Immune-complex small-vessel vasculitis
- Lesion
Antibody–antigen clumps lodge in tiny vessels, mostly venules of the skin, and attract neutrophils: the result is purpura you can feel.
What it is
When immune complexes are deposited in the walls of small vessels, complement is activated and neutrophils destroy the wall, breaking up as they do (leukocytoclasia). The skin shows palpable purpura; kidney, gut and joints may follow. Triggers include drugs and infections (hypersensitivity or cutaneous small-vessel vasculitis), IgA-containing complexes (IgA vasculitis), cryoglobulins linked to hepatitis C (cryoglobulinemic vasculitis) and autoimmune disease such as lupus. Behçet disease is a variable-vessel vasculitis that can affect arteries and veins of any size.
Structure
- Skin biopsy: neutrophils in and around venule walls, nuclear debris, fibrin in the wall and extravasated red cells.
- Direct immunofluorescence: IgA in IgA vasculitis; IgM, IgG and C3 in cryoglobulinemia.
Step by step
- An antigen (drug, microbe, autoantigen or IgA aggregates) forms complexes with antibodies in the blood.
- Complexes lodge in the walls of small vessels where flow is slow and permeability high (venules of the skin).
- Complement activation releases C5a, which attracts neutrophils.
- Neutrophils damage the wall and fragment; red cells leak into the tissue.
- If the antigen is removed, lesions heal in weeks; persistent antigen causes recurrent or chronic disease.
Immune-complex and variable-vessel vasculitides
| Disease | Deposits or trigger | Organs | Clue |
|---|---|---|---|
| Cutaneous small-vessel (hypersensitivity) vasculitis | Drug or infection immune complexes | Skin | Palpable purpura after a new drug |
| IgA vasculitis | IgA1-dominant complexes | Skin, joints, gut, kidney | Child, purpura on buttocks and legs |
| Cryoglobulinemic vasculitis | Mixed cryoglobulins (IgM rheumatoid factor with IgG) | Skin, nerves, kidney | Hepatitis C, low complement |
| Lupus vasculitis | DNA–anti-DNA complexes | Skin, kidney, brain | Positive antinuclear antibodies, low complement |
| Behçet disease | Neutrophil-driven, HLA-B51 associated | Mouth, genitals, eye, veins, arteries | Recurrent oral and genital ulcers |
Clinical notes
- Many drug- or infection-triggered cases resolve when the trigger is removed.
- Kidney involvement determines the long-term outlook in IgA and cryoglobulinemic vasculitis.
Test yourself
Think of the answer, then tap the question to see it.
What does ‘leukocytoclastic’ mean?
That neutrophils in the vessel wall break apart, leaving nuclear dust (fragments) around damaged venules.
Which infection is the usual cause of mixed cryoglobulinemic vasculitis?
Chronic hepatitis C virus infection.
Which immunoglobulin is deposited in IgA vasculitis, and which organ decides the prognosis?
IgA (mainly IgA1); the kidney decides the long-term outlook.
Elsewhere in DurgiPedia
Connections
Microorganisms1
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Vasculitis| Angiitis | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.