immune complex deposition
Summary
Immune complex deposition occurs when antigen-antibody complexes accumulate in tissues, triggering complement activation and inflammatory responses. This mechanism underlies Type III hypersensitivity reactions and causes diseases like systemic lupus erythematosus, post-streptococcal glomerulonephritis, and serum sickness.
Detail
Immune complex deposition is a pathological process where circulating antigen-antibody complexes become trapped in tissues, particularly in blood vessel walls, glomerular basement membranes, and synovial membranes. These complexes form when antigens (self or foreign) bind to antibodies, creating immune complexes that should normally be cleared by the reticuloendothelial system. When clearance mechanisms are overwhelmed or impaired, complexes deposit in tissues and activate complement (particularly C3a and C5a), leading to neutrophil chemotaxis, release of inflammatory mediators, and tissue damage. The size and charge of immune complexes determine their deposition pattern - intermediate-sized complexes are most pathogenic as they're too large for easy clearance but too small to be rapidly removed by phagocytes. This mechanism is responsible for the glomerulonephritis seen in SLE, the arthritis in rheumatoid arthritis, and the vasculitis in polyarteritis nodosa. Diagnosis often involves measuring complement levels (C3, C4 typically decreased), detecting circulating immune complexes, and tissue biopsy showing granular immunofluorescence patterns.
Sources
- Robbins and Cotran Pathologic Basis of Disease
- Abbas Basic Immunology
- First Aid for the USMLE Step 1
- Janeway's Immunobiology
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