True about Henoch-Schonlein purpura?

Henoch-Schonlein purpura also referred to as anaphylactoid purpura, is a small-vessel vasculitis characterized by palpable purpura (most commonly distributed over the buttocks and lower extremities), ahralgias, gastrointestinal signs and symptoms, and glomerulonephritis. Henoch-Schonlein purpura is usually seen in children; most patients range in age from 4 to 7 years; however, the disease may also be seen in infants and adults.The presumptive pathogenic mechanism for Henoch-Schonlein purpura is an immune-complex deposition. A number of inciting antigens have been suggested including upper respiratory tract infections, various drugs, foods, insect bites, and immunizations. IgA is the antibody class most often seen in the immune complexes and has been demonstrated in the renal biopsies of these patients.(Harrison&;&;s principle of internal medicine,18th edition, pg no.2797)