What is the immunological cause of Henoch-Schönlein purpura?

Henoch-Schönlein purpura (HSP), also known as IgA vasculitis, is primarily associated with the deposition of IgA antibodies and complement component C3 in small blood vessels. This immunological mechanism results in a type of small-vessel vasculitis that leads to characteristic symptoms such as purpura, abdominal pain, arthritis, and renal involvement.

The presence of IgA deposition is crucial because it indicates the underlying pathophysiology of this condition, which often follows an upper respiratory tract infection. IgA is a key immunoglobulin involved in mucosal immunity, and its deposition in the vascular structures epitomizes the dysregulated immune response that characterizes HSP.

Furthermore, the role of complement component C3 in this process highlights the activation of the complement pathway, which is essential in mediating the inflammatory response in the small blood vessels affected by HSP. The combination of IgA and C3 deposition is what leads to the clinical manifestations seen in patients with this condition.

The other combinations of immunological components listed do not accurately represent the pathogenesis of Henoch-Schönlein purpura, as they involve different immunoglobulin types and complement components not relevant to this specific vasculitis.