CD8Tceller

CD8Tceller, commonly referred to as CD8+ T cells, are a subset of T lymphocytes that express the CD8 co-receptor and recognize peptide antigens presented by MHC class I molecules on nearly all nucleated cells. They form a central component of cell-mediated immunity, particularly against intracellular pathogens such as viruses and certain intracellular bacteria, as well as against transformed or cancerous cells.

Development and activation begin in the thymus, where naive CD8+ T cells express the T cell receptor (TCR) and CD8. Activation requires recognition of peptide–MHC I complexes by the TCR on professional antigen-presenting cells, in conjunction with co-stimulatory signals (for example, CD28 binding CD80/86) and cytokines such as IL-2. This leads to clonal expansion and differentiation into effector CTLs and memory CD8+ T cells that provide rapid responses on re-exposure to the antigen.

Effector CD8+ T cells eliminate target cells primarily through cytotoxic mechanisms. They release perforin and granzymes contained in lytic granules to induce apoptosis in infected or malignant cells. They can also engage death receptor pathways (for example, FasL–Fas) and secrete cytokines such as interferon-gamma (IFN-γ) and TNF-α to modulate the immune response and hinder pathogen replication.

Subsets include effector CTLs, central and effector memory CD8+ T cells, and tissue-resident memory T cells (Trm). Chronic antigen exposure can lead to exhaustion, marked by inhibitory receptor expression (e.g., PD-1, LAG-3) and diminished effector function.

Clinically, CD8+ T cells are central to cancer immunotherapy and vaccination strategies. Therapies such as adoptive cell transfer and checkpoint inhibitors seek to enhance CD8+ T cell responses against tumors or infections, underscoring the importance of their regulation in health and disease.