Inhaled Corticosteroid Treatment Reduces Airway Adaptive Immune Cells in Asthma

<bold>Background:</bold> Inhaled steroids (ICS) are the cornerstone of anti-inflammatory treatment in asthma. Surprisingly, little is known about the effect of ICS on late effector cells of the adaptive immune response, such as B lymphocytes and immunoglobulin-producing plasma cells. <bold>Aim:</bold> To elucidate the effects of ICS on tissue-infiltrating immune cells, foremost B lymphocytes and plasma cells (PC), in asthma patients. <bold>Methods:</bold> Airway mucosal cryobiopsies were collected from 50 corticosteroid-free patients with airway hyperresponsiveness, before and after six weeks of daily treatment with 1600 μg of budesonide and from ten healthy subjects serving as controls. Multiple immune cell populations in the airway tissue were visualized histologically by immunohistochemistry and quantified by computerized image analysis. <bold>Results:</bold> Multivariate Analysis of Variance (MANOVA) showed that treatment with ICS had a highly significant multivariate effect on the composition of immune cell populations (Wilks' lambda: 0.033, F-value: 62.77). Post-ICS treatment, there was a clear trend towards reduced B-cells (p = 0.074) and a robust reduction ininfiltrating PCs (p < 0.0001), eosinophils, and MCT mast cells (p = 0.017 and p = 0.001, respectively). No overall reduction was observed for MCTC, neutrophils, or monocytes/macrophages. Notably, post-treatment PC levels were lower than those in healthy controls (p = 0.037). <bold>Conclusions:</bold> The study reveals a surprisingly strong effect of ICS on plasma cells, thereby supporting the notion of ICS's influence on late adaptive immune responses.