CD49b, also known as integrin alpha 2, is a protein that plays a significant role in the immune system, particularly in the function of natural killer (NK) cells. It is a component of the integrin family, which are cell surface receptors involved in cell adhesion and migration. CD49b pairs with CD29 (Integrin beta 1) to form the heterodimeric integrin VLA-2 (integrin alpha 2 beta 1, or GPIa/IIa) complex. This complex serves as an extracellular receptor for laminin, collagen, and fibronectin, and its interaction with these ligands activates intracellular signaling pathways. In the context of NK cells, CD49b is used as a marker for the identification and characterization of these cells. In mice, CD49b (clone DX5) is a common marker used to define NK cells, along with NK1.1 and NKP46. The choice of marker can depend on the mouse strain, as NK1.1 is not expressed in certain strains such as AKR, BALB/c, CBA/J, and others, while CD49b is more widely expressed across different strains. CD49b is also expressed on other immune cells, including a subset of T cells, monocytes, platelets, and epithelial cells. It has been implicated in various biological processes such as cell adhesion, lymphocyte activation, and angiogenesis. The expression of CD49b on the surface of cells can influence their behavior and interaction with the microenvironment. Recent studies have also explored the prognostic significance of CD49b in cancer. Overexpression of CD49b has been associated with poor survival rates in several types of cancer, including lung cancer.