2F1 antigen, the mouse homolog of the rat "mast cell function-associated antigen", is a lectin-like type II transmembrane receptor expressed by natural killer cells

Inhibitory lectin-like receptors expressed on the surface of hematopoietic cells are critically involved in regulation of their effector functions. He re we report that a novel mAb specific for mouse NK cells, 2F1, recognizes the mouse homolog of the mast cell function-associated antigen (MAFA), an i nhibitory lectin-like transmembrane receptor expressed on rat mast cells. T he 2F1 antigen (2F1-Ag) and rat MAFA are structurally highly conserved and contain a cytoplasmic motif similar to the immunoreceptor tyrosine-based in hibitory motif that is presumably utilized for inhibitory signaling. We als o identified a human homolog that is closely related to the rodent MAFA/2F1 -Ag proteins. Like rat MAFA, 2F1-Ag is probably encoded by a single gene, w hich exhibits relatively little polymorphism. Strikingly, while rat MAFA is considered a mast cell antigen, we have been unable to detect cell surface expression of 2F1-Ag by mouse mast cell lines, bone marrow-derived mast ce lls, or peritoneal mast cells. Furthermore, mouse bone marrow-derived mast cells were devoid of 2F1-Ag mRNA. Instead, we find that approximately 40 % of mouse NK cells express 2F1-Ag. Thus, MAFA/2F1-Ag may modulate immunologi cal responses on at least two different cell types bridging the specific an d innate immune system.