Background Systemic lupus erythematosus (SLE) is accompanied by alterations in T cell homeostasis including an increased effector response. Migrated effector memory T cells (CD45RO⁺CCR7^–; T_EM) appear to be involved in tissue injury. The objective of this study was to investigate the distribution and phenotype of effector memory T cells in the peripheral blood (PB), and their presence in renal biopsies and urine of patients with SLE. The hypothesis that these T_EM cells migrate to the kidney during active disease was tested.

Methods A total of 43 patients with SLE and 20 healthy controls were enrolled. CD4⁺T_EM cells and CD8⁺T_EM cells were analysed in PB and urine using flow cytometric analysis. In 10 patients with active lupus nephritis a parallel analysis was performed on the presence of T_EM cells in kidney biopsies.

Results The percentage of circulating CD8⁺T_EM cells in patients with SLE was significantly decreased versus healthy controls (33.9±18.3% vs 42.9±11.0%, p=0.008). In patients with active renal involvement (n=12) this percentage was further decreased to 30.4±15.9%, p=0.01. Analysis of the urinary sediment in active renal disease showed increased numbers of CD4⁺T cells (134±71 cells/ml) and CD8⁺T cells (287±220 cells/ml), respectively, while in healthy controls and patients without active renal disease almost no T cells were present. In all, 73.6±8.3% of urinary CD4⁺T cells and 69.3±26.0% of urinary CD8⁺T cells expressed the T_EM phenotype. CD8⁺ cells were also found in renal biopsies.

Conclusions The data presented are compatible with the hypothesis that CD8⁺ effector memory cells migrate from the PB to the kidney and appear in the urine during active renal disease in patients with SLE. These cells could serve as an additional marker of renal activity in patients with SLE.