Functional and phenotypic characterization of CD8+CD28+ and CD28- T cells in atopic individuals sensitized to Dermatophagoides pteronyssinus.

BACKGROUND CD8+ T suppressor cells may play a role in immunoregulation. Recent studies have characterized this population by the lack of the CD28 molecule. These CD8+CD28 T cells differ phenotypically and functionally from CD8 + CD28 + T cells. Little is known about CD8 + CD28 cells in atopy. Our aim was to analyze the phenotype and functional properties of CD8 + CD28T cells in atopic and non-atopic individuals. METHODS Peripheral blood mononuclear cells (PBMC) were obtained after density gradient centrifugation. CD8 + CD28 and CD8 + CD28 + T cells were isolated using immunomagnetic beads. Relative percentages of these cells and expression of several phenotypic markers were analyzed by flow cytometry. Proliferation was assessed by thymidine incorporation in isolated populations and in co-cultures with PBMC using Dermatophagoides pteronyssinus as stimulus. Cytokine synthesis was evaluated in culture supernatants by cytometric bead array. RESULTS The relative percentages of CD8+CD28 T cells and their phenotypic expression in atopic and non-atopic volunteers were not significantly different. However, CD8 + CD28 T cells showed greater proliferation than did CD8+CD28+ T cells when stimulated with D. pteronyssinus, although cytokine synthesis patterns were similar. CD8+CD28 co-cultures with PBMC showed greater proliferation than CD8+CD28+ T cell co-cultures, but cytokine synthesis patterns were not different. CONCLUSIONS Our data confirm phenotypic and functional differences between CD28+ and CD28 T cells, irrespective of atopic status. Purified human CD8+CD28 T cells, freshly isolated from peripheral blood, do not have suppressor properties on allergen-specific proliferation or on cytokine synthesis in PBMC.