The immune system is generally divided into two different categories: innate immunity and acquired immunity.
All humans are born with innate immunity that provides the early line of defence against microbes/pathogens. Innate immunity is nonspecific and it comes into play immediately after an antigen's appearance in the body. An antigen is a foreign substance which induces an immune response in the body. It may be a substance from the environment, such as bacteria, viruses, chemicals or pollen. Innate immunity consist of the following:
· Skin: Physical barrier that prevents microbes and pathogens from entering the body.
· Saliva: Rinses of teeth and mouth.
· Enzymes: Present in tears and skin oils and kill pathogens and other microbes.
· Mucous membranes: Found in the nose and mouth. These membranes trap microbes such as viruses and bacteria.
· Gastric acid: Present in the stomach that kills microbes in ingested food.
The immune system uninterruptedly monitors antigens on the surface of all cells. The acquired immune system encounters foreign invaders (pathogens and microbes) and recognizes antigens. Thereupon, the different components of the acquired immune system learn the best way to attack each antigen and begin to develop a memory for that antigen. This immune response can cause inflammation. Inflammation can be defined as the process by which the body's white blood cells protect the body from infection caused by foreign invaders.
Allergies and the Immune System Allergic reactions begin in the immune system. Allergies are caused by the immune system responding too strongly to something that is usually harmless. Diseases of the Immune System
An autoimmune disease is a condition in which the immune system mistakenly attacks the body or a part of the body as an alien invader and triggers an immune response. Rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis and psoriasis are all examples of autoimmune diseases.