β2-microglobulin also B2MG, B2M is a serum protein found in association with the major histocompatibility complex (MHC) class I heavy chain on the surface of nearly all nucleated cells. This presentation is vital for the recognition of infected or malignant cells by CD8+ cytotoxic T lymphocytes, thereby facilitating an effective immune response. β2-Microglobulin is located on the cell surface, where β2-Microglobulin associates non-covalently with the heavy chain of MHC class I molecules, contributing to their stability and proper folding. Notably, the absence of β2-Microglobulin leads to a lack of mature CD4-8+ T cells, highlighting β2-Microglobulin′s importance in T cell development and function.