The Mar-1 monoclonal antibody binds to the Fc ε Receptor I α subunit (FceR1a), which is a transmembrane glycoprotein from the immunoglobulin superfamily. FceR1a lacks signal-transducing ability and is expressed by mast and basophil cells.

The Fc ε Receptor I α subunit is upregulated by IgE and forms a tetramer with a beta subunit and two gamma subunits, which have ITAM (immunoreceptor tyrosine-based activation motifs). The complex formed by the four subunits has very important roles in the IgE-facilitated allergic reactions.