Regulatory T cells in healthy and asthmatic subjects challenged with rhinovirus

Background: Allergic asthma is characterised by an imbalance in Th2/Th1 response and elevated secretion of Th2 cytokines. Regulatory T cells (Tregs), expressing FoxP3, are thought to play a prominent role in the suppression of Th1 lymphocytes in asthma patients. Objectives: The aim was to address whether the number of Tregs differ between asthmatic patients and healthy controls and how these numbers are affected by a Th1 response, i.e. a provocation with rhinovirus type 16 (RV16). Methods: Mild allergic asthma patients (n=9) and healthy non-allergic controls (n=14) were inoculated with RV16 (10 TCID50). One day before and six days after the provocation, blood was drawn and bronchoalveolar lavage (BAL) fluid was collected. Lymphocytes and peripheral blood mononuclear cells (PBMCs) were analysed by multi-colour flow cytometry to quantify the CD4+CD25+FoxP3+ Tregs. Results: Mild asthma patients had more CD4+CD25+FoxP3+ Tregs (6.1±0.7%) in peripheral blood compared to the healthy controls (3.7±1.1%, p=0.003). FoxP3 was expressed in a larger proportion of CD4+ cells in the BAL than in peripheral blood of both asthmatic (7.9±3.0 in BAL and 5.1±1.4 in blood) and control subjects (7.5±2.6 in BAL and 3.9±1.6 in blood), but no difference between the prevalence in BAL lymphocytes from both groups was observed. RV16 provocation did not affect the CD4+CD25+FoxP3+ Treg numbers in blood and BAL in either patients with mild asthma or healthy controls. Conclusion: There is a higher number of CD4+CD25+ cells expressing FoxP3+ in peripheral blood of mild allergic asthma patients. Rhinovirus challenge did not have an impact on PBMC and BAL Treg numbers in both healthy and asthmatic individuals.