Impact of Transport Media on IL-33 Levels in Samples From Patients With Viral Respiratory Infections

Interleukin-33 (IL-33) is an IL-1 family cytokine that activates various immune cells and induces both systemic and localized Th2 responses during infection. An association between IL-33 and its suppresion of tumorigenicity 2 (ST2) receptor with inflammation during respiratory tract infection has been previously reported. Furthermore, some data suggest that during respiratory infections, IL-33 may serve as an indicator of disease severity, as high levels of this cytokine have been found in nasopharyngeal swab (NPS) samples of infants with lower respiratory tract disease caused by respiratory syncytial virus (RSV). As viral diagnosis is mostly compartmentalized in NPS, in this report, we aimed at detecting IL-33 in NPS from patients with respiratory tract infections that were collected in two different transport media (universal transport medium [UTM], and phosphate-buffered saline [PBS]). IL-33 levels were evaluated in 230 NPS samples, 121 obtained in PBS, and 109 in UTM. The samples were tested for RSV, metapneumovirus, adenovirus (ADV), influenza, and parainfluenza. In this cohort, higher levels of IL-33 were detected in virus-positive samples collected in PBS compared to virus-negative samples collected in the same transport medium. In addition, RSV- and FLU-positive samples collected in PBS showed higher measured IL-33 levels than those collected in UTM. No significant differences were found for the other viruses included in this study. These findings highlight the importance of considering sample collection and transport conditions when interpreting IL-33 measurements in NPS, particularly in future studies evaluating IL-33 as a potential severity-associated biomarker during RSV or influenza infection.