In type V hypersensitivity, what is the mechanism that leads to the overreaction of target cells?

Type V hypersensitivity, also known as antibody-mediated hypersensitivity, involves the production of autoantibodies that bind to specific receptors on target cells. This binding results in the abnormal activation of those cells, leading to an exaggerated physiological response.

In this case, the mechanism that leads to the overreaction of target cells is primarily through the autoantibodies that mimic natural ligands for receptors. For example, in conditions like Graves' disease, autoantibodies stimulate the thyroid-stimulating hormone (TSH) receptor, which causes the thyroid gland to produce excessive thyroid hormone.

This hypersensitivity response is distinct because it does not involve traditional inflammatory mediators such as histamines, nor does it require complement activation or eosinophil influx, which are more commonly associated with other types of hypersensitivity reactions. Instead, the primary action is through these self-targeting antibodies leading to direct cell activation and disruption of normal cellular function.