Introduction: Severe asthma is a special clinical problem. CD4⁺CD25^highCD127^lowFoxp3⁺ Tregs play a role in maintaining appropriate immunological response. It is a known fact that Treg cells with CCR5 expression represent strong suppressive activity. It has been shown that a low number or altered function of FoxP3⁺ Tregs is associated with the inflammatory process and airway obstruction in asthma.

Aim: To evaluate whether CCR5 Tregs expression and surface density on FoxP3⁺ Treg cells depend on the severity of asthma.

Material and methods: The study included 50 patients with asthma (25 with severe and 25 with mild-to-moderate asthma). The control group comprised 25 healthy volunteers. The phenotype of CD4⁺CD25^highCD127^lowFoxp3⁺CCR5⁺ cells was evaluated by multicolour flow cytometry. The degree of airflow obstruction was assessed by spirometry as forced expiratory volume in 1 s (FEV₁) and peak expiratory flow (PEF).

Results: The absolute count of FoxP3⁺ Treg cells in patients with severe asthma was significantly decreased in comparison with the control group. MFI (median fluorescence intensity) of CCR5 expression on FoxP3⁺ Treg cells was significantly decreased in severe asthma compared to the mild-to-moderate asthma and control groups. CCR5 expression on FoxP3⁺ Treg cells as MFI positively correlated with lung function parameters FEV₁% and PEF% in patients with severe asthma.

Conclusions: High CCR5 Tregs expression as MFI is associated with improved in lung function parameters: FEV₁% and PEF% in patients with severe asthma. The measurement of CCR5 expression on the surface of peripheral blood FoxP3⁺ Treg cells as MFI could be an additional tool to estimate the severity of asthma.