Background: The role of the nucleosome in the induction of antibody response in lupus mediated tissue damage especially glomerulonephritis, may provide a new insight in the early diagnosis and alternative therapeutic developments in systemic lupus erythematosus (SLE). Objectives: To evaluate the frequency and specificity of antinucleosome antibody expression in SLE patients in relation to disease activity. Also, to assess their predictive value in subclinical lupus nephritis. Methods: This study included 26 patients with SLE and 52 control subjects (26 were healthy and 26 had juvenile rheumatoid arthritis "JRA"). Among lupus patients, 15 had clinical evidence of renal involvement. After clinical evaluation to calculate the SLE disease activity index (SLEDAI), measurements of urinary microalbumin and serum antinucleosome antibodies (antinucleosome specific, antihistone and anti ds-DNA antibodies by ELISA) were performed. Patients without clinical evidence of renal involvement were followed up for one year and measurement of urinary microalbumin was repeated at the end of the study period. Those who later developed microalbuminurea were categorized as patients with subclinical lupus nephritis. Results: The expression of the 3 studied antinucleosome antibodies was significantly higher among lupus patients as compared to JRA patients and healthy controls. Seropositivity for one or more antinucleosome antibodies was elicited in 84.5% of lupus patients. Serum levels of the 3 antinucleosome antibodies were significantly higher among lupus patients with clinical nephritis than those without nephritis. ANSAb had higher sensitivity, specificity and positive and negative predictive values for subclinical lupus nephritis (100%) than antihistone and anti ds-DNA antibodies (43%, 100%, 100% and 50% respectively for either antibodies). All patients with lupus nephritis were seropositive for at least one of the antinucleosome antibodies, while those without clinical or subclinical nephritis were seronegative for the 3 antinucleosome antibodies. In 27.3% of patients with lupus nephritis, ANSAB was positive while both antihistone and ds-DNA antibodies were negative. Antinucleosome antibodies correlated positively with SLEDAI and cumulative steroid dose and negatively with corrected creatinine clearance. Conclusions: The observed sensitivity and specificity of antinucleosome specific antibodies as early indicators of subclinical lupus nephritis appear encouraging and deserve further analysis on a large scale in order to confirm their validity, especially in the anti ds-DNA seronegative lupus patients.
