CD3/CD4/CD8

CD3, CD4 and CD8 are surface proteins on T lymphocytes. CD3 is part of the T‑cell receptor complex on all mature T cells and mediates activation. CD4 marks helper T cells that coordinate immune responses and assist B cells; they are primary HIV targets. CD8 marks cytotoxic T cells that recognize and kill virus‑infected or malignant cells.

The CD3, CD4 and CD8 test measures T‑lymphocyte subsets in blood using flow cytometry. CD3 identifies total T cells; CD4 marks helper T cells; CD8 marks cytotoxic T cells, and the test also reports the CD4/CD8 ratio. It’s used to assess immune function—monitor HIV and antiretroviral therapy, diagnose immunodeficiencies, evaluate immune suppression after transplant or chemotherapy, and investigate lymphoproliferative disorders.

CD3 is a pan‑T‑cell marker expressed on the surface of mature T lymphocytes as part of the T‑cell receptor–CD3 complex. It identifies all T‑cell subsets (including CD4+ and CD8+), is used in immunophenotyping and diagnostics, and plays a central role in T‑cell activation and signal transduction through its CD3 subunits (γ, δ, ε, ζ).

CD4+/CD3+ refers to T lymphocytes expressing both CD3 (a pan‑T‑cell receptor complex marker) and CD4 (a co‑receptor on helper T cells). These are helper T cells that coordinate immune responses by recognizing antigen‑MHC II, secreting cytokines, and aiding B cells and cytotoxic T cells. CD4+/CD3+ counts are used clinically to monitor immune status, especially in HIV and immunodeficiency assessment.

CD3 (cluster of differentiation 3) is also known as the T‑cell co‑receptor or the T‑cell receptor (TCR)–associated CD3 complex. It is a multisubunit membrane protein (CD3γ, CD3δ, CD3ε, CD3ζ) that associates with the TCR on T lymphocytes and transmits activation signals after antigen recognition, playing a central role in T‑cell development, activation, and immune responses.

The four main types of T cells are: helper T cells (CD4+), which coordinate immune responses; cytotoxic T cells (CD8+), which kill infected or cancerous cells; regulatory T cells (Tregs), which suppress excessive immune activity and maintain tolerance; and memory T cells, which persist after infection to provide faster, stronger responses on re‑exposure.