Thymic stromal lymphopoietin expression in different biological specimens in asthma: a systematic review and meta-analysis.

Background: Thymic stromal lymphopoietin (TSLP) is an epithelial-derived cytokine implicated in the pathogenesis of asthma. However, its expression across different biological specimens and its clinical correlates remain unclear. The objective of this study was to summarize available data on TSLP concentrations in blood and airway specimens in asthmatic patients. Methods: Studies reporting TSLP concentrations in blood and/or airway specimens [e.g., bronchial biopsy, bronchoalveolar lavage fluid (BALf), induced sputum, exhaled breath condensate (EBC), and nasal specimens] of asthmatic patients compared with healthy controls were eligible. PubMed, Web of Science, Embase, and Cochrane Library were searched from inception to October 2024. A total of 40 studies were included for qualitative synthesis, and 5 were eligible for meta-analysis. Differences in TSLP levels of asthmatic patients and controls were summarized by standardized mean differences (SMD) using a random effects model. Results: Based on meta-analysis, blood TSLP concentration was significantly higher in patients with asthma than in controls (SMD = 3.66, 95% CI 1.63-5.69, I 2 = 98.26%). The sensitivity analysis showed that no individual study influenced the pooled effect estimate. Based on a systematic review, all studies analyzing bronchial biopsies and BALf reported significantly higher TSLP concentration in asthmatics compared with controls, whereas results in induced sputum, EBC, and nasal specimens were variable. Conclusions: Most studies reported higher blood TSLP concentration in asthma patients compared with healthy controls, while results in airway specimens were diverse. Higher concentration of TSLP in asthmatic patients might be a useful disease-related marker. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD42024537964, PROSPERO CRD42024537964.