Qualification In Immunohistochemistry (QIHC) Practice Exam

The immune response is finely balanced by regulatory mechanisms, and the subset that suppresses immune activity is the regulatory T cell, often described as suppressor T cells. These cells act to dial down activation of other T cells and effector responses after an infection or challenge, helping prevent excessive inflammation and autoimmunity. They can dampen responses through direct cell-to-cell interactions and by releasing inhibitory cytokines such as IL-10 and TGF-β, and they typically express markers like FOXP3 (with CD4 and CD25 in humans). In tissue studies, FOXP3+ cells within the CD4+ T cell population point to regulatory/suppressor activity. The other T cell types have opposite roles: helper T cells coordinate and amplify responses, cytotoxic T cells kill infected or malignant cells, and B cells produce antibodies. Therefore, the suppressor (regulatory) T cell is the one responsible for dampening immune responses.