Omalizumab inhibits human mast cell responses by sequestering pre-bound IgE (64.6)

Abstract Mast cells are key effectors of allergic inflammation. IgE-mediated mast cell activation induces degranulation and inflammatory mediator release. Omalizumab (Xolair; Genentech Inc.) is a recombinant humanized monoclonal anti-IgE antibody that prevents IgE binding to its receptor, FcϵRI. Objective: We investigated the effects of omalizumab on IgE pre-sensitized human LAD2 mast cells. Methods: LAD2 degranulation was determined by β-hexosaminidase assay. Chemokine expression and prostaglandin synthesis was measured by quantitative PCR analysis and ELISA, respectively. IgE binding and FcϵRI expression was determined by flow cytometry. Results: Omalizumab pretreatment inhibited IgE binding to LAD2 cells and entirely prevented IgE-dependent upregulation of FcϵRI expression. In addition, omalizumab removed FcϵRI-prebound IgE as early as 24 hrs after treatment. After 5 days, bound IgE was reduced by 92%. Furthermore, omalizumab concomitantly reversed IgE-dependent FcϵRI upregulation by 49% 48 hrs post treatment and by 93% 5 days post treatment. Consequently, omalizumab attenuated ongoing IgE-mediated responses, reducing degranulation by 34%, chemokine expression up to 79% and prostaglandin synthesis by 34% after 7 days of omalizumab treatment. Conclusions: Omalizumab is able to remove pre-bound IgE from sensitized mast cells thereby reducing ongoing response to FcϵRI-dependent signals. This data suggests that omalizumab is an effective inhibitor of sensitized human mast cells.