Henoch Schonlein purpura presents with deposition of:
**Core Concept**
Henoch Schonlein purpura (HSP) is a form of vasculitis that affects small blood vessels, particularly in children. It is characterized by the deposition of immune complexes in the walls of these vessels, leading to inflammation and subsequent symptoms.
**Why the Correct Answer is Right**
The correct answer is IgA immune complexes. These complexes are formed when IgA antibodies bind to antigens, such as bacterial or viral proteins, and are deposited in the walls of small blood vessels. The deposition of these immune complexes triggers an inflammatory response, which is mediated by the activation of complement and the release of various cytokines. This leads to the characteristic symptoms of HSP, including palpable purpura, arthritis, gastrointestinal symptoms, and renal involvement.
**Why Each Wrong Option is Incorrect**
* **Option A:** IgM immune complexes are not typically associated with HSP. While IgM can also form immune complexes, the pathogenesis of HSP is primarily attributed to IgA.
* **Option B:** C3b is a fragment of the complement component C3, which is activated during the complement cascade. While C3b is involved in the inflammatory response, it is not directly related to the deposition of immune complexes in HSP.
* **Option D:** Fibrinogen is a clotting factor that plays a crucial role in blood coagulation. While fibrinogen is involved in the formation of blood clots, it is not related to the pathogenesis of HSP.
**Clinical Pearl / High-Yield Fact**
HSP is often associated with a preceding upper respiratory tract infection, and the deposition of IgA immune complexes is thought to be triggered by an immune response to these infections. This highlights the importance of a thorough history and physical examination in diagnosing HSP.
**Correct Answer:** C. IgA immune complexes.