Glomerular Autoimmune Multicomponents of Human Lupus Nephritis In Vivo (2): Planted Antigens

Glomerular planted antigens (histones, DNA, and C1q) are potential targets of autoimmunity in lupus nephritis (LN). However, the characterization of these antigens in human glomeruli in vivo remains inconsistent. We eluted glomerular autoantibodies recognizing planted antigens from laser-microdissected renal biopsy samples of 20 patients with LN. Prevalent antibody isotypes were defined, levels were determined, and glomerular colocalization was investigated. Renal and circulating antibodies were matched, and serum levels were compared in 104 patients with LN, 84 patients with SLE without LN, and 50 patients with rheumatoid arthritis (RA). Autoantibodies against podocyte antigens (anti-α-enolase/antiannexin AI) were also investigated. IgG2 autoantibodies against DNA, histones (H2A, H3, and H4), and C1q were detected in 50%, 55%, and 70% of biopsy samples, respectively. Anti-DNA IgG3 was the unique non-IgG2 anti-DNA deposit, and anti-C1q IgG4 was mainly detected in subepithelial membranous deposits. Anti-H3, anti-DNA, and anti-C1q IgG2 autoantibodies were also prevalent in LN serum, which also contained IgG3 against the antigen panel and anti-C1q IgG4. Serum and glomerular levels of autoantibodies were not strictly associated. High serum levels of all autoantibodies detected, including anti-α-enolase and antiannexin AI, identified LN versus SLE and RA. Anti-H3 and anti-α-enolase IgG2 levels had the most remarkable increase in LN serum and represented a discriminating feature of LN in principal component analysis. The highest levels of these two autoantibodies were also associated with proteinuria>3.5 g/24 hours and creatinine>1.2 mg/dl. Our findings suggest that timely autoantibody characterization might allow outcome prediction and targeted therapies for patients with nephritis.