Asthma-related SNP in FCER2 is associated with increased expression of IL-4R on human B cells

PTGDR expression is upregulated through retinoic acid receptors (RAR) mechanism in allergy

Functional studies suggest that promoter polymorphisms of the Prostaglandin D Receptor (PTGDR) gene can be involved in asthma. All-trans Retinoic acid (ATRA) has also been linked to allergic diseases. We have previously described the PTGDR promoter activation mediated by ATRA through response elements (RARE) at position -549T> C. In this study we aimed to analyze the effect of retinoic acid (RA) on the expression of PTGDR, the production of cytokines as well as to evaluate the binding of RA receptors to RA-Response Elements (RARE) sequences. A549 cells were transfected with vectors carrying different PTGDR haplotypes and treated with all-Trans Retinoic Acid (ATRA). PTGDR expression was measured by qPCR. Chromatin Immunoprecipitation assays (ChIP) were performed in ATRA stimulated KU812 cells and in PBMCs of patients carrying CTCT, CCCC or CCCT haplotypes. In addition, a broad panel of cytokines was analyzed by cytometric bead assay in A549 cells. The expression of PTGDR increased in A549 cells transfected with PTGDR-variants. The CCCC haplotype showed a significantly higher expression compared with CTCT. However, we found that RA up-regulated PTGDR expression through RARα mainly in the CTCT variant. Experiments on PBMCs from allergic patients carrying the -549T and -549C variant of the PTGDR promoter after ATRA and RAR antagonist administration confirmed the modulation of PTGDR by ATRA. The cytokine analysis showed that IL4 and IL6 levels were significantly increased in A549 cells transfected with PTGDR. In addition, ATRA treatment decreased the levels of IL4, IL6 and TNFα in A549 cells, whereas it increased IL4 and TNFα levels in PTGDR-transfected cells. We observed genetic differences in the regulation of PTGDR by ATRA that could contribute to the phenotypic differences observed in allergic patients. Our findings showed that RAR modulation by PTGDR might have an impact on Th2 responses, suggesting that RAR could be a potential therapeutic target in allergic inflammation.

A novel recycling mechanism of native IgE-antigen complexes in human B cells facilitates transfer of antigen to dendritic cells for antigen presentation

BACKGROUND

IgE-immune complexes (IgE-ICs) have been shown to enhance antibody and T-cell responses in mice by targeting CD23 (FcεRII), the low-affinity receptor for IgE on B cells. In humans, the mechanism by which CD23-expressing cells take up IgE-ICs and process them is not well understood.

OBJECTIVE

To investigate this question, we compared the fate of IgE-ICs in human B cells and in CD23-expressing monocyte-derived dendritic cells (moDCs) that represent classical antigen-presenting cells and we aimed at studying IgE-dependent antigen presentation in both cell types.

METHODS

B cells and monocytes were isolated from peripheral blood, and monocytes were differentiated into moDCs. Both cell types were stimulated with IgE-ICs consisting of 4-hydroxy-3-iodo-5-nitrophenylacetyl (NIP)-specific IgE JW8 and NIP-BSA to assess binding, uptake, and degradation dynamics. To assess CD23-dependent T-cell proliferation, B cells and moDCs were pulsed with IgE-NIP-tetanus toxoid complexes and cocultured with autologous T cells.

RESULTS

IgE-IC binding was CD23-dependent in B cells, and moDCs and CD23 aggregation, as well as IgE-IC internalization, occurred in both cell types. Although IgE-ICs were degraded in moDCs, B cells did not degrade the complexes but recycled them in native form to the cell surface, enabling IgE-IC uptake by moDCs in cocultures. The resulting proliferation of specific T cells was dependent on cell-cell contact between B cells and moDCs, which was explained by increased upregulation of costimulatory molecules CD86 and MHC class II on moDCs induced by B cells.

CONCLUSIONS

Our findings argue for a novel model in which human B cells promote specific T-cell proliferation on IgE-IC encounter. On one hand, B cells act as carriers transferring antigen to more efficient antigen-presenting cells such as DCs. On the other hand, B cells can directly promote DC maturation and thereby enhance T-cell stimulation.

FCER2 (CD23) asthma-related single nucleotide polymorphisms yields increased IgE binding and Egr-1 expression in human B cells

CD23 is the low-affinity Fc receptor for IgE. When expressed on B cells, CD23 appears to play a role in regulation of IgE synthesis. Polymorphisms within FCER2, the gene encoding CD23, have been associated with atopy, increased risk of exacerbations in patients with asthma, and high serum IgE levels. A single-nucleotide polymorphism (rs2228137) present in exon 4 of FCER2 encodes a nonsynonymous amino acid change (R62W) and is the subject of the present analysis. Human B cell stable transfectants were established to characterize the functional relevance of the R62W SNP. We demonstrate that CD23b-R62W-expressing human B cells bind IgE with greater affinity than wild-type cells and display differences in kinetics of CD23-mediated ERK1/2 activation that may be responsible for the increased levels of Egr-1 mRNA observed after stimulation through CD23. Finally, the R62W SNP seems to alter the tertiary or quaternary structure of CD23 because in the absence of N-glycosylation the CD23b-R62W-expressing cells appear to be less sensitive to endogenous proteases. These observations may have implications in mechanisms responsible for the atopic phenotypes observed in patients with asthma who possess this genotype.

A role of FCER1A and FCER2 polymorphisms in IgE regulation

BACKGROUND

Both FCER2 and FCER1A encode subunits of IgE receptors. Variants in FCER1A were previously identified as major determinants of IgE levels in genome-wide association studies.

METHODS

Here we investigated in detail whether FCER2 polymorphisms affect IgE levels alone and/or by interaction with FCER1A polymorphisms. To cover the genetic information of FCER2, 21 single-nucleotide polymorphisms (SNPs) were genotyped by Illumina HumanHap300 BeadChip (5 SNPs) and the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS; 14 SNPs) in at least 1303 Caucasian children (651 asthmatics) (ISAAC II/ MAGICS population); genotypes of two SNPs were imputed.

RESULTS

SNP rs3760687 showed the most consistent effect on total serum IgE levels (b [SE] = -0.38 [0.16]; P = 0.016), while FCER2 polymorphisms in general were predominantly associated with mildly-to-moderately increased IgE levels (50th and 66th percentiles). Gene-by-gene interaction analysis suggests that FCER2 polymorphism rs3760687 influences IgE levels mainly in individuals not homozygous for the risk allele of FCER1A polymorphism rs2427837, which belongs to the major IgE-determining tagging bin in the population.

CONCLUSION

FCER2 polymorphism rs3760687 affects moderately elevated total serum IgE levels, especially in the absence of homozygosity for the risk allele of FCER1A SNP rs2427837.