Relationship of age-specific incidence rates to immunological aspects of Hashimoto's thyroiditis.

Studies of the age-specific incidence rates of the appearance of Hashimoto's thyroiditis indicate that this disorder appears at random in a genetically preselected population. Following an initial lag in the first few years of life, the disease appears at a constant rate thereafter in this population.The age-specific incidence rates were similar to those previously reported for Graves' disease. Moreover, there is considerable evidence implicating cell-mediated immunity in both diseases, with the likelihood of cooperating humoral antibodies as well. It may be hypothesized that the two diseases are primarily due to genetic defects in immunological surveillance, which result in an inability to destroy or control a specific forbidden clone of thymicderived lymphocytes which may arise by normal random mutation. The T-lymphocyte interacts with its complementary antigen (on a hitherto normal thyroid cell), setting up a cell-mediated immune response; in addition it may cooperate with bursa-equivalent lymphocytes, which then produce humoral antibodies. It is possible that both cell-mediated immunity and humoral antibodies are necessary for the full expression of the disease.