T regulatory cells in atopic dermatitis and subversion of their activity by superantigens

Background: Atopic dermatitis (AD) is a chronic inflammatory skin disease involving colonization by superantigen (SAg) - secreting Staphylococcus aureus. CD4⁺CD25⁺ T regulatory (Treg) cells are thought to play an important role in controlling inflammatory responses. Objective: In this study we examined whether Treg cells might be deficient in patients with AD. Methods: CD4⁺CD25⁺ and CD4⁺CD25^- T cells were isolated from PBMCs by using immunomagnetic beads. Cells were cultured with anti-CD3 or SAg, staphylococcal enterotoxin B (SEB), for 72 hours. Proliferation was measured by means of tritiated thymidine incorporation. CD4, CD8, CD2S, and cutaneous lymphocyte-associated antigen expression on PBMCs was assessed by means of flow cytometry. RNA was extracted from isolated subsets of T cells, and the results of real-time PCR for FoxP3 mRNA were determined. Results: Surprisingly, CD4⁺CD25⁺ T cells were significantly (P < .01) increased in patients with AD (6.68% ± 0.99%, n = 15) compared with in asthmatic patients (3.42% ± 0.58%, n = 12) or nonatopic healthy control subjects (3.34% ± 0.43%, n = 14). Patients with AD also had a higher expression of CD25⁺ in skin-homing, CD4⁺, cutaneous lymphocyte-associated antigen-positive T cells than asthmatic and nonatopic subjects, with values of 35.95% versus 22.44% versus 23.03%, respectively (P < .006). Only CD4⁺CD25⁺ cells expressed FoxP3, whereas CD4⁺CD25^- T cells and CD4^- cells did not. Consistent with known properties of Treg cells, CD4⁺CD25⁺ cells were anergic to anti-CD3 stimulation. When CD4⁺CD25⁺ cells from each study group were mixed with CD4⁺CD25^- cells, proliferative responses were equally suppressed after anti-CD3 stimulation. In contrast, after SEB stimulation, CD4⁺CD25⁺ cells were no longer anergic. Furthermore, when CD4⁺CD25⁺ cells were mixed with CD4⁺CD25^- cells and stimulated with SEB, the suppressive function of Treg cells was reversed. Conclusion: Patients with AD have significantly increased numbers of peripheral blood Treg cells with normal immunosuppressive activity. However, after SAg stimulation, Treg cells lose their immunosuppressive activity. These data suggest a novel mechanism by which SAgs could augment T-cell activation in patients with AD.