CD8 (Suppressor T Cell Marker)

The defining marker for CD8 T cells is the CD8 glycoprotein, typically an alpha–beta heterodimer expressed on cytotoxic T lymphocytes. CD8 acts as a co-receptor binding MHC class I on target cells, commonly identified immunophenotypically as CD3+ CD8+. These cells mediate cytotoxic responses using perforin and granzymes to kill infected or malignant cells.

CD8 suppressor T cells (CD8+ regulatory T cells) are a heterogeneous subset of CD8+ lymphocytes that downregulate immune responses and maintain tolerance. They limit autoreactive and excessive immune activity by direct cytotoxicity against antigen-presenting cells, by cell–cell contact, or by secreting inhibitory cytokines such as IL-10 and TGF-β. They help control inflammation, viral immunity, and prevent autoimmunity.

High CD8 (suppressor) means an increased number or activity of CD8+ T lymphocytes—cells that kill infected or abnormal cells and can downregulate immune responses. This often reflects immune activation from recent or chronic infection, inflammation, or immune dysregulation (including some cancers). It’s not diagnostic alone; clinical context, symptoms and further tests are needed, so discuss results with your clinician.

CD27 is a TNF-receptor family surface protein expressed on T cells that functions as a costimulatory molecule. It marks naive and memory T-cell populations and supports survival, proliferation and differentiation after activation. High CD27 expression identifies less-differentiated or central memory T cells, whereas loss of CD27 is associated with terminally differentiated effector T cells.

Yes — CD8+ T cells express CD45, a pan-leukocyte transmembrane tyrosine phosphatase (PTPRC). All mature T lymphocytes are CD45-positive; isoforms differ by activation/memory status (naive T cells often CD45RA, memory T cells CD45RO). CD45 regulates T-cell receptor signaling and is used as a marker to identify and subset T cells. This is routinely applied in immunophenotyping and flow cytometry.

CD25 is the alpha chain of the interleukin‑2 receptor and marks T‑cell activation and regulatory T cells (commonly CD4+CD25+FoxP3+). It’s also found on activated B cells, NK cells and some dendritic cells, and is used diagnostically in certain hematologic malignancies (for example, adult T‑cell leukemia/lymphoma). High, persistent CD25 expression indicates regulatory or activated immune states.