Anti-C1q antibodies in lupus nephritis and their correlation with the disease activity

Systemic lupus erythematosus (SLE) is an autoimmune connective tissue disorder. Renal involvement usually develops in the first few years of illness and should be detected early by periodic urine analysis and quantitation of proteinuria. The aim of our work was to evaluate the biological marker [anti-complement 1q antibodies (anti-C1q Ab)] in lupus nephritis (LN) patients and its correlation to SLE disease activity. Sixty-five subjects were divided into four groups; Group I: SLE patients with LN (proteinuria >0.5 g/day), Group II: SLE patients without LN (all of them had a lupus flares rather than nephritis; active nonrenal), Group III: SLE patients without any activity (inactive disease), and Group IV: Control group. All subjects underwent urine analysis, complete blood picture, liver function tests, kidney function tests, albumin/ creatinine ratio, antinuclear antibody, anti-double stranded DNA (anti-dsDNA) antibody, C3, C4, and anti-C1q Ab. All patients in the first group underwent renal biopsy and pathological diagnosis showed: Class II in two patients, Class III and IV in nine patients, and Class V in four patients. Anti-C1q Ab were found in the serum of SLE patients and not in the control group and showed an association with active lupus with much higher concentration in active renal group, specifically those with severe renal histological lesions (proliferative form). There was significant statistical positive correlation between anti-C1q Ab with anti-dsDNA and SLE disease activity index in both active groups. There was statistically significant negative correlation between anti-C1q Ab with C3 and C4 in both active groups. Anti-C1q Ab could be used as useful marker for active lupus, especially with nephritis.