The 2F1 monoclonal antibody is specific for the mouse Killer cell Lectin-like Receptor G1 (KLRG1), a homodimer consisting of two N-glycosylated subunits of 30-38 kDa, also known as MAFA (Mast cell Function-associated Antigen). The antigen contains a cytoplasmic motif similar to ITIM (the immunoreceptor tyrosine-based inhibitory motif). KLRG1 is a receptor for cadherin, a family of transmembrane glycoproteins that mediate cell adhesion, and a common marker of T cell senescence. The receptor is believed to play an important role in the innate and adaptive immune system through the regulation of leukocytes. It is expressed on lymphokine-activated killer (LAK) cells, adherent LAK (A-LAK) cells, a sub-set of natural killer (NK) cells, T cells. In NK cells, it inhibits cytokine production and cytotoxicity activity.

The receptor expression was not detected on the mouse peritoneal mast cells, or bone marrow mast cells.