CD4s

CD4s, or CD4+ T cells, are a type of white blood cell critical to the immune system. They are a subset of lymphocytes, specifically T lymphocytes, which play a central role in cell-mediated immunity. The name "CD4" refers to the cluster of differentiation (CD) antigen CD4, a glycoprotein found on the surface of these cells that serves as a co-receptor for the T-cell receptor (TCR). This interaction is essential for the activation of T cells by antigen-presenting cells, such as dendritic cells, macrophages, and B cells.

CD4+ T cells are classified into several subtypes based on their function and the cytokines they produce. Helper T cells (Th cells) are the most well-known subtype, which further differentiate into Th1, Th2, Th17, and regulatory T cells (Tregs). Th1 cells primarily produce interferon-gamma (IFN-γ) and are involved in combating intracellular pathogens like viruses and certain bacteria. Th2 cells secrete interleukin-4 (IL-4), IL-5, and IL-13, and are key in combating extracellular parasites and promoting antibody production. Th17 cells produce interleukin-17 (IL-17) and are involved in autoimmune diseases and defense against some bacterial infections. Regulatory T cells (Tregs) secrete anti-inflammatory cytokines like IL-10 and TGF-β, helping to maintain immune tolerance and prevent autoimmune responses.

CD4+ T cells are also a primary target of the human immunodeficiency virus (HIV). HIV infects and destroys CD4+ T cells, leading to a progressive decline in immune function known as acquired immunodeficiency syndrome (AIDS). Monitoring CD4+ T cell counts is a standard practice in the diagnosis and management of HIV infection, as it provides an indicator of immune status and disease progression.

In summary, CD4+ T cells are vital components of the adaptive immune system, coordinating immune responses and maintaining immune homeostasis. Their dysfunction or depletion can lead to severe immune deficiencies and susceptibility to infections.