Q.Where could I find a list of all the autoimmune diseases? I read there are about 24 of them. Is that correct? Someone once told me I have an autoimmune disease, and I always wondered which one he was talking about. I have not seen this person since to ask him what he meant. I have been diagnosed with osteoarthritis and anemia. Are these immune diseases?

Judy

A.Autoimmune diseases are not typically thought of as infectious, but there are some cases when they may be. Long before birth, the immune system begins to develop. This disease-fighting system has to do battle with all the different infectious agents that it may encounter. To do this, immune system cells learn to distinguish different substances, mainly proteins. The immune response obviously is not perfect, given that death from infections can still occur, but it is adept at fighting most of the viruses and bacteria we encounter.

A.Antibodies are one of the immune system’s major infection-fighting tools. These remarkable proteins recognize distinct chemical structures called epitopes (usually portions of proteins) on viruses and bacteria. When the immune system encounters a new pathogen (disease-causing microbe), white blood cells called B cells produce antibodies directed against specific epitopes on the organism. These antibodies also interact with other cells, including white blood cells called T cells and a group of chemicals called the complement system, to help eradicate the threat. T cells, as well as natural killer cells, macrophages and other immune cells, can also act independently of antibodies to attack some pathogens.

How does the immune system distinguish the proteins that are pathogenic from those that are “self” and therefore should be left alone? In a very complex manner, each person develops tolerance to his or her own proteins and cells. This is why a person’s immune system does not attack his or her own blood cells, but it does quickly destroy transfused blood cells that are the wrong blood type.

A.As with any organ system, however, the immune system can become defective. Sometimes antibodies are formed that do attack “self” proteins — that is, proteins that are normal constituents of the body. In fact, there are probably always very small numbers of antibodies against self, but their activity does not cause any significant effect. But when antibodies and even cells with activity against self are present in significant numbers, an autoimmune disease can develop. The number you mentioned — 24 — seems like too low a number for all the autoimmune diseases that have been described, and I think it is pointless to try to name all of them.

Many of these diseases — such as lupus, rheumatoid arthritis, Sjogren’s syndrome and scleroderma — can cause joint problems. Several others, such as Goodpasture syndrome and Wegener’s disease, can cause kidney damage. Infectious diseases are thought to trigger some, if not most, autoimmune diseases. Rheumatic fever, caused by strep bacteria, occurs when antibodies that form to fight the strep also act on cells in the heart and joints. Certain forms of encephalitis can be triggered indirectly by viruses and even vaccines (such as the old rabies vaccine, which is no longer in use). Some investigators believe that multiple sclerosis develops in this same.

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