C3 and systemic lupus erythematosus: There was a negative correlation between CD55 (r = −0.278, P = 0.019) and CD59 (r = −0.23, P = 0.048) expression on neutrophils and the SLEDAI; beside that, there was a positive correlation between CD55 (r = 0.237, P = 0.021) and CD35 (r = 0.334, P = 0.030) expression on neutrophils and C3 serum levels in SLE patients, and CD55 (r = 0.334, P = 0.001) with C4 level.