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. 2026 Jun 8;12(3):01146-2025. doi: 10.1183/23120541.01146-2025

Comparison of airway mucin 5AC and 5B expression in preterm-born adults and asthma

Mervi Kreus 1,2,3,4,✉, Petra Um-Bergström 5,6, Heta Merikallio 3,4, Elisa Lappi-Blanco 7,8, Ilkka Miinalainen 9, Nicole Y Wagner 1,2, Eva Berggren-Broström 5,6, Erik Melén 6, Anders Lindén 2,10, Åsa M Wheelock 1,2, Riitta Kaarteenaho 3,11,12, C Magnus Sköld 1,2,12
PMCID: PMC13244201  PMID: 42267373

Abstract

Background

As preterm birth is a risk factor for developing chronic lung disease later in life and has been associated with asthma-like symptoms, we hypothesised that preterm-born adults with and without a history of bronchopulmonary dysplasia (BPD) resemble patients with asthma with respect to altered mucin expression in the airways.

Methods

Bronchial biopsies were retrieved from 39 adults born very-to-extremely preterm (of which 22 had a history of BPD), 18 adults with mild allergic asthma and 24 healthy controls. Mucin (MUC) 5AC and MUC5B protein expressions were determined by immunohistochemistry and immunoelectron microscopy. Additionally, the percentage of goblet cells was estimated.

Results

MUC5AC expression and the percentage of goblet cells were lower in preterm-born adults than in asthma patients but did not markedly differ from those of healthy controls. In the preterm-born adults, MUC5AC expression correlated negatively with forced expiratory volume in 1 s to forced vital capacity ratio (FEV1/FVC) and positively with St George's Respiratory Questionnaire scores. Preterm-born adults with high MUC5AC expression had more bronchial hyperreactivity than those with low expression. MUC5B expression was lower in preterm-born adults with bronchial hyperreactivity and higher in those who reported having phlegm compared with those who did not have these signs.

Conclusions

Unlike patients with asthma, preterm-born adults with or without BPD do not exhibit increased MUC5AC expression compared with healthy controls. However, the associations of MUC5AC and MUC5B expression with lung function, symptoms and quality-of-life indices suggest a potential clinical role for these mucins in this population.

Shareable abstract

In preterm-born adults with and without a history of bronchopulmonary dysplasia, MUC5AC and MUC5B expression is associated with lung function, symptoms and quality of life, suggesting a potential clinical role for these mucins in this population https://bit.ly/48IhpqJ

Introduction

Preterm-born infants, particularly those who develop bronchopulmonary dysplasia (BPD), have disrupted lung architecture and may have increased respiratory symptoms and lung function impairment persisting through life [1–5]. Adults with BPD have been shown to have chronic obstructive lung function impairment and a T-cell subset pattern in the bronchoalveolar lavage samples resembling features of chronic obstructive lung disease (COPD) [6–8]. Some of the individuals with BPD may exhibit asthma-like symptoms, which may lead to prescription of asthma medications [9, 10]. They may also suffer from emphysema and pulmonary hypertension [11]. Thus, individuals with BPD suffer from a diverse spectrum of respiratory impairments.

In chronic respiratory diseases, such as asthma and COPD, alterations in mucus composition may lead to dysfunctional mucociliary clearance [12–14] associated with goblet cell hyperplasia [15]. The major secreted mucins expressed in the airway epithelium and mucus are mucin 5AC (MUC5AC) and mucin 5B (MUC5B) [16]. MUC5AC-positive cells are elevated in COPD [17], and MUC5AC gene and protein expression are increased in the airway epithelium in mild-to-severe asthma [15, 18]. In an allergic asthma model, MUC5AC-deficient mice have preserved mucociliary transport and are protected from mucus plugging, whereas in MUC5B-deficient mice, mucociliary clearance is impaired, leading to pulmonary infections [19]. While their expression has been studied in lung tissue samples from different chronic lung diseases, the localisation and cellular sources of MUC5AC and MUC5B in airway mucosa in preterm-born adults with and without BPD has not been investigated previously.

We hypothesised that preterm-born adults with and without BPD exhibit mucin expression pattern resembling that seen in asthma in the airways. To evaluate this hypothesis, we characterised the immunohistochemical expression of MUC5AC and MUC5B in the large airways of preterm-born adults with and without BPD and compared the expression with full term-born individuals with asthma using healthy individuals as controls. We also explored the association of mucin expression in the airways with lung function, quality-of-life indices and neonatal characteristics in preterm-born adults. Additionally, we examined the ultrastructural localisation of MUC5AC and MUC5B using immunoelectron microscopy.

Methods

Participants

This case–control study was conducted on participants from the Lung Obstruction in Adulthood of Prematurely Born study (LUNAPRE; https://www.clinicaltrials.gov/study/NCT02923648), including four adult study groups: preterm-born at gestational age (GA) ≤32 weeks with a neonatal diagnosis of BPD, preterm (born ≤32 weeks GA) without BPD, patients (born ≥37 weeks GA) with mild allergic asthma and healthy controls (born ≥37 weeks GA) [6, 7]. The study was approved by the Regional Ethics Committee in Stockholm (ref. 2012/1872-31/4) and it was conducted in accordance with the Declaration of Helsinki. All participants provided written informed consent. More details are provided in supplementary methods. Data on lung function and symptoms have been described previously [6].

Bronchoscopy

Bronchoscopy was performed according to a standardised protocol as previously described [7, 20]. Details are provided in supplementary methods.

Histochemistry and immunohistochemistry

The quality of the formalin-fixed and paraffin-embedded samples was evaluated on haematoxylin and eosin-stained sections. A tissue block containing the highest amount of intact epithelium from each individual was selected for immunohistochemical analyses. Alcian blue-periodic acid Schiff (AB-PAS) staining was used for phenotyping goblet cells. Details on immunohistochemical staining for MUC5AC and MUC5B and acquisition of whole-slide images are provided in supplementary methods.

Analysis of immunohistochemical and histochemical staining

Whole-slide images were examined using NDP.view2 (Hamamatsu, Hamamatsu City, Japan) or open-source digital pathology image analysis software QuPath [21]. Expression scores for MUC5AC and MUC5B were assessed by combining the staining intensity with the percentage of positive cells, and the area of MUC5AC- and MUC5B-positive staining was measured using QuPath. The percentage of goblet cells was counted from AB-PAS-stained slides. The expression of MUC5AC and MUC5B and goblet cells were analysed in intact epithelium. Details are provided in supplementary methods.

Immunoelectron microscopy

The ultrastructural localisations of MUC5AC and MUC5B in bronchial biopsies derived from two patients with asthma and two preterm-born adults with BPD were studied by immunoelectron microscopy as described in supplementary methods.

Statistical analysis

The data are presented as median and interquartile range for continuous variables, and as numbers and percentages for categorical variables. Comparisons between the study groups were performed using a Kruskal–Wallis test, followed by a Mann–Whitney U-test. The preterm and BPD groups were combined (pooled preterm group) when the associations of MUC5AC, MUC5B and goblet cells and clinical parameters were studied. Correlations were assessed using Spearman's rank correlation coefficient. To assess whether associations between clinical parameters and mucin expression differ between preterm and BPD groups, median regression analyses with a group (preterm versus BPD)×MUC5AC or group×MUC5B interaction term were performed. Comparisons between two groups were conducted using a Mann–Whitney U-test or Fisher's exact test. p-values were adjusted for multiple testing using the false discovery rate according to Benjamini and Hochberg [22]. A false discovery rate of <0.1 was considered statistically significant [7]. Non-adjusted p-values are shown in the text and figures and adjusted p-values are shown in supplementary tables S1–S14. Statistical analysis was performed using IBM SPSS Statistics for Windows, v.28.0 (IBM, Armonk, NY, USA). Further details are provided in supplementary methods.

Results

Participants

The original LUNAPRE cohort consisted of 96 study participants [6], of which 92 underwent bronchoscopy with collection of airway samples. Tissue sections stained with MUC5AC and MUC5B antibodies from 81 individuals (24 healthy, 18 asthma, 17 preterm and 22 BPD) contained intact epithelium and were included in this study. Tissue sections stained with AB-PAS from 79 individuals (24 healthy, 16 asthma, 17 preterm and 21 BPD) contained intact epithelium. The characteristics of the individuals included in the evaluation of MUC5AC and MUC5B expression in the bronchial biopsies are shown in table 1. As previously reported [6], the BPD group had lower lung function values (forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC, and diffusing capacity of the lung for carbon monoxide (DLCO)) than healthy controls (table 1).

TABLE 1.

Characteristics of study participants

Healthy
n=24		 Asthma
n=18		 Preterm
n=17		 BPD
n=22
Sex, males 12 (50.0) 8 (44.4) 8 (47.1) 11 (50.0)
Age, years 20.6 (19.3–21.1) 20.3 (19.8–22.1) 19.3 (19.0–19.7)* 19.6 (19.2–20.2)*
BMI, kg·m−2 21.8 (20.5–23.6) 22.3 (20.6–25.3) 20.4 (19.3–23.7) 21.3 (19.3–24.6)
Positive Phadiatop test 0.0 (0.0) 18 (100.0) 6 (35.3) 2 (9.1)
Positive methacholine challenge test # 0.0 (0.0) 18 (100.0) 10 (58.8) 15 (75.0)
FEV1, % pred 108.9 (101.2–113.5) 104.5 (98.1–111.5) 103.3 (98.5–116.0) 91.4 (83.8–100.7)**
FEV1, z-scores 0.78 (−0.04–1.19) 0.27 (−0.17–1.00) 0.28 (−0.13–1.37) −0.75 (−1.37– −0.15)**
FVC, % pred 105.2 (98.6–111.2) 103.0 (98.5–110.4) 98.0 (94.3–114.0) 96.0 (85.6–101.0)*
FVC, z-scores 0.37 (−0.12–0.80) 0.20 (−0.12–0.90) −0.16 (−0.49–0.82) −0.32 (−1.24–0.06)**
FEV1/FVC 0.90 (0.86–0.92) 0.86 (0.82–0.89) 0.89 (0.86–0.93) 0.80 (0.74–0.88)**
FEV1/FVC, z-scores 0.42 (−0.28–0.88) −0.12 (−0.62–0.33) 0.14 (−0.04–0.98) −1.05 (−1.79–0.03)**
FENO, ppb 10.9 (9.7–17.1) 29.5 (10.9–49.2) 13.5 (11.7–19.0) 14.9 (9.2–22.2)
DLCOadj, % pred 86.5 (80.0–96.0) 81.5 (75.0–95.0) 73.0 (65.0–83.0)** 69.0 (64.0–73.0)**
RV, % pred 84.5 (68.5–105.5) 75.5 (52.0–96.0) 85.0 (68.0–132.0) 88.0 (60.0–98.0)
RV/TLC 19.0 (17.0–22.5) 18.5 (14.0–23.0) 20.0 (18.0–22.0) 20.0 (17.0–24.0)
Prenatal corticosteroid therapy+ N/A N/A 9 (60.0) 9 (40.9)
Gestational age, weeks 40.0 (39.0–40.0) 39.5 (38.0–41.0) 30.0 (29.0–31.0)** 26.0 (26.0–29.0)**
Birthweight, grams 3457.5
(3245.0–3770.0)		 3580.0
(3024.0–3940.0)		 1520.0
(1175.0–1615.0)**		 971.0
(727.0–1145.0)**
Mechanical ventilation, days N/A N/A 0 (0–0) 4 (0–8)
CPAP, days N/A N/A 3 (2–6.5) 41 (30–52)
Supplemental oxygen, days N/A N/A 4 (1–10.5) 65 (58–83.5)
Surfactant treatment N/A N/A 3 (18.8) 7 (35.0)
Inhaled corticosteroids N/A N/A 0 (0.0) 14 (63.6)
BPD severity, mild/moderate/severe N/A N/A N/A 9/6/7
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Data are presented as median (interquartile range) or n (%). BPD: bronchopulmonary dysplasia; BMI: body mass index; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; DLCOadj: diffusing capacity of the lung for carbon monoxide adjusted for blood haemoglobin; RV: residual volume; TLC: total lung capacity; FENO: fractional exhaled nitric oxide; CPAP: continuous positive airway pressure; N/A: not applicable. All dynamic spirometry measures (FEV1, FVC and FEV1/FVC) are post-bronchodilator measures. Comparisons between study groups were performed with a Mann–Whitney U-test and p-values were adjusted according to the Benjamini–Hochberg procedure. #: data missing from two preterm-born adults with BPD. : data missing from one preterm-born adult with BPD. +: data missing from two preterm-born adults without BPD. *: padj<0.10 compared with healthy control group. **: padj<0.05 compared with healthy control group.

Expression pattern of MUC5AC and MUC5B in the large airways

Immunohistochemical cytoplasmic MUC5AC expression was detected in goblet cells for all study groups (figure 1). Immunohistochemical cytoplasmic MUC5B expression was detected both in goblet cells and submucosal glands (figure 2). We quantified immunostaining solely within the epithelium given that only a few biopsies in each group contained submucosal glands.

FIGURE 1.

FIGURE 1

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Immunohistochemical mucin 5AC (MUC5AC) expression in large airways. Bronchial biopsy specimens derived from a healthy control (a), a patient with asthma (b), a preterm-born without bronchopulmonary dysplasia (c) and a preterm-born with bronchopulmonary dysplasia (d,e). MUC5AC-positive staining (brown colour) was detected in goblet cells (arrows). f) A negative control staining in which primary antibody was substituted with mouse isotype control. Scale bars are 50 µm.

FIGURE 2.

FIGURE 2

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Immunohistochemical mucin 5AC (MUC5B) expression in large airways. Bronchial biopsy specimens derived from a healthy control (a), a patient with asthma (b), a preterm-born without bronchopulmonary dysplasia (c) and a preterm-born with bronchopulmonary dysplasia (d,e). MUC5B-positive staining (brown colour) was detected in goblet cells (arrows) and submucosal glands (arrowheads). f) A negative control in which primary antibody was substituted with rabbit isotype control. Scale bars are 50 µm.

Quantitative MUC5AC and MUC5B expression

MUC5AC expression score was lower in the pooled preterm group (preterm and BPD) and in the healthy control group compared with the asthma group (figure 3a). There were no statistically significant differences between the preterm and BPD groups (figure 3b). There were no differences in MUC5B expression scores between the study groups (figure 3c and d).

FIGURE 3.

FIGURE 3

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Comparison of mucin 5AC (MUC5AC) and mucin 5B (MUC5B) expression scores in healthy controls, patients with asthma and preterm-born adults. a) MUC5AC expression score in healthy control group, asthma group, and pooled preterm group (preterm and bronchopulmonary dysplasia (BPD)). Analysis with Mann–Whitney U-test. b) Comparison of MUC5AC expression score between preterm and BPD groups. c) MUC5B expression score in healthy control group, asthma group and pooled preterm group (preterm and BPD). d) MUC5B expression scores in preterm and BPD groups.

The MUC5AC- and MUC5B-positive areas in the epithelium were in line with the expression scores. Specifically, the MUC5AC-positive area was lower in the pooled preterm group and in the healthy control group than in the asthma group while the MUC5B-positive area did not differ between the study groups (supplementary figure S1).

Association of MUC5AC and MUC5B expression with lung function

The correlations of MUC5AC and MUC5B expression scores with lung function values for the preterm, BPD, and pooled preterm groups are shown in supplementary tables S1 and S2, and those for the asthma group are presented in supplementary table S3. The FEV1/FVC ratio and FEV1/FVC z-scores correlated negatively with MUC5AC and MUC5B expression scores in the preterm group (supplementary figure S2a,c and supplementary tables S1 and S2). In the pooled preterm group, a modest negative correlation was detected between MUC5AC expression score and post-bronchodilator FEV1/FVC ratio and FEV1/FVC z-scores (figure 4a and supplementary table S1). In the asthma group, MUC5AC or MUC5B expression score did not correlate with any of the lung function parameters (supplementary table S3).

FIGURE 4.

FIGURE 4

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Association of mucin 5AC (MUC5AC) and mucin 5B (MUC5B) and lung function in preterm-born adults (preterm and bronchopulmonary dysplasia (BPD)). a) Correlation between MUC5AC expression scores and post-bronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) z-scores. Preterm-born adults with positive and negative methacholine challenge tests are indicated. b) MUC5B expression scores in preterm-born adults with FEV1 z-scores above and below the lower limit of normal (−1.645 z-scores). c) MUC5B expression scores in preterm-born adults who were negative and positive in methacholine challenge test. Correlation was assessed using Spearman rank correlation coefficient and groups were compared with Mann–Whitney U-test. p-values were adjusted according to Benjamini–Hochberg procedure (supplementary tables S1 and S8). NA: not analysed.

In the median regression analysis, a statistically significant group (preterm versus BPD)×MUC5B interaction was observed for FEV1/FVC and FEV1/FVC z-scores, indicating differing associations between the groups, whereas the group×MUC5AC interaction was not statistically significant (supplementary table S4). Although the MUC5B–lung function association differed between preterm-born groups (p<0.05), the groups were pooled for subsequent analyses to present MUC5AC and MUC5B results consistently and preserve statistical power.

The association between lung function values and MUC5AC and MUC5B expression scores was also studied by dividing the pooled preterm group into low and high expression groups based on the median values of expression scores (supplementary tables S5–S8). 15 (88.2%) of 17 preterm-born adults with a high MUC5AC expression score and 10 (50.0%) of 20 who had a low MUC5AC expression score were positive on the methacholine challenge test (p=0.017) (supplementary table S5).

We also separately analysed the mucin expression in preterm-born adults with lung function below the lower limit of normal (≤−1.64 z-scores), in individuals who were positive in methacholine challenge test, and who reported having respiratory symptoms (supplementary tables S9 and S10). Preterm-born adults with post-bronchodilator FEV1 z-scores below the lower limit of normal had lower MUC5B expression score than individuals with FEV1 z-scores above that limit (figure 4b and supplementary table S10). Additionally, preterm-born adults who were positive in methacholine challenge test had lower MUC5B expression scores than those who were negative (figure 4c and supplementary table S10).

Association of MUC5AC and MUC5B expression with health-related quality of life and symptoms

Correlations between MUC5AC and MUC5B expression scores and quality-of-life scores in the preterm, BPD and pooled preterm groups are shown in supplementary tables S1 and S2 and for the asthma group in supplementary table S3. In the pooled preterm group, MUC5AC expression score correlated in a modest positive manner with St George's Respiratory Questionnaire (SGRQ) symptom score, activity score, impacts score and total score (figure 5a and supplementary table S1). In the median regression analysis, the group (preterm versus BPD)×MUC5AC interaction was not statistically significant for SGRQ total scores, indicating similar associations across the preterm-born groups. SF-36 mental component summary scores correlated positively with MUC5B in the preterm group (supplementary table S2), and a significant group×MUC5B interaction indicated differing associations between groups (supplementary table S4).

FIGURE 5.

FIGURE 5

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Association of mucin 5AC (MUC5AC) and mucin 5B (MUC5B) expression scores and respiratory symptoms in preterm-born adults (preterm and bronchopulmonary dysplasia (BPD)). a) Correlation between MUC5AC expression scores and St George's Respiratory Questionnaire (SGRQ) scores assessed with Spearman rank correlation coefficient. b) MUC5B expression score in preterm-born adults who reported to have phlegm that is hard to expectorate. Analysis with Mann–Whitney U-test. p-values were adjusted according to the Benjamini–Hochberg procedure (supplementary tables S1 and S8).

In the pooled preterm group, quality-of-life scores and symptoms were compared between individuals with low and high MUC5AC and MUC5B expression scores and the results are shown in supplementary tables S5–S8. Six (31.6%) of 19 preterm-born adults with a high MUC5B expression score and 0 (0.0%) of 20 who had a low MUC5B expression score reported having phlegm that is hard to expectorate (p=0.008) (supplementary table S8).

MUC5AC and MUC5B expression scores were also separately analysed in preterm-born adults who reported having respiratory symptoms or allergies and who were sensitised to IgE (supplementary tables S9 and S10). MUC5B expression was higher in preterm-born adults who reported having phlegm that is hard to expectorate compared with those without phlegm (figure 5b and supplementary table S10).

Association of MUC5AC and MUC5B expression with neonatal characteristic

We did not observe any statistically significant associations between MUC5AC or MUC5B expression scores and neonatal characteristics or severity of BPD in preterm-born adults (supplementary tables S1, S2, S5 and S6 and supplementary figure S3).

Goblet cells

Representative images of AB-PAS staining in each group are shown in supplementary figure S4. The pooled preterm group and healthy control group had lower percentage of goblet cells than the asthma group (figure 6a). The percentage of goblet cells was comparable in the preterm and BPD groups (figure 6b).

FIGURE 6.

FIGURE 6

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Percentage of goblet cells in large airways. a) The percentage of goblet cells of large airway epithelial cells in healthy control group, asthma group and pooled preterm group (preterm and bronchopulmonary dysplasia (BPD)). Analysis with Mann–Whitney U-test. b) The percentage of goblet cells in preterm and BPD groups.

Association of goblet cells and lung function

The percentage of goblet cells in the airway epithelium did not associate with lung function or airway hyperreactivity in the preterm, BPD, or asthma group (supplementary tables S11–S14).

Association of goblet cells with symptoms, health-related quality of life and neonatal characteristics

We detected no statistically significant associations between the percentage of goblet cells and quality-of-life indices, symptoms or neonatal characteristics in the preterm, BPD or asthma groups (supplementary tables S11–S14).

Ultrastructural localisation of MUC5AC and MUC5B in the large airway epithelium

MUC5AC labelling was detected mainly in the endoplasmic reticulum and occasionally in the Golgi apparatus of some of the goblet cells, whereas MUC5B labelling was detected in the secretory vesicles of almost all goblet cells in individuals with asthma and BPD (supplementary figure S5).

Discussion

In this study, we investigated qualitative and quantitative aspects of mucus production in preterm-born adults with and without BPD, full term-born individuals with mild allergic asthma and healthy controls. We observed that the expression of MUC5AC and percentage of airway goblet cells was lower in the pooled preterm group (preterm and BPD) than in the asthma group while the pooled preterm group resembled healthy controls in this respect.

Previous studies have indicated that the expression of MUC5AC is higher in severe asthma compared with healthy controls [17], but the literature is not conclusive in patients with mild asthma. One study reported higher semiquantitative MUC5AC expression in bronchial biopsies of patients with asthma than in healthy controls [15] while no difference in MUC5AC expression between patients with mild-moderate asthma and healthy controls was observed in a study measuring the positively stained area [23]. In accordance with Ordoñez et al. [15] we observed higher immunohistochemical MUC5AC expression in the large airways of patients with mild asthma than in healthy controls. We did not observe differences between the pooled preterm group and healthy controls. However, we found that MUC5AC expression score correlated negatively with post-bronchodilator FEV1/FVC, and a high score was associated with high incidence of bronchial hyperreactivity in preterm-born adults. MUC5AC expression score correlated positively with SGRQ scores in the pooled preterm group. High MUC5AC concentration in sputum has been associated with low FEV1 and FEV1/FVC and high SGRQ overall score in patients with COPD [24]. Thus, MUC5AC expression in the airway epithelium might be altered in a subgroup of preterm-born adults with bronchial hyperreactivity and low FEV1/FVC.

Interestingly, MUC5B is believed to be essential for lung homeostasis, defence and mucociliary clearance [18, 25]. In this study, we did not observe significant differences in MUC5B expression between preterm-born adults with and without BPD, patients with asthma and healthy controls. There are only a few studies on immunohistochemical MUC5B expression in the airways of patients with mild asthma [14, 15, 23]. Consistent with our findings, they observed no significant differences between patients with mild asthma and healthy controls [15, 23]. Sputum MUC5B level has been shown to be higher in mild, steroid-untreated asthma than in controls [26]. In this study, we evaluated MUC5B expression in goblet cells but not in submucosal glands or secreted MUC5B. Importantly, comparing studies measuring secreted and cell-bound mucins is difficult because MUC5B is also produced by submucosal glands and small-airway epithelial cells [27]. Additionally, stored mucins in goblet cells have been shown to inversely correlate with induced sputum mucin concentration in mild-to-moderate asthma [15]. However, MUC5B expression score was lower in preterm-born adults with low FEV1 z-scores and in those with a positive methacholine challenge test. Furthermore, MUC5B expression was higher in preterm-born adults with phlegm compared with those without, in agreement with studies in COPD [24]. Interestingly, we detected a correlation between MUC5B expression and FEV1/FVC only in the preterm group, and a statistically significant group (preterm versus BPD) ×MUC5B interaction for lung function, suggesting that MUC5B may play different roles in preterm-born adults with and without BPD.

Previous studies indicate that MUC5B is localised in the secretory granules of mucous cells palatal and buccal glands [28]. In the current study, we detected MUC5AC in the endoplasmic reticulum of some goblet cells and MUC5B in the secretory vesicles of almost all goblet cells in the airway epithelium of preterm-born adults with BPD and patients with asthma. Thus, the ultrastructural localisation of MUC5AC and MUC5B in preterm-born adults with BPD and patients with asthma might be similar. These findings support our observations in immunohistochemistry, as we detected immunohistochemical expression of MUC5AC in some of the goblet cells, whereas MUC5B was expressed in nearly all goblet cells. Previous studies have shown that MUC5AC and MUC5B are expressed partially in the same cells, whereas some cells express only MUC5AC or MUC5B [27, 29].

We observed lower percentage of goblet cells in preterm-born adults with and without BPD and healthy controls compared with patients with mild allergic asthma. Goblet cell hyperplasia has previously been associated with severe asthma [30], but studies in mild asthma have been controversial [15, 23, 31]. More specifically, Lozewicz et al. [31] and Wilson et al. [23] found no difference in the percentage of goblet cells from epithelial cells, whereas Ordoñez et al. [15] reported an increased number of goblet cells per unit of epithelial volume. We did not observe associations between goblet cells and clinical characteristics in preterm-born adults or in the asthma group.

A major strength of this study is a well-characterised study cohort, which includes neonatal data, demographics and lung function. Additionally, only nonsmokers were included, which eliminates the confounding influence of smoking, known to affect goblet cell density and the expression of MUC5AC and MUC5B [32–34]. The potential effect of ongoing medication was minimised by conducting clinical investigation when the study participants reported that they had been without any anti-inflammatory treatment for at least 3 months. One of the limitations of this study is modest sample size. However, to our knowledge, this is the largest cohort of adults with BPD examined through bronchoscopy and immunohistochemistry. The participants were born between 1992 and 1998, a period when few individuals received surfactant and prenatal corticosteroids, which are additional factors that could potentially confound the study outcomes.

Conclusions

We provide original evidence that preterm-born adults with and without BPD differ from those with mild allergic asthma in terms of mucin expression. Although MUC5AC and MUC5B expressions and the percentage of goblet cells were similar in preterm-born adults with and without BPD and healthy controls, MUC5AC expression was associated with lung function and quality-of-life indices and MUC5B expression was associated with airway hyperreactivity and symptoms in preterm-born adults. Thus, mucins may play a pathogenic role in these phenotypes, although it may not be specific for BPD.

Acknowledgements

We thank all the study subjects for participating. The authors would also like to thank the members of the LUNAPRE research team at Karolinska University Hospital and Sachs’ Children and Youth Hospital, Södersjukhuset, Stockholm, Sweden, in particular the research nurses Margareta Eriksson, Christina Ebersjö, Margitha Dahl, Helene Blomqvist, the late Gunnel de Forest, Emma Sundström, and biomedical technician Benita Engvall. The authors would also like to thank Riitta Vuento for technical assistance with immunohistochemistry, and the Biocenter Oulu, Transgenic and Tissue Phenotyping Core Facility, endowed by the University of Oulu, Finland and Biocenter Finland.

Footnotes

Provenance: Submitted article, peer reviewed.

Ethics statement: The study was approved by the Regional Ethics Committee in Stockholm (ref.: 2012/1872-31/4) and it was conducted in accordance with the Declaration of Helsinki. All participants provided written informed consent.

Author contributions: C.M. Sköld conceived, designed and coordinated the study. C.M. Sköld and P. Um-Bergström included study participants and generated clinical data. P. Um-Bergström and E. Melén were responsible for lung function tests. C.M. Sköld, R. Kaarteenaho, Å.M. Wheelock, E. Melén, A. Lindén and E. Berggren-Broström provided financial support and essential infrastructure. C.M. Sköld performed bronchoscopies. H. Merikallio and E. Lappi-Blanco evaluated biopsy quality. I. Miinalainen participated in the immunoelectron microscopy imaging and interpretation. M. Kreus analysed histochemical and immunohistochemical staining, and performed data analysis. N.Y. Wagner participated in the statistical analysis. M. Kreus, R. Kaarteenaho and C.M. Sköld interpreted data. M. Kreus drafted the manuscript. All authors reviewed the manuscript and approved the final version.

Conflict of interest: E. Melén reports advisory board fees from ALK and AstraZeneca and lecture fees from Chiesi and Sanofi. A. Lindén reports unrestricted research grants from AstraZeneca AB, GlaxoSmithKline AB, Boehringer Ingelheim AB and Chiesi AB in Sweden; consulting fees from AstraZeneca AB, GlaxoSmithKline AB, Boehringer Ingelheim AB, Chiesi AB and Roche AB in Sweden; lecture fees from Chiesi AB; and being member of the Scientific Board of the Swedish Heart-Lung Foundation. R. Kaarteenaho reports grants for the study group from the Tampere Tuberculosis Foundation; consulting fees from Boehringer Ingelheim, and MSD; lecture fees from Boehringer Ingelheim; being member of the board of the Finnish Medical Foundation between January 2020 and December 2022; being member of the board Finnish Lung Health Association from January 2021 onwards; and randomised controlled trial studies with Boehringer Ingelheim. C.M. Sköld reports research grants from Boehringer Ingelheim, and consultancies from AstraZeneca, GlaxoSmithKline, Boehringer Ingelheim, Novartis, Nordic InfuCare, Chiesi, CSL Behring and Grifols outside the submitted work. The rest of the authors declare that they have no relevant conflicts of interest.

Support statement: This work was supported by the Swedish Heart-Lung Foundation (C.M. Sköld: 20160418, 20180235 and 20190320; A. Lindén: 20210286 and 20240343; Å.M. Wheelock: 20190017 and 20190421), the Swedish Research Council (A. Lindén: 2016-01653 and 2021-01527; Å.M. Wheelock: 2018-00520), the Swedish Asthma and Allergy Foundation (C.M. Sköld: F2014-0016 and F2017-0009; A. Lindén: F2019-0031), Swedish Respiratory Society (C.M. Sköld: 2016), Samariten Foundation (P. Um-Bergström: 2016), Hesselman Foundation (P. Um-Bergström: 2016, 2018 and 2019), through the Regional Agreement on Medical Training and Clinical Research between Stockholm County Council and Karolinska Institutet (C.M. Sköld: 20170393 and 20200287; A. Lindén: 20180088 and 10202932025), and the state subsidy of Oulu University Hospital (R. Kaarteenaho). The sponsors were not involved in study design; in the collection, analysis or interpretation of data; in the writing of the report; or in the decision to submit the article for publication. Funding information for this article has been deposited with the Open Funder Registry.

Supplementary material

Please note: supplementary material is not edited by the Editorial Office, and is uploaded as it has been supplied by the author.

Supplementary material

01146-2025.SUPPLEMENT.pdf (1.2MB, pdf)
DOI: 10.1183/23120541.01146-2025.Supp1
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Data availability

Anonymised data from the current study are available from the corresponding author on reasonable request.

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Associated Data

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Supplementary Materials

Please note: supplementary material is not edited by the Editorial Office, and is uploaded as it has been supplied by the author.

Supplementary material

01146-2025.SUPPLEMENT.pdf (1.2MB, pdf)
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Data Availability Statement

Anonymised data from the current study are available from the corresponding author on reasonable request.

Articles from ERJ Open Research are provided here courtesy of European Respiratory Society

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