T lymphocyte and natural killer cell

The entry "T-lymphocytes and NK-cells" refers collectively to two distinct types of immune effector cells—**T lymphocytes** (T cells) and **natural killer (NK) cells**. Both are classified as lymphocytes but differ fundamentally in their origin, activation mechanisms, molecular markers, and roles within the immune system. **T lymphocytes**, also known as T cells, are central components of the adaptive immune system. They require antigen-specific activation via presentation on major histocompatibility complex (MHC) molecules by antigen-presenting cells. There are several subtypes including cytotoxic T cells that kill infected or malignant host cells directly, helper T cells that coordinate other aspects of immunity through cytokine secretion, regulatory T cells that suppress excessive responses to prevent autoimmunity, and memory T cells for long-term immunity[5]. **Natural killer (NK) cells**, in contrast, belong to the innate immune system. They do not require prior sensitization or antigen-specific activation; instead they recognize stressed or abnormal self-cells—such as virus-infected or tumorigenic targets—primarily by detecting changes in MHC class I expression. Their killing is mediated through release of perforin/granzymes leading to apoptosis in target tissues[2][3][4]. NK cell activity is regulated by a balance between activating receptors recognizing stress ligands on target surfaces and inhibitory receptors binding self-MHC I molecules[2][3]. Additionally, they secrete cytokines such as IFN-gamma which modulate both innate and adaptive responses—including influencing differentiation/activation of certain subsets of T lymphocytes[1][6]. While both play critical roles in defense against infection and cancer—and interact functionally—the term "T‑lymphocytes and NK‑cells" does not refer to a single molecular entity but rather two separate cellular populations with overlapping yet distinct functions within immunology. Because this entry describes **two different classes of immune effector cell types rather than a specific molecule/receptor**, it is considered incorrect for use as a canonical therapeutic target name under standard conventions for drug discovery databases. ---

Other names

T cell and NK cellT-lymphocyte and NK-cellcytotoxic lymphocytes (collective term)