Defining the Blood Cytokine Profile in Asthma to Understand Asthma Heterogeneity

Abstract

Background: Asthma is a heterogeneous disease characterized by overlapping clinical and inflammatory features.

Objective: This study aimed to provide insight into the systemic inflammatory profile in asthma, greater understanding of asthma endotypes and the contribution of genetic risk factors to both.

Methods: 4205 patients with asthma aged 16-60 were recruited from UK centers; serum cytokines were quantified from 708, including cytokines associated with Type 1, 2 and 17 inflammation. 3037 patients were genotyped for 25 single nucleotide polymorphisms associated with moderate-severe asthma.

Results: Serum cytokines associated with Th2 inflammation showed high coordinated expression for example, IL-4/IL-5 (R² = 0.513). The upper quartile of the serum cytokine data identified 43.7% of patients had high levels for multiple Th2 cytokines. However, the groups defined by serum cytokine profile were not clinically different. Childhood-onset asthma was characterized by elevated total IgE, allergic rhinitis and dermatitis. Exacerbation prone patients had a higher BMI, smoking pack-years, asthma control questionnaire score and reduced lung function. Patients with blood eosinophils of > 300 cells/µL had elevated total IgE and lower smoking pack-years. None of these groups had a differential serum cytokine profile. Asthma risk alleles for; rs61816764 (FLG) and rs9303277 (IKFZ3) were associated with childhood onset disease (p = 2.67 × 10^{- 4} and 2.20 × 10^{- 7}; retrospectively). No genetic variant was associated with cytokine levels.

Conclusion: Systemic inflammation in asthma is complex. Patients had multiple overlapping inflammatory profiles suggesting several disease mechanisms. Genetic risk factors for moderate-severe asthma confirmed previous associations with childhood onset of asthma.

Keywords: asthma; blood cytokines; endotypes; genetics.

Figure 1

A correlation heat map between each serum cytokine level indicative of Th1 (IFN‐γ), Th2 (IL‐4, IL‐5, IL‐13) and Th17 (IL‐17) and upstream (IL‐33, ST2, TSLP) and downstream (periostin, Eotaxin) markers of inflammatory pathways: (A) R ² value is presented for all the correlations between each analyte with red indicating a high R ² value and green low. An R ² value of > 0.5 was considered biologically significant. p values were calculated with spearman correlation and a p value of 4 × 10^{− 4} was considered as statistically significant after Bonferroni correction which are highlighted in bold. N = 708 subjects. (B–I) Correlation graphs with line of best fit between serum cytokines that met R ² value of > 0.5 and correction, data was plotted as Log₁₀. (J–L) Overlap of inflammatory profiles in the serum of asthma patients: (J) patients in the top 25% for cytokines that are current targets of monoclonal antibody drugs (anti‐IL‐5/5 R: Mepolizumab, Reslizumab and Benralizumab, anti‐IL‐4/IL‐13: Dupilumab and anti‐TSLP: Tezepelumab) and their percentage overlap n = 208 and (K) patients in the top 25% for the Th2 cytokines (IL‐13, IL‐4 and IL‐5) and their percentage overlap n = 238.

Figure 2

Summary of genetic association data for moderate‐severe risk alleles for clinical features and Th1, Th2 and Th17 serum biomarkers: each square is associated with how the risk allele for that SNP drives the clinical feature or serum biomarker with red meaning it decreases and green it increases. Those in red and green met statistical significance of > 5 × 10^{− 2} and * met Bonferroni correction of p < 2 × 10^{− 3}.