The GL3 antibody reacts with the δ chain of the murine T cell receptor γ/δ (TCRγ/δ or TCR gamma/delta), a subtype of the TCR involved in the recognition of both peptide and lipid antigens. TCRγ/δ comprises a heterodimer (~ 80 kDa in humans) of disulfide-linked γ and δ subunits that associates with CD3 on the cell surface. It is a member of the immunoglobulin superfamily. TCRγ/δ is expressed on a subpopulation of T cells in the circulation but may be found on up to 50% of the T cells in epithelial cell-rich tissues. These cells have roles in oral and tumor-associated tolerance as well as autoimmune disease and have been described as a link between the adaptive and innate immune responses. Once activated, they secrete effector cytokines in a subtype- and context-specific manner. Most γ/δ T cells are CD4-/CD8-, though some express CD8. The GL3 antibody recognizes an epitope in the constant region of the δ chain and can reportedly activate TCRγ/δ+ cells.