Anti-properdin autoantibodies in patients with LN
The screening by ELISA revealed a presence of autoantibodies against properdin in patients with LN. 22.53% (16/71) of the patients were seropositive for anti-properdin IgG autoantibodies. For positivity cut-off was taken the average value of determined autoantibodies against properdin in healthy volunteers +3SD. (Fig.1A). The binding of IgG from positive patients to properdin was dose-dependent (Fig. 1B). Detection of anti-properdin antibodies by ELISA was validated by SPR. Purified IgG from three LN patients positive for anti-Properdin antibodies (P33, P35 and P38) showed presence and specificity the binding of purified IgG from patients to immobilized properdin (Fig. 1C, D, E). The SPR analyses revealed slow off-rate and lack of complete dissociation of the complexes, suggesting stable interaction.
Positive men for anti-properdin were 4/15 (26.67%) and positive women – were 12/56 (21.43%). The presence of elevated levels of anti-properdin antibodies was not realated to the sex of the patients (p=0.112, data not shown). There was no correlation between the age of patients (r=-0.022, p=0.854) or duration of LN (r=-0.083, p=0.498) and levels of anti-properdin (data not shown).