Immune Complex Glomerulonephritis

Immune complex glomerulonephritis is the mechanistic category of glomerular injury driven by the deposition of antigen-antibody complexes in the glomerulus, identifiable on immunofluorescence as granular deposits of immunoglobulin and complement. It groups together several otherwise distinct diseases — including IgA nephropathy, post-infectious glomerulonephritis, and many membranoproliferative patterns — that share this common pathway of injury.

Definition

Immune complex glomerulonephritis is glomerular inflammation caused by deposition of antigen-antibody complexes within the glomerulus, characteristically producing granular immunoglobulin and complement staining on immunofluorescence, in contrast to pauci-immune and anti-GBM patterns.

Scope

This entry describes the immune-complex pathway: how circulating or in-situ complexes localise in the glomerulus, how complement activation amplifies injury, and how the resulting granular deposition pattern unifies a set of diseases. It situates the category against the pauci-immune and anti-GBM patterns and uses IgA nephropathy and membranoproliferative glomerulonephritis as illustrations. It is a reference description of mechanism and classification, not treatment guidance.

Core questions

• How do immune complexes come to localise in the mesangium and capillary wall?
• What role does complement activation play in amplifying glomerular injury?
• Why does this pathway present along a spectrum from nephritic to nephrotic features?
• Which diseases share the immune-complex deposition pattern, and how are they distinguished?

Key concepts

• Granular immunofluorescence (immune-complex) pattern
• Circulating versus in-situ immune complex formation
• Mesangial versus subendothelial versus subepithelial deposits
• Complement activation and hypocomplementaemia
• IgA nephropathy
• Post-infectious glomerulonephritis
• Membranoproliferative glomerulonephritis

Mechanisms

Glomerular immune-complex disease arises when antigen-antibody complexes accumulate in the glomerulus, either by trapping of preformed circulating complexes or by in-situ formation against planted or intrinsic antigens. The location of deposits — mesangial, subendothelial, or subepithelial — shapes the histologic pattern and clinical expression, with subendothelial and mesangial deposits tending toward proliferative, nephritic injury and subepithelial deposits toward a more nephrotic picture. Deposited complexes activate complement, and the degree of activation can lower circulating complement levels, a useful classifying feature in some forms. IgA nephropathy exemplifies mesangial deposition of galactose-deficient IgA1 immune complexes, while membranoproliferative patterns reflect chronic subendothelial deposition with capillary-wall remodelling; reclassification has increasingly separated immune-complex-mediated from complement-mediated membranoproliferative disease (Jennette 2012; Sethi 2012; Wyatt 2013; Donadio 2002).

Clinical relevance

The immune-complex category is a reference organising principle: identifying granular deposition on biopsy groups a presentation with a particular set of diseases and serologic associations and separates it from pauci-immune and anti-GBM injury. This entry describes that conceptual framework and the underlying mechanisms; it does not provide diagnostic criteria or treatment for individual patients, which are addressed by current guidelines and clinicians.

Epidemiology

Immune-complex diseases include some of the most common glomerulonephritides: IgA nephropathy is among the most frequent primary glomerular diseases worldwide, post-infectious glomerulonephritis remains important especially in children and in some regions, and membranoproliferative patterns are less common. Frequencies vary by age, geography, and biopsy practice (Wyatt 2013; Sethi 2012; Rovin 2021).

History

The recognition that many glomerulonephritides share immune-complex deposition followed the application of immunofluorescence and electron microscopy in the mid-twentieth century, which distinguished granular (immune-complex) from linear (anti-GBM) and pauci-immune patterns. Membranoproliferative glomerulonephritis, historically defined by light-microscopic appearance, was later reorganised by immunofluorescence into immune-complex-mediated and complement-mediated forms (Sethi 2012; Jennette 2012).

Debates

How should membranoproliferative glomerulonephritis be classified?

A reappraisal has moved from the older light-microscopic typing toward an immunofluorescence-based scheme separating immune-complex-mediated disease from complement-mediated (C3) glomerulopathy, reflecting differing mechanisms despite a shared histologic pattern.

Key figures

• J. Charles Jennette
• Sanjeev Sethi
• Fernando C. Fervenza
• Bruce A. Julian

Seminal works

• jennette2012
• sethi2012
• wyatt2013

Frequently asked questions

How is immune-complex glomerulonephritis distinguished from pauci-immune disease?

On immunofluorescence, immune-complex disease shows granular deposits of immunoglobulin and complement, whereas pauci-immune disease (typically ANCA-associated) shows little or no such staining despite active inflammation.

Why do complement levels matter in some of these diseases?

Because deposited immune complexes can activate complement, circulating complement may fall in certain immune-complex glomerulonephritides; the pattern of complement consumption is used as a reference clue in classification.