FcεRI expression and IgE binding by dendritic cells and basophils in allergic rhinitis and upon allergen immunotherapy

BACKGROUND

In humans, both basophils and dendritic cells (DCs) express the high-affinity IgE receptor (FcεRI).

OBJECTIVE

To gain more insight into the relation between serum IgE levels and FcεRI expression and IgE binding by DCs and basophils in house dust mite (HDM) allergy and during subcutaneous immunotherapy (SCIT).

METHODS

We measured FcεRI, IgE and HDM allergen on DCs (conventional type 2 DCs, cDC2s; plasmacytoid dendritic cells, pDCs) and basophils by flow cytometry in 22 non-allergic vs 52 allergic subjects and upon HDM SCIT in 28 allergic subjects. IgE levels were measured in serum.

RESULTS

Serum IgE correlated differentially with FcεRI expression and IgE binding depending on cell type and allergic status. In non-allergic subjects, FcεRI/IgE surface densities increased with serum IgE to a significantly stronger degree on basophils compared to cDC2s. By contrast, in allergic subjects FcεRI/IgE surface densities increased with serum IgE to a slightly stronger degree on cDC2s compared to basophils. In addition, the data set suggests sequential loading of IgE onto FcεRI expressed by these cells (basophils>cDC2s>pDCs). Finally, HDM SCIT induced a temporary increase in serum IgE, which was paralleled by a peak in FcεRI and IgE on DCs, but not on basophils.

CONCLUSIONS & CLINICAL RELEVANCE

This study provides a comprehensive insight into the relation between serum IgE and FcεRI/IgE on basophils and DC subsets. The novel finding that HDM SCIT induces a temporary increase in FcεRI expression on DCs, but not on basophils, can be an incentive for future research on the potential tolerogenic role of IgE/FcεRI signalling in DCs in the setting of allergen immunotherapy.

Induction of interleukin-4 production in neonatal IgE+ cells after crosslinking of maternal IgE

Transfer of maternal IgE antibodies to the neonate with the colostrum has been described in different mammalian species. Previous work in horses has shown that IgE bound to the surface of neonatal basophils is solely of maternal origin. However, the functional role of the maternal IgE transfer remained unclear. We hypothesized that maternal IgE mediates the onset of innate IL-4 production in equine neonatal basophils. Intracellular IL-4 production was measured in PBMC of newborn and older foals by flow cytometric analysis. A small population of IL-4(+) cells was observed in the peripheral blood at days 3-5 after birth. Phenotyping of the IL-4(+) cells showed that they were IgE(+)/MHCII(low)/CD4(-) cells. Magnetic cells sorting of the IgE(+)/MHCII(low) cells identified them as basophils. Anti-IgE stimulation in vitro induced IL-4 in IgE(+)/MHCII(low) basophils, but not in MHCII(+) cells or cells collected before colostrum ingestion. In conclusion, stimulation via maternal IgE antibodies mediated innate IL-4 production in neonatal basophils which might provide a paragenetic mechanism to promote the development of adaptive T-cell responses in the neonate after birth.