Circulating CD4+ CD25brightFOXP3+ regulatory T-cells are significantly reduced in bullous pemphigoid patients

Bullous pemphigoid (BP) is the most frequent autoimmune bullous skin disease, characterised by auto-antibodies against the hemidesmosome complex. Recently, regulatory T cells (Tregs) have been implicated in the development of several autoimmune diseases; few data are available in BP, failing to demonstrate a role of this subset in disease pathogenesis. The aim of this study was to investigate the expression and phenotypes of different Tregs (CD4+ CD25brightFOXP3+ and CD8+ CD28- cells) in BP to clarify whether the depletion of this subset constitutes one mechanism of tolerance loss. The CD4+ CD25brightFOXP3 and CD8+ CD28- circulating subsets were determined by flow-cytometry in 26 untreated BP patients and compared with a group of age- and sex-matched healthy controls (HC, n = 30). Absolute and percentage values of the CD4+ CD25brightFOXP3+ cells were significantly reduced in BP compared with HC (median CD25brightFOXP3+ expression within CD4+ cells: 1.8 vs. 3.5%, p = 0.002); conversely, BP patients were characterised by a significant expansion of the CD25brightFOXP3- "activated" T-cell subset. CCR4 and CD62L were expressed on the majority of CD4+ CD25brightFOXP3+ cells (75.2 and 82.3%, respectively). No differences in the CD8+ CD28- subset were found between BP and HC. This is the first report showing a significant reduction of circulating CD4+ CD25brightFOXP3+ Treg frequency in BP patients.