Final answer:
Suppressor T cells, also known as regulatory T cells, are the lymphocyte subtype that controls autoimmunity in peripheral blood, preventing the immune system from attacking the body's own tissues.
Step-by-step explanation:
The lymphocyte subtype that controls autoimmunity in peripheral blood is the suppressor T cells. These are a type of T cell also known as regulatory T cells. The suppressor T cells are involved in deactivating other T cells and B cells when necessary, preventing the immune response from becoming overly intense and resulting in autoimmunity. These cells play a critical role in maintaining immune homeostasis and self-tolerance, ensuring that the immune system does not attack the body's own tissues. T cells consist of different types, including cytotoxic, helper, and suppressor (regulatory) T cells. While each type has a distinct function, it is the suppressor or regulatory T cells that are essential in controlling autoimmunity.