Dendritic cells (DCs) are important in the initiation of Th1 and Th2 responses. In humans, the high affinity IgE receptor, FceRI, is expressed by type 1 DCs (DC1), whereas expression by DC2 cells has not been previously reported. We sought 1.) to characterize FceRI expression on DC subpopulations and 2.) to determine if DC expression of FceRI is regulated by serum IgE.

FceRI expression by DCs was determined by flow cytometry. Study A examined 21 non-allergic healthy controls and 23 allergic asthmatic subjects. Study B was a clinical trial of 24 subjects with ragweed allergic rhinitis who received omalizumab (anti-IgE) or placebo.

Study A: FceRI was expressed by both DC1 and DC2 cells, and was found in both peripheral blood precursor DC (pDC) and mature tissue DC populations. FceRI expression by pDC1 and pDC2 cells was highly correlated to serum IgE and was significantly greater in subjects with allergic asthma compared to the non-atopic controls. Study B: Omalizumab treatment significantly decreased FceRI expression in both the pDC1 and pDC2 subsets (maximum decrease: 52% and 83%, respectively). The decrease in DC FceRI expression correlated with the drop in serum IgE.

FceRI is expressed by both the DC1 and DC2 subpopulations. The correlation of FceRI expression and serum IgE in Study A, and the drop in FceRI expression in Study B, support the conclusion that serum IgE is a major factor regulating DC expression of FceRI in vivo. These results suggest that FceRI expression by DC may be a useful therapeutic target.