Circulating CD4+CD28null and extra-thymic CD4+CD8+ double positive T cells are independently associated with disease damage in systemic lupus erythematosus patients

Objective To determine whether circulating CD4+CD28null and extra-thymic CD4+CD8+ double positive (DP) T cells are independently associated with damage accrual in systemic lupus erythematosus (SLE) patients. Methods This cross-sectional study was conducted between September 2013 and April 2014 in consecutive SLE patients from our Rheumatology Department. CD4+CD28null and CD4+CD8+ DP T-cell frequencies were analyzed by flow-cytometry. The association of damage (SLICC/ACR Damage Index, SDI) and CD4+CD28null and CD4+CD8+ DP T cells was examined by univariable and multivariable Poisson regression models, adjusting for possible confounders. All analyses were performed using SPSS 21.0. Results Patients’ (n = 133) mean (SD) age at diagnosis was 35.5 (16.8) years, 124 (93.2%) were female; all were mestizo (mixed Caucasian and Amerindian ancestry). Disease duration was 7.4 (6.8) years. The SLE Disease Activity Index was 5.5 (4.2), and the SDI 0.9 (1.2). The percentages of CD4+CD28null and CD4+CD8+ DP T cells were 17.1 (14.4) and 0.4 (1.4), respectively. The percentage of CD4+CD28null and CD4+CD8+ DP T cells were positively associated with a higher SDI in both univariable (rate ratio (RR) 1.02, 95% confidence interval (CI): 1.01–1.03 and 1.17, 95% CI: 1.07–1.27, respectively; p