This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vasculitis, Subject name: Medicine
Which antibody is incriminated in causing Henoch Schonlein Purpura? 
Select and explain. 
A. IgA, B. IgG, C. IgM, D. IgD
A: IgA
Answer: A: IgA 
Explanation: Ans. (a) IgARef: Harrison 18th edition, Chapter 326* The Presumptive pathogenic mechanism for Henoch- Schonlein purpura is immune-complex deposition.* IgA is the antibody class most often seen in the immune complexes and has been demonstrated in the renal biopsies of these patients.* A number of inciting antigens have been suggested including upper respiratory tract infections, various drugs, foods, insect bites, and immunizations.