Detection of glomerular complement C3 fragments by magnetic resonance imaging in murine lupus nephritis

Abstract

One of the challenges of treating patients with glomerulonephritis (GN) is to accurately assess disease activity. We recently developed a magnetic resonance imaging (MRI)-based method of detecting glomerular C3, and hypothesized that this agent could be used to monitor the severity of GN. In the current study we used this imaging method to track the progression of renal disease in the MRL/lpr mouse model of lupus nephritis (LN). The targeting agent is comprised of superparamagnetic iron oxide (SPIO) nanoparticles conjugated to complement receptor type 2 (CR2-targeted SPIO). Glomerular C3b/iC3b/C3d deposition in progressively aging MRL/lpr and control mice was monitored with quantitative immunofluorescence or with CR2-targeted SPIO and T2-weighted MRI. Immunofluorescence showed that glomerular C3b/iC3b increased with disease activity. This finding was replicated with the T2-weighted MRI: T2-relaxation times decreased (as SPIO reduce T2-relaxation times) with disease activity in the cortex and medullas of MRL/lpr mice, but not of control mice. Our findings demonstrate that an MRI contrast agent targeted to glomerular C3b/iC3b/C3d can be used to non-invasively monitor disease activity in GN. Further, therapeutic complement-inhibitors have recently been used in patients with renal disease, and this method could identify patients likely to benefit from complement inhibition.

Non-invasive imaging to monitor lupus nephritis and neuropsychiatric systemic lupus erythematosus

“…CR2 binds the C3d cleavage fragment of C3 with a K D of approximately 0.5 μM 77 . Because CR2 does not bind intact plasma C3 it can be used to target therapeutic and diagnostic agents to sites of complement activation 8, 78– 80 . We have also developed several monoclonal antibodies to C3d that do not bind to intact C3 or to C3b 81 .…”

“…To determine whether this method can be used to assess disease severity, we repeated the protocol at four week intervals in MRL/lpr mice 80 . Kidney disease worsens as MRL/lpr mice age, and the abundance of C3 fragments in the glomeruli increases until the terminal stages of the disease 80 .…”

“…Kidney disease worsens as MRL/lpr mice age, and the abundance of C3 fragments in the glomeruli increases until the terminal stages of the disease 80 . The degree of negative enhancement in the kidneys of the mice increased between 12 and 20 weeks of age.…”

“…The degree of negative enhancement in the kidneys of the mice increased between 12 and 20 weeks of age. These results suggest that MRI-based detection of glomerular C3 can be used to monitor the severity of the underlying disease, although this method still has limited sensitivity for detecting small differences in glomerular C3 80 . A study to determine whether this method can detect the response of MRL/lpr mice to immunosuppressive treatment is currently underway.…”

“…Unfortunately, these changes are not accurate for identifying patients with severe disease that is amenable to treatment. The abundance of glomerular C3 deposits increases with disease severity but falls off in end stage disease 80 , raising the possibility that non-invasive detection of glomerular C3 will be useful for guiding treatment of patients with lupus nephritis.…”