CCL22 is involved in the recruitment of CD4+CD25high T cells into tuberculous pleural effusions.

Background and Objective:  CD4+CD25high regulatory T cells are increased in tuberculous pleural effusions (TPE). However, the mechanism by which CD4+CD25high T cells infiltrate into the pleural cavity is unknown. The aim of this study was to investigate whether the chemokines CCL22 and CCL17 are present in TPE, and the chemoattractant activity of these chemokines for infiltration of CD4+CD25high T cells into the pleural space. Methods:  The concentrations of CCL22 and CCL17 were measured in pleural effusions from 33 patients with tuberculous pleurisy, 21 patients with pleural bacterial infections and 18 patients with transudative pleural effusions. T lymphocyte subsets in pleural effusions were assessed by flow cytometry. Pleural effusion cells were analysed for the expression of CCL22. The chemoattractant activity of CCL22 for CD4+CD25high T cells was assessed in vitro. Results:  The frequency of CD4+CD25high T cells was significantly higher in TPE than in blood. High concentrations of CCL22 were detected in tuberculous effusions, but not in bacterial effusions or transudates. Macrophages and T cells in TPE expressed CCL22. Tuberculous pleural fluid was chemotactic for CD4+CD25high T cells in vitro, and anti-CCL22 antibody partly inhibited this chemotactic activity. Conclusions:  CCL22 appeared to be increased in TPE compared with bacterial pleural effusions or transudates. CCL22 may be responsible for the infiltration of CD4+CD25high T cells into the pleural space of patients with tuberculous pleurisy.