Immune Deficiencies And Excesses Both Occur.
A natural balance exists within the immune system between cells called helper and suppressor T-cells. In good health, antibodies are produced only when needed. Under certain conditions, for example an over-active adrenal gland (Cushingoid Syndrome in the dog) suppressor cells become dominant and the immune system is weakened. In this 'immune suppressed' state a dog is susceptible to secondary infections. The opposite is even more harmful. If helper T-cells dominate, the immune system becomes overactive and loses its ability to differentiate between normal cells in the body (called 'self') and real invaders. The immune system starts attacking its own body tissues, for example its own red blood cells. This is called either "auto-immune" or "immune-mediated" disease. For example, most dogs with underactive thyroid glands, a condition most common in cocker spaniels are suffering from an auto-immune disease. Their excess helper T-cells have attacked and destroyed their own thyroid glands. There is mounting evidence that other clinical conditions including certain forms of heart disease in breeds such as the Doberman are in fact auto-immune conditions. Finally, the immune system may become over sensitive, reacting to harmless substances such as flea saliva, dust mite droppings, plant pollens or foods. This is how allergic disorders develop.