens, or inject them, and watch which one produces a reaction. Anti-histamines, adrenalin and steroids quickly reduce the symptoms.

Modern life style seems to have lowered immunity and raised sensitivity: more children in Indian metro cities suffer from allergies and asthma, possibly because of the protected environment they grow up in.

Memory-based acquired immunity evolved in higher vertebrates from the ability to tell foreign organisms from self cells; they can distinguish foreign molecules as well as foreign organisms.

Sometimes, for genetic and other unknown reasons, the body attacks its own cells. The damage that follows is an auto-immune disease; rheumatoid arthritis is an example.