Nuclear antigen-reactive CD4+ T cells expand in active systemic lupus erythematosus, produce effector cytokines, and invade the kidneys.

Systemic lupus erythematosus is a systemic and chronic autoimmune disease characterized by loss of tolerance towards nuclear antigens with autoreactive CD4+ T cells implicated in disease pathogenesis. However, very little is known about their receptor specificity since the detection of human autoantigen specific CD4+ T cells has been extremely challenging. Here we present an analysis of CD4+ T cells reactive to nuclear antigens using two complementary methods: T cell libraries and antigen-reactive T cell enrichment. The frequencies of nuclear antigen specific CD4+ T cells correlated with disease severity. These autoreactive T cells produce effector cytokines such as interferon-γ, interleukin-17, and interleukin-10. Compared to blood, these cells were enriched in the urine of patients with active lupus nephritis, suggesting an infiltration of the inflamed kidneys. Thus, these previously unrecognized characteristics support a role for nuclear antigen-specific CD4+ T cells in systemic lupus erythematosus.

Identification and characterization of antigen-specific CD4+ T cells targeting renally expressed antigens in human lupus nephritis with two independent methods.

In the search for anti-renal autoreactivity in human lupus nephritis, we stimulated blood-derived CD4+ T cells from patients with systemic lupus erythematosus with various kidney lysates. Although only minor responses were detectable, these experiments led to the development of a search algorithm that combined autoantibody association with human lupus nephritis and target gene expression in inflamed kidneys. Applying this algorithm, five potential T cell antigens were identified. Blood-derived CD4+ T cells were then stimulated with these antigens. The cells were magnetically enriched prior to measurement with flow cytometry to facilitate the detection of very rare autoantigen-specific cells. The detected responses were dominated by IFN-γ-producing CD4+ T cells. Additionally, IL-10-producing CD4+ T cells were found. In a next step, T cell reactivity to each single antigen was independently evaluated with T cell libraries and [3H]-thymidine incorporation assays. Here, Vimentin and Annexin A2 were identified as the main T cell targets. Finally, Vimentin reactive T cells were also found in the urine of three patients with active disease. Overall, our experiments show that antigen-specific CD4+ T cells targeting renally expressed antigens arise in human lupus nephritis and correlate with disease activity and are mainly of the Th1 subset.

Mapping urinary chemokines in human lupus nephritis: Potentially redundant pathways recruit CD4+ and CD8+ T cells and macrophages.

Renal infiltration of inflammatory cells contributes to the pathogenesis of lupus nephritis (LN). Current knowledge on the recruitment mechanisms relies mainly on findings in rodent models. Here, we assess various chemokine pathways in human LN by comparing urinary chemokine concentrations (in 25 patients with acute LN and in 78 lupus patients without active LN) with the expression of corresponding chemokine receptors on urinary leukocytes (in ten acute LN patients). Nine urinary chemokines were significantly elevated in LN patients and correlated with renal disease activity and urinary cell counts; however, their concentrations displayed considerable interindividual heterogeneity. Analysis of the corresponding receptors revealed abundance of urinary CD8+ T cells for CCR5 and CXCR3, while CD4+ T cells were additionally enriched for CCR1, CCR6 and CXCR6. Urinary Treg showed similar CCR expression, and urinary CD14+ macrophages were enriched for CCR5 expressing cells. In conclusion, cell specific recruitment patterns seem to involve CCR5 and CXCR3 in all cells studied, while CD4+ T-cell subset recruitment is probably much more varied. However, urinary chemokine abundance in active LN is individually variable in our cohort and does not offer a singular chemokine usable as universal biomarker or potential future treatment target.

The cellular signature of urinary immune cells in Lupus nephritis: new insights into potential biomarkers.

INTRODUCTION: Urinary T cells represent a reliable noninvasive biomarker for proliferative Lupus nephritis (LN). Little is known about the presence of T cell subsets, B cells and macrophages in the urine although they may further improve the validity of urinary cellular biomarkers for LN. METHODS: We analyzed contemporaneous blood and urine samples of patients with active LN (n = 19), other Systemic Lupus Erythematosus (SLE) patients (n = 79) and urine samples of patients with diabetic nephropathy (DN; n = 14) and anti-neutrophil cytoplasmatic antibody (ANCA) associated vasculitis (AAV; n = 11) by flow cytometry. RESULTS: Numbers of urinary T cells, B cells and macrophages correlated with disease activity and were significantly higher in the active LN group. Urinary T cells showed excellent distinction of patients with active LN, CD8+ T cells (AUC of ROC = 1.000) and CD4+ T cells (AUC = 0.9969) alike. CD19+ B cells (AUC = 0.7823) and CD14+ macrophages (AUC = 0.9066), as well as the clinical standard proteinuria (AUC = 0.9201), failed to reach these high standards. Patients with DN or AAV also showed increased urinary cell counts, although the CD4/CD8-ratio was significantly lower in SLE compared to in DN (p = 0.0006). Urinary CD4+ T cells of active LN patients proved to be mainly of effector memory phenotype and expressed significantly more CD40L and ki67 than corresponding blood cells. Urinary Treg counts correlated with disease activity. CONCLUSIONS: Despite of detectable urinary cell counts for B cells and macrophages, T cells remain the best urinary cellular biomarker for LN. A low CD4/CD8-ratio seems to be characteristic for LN.