CD8-positive T cell activation

CD8-positive T cell activation refers to the process by which naïve CD8+ T cells (also known as cytotoxic T lymphocytes, or CTLs) become activated in response to specific antigens. This activation is a critical component of the adaptive immune response, enabling these cells to recognize and eliminate infected or malignant cells. Naïve CD8+ T cells are activated when their T cell receptor (TCR) recognizes peptide antigens presented on major histocompatibility complex class I (MHC I) molecules on the surface of professional antigen-presenting cells (pAPCs), such as dendritic cells. The CD8 co-receptor binds to a region of MHC I distinct from the peptide-binding groove, stabilizing the interaction between the TCR and MHC I-peptide complex and enhancing signal transduction. Optimal activation requires additional signals from costimulatory molecules expressed by pAPCs, such as CD28 on the T cell binding B7 family members on APCs. Cytokines produced by pAPCs further promote proliferation and differentiation of activated CD8+ T cells into effector CTLs capable of killing target cells. Once activated, CD8+ T cells undergo clonal expansion and differentiate into effector CTLs that can induce apoptosis in target (infected or cancerous) cells via release of perforin and granzymes, Fas-FasL interaction, and secretion of cytokines. Activated CD8+ CTLs are essential for eliminating virus-infected host cells, destroying tumor/abnormal somatic cells, and contributing to immunological memory after infection clearance. Activation is tightly regulated and requires both antigen-specific stimulation and costimulatory/cytokine signals. Alternative/atypical activation pathways exist but are less common. After primary response resolution, most effector CTLs die via apoptosis; a subset persists as memory CD8+ T-cells for rapid future responses.

Other names

Cytotoxic T lymphocyte activationCTL activation