The anti-FcepsilonRI antibody MAR-1 depletes basophils and cross-reacts with myeloid cells through its Fc portion.

Worrall WPM*, Kamphuis JBJ*, Stackowicz J, Mougel A, Maure E, Pecalvel C, et al

Allergy. 2022; 00:1–4.

MAR-1 is the only monoclonal antibody used to label the IgE FceRI receptor in mice. This clone is also used in vivo to deplete basophils. We verified that MAR-1 marks mast cells and basophils through its interaction with FceRI. However, we show that MAR-1 also recognizes myeloid cells such as monocytes and macrophages in an FceRI-independent manner, by engaging IgG receptors (FcgRI and FcgRIV) through its Fc portion. Indeed, a recombinant “Fc silent” version of MAR-1 only recognizes basophils and mast cells. Strikingly, basophil depletion is also mediated by the Fc portion of MAR-1. Our results demonstrate that the expression of FceRI is restricted to mast cells and basophils in mice, and call into question the whole body of literature based on the use of MAR-1 in vivo.

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