## **Core Concept**
Henoch-Schonlein purpura (HSP) is a form of vasculitis that primarily affects small blood vessels. It is characterized by the deposition of immune complexes around these vessels, leading to inflammation and purpura. The condition is often associated with IgA nephropathy and involves the deposition of specific immunoglobulins.

## **Why the Correct Answer is Right**
The correct answer, **IgA**, is right because Henoch-Schonlein purpura is indeed characterized by the deposition of IgA immune complexes around the vessels. This deposition leads to the activation of complement and the subsequent inflammation of the vessel walls, which is a hallmark of the disease. IgA deposition is a key diagnostic criterion and is involved in the pathogenesis of HSP.

## **Why Each Wrong Option is Incorrect**
- **Option A: IgG** - While IgG is the most abundant immunoglobulin in the circulation and plays a significant role in immune responses, it is not specifically associated with the deposition seen in Henoch-Schonlein purpura.
- **Option B: IgM** - IgM is primarily involved in the ABO blood group antigens and is not characteristically deposited in HSP.
- **Option C: IgE** - IgE is associated with allergic reactions and parasitic infections, not with the vascular deposition seen in HSP.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Henoch-Schonlein purpura often presents with a tetrad of symptoms: palpable purpura, arthritis, abdominal pain, and renal involvement. The disease is more common in children but can occur in adults as well, with a worse prognosis in the latter group. The deposition of IgA is not only diagnostic but also pathogenic.

## **Correct Answer:** . IgA