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Abstract
Background: Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the loss of tolerance to nuclear self-antigens, the production of pathogenic autoantibodies and damage to multiple organ systems. Major histocompatibility complex (MHC) class II-mediated priming of T and B lymphocytes is a central element of autoimmunity in systemic lupus erythematosus (SLE). Cathepsin S (Cat S), a cysteine protease, degrades the invariant peptide chain during MHC II assembly with antigenic peptide in antigen-presenting cells. Objective: This study aims to correlate the plasma levels of cathepsin S activity to the activity of the disease, as well as assess the plasma levels of cathepsin S activity as a possible biomarker of activity in patients with SLE. Subjects and methods: Disease activity was assessed using the systemic lupus erythematosus disease activity Index 2000 (SLEDAI-2K). Plasma samples were taken from 50 female patients suffering from SLE as well as 30 age and sex matched apparently healthy control subjects. Cat S activity in all plasma samples was assessed using cathepsin S activity fluorometric assay kit. C3 and C4 were done to every patient by nephelometry. Routine laboratory investigations were done for every patient. Results: The present data showed a significant increase in the mean levels of Cat S activity in SLE patients compared to control group (p{u2264}0.001). The mean levels of cat S activity were significantly higher in active versus inactive SLE patients p<0.001