[Anti-C1q antibodies in patients with systemic lupus erythematosus treated by rituximab]

To determine the time course of changes in the blood levels of antibodies (Ab) to complement component C1q (a-C1q) in patients with systemic lupus erythematosus (SLE) during rituximab (RTM) therapy and the association with organ injuries in SLE.

The study involved 41 patients (3 men and 38 women; their median age was 27.5 (range 22-36) years) with definite SLE. Their blood a-C1q levels were determined by enzyme immunoassay. The levels and detection rates of a-C1q were estimated in relation to organ injuries, the time course of RTM therapy-induced changes in a-C1q levels were determined. High-positive (> 30 U/ml), low-positive (10-30 U/ml), and negative (< or = 10 U/ml) a-C1q levels were found.

A-C1q was detected in 19 (46.3%) patients with different clinical manifestations of SLE. The patients with renal diseases had high-positive levels of a-C1q statistically significantly more frequently than those without renal involvement (p = 0.04). Low-positive and negative a-C1q levels were found in 15 of 16 without nephritis. There was a statistically significant positive correlation of the concentration of a-C1q with Ab to double-stranded DNA (a-dsDNA), Ab to nucleosomes, the SLE Disease Activity Index 2000 (SLEDAI-2K), erythrocyturia, hematuria and a negative correlation between a-C1q and complement components C3 and C4. Just after one month of RTM therapy, the patients with nephritis were observed to have a statistically significant decrease in the levels of a-C1q (p = 0.002), which persisted 1 year after the treatment (p = 0.006). Nineteen patients with the higher baseline concentrations of a-C1q after RTM treatment showed a statistically significant decrease in the levels of a-C1q at 1-, 3-, 6-, and 12-month follow-up (p = 0.016, 0.02, 0.035, and 0.04, respectively) which was accompanied by the decreased SLEDAI-2K (p < 0.00004 at 1-, 3-, 6-, and 12-month follow-up).

The high levels of a-C1q were found statistically significantly more often in the patients with lupus nephritis than in those with SLE without renal involvement. The level of a-C1q statistically significantly reduced after RTM therapy and remained within the normal range during a year.