Involvement of activated cytotoxic T lymphocytes and natural killer cells in Henoch–Schönlein purpura nephritis

OBJECTIVES: Immunoglobulin A vasculitis/Henoch–Schönlein purpura (IgAV/HSP) is a major cause of vasculitis in children. It is often accompanied by nephritis (HSPN) and could progress to chronic kidney disease. Galactose‐deficient IgA(1) was recently reported to be involved in the pathogenesis of HSPN, for which immunosuppressive drugs are considered key treatment. However, the involvement of immune cells in the development of HSPN remains unclear. METHODS: We compared gene expressions of peripheral blood mononuclear cells (PBMCs) among healthy controls (n = 10), IgAV/HSP patients (n = 21) and HSPN patients (n = 8), which required nephritis development within 3 months of IgAV/HSP onset. Immunohistochemistry analysis and flow cytometry were performed to assess renal biopsy specimens and PBMCs, respectively. Serum CX3CL1 levels were measured by ELISA. RESULTS: GNLY and GZMB expressions increased in HSPN patients, consistent with increased number of glomerular granulysin‐ and/or granzyme B‐positive cells demonstrated by immunohistochemistry analysis. Additionally, circulating cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells were activated with the up‐regulated surface expressions of human leucocyte antigen DR (HLA‐DR) and CX3CR1 in HSPN patients with severe proteinuria. Renal biopsies demonstrated increased number of CD8(+) cells and/or CD56(+) cells and up‐regulated expression of glomerular CX3CL1, a specific ligand for CX3CR1, along with increased serum CX3CL1 level. CONCLUSION: Activated CTLs and NK cells play roles in the development of nephritis in IgAV/HSP patients and can be used as novel biomarkers for HSPN.