Interleukin-2 Receptor, Soluble Unit Converter

Soluble interleukin-2 receptor (sIL-2R) is a fragment of the IL-2 receptor alpha chain (CD25) that is shed from the surface of activated immune cells into the bloodstream. The full IL-2 receptor sits on the surface of T cells and other immune cells, where it binds the signaling molecule interleukin-2 to regulate immune responses.

When T cells become activated, enzymes clip the alpha chain from the cell surface and release it into the blood. The rate of shedding is directly proportional to how actively the immune system is responding, making sIL-2R a quantitative marker of immune activation.

Healthy individuals have low, stable levels of sIL-2R in circulation. Elevated levels signal that the immune system is abnormally active, which can occur in infections, autoimmune diseases, certain cancers, and other inflammatory conditions.

sIL-2R is shed primarily by activated T lymphocytes (both CD4+ and CD8+), with smaller contributions from activated B cells, natural killer cells, and macrophages. Enzymes called metalloproteinases clip the receptor's alpha chain from the cell surface and release it into the bloodstream.