## **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 the vessels, leading to inflammation and purpura. The condition is often associated with **IgA** deposition.

## **Why the Correct Answer is Right**
The correct answer, **IgA**, is right because Henoch-Schonlein purpura is known for the deposition of IgA immune complexes around the small vessels. This deposition leads to the activation of complement and subsequent inflammation of the vessel walls, resulting in the characteristic purpura, arthritis, abdominal pain, and renal involvement. The presence of IgA deposits is a hallmark of HSP and is used in diagnostic criteria.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *IgG* - While IgG is a common immunoglobulin involved in many immune responses and can be found in some types of vasculitis, it is not the primary immunoglobulin deposited in Henoch-Schonlein purpura.
- **Option B:** *IgM* - IgM is often associated with primary immune responses and certain types of lymphoproliferative disorders but is not characteristically deposited in HSP.
- **Option D:** *IgE* - IgE is primarily involved in allergic reactions and parasitic infections, not in the pathogenesis of Henoch-Schonlein purpura.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Henoch-Schonlein purpura often presents with a tetrad of symptoms: **purpura**, **arthralgias/arthritis**, **abdominal pain**, and **renal involvement**. The presence of IgA deposits is crucial for the diagnosis, especially in cases with atypical presentations.

## **Correct Answer:** .