What type of hypersensitivity is characterized by Hashimoto's thyroiditis?

Hashimoto's thyroiditis is classified as a Type IV hypersensitivity reaction, which is characterized by cell-mediated immune responses rather than antibody-mediated ones. In this autoimmune condition, the immune system attacks the thyroid gland, leading to inflammation and ultimately hypothyroidism.

In Type IV hypersensitivity, T lymphocytes (particularly CD4+ T-helper cells and CD8+ cytotoxic T cells) play a central role. Their activation leads to the recruitment of other immune cells, causing tissue damage. In the case of Hashimoto's thyroiditis, the body produces autoantibodies against thyroid peroxidase and thyroglobulin, but the primary damage is driven by the cellular immune response rather than antibodies.

This understanding distinguishes Hashimoto's from other types of hypersensitivity. For instance, Type I hypersensitivity involves IgE-mediated allergic responses, Type II hypersensitivity is characterized by antibody-mediated attacks on specific cell types or tissues, and Type III involves immune complexes that can lead to inflammation and tissue damage. Therefore, the involvement of T cells and cellular mechanisms in Hashimoto's thyroiditis aligns it with Type IV hypersensitivity.