Virus or bacteria with antibodies opsonized or "stuck" to them highlight them to other cells of the immune system for clearance.

C1q is an integral component within the complement pathway – a complicated cascade of protein interactions, culminating in an immune response against a broad variety of pathogens.

[3] Case studies of individuals with HUV have also highlighted other potential complicating factors which it seems the anti-C1q antibodies play a role in.

Diagnosis is confirmed with the identification of at least two conditions from: venulitis on skin biopsy, arthritis, ocular inflammation, abdominal pain or positive C1q antibodies to immune complexes.

Treatments include systemic corticosteroids, dapsone, colchicine, hydroxychloroquine, and various immunosuppressant medications, such as methotrexate, mycophenolate, and azathioprine.