Intensity of CD23 expression on IgG₁⁺ B cells reflects serum IgE level in asthma

Abstract

Background

IgE plays a key role in asthma pathogenesis. To produce high-affinity IgE, B cells can undergo IgE class switching through an IgG₁ intermediate stage with repeated antigenic stimulation. Nonetheless, the phenotype of B cells that holds IgE response in asthma patients remains to be fully investigated.

Objectives

We investigated whether IgG₁⁺ B cells reflect the magnitude of the IgE response and correlate with asthma phenotype and disease severities in adult asthma patients.

Methods

The frequencies of IgG₁⁺, CD23⁺, and CD23⁺IgG₁⁺ B cells, along with surface CD23 expression levels in the blood of adult asthma patients (n = 40), were compared with those of nonasthmatic control subjects (n = 24). We then investigated whether the frequencies of individual B-cell populations and their surface CD23 expression levels were linked to serum IgE concentrations, eosinophil counts, and lung functions. Additionally, we also investigated whether serum IgE could affect the frequencies of these B-cell populations in patients with moderate-to-severe asthma (n = 16).

Results

Serum IgE concentrations correlated with CD23 expression levels on CD23⁺IgG₁⁺ B cells, but not their numbers that were linked to blood eosinophil counts and lung functions (forced expiratory volume in 1 second). Neither the frequency of CD23⁺IgG₁⁺ B cells nor the CD23 expression levels were affected by steroid treatment or leukotriene inhibitors. Neutralizing IgE with omalizumab did not alter the frequency of CD23⁺, IgG₁⁺, or CD23⁺IgG₁⁺ B cells in asthma patients.

Conclusions

Surface CD23 expression levels on CD23⁺IgG₁⁺ B cells, but not their numbers, correlate with the magnitude of IgE response in adult asthma patients.

Introduction

B cells contribute to the pathogenesis of asthma by producing IgE in response to inhaled allergens. IL-4 can induce IgE class switching in activated mature B cells.¹ Once switched, the affinity of IgE can determine the fate of IgE⁺ B cells.²

IgE class switching can occur through an IgG₁ intermediate stage with repeated antigenic stimulation.³ This sequential class-switching process can generate high-affinity IgE⁺ B cells.^2,4 In a 2024 study, Koenig et al⁵ reported that IgG₁⁺ B cells expressing CD23 can become IgE-producing plasma cells. Another study showed that the frequency of CD23⁺ B cells was higher in peanut-allergic pediatric patients than nonallergic control subjects.⁶ Furthermore, the frequency of CD23⁺IgG₁⁺ B cells in the blood of allergic patients correlated with serum IgE concentration.⁶ Nonetheless, the roles of CD23 expressed on B cells in asthma remains unclear,^7,8 as it can either promote or control IgE production by B cells.^8,9 Therefore, the phenotype of B cells that can reflect the magnitude of IgE response in asthma remains to be fully investigated.

This study assessed the frequencies of CD23⁺, IgG₁⁺, and CD23⁺IgG₁⁺ B cells, along with surface CD23 expression levels, in the blood of adult asthma patients and compared them with those of nonasthmatic control subjects. We found that the magnitude of IgE responses in asthma patients correlated with the surface expression levels of CD23 on CD23⁺IgG₁⁺ B cells, but not with the frequency of CD23⁺IgG₁⁺ B cells, which was instead linked to the blood eosinophil count and lung function.

Results and discussion

Asthma patients have increased numbers of CD23⁺IgG₁⁺ B cells, but not CD23⁺ or IgG₁⁺ B cells

The increased frequency of CD23⁺ B cells in a cohort of pediatric peanut allergy patients has been previously reported.⁶ In addition, children with atopic dermatitis and pediatric patients (average age, 48.87 months) with mild-to-moderate asthma^10,11 also had increased CD23⁺ B cells that were associated with serum IgE concentration.⁸ Therefore, we tested whether adult asthma patients also had altered frequencies of CD23⁺, IgG₁⁺, and CD23⁺IgG₁⁺ B cells (see Fig E1 in the Online Repository available at www.jaci-global.org). Both the percentages of individual B-cell populations in total CD19⁺ B cells and actual numbers of these B-cell populations per 1 × 10⁶ peripheral blood mononuclear cells (PBMCs) were assessed.

We found that nonasthmatic control subjects and asthma patients had similar percentages of CD23⁺ (Fig 1, A, left), IgG₁⁺ (Fig 1, A, middle) and CD23⁺IgG₁⁺ B cells in total CD19⁺ B cells (Fig 1, A, right).

Fig 1.

Patients have increased numbers of CD23⁺IgG₁⁺ B cells associated with eosinophil counts and lung function. Percentages (A) and numbers (B) of CD23⁺, IgG₁⁺, and CD23⁺IgG₁⁺ B cells. Correlations (C) between numbers of CD23⁺, IgG₁⁺, and CD23⁺IgG₁⁺ B cells and serum IgE concentrations. Associations (D) between numbers of CD23⁺IgG₁⁺ B cells and eosinophil counts (left) and lung function (right).

The numbers of CD23⁺ (Fig 1, B, left) and IgG₁⁺ B cells (Fig 1, B, middle) per 1 × 10⁶ PBMCs were also similar across the two groups. Of interest, asthma patients had greater numbers of CD23⁺IgG₁⁺ B cells than nonasthmatic control subjects (Fig 1, B, right). However, the numbers of CD23⁺ (Fig 1, C, left), IgG₁⁺ (Fig 1, C, middle), or CD23⁺IgG₁⁺ B cells (Fig 1, C, right) did not correlate with serum IgE concentrations. We further found that the frequency of CD23⁺ (see Fig E2, A, in the Online Repository available at www.jaci-global.org) and CD23⁺IgG₁⁺ B cells (Fig E2, B) were not affected by steroid treatment (oral and inhaled; left in figures), oral steroids alone (middle), or leukotriene inhibitors (right).

CD23⁺IgG₁⁺ B-cell numbers are associated with blood eosinophil counts and lung function

To understand the clinical relevance of the increased numbers of CD23⁺IgG₁⁺ B cells in asthma patients (Fig 1), we investigated whether it could be associated with blood eosinophil counts and lung function (forced expiratory volume in 1 second [FEV₁]). Elevated eosinophil counts in the blood (particularly >300 cells/μL) are often associated with eosinophilic asthma.¹² Of interest, asthma patients with >300 eosinophils per microliter of blood (eos/μL) had greater numbers of CD23⁺IgG₁⁺ B cells than patients with <300 eos/μL (Fig 1, D, left). CD23 expression was previously reported to be associated with eosinophilic inflammation in chronic sinusitis with nasal polyps¹³ and atopic dermatitis,¹⁴ suggesting its potential to be a clinically informative biomarker across a range of T_H2-driven inflammatory diseases, which is warranted to be further investigated in future studies. Although there was no statistically significant difference between the 3 groups of patients with different lung functions (mild, FEV₁ > 80% predicted; moderate, 50% < FEV₁ < 80% predicted; severe, FEV₁ < 50% predicted), there was a trend toward increased numbers of CD23⁺IgG₁⁺ B cells in patients with more severe asthma (Fig 1, D, right).

Therefore, we concluded that the increased numbers of CD23⁺IgG₁⁺ B cells were associated with blood eosinophil counts and potentially lung function as well, but not serum IgE levels. The numbers of CD23⁺ or IgG₁⁺ B cells were not associated with blood eosinophil counts (see Fig E3 in the Online Repository available at www.jaci-global.org).

Surface CD23 expression levels on CD23⁺IgG₁⁺ B cells correlate with serum IgE concentrations

Because the numbers of CD23⁺IgG₁⁺ B cells did not correlate with serum IgE concentrations (Fig 1, C, right), we next investigated whether surface CD23 expression levels were associated with the magnitude of the IgE response. Although the roles of CD23 in IgE response remain elusive,¹⁵ previous studies have demonstrated that CD23 can contribute to IgE isotype switching.¹⁶

As shown in Fig 2, A, asthma patients and nonasthmatic control subjects expressed similar levels of surface CD23 on total CD19⁺ B cells. Interestingly, we found that CD23⁺IgG₁⁺ B cells in asthma patients expressed higher levels of surface CD23 than those in nonasthmatic control subjects (Fig 2, B). More importantly, surface CD23 expression levels on CD23⁺IgG₁⁺ B cells correlated with serum IgE concentrations in asthma patients (Fig 2, C). Asthma patients with >300 eos/μL and those with <300 eos/μL exhibited similar levels of surface CD23 expression (Fig 2, D). Additionally, there was a trend toward increased surface CD23 expression with decreasing lung function (Fig 2, E), although surface CD23 expression levels did not differ significantly among the 3 patient groups defined by lung function. The surface expression levels of CD23 on CD23⁺IgG₁⁺ B cells were not affected by the receipt of steroid (inhaled and oral) therapy (see Fig E4, left, in the Online Repository available at www.jaci-global.org), oral steroids alone (Fig E4, middle), or leukotriene inhibitors (Fig E4, right).

Fig 2.

Surface CD23 expression levels on CD23⁺IgG₁⁺ B cells correlate with serum IgE concentrations. Expression levels of CD23 in total CD19⁺(A) and CD23⁺IgG₁⁺ B cells (B). Correlation between CD23 expression levels on CD23⁺IgG₁⁺ B cells and serum IgE concentrations (C). Associations between CD23 expression levels on CD23⁺IgG₁⁺ B cells and eosinophil counts (D) or lung function (E).

Neutralizing IgE with omalizumab does not alter frequency of CD23⁺IgG₁⁺ B cells

IgE receptors are known to be upregulated in the presence of circulating IgE.^8,17 Therefore, we hypothesized that neutralizing IgE with omalizumab could decrease the frequency of CD23⁺IgG₁⁺ B cells by the downregulation of surface CD23 expression.

Adult patients (n = 16; see Table E1 in the Online Repository available at www.jaci-global.org) with moderate-to-severe asthma were treated with omalizumab; treatment outcomes are summarized in Table E2, also in the in the Online Repository. We assessed the percentages of CD23⁺IgG₁⁺ B cells in total CD19⁺ B cells and numbers of CD23⁺IgG₁⁺ B cells per 1 × 10⁶ PBMCs from week 0 to week 26. Omalizumab did not significantly alter the percentages of CD23⁺ B cells (Fig 3, A, left), IgG₁⁺ B cells (Fig 3, A, middle), or CD23⁺IgG₁⁺ B cells (Fig 3, A, right). Fig 3, B, also demonstrates that omalizumab did not alter actual numbers of these B-cell populations including CD23⁺IgG₁⁺ B cells. However, this might need to be further investigated with larger patient cohorts, which would allow us to determine whether CD23 expression levels or the frequency of CD23⁺IgG₁⁺ B cells differ between those with and without response.

Fig 3.

Neutralizing IgE with omalizumab does not alter frequency of CD23⁺IgG₁⁺ B cells. Percentage in total CD19⁺ B cells (A) and numbers (B) of CD23⁺(left), IgG₁⁺(middle), and CD23⁺IgG₁⁺ B cells (right) at indicated time points throughout omalizumab treatment in 16 patients with moderate-to-severe asthma.

In summary, this study reports that the surface CD23 expression levels on CD23⁺IgG₁⁺ B cells correlates with the serum IgE concentrations in adult asthma patients. The increased numbers of CD23⁺IgG₁⁺ B cells in asthma patients are associated with blood eosinophil count and lung function (FEV₁), but not with serum IgE concentrations. Therefore, the frequency of CD23⁺IgG₁⁺ B cells and the intensity of CD23 expression possess distinct biological and clinical relevance. These findings emphasize that CD23⁺IgG₁⁺ B cells are not merely surrogate markers of IgE production but rather reflect a functionally relevant and clinically informative B-cell subset engaged in allergic inflammation even in the context of therapies with steroids or leukotriene inhibitors.

This study also proposes that CD23 expressed on IgG₁⁺ B cells contributes to IgE class switching and/or IgE secretion in asthma patients, which is different from the previously proposed hypothesis that CD23 promotes IgE response by enhancing IgE-facilitated allergen uptake.⁸ In support of our notion, CD23 can form aggregates with CD21 on the B-cell surface, leading to IgE class switching.^16,18 Additionally, CD23 is also known to either promote or inhibit IgE synthesis and production, depending on IgE concentrations. At low IgE levels, surface CD23 can be cleaved from the B-cell membrane by proteases. Once released, soluble CD23 trimers could coligate membrane-bound IgE and CD21, leading to IgE synthesis.⁹ Alternatively, CD23 can also promote inflammatory responses via the release of proinflammatory mediators and the enhancement of cell adhesion activity.¹⁹ Thus, CD23 activation and its role in B-cell growth and differentiation may represent an additional mechanism for upregulating IgE production. However, CD23 can also restrain IgE synthesis, at least in part, by negatively regulating B-cell receptor signaling.^15,20

Because the frequency of CD23⁺IgG₁⁺ B cells in asthma was not affected by omalizumab or steroid treatment, it could also serve as a biomarker for asthma pathogenesis. Steroids can inhibit IL-4 expression as well as IL-4–induced signaling pathways, which can result in the reduction of CD23 expression.^21,22 The persistent CD23 expression in CD23⁺IgG₁⁺ B cells observed in this study suggests the presence of an IL-4–independent programs supporting CD23 expression on B cells or steroid insensitive, rendering the CD23⁺IgG₁⁺ subset less sensitive to steroid-mediated suppression. Indeed, both IL-13 and IL-2 are also known to upregulate CD23 expression.^23,24 In asthma patients, IL-2 produced by activated peripheral blood cells positively correlated with a daily dose of inhaled glucocorticoids. When patients were stratified by IL-2 level, those with high IL-2 production also made more IL-13.²⁵

One limitation of this study is the relatively small sample size of study participants, which may have limited the statistical power to detect significant changes in some readouts. Future studies with larger cohorts and multicenter studies across more diverse patient populations are needed to validate our findings, including the observed associations between the numbers of CD23⁺IgG₁⁺ B cells and blood eosinophils as well as lung function that are unaffected by common treatments such as steroids and leukotriene inhibitors.

Key messages.

• •The intensity of CD23 expression on CD23⁺IgG₁⁺ B cells, but not their numbers, correlated with serum IgE concentrations in adult asthma patients.
• •The number of CD23⁺IgG₁⁺ B cells was associated with blood eosinophil counts and lung function.
• •This study provides a new insight into the phenotypes of B cells reflecting the magnitude of IgE response in asthma.

Disclosure statement

Supported by the American Asthma Foundation (AAF15-0038, S.O.), Investigator-Initiated Study from Genentech (ML28019, S.O.), and Mayo Clinic.

Disclosure of potential conflict of interest: The authors declare that they have no relevant conflicts of interest.