Enhanced plasmacytoid dendritic cell antiviral responses after omalizumab

Abstract

Background: Atopy and viral respiratory tract infections synergistically promote asthma exacerbations. IgE cross-linking inhibits critical virus-induced IFN-α responses of plasmacytoid dendritic cells (pDCs), which can be deficient in patients with allergic asthma.

Objective: We sought to determine whether reducing IgE levels in vivo with omalizumab treatment increases pDC antiviral IFN-α responses in inner-city children with asthma.

Methods: PBMCs and pDCs isolated from children with exacerbation-prone asthma before and during omalizumab treatment were stimulated ex vivo with rhinovirus and influenza in the presence or absence of IgE cross-linking. IFN-α levels were measured in supernatants, and mRNA expression of IFN-α pathway genes was determined by using quantitative RT-PCR (qRT-PCR) in cell pellets. FcεRIα protein levels and mRNA expression were measured in unstimulated cells by using flow cytometry and qRT-PCR, respectively. Changes in these outcomes and associations with clinical outcomes were analyzed, and statistical modeling was used to identify risk factors for asthma exacerbations.

Results: Omalizumab treatment increased rhinovirus- and influenza-induced PBMC and rhinovirus-induced pDC IFN-α responses in the presence of IgE cross-linking and reduced pDC surface FcεRIα expression. Omalizumab-induced reductions in pDC FcεRIα levels were significantly associated with a lower asthma exacerbation rate during the outcome period and correlated with increases in PBMC IFN-α responses. PBMC FcεRIα mRNA expression measured on study entry significantly improved an existing model of exacerbation prediction.

Conclusions: These findings indicate that omalizumab treatment augments pDC IFN-α responses and attenuates pDC FcεRIα protein expression and provide evidence that these effects are related. These results support a potential mechanism underlying clinical observations that allergic sensitization is associated with increased susceptibility to virus-induced asthma exacerbations.

Keywords: FcεRα; IFN-α; IgE; Plasmacytoid dendritic cells; asthma; omalizumab; rhinovirus.

FIG 1

Enhanced PMBC and pDC IFN-α responses after omalizumab. PBMC and pDC IFN-α responses to rhinovirus (RV) and influenza virus (FLU) significantly increased during the intervention phase of the study in the omalizumab group. Bars represent geometric mean IFN-α concentrations (in picograms per milliliter) measured in supernatants. Ratio of geometric means comparing postintervention versus preintervention values within each group are annotated above the bars, along with associated 95% CIs. Boldface indicates a P value of less than .05, as determined by using the paired t test. A, A 2.06-fold increase in PBMC IFN-α response to rhinovirus plus IgE cross-linking (P = .01). B, A 1.57-fold increase in PBMC IFN-α response to influenza virus plus IgE cross-linking (P = .02). C, A 4.15-fold increase in pDC IFN-α response to rhinovirus plus IgE cross-linking (P = .003) was observed between prerandomization (green bars) and postrandomization (blue bars) values in the omalizumab group.

FIG 2

Loss of pDC FcεRIα surface expression is associated with restoration of IFN-α responses and decreased exacerbations. A, pDC surface FcεRIα expression is expressed as mean equivalent soluble fluorochrome values in the omalizumab group (represented in pink) and placebo group (represented in blue). Points represent geometric mean values at corresponding time points; vertical segments cover the 95% CI around the geometric mean. B, Correlation between change in IFN-α level and change in pDC FcεRIα surface expression in the omalizumab group. IFN-α levels were measured in PBMC (left) or pDC (right) supernatants after stimulation with anti-IgE plus rhinovirus; pDC FcεRIα expression was measured in unstimulated cells. Change is calculated as a log difference. Blue line and shading represent a linear model fit and its 95% CI. C, Proportion of exacerbations in the omalizumab group is associated with FcεRIα change. Bars represent the proportion of exacerbations during the study for each group (less than and greater than the median level of change in FcεRIα), and error bars represent SEs. Numbers annotated on the bars represent the number of subjects. Odds ratios, associated 95% CIs, and P values are annotated above the bars.