Characterization of CD3+CD4-CD8- (double negative) T cells in patients with systemic lupus erythematosus: activation markers

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Abstract
Systemic lupus erythematosus (SLE) is characterized by B cell hyperactivity and the production of autoantibodies, some of which (antibodies to dsDNA) are thought to be pathogenic. T helper cells drive the production of autoantibodies and the aim of this study is to characterize phenotypically a subpopulation of T cells (the CD3+CD4-CD8-, double negative (DN) T cells) previously identified as helping to enhance anti-DNA antibodies in patients with SLE. Data were obtained using FACS staining of DN T cells that had been purified from PBMCs by magnetic bead separation. The percentage of TCR ab‡ DN T cells was found to be significantly higher in patients with SLE as compared with controls (P ^ 0.02), although there was no significant increase in total percentage of DN T cells, which includes TCR gd ‡ cells. Activation markers HLA-DR and CD69, the costimulatory molecule CD28 and CTLA-4 were all expressed on the surface of a higher percentage of DN T cells in patients with SLE than in patients with rheumatoid arthritis (RA) or healthy controls (HC). More DN T cells from patients with SLE were of CD45RA phenotype than was found in controls, while CD45RO-expressing cells were reduced. In addition, DN T cells from patients with SLE expressed significantly higher levels of HLA-DR (P ^ 0.006), CD28 (P ^ 0.05), CTLA4 (P ^ 0.03) and CD45RA (P ^ 0.05) on the cell surface than those from the CD4=8 population. Correlation of expression of the markers measured with various parameters of disease activity and severity showed that high levels of HLA-DR expression correlated with high circulating serum C3 (> 0.9 IU/ml), indicating that an activated phenotype is consistent with severe disease.