Objectives Delineation of mechanisms underlying neuropsychiatric systemic lupus erythematosus (NPSLE) and determination of biological markers could guide treatment choice. A study was undertaken to analyse the potential role of activated CD8+ T cells in NPSLE as previously reported in SLE nephritis.

Methods Flow cytometric immunophenotyping of blood lymphocytes was performed in 30 patients with NPSLE and 36 healthy individuals. The antigenic specificity of CD8+ T cells was studied using HLA-A0201 tetramers loaded with several myelin-derived peptides. The intracellular level of interferon γ (IFNγ) produced by activated CD8+ T cells was determined by flow cytometry.

Results A large increase in circulating activated CD8+ T lymphocytes expressing surface HLA-DR was found in patients with NPSLE without antiphospholipid syndrome (APS) (n=18) compared with patients with APS (n=12) or healthy controls (n=36). IFNγ-secreting myelin-specific CD8+ T cells were detected exclusively in the blood of patients with NPSLE without APS but with white matter lesions.

Conclusions These data strongly support the existence of a new immune effector mechanism responsible for CNS involvement in patients with NPSLE and suggest that analysing HLA-DR expression combined with myelin-specific tetramer staining on CD8+ T lymphocytes may be a valuable additional tool for the monitoring of these patients.