Human Basophils Express the Glycosylphosphatidylinositol-Anchored Low-Affinity IgG Receptor FcγRIIIB (CD16B)

Basophils express not only high-affinity IgE receptors, but also low-affinity IgG receptors. Which, among these receptors, are expressed by human basophils is poorly known. Low-affinity IgG receptors comprise CD32 (Fc gamma RIIA, Fc gamma RIIB, and Fc gamma RIIC) and CD16 (Fc gamma RIIIA and Fc gamma RIIIB). Fc gamma RIIA, Fc gamma RIIC, and Fc gamma RIIIA are activating receptors, Fc gamma RIIB are inhibitory receptors, Fc gamma RIIIB are GPI-anchored receptors whose function is poorly understood. Basophils were reported to express Fc gamma RII, but not Fc gamma RIII We aimed at further identifying basophil IgG receptors. Basophils from normal donors and from patients suffering from an allergic skin disease (atopic dermatitis), allergic respiratory diseases (allergic rhinitis and asthma), or a non-allergic skin disease (chronic urticaria) were examined. We found that normal basophils contain Fc gamma RIII transcripts and express Fc gamma RIIIB, but not Fc gamma RIIIA, which were detected on 24-81% basophils from normal donors and on 12-100% basophils from patients. Noticeably, the proportion of Fc gamma RIIIB+ basophils was significantly lower in atopic dermatitis patients than in other subjects. This decreased Fc gamma RIII expression was not correlated with an activated phenotype of basophils in atopic dermatitis patients, although Fc gamma RIIIB expression was down-regulated upon basophil activation by anti-IgE. Our results challenge the two dogmas 1) that basophils do not express Fc gamma RIII and 2) that Fc gamma RIIIB is exclusively expressed by neutrophils. They suggest that a proportion of basophils may be lost during enrichment procedures in which Fc gamma RIII+ cells are discarded by negative sorting using anti-CD16 Abs. They unravel an unexpected complexity of IgG receptors susceptible to modulate basophil activation. They identify a novel systemic alteration in atopic dermatitis. The Journal of Immunology, 2009, 182: 2542-2550.