How do immune complexes cause disease?

Type III hypersensitivity: Immune complexes usually deposit in blood vessels, especially vessels through which plasma is filtered at high pressure (e.g., in renal glomeruli and joint synovium). Therefore, in contrast to diseases caused by tissue antigen-specific antibodies, immune complex diseases tend to be systemic and often manifest as widespread vasculitis involving sites that are particularly susceptible to immune complex deposition, such as kidneys and joints.