Impaired responses of peripheral blood mononuclear cells to staphylococcal superantigen in patients with severe atopic dermatitis: a role of T cell apoptosis

Staphylococcus aureus colonization is an almost universal feature of atopic dermatitis. In order to investigate the role of staphylococcal enterotoxin B in the pathogenesis of atopic dermatitis, we assessed the correlation between clinical disease severity and proliferative response of peripheral blood mononuclear cells to staphylococcal enterotoxin B in patients with atopic dermatitis. Peripheral blood mononuclear cells from patients with mild atopic dermatitis showed significantly increased proliferative responses to staphylococcal enterotoxin B compared to controls. In contrast, peripheral blood mononuclear cells from patients with severe atopic dermatitis showed markedly suppressed proliferative responses. Additionally, longitudinal evaluation of peripheral blood mononuclear cell samples from the same patient demonstrated that proliferative responses were suppressed only at times of severe disease exacerbation. Mixing experiments, using autologous T cells and antigen presenting cells that were isolated at different time points from the same patient, demonstrated that T cells of severe atopic dermatitis patients were dysfunctional, but their antigen presenting cell function remained intact. We found no significant differences of interleukin-2 levels in the culture supernatants between healthy controls and atopic dermatitis groups. Fluorescence-activated cell sorter analysis for APO2.7 antigen, an early apoptosis cell marker, demonstrated that approximately 60% of staphylococcal-enterotoxin-B-stimulated T cells expressed APO2.7 antigen in severe atopic dermatitis cases. By contrast, 5%-20% of T cells expressed APO2.7 after staphylococcal enterotoxin B stimulation in cases of mild atopic dermatitis and in healthy controls. Nuclear staining with Hoechst 33258 also showed approximately 40% apoptotic cells in the CD19-CD16-PBMC of severe atopic dermatitis patients, compared with only 5%-10% in the mild atopic dermatitis group and in healthy controls. Blocking monoclonal antibody to Fas ligand partially prevented the staphylococcal-enterotoxin-B-induced apoptosis detected by APO2.7 expression and Hoechst 33258 staining. Suppressed proliferation of peripheral blood mononuclear cells in severe atopic dermatitis patients may be secondary to T cell death by apoptosis. These results suggest that an infection of S. aureus producing staphylococcal enterotoxin B may play a role in aggravation of atopic dermatitis by inducing apoptosis in T cells.