Urticarial vasculitis is a skin condition characterized by fixed urticarial lesions that appear histologically as a vasculitis.
Antibodies to foreign proteins, as in a virus or invading bacterium, become opsonized/stuck to them highlighting them to other cells of the immune system for clearance.
These autoantibodies are not found in healthy individuals.
C1q is an integral component within the complement pathway, a complicated cascade of protein interactions in an immune response against a broad variety of pathogens.
The anti-C1q antibodies found in patients with hypocomplementemic urticarial vasculitis activate C1q, which activates the entire complement pathway.
Consequently, levels of all complement proteins become low.
Impaired classical complement pathway
The complement pathway is composed of several subset pathways: the lectin/mannose pathway, alternative pathway and the classical pathway.
All pathways culminate in the production of a C3 convertase, which catalyses C3 into its constitutive parts.
C1q is essential as the first protein to start the complement cascade which ends in the destruction of the invading bacteria or virus, and its ability to link the innate immune system: a broad defense system; and the adaptive immune system: the strong immune response capable of remembering previous infections, allowing fast response against recurrent infections.
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.
TREATMENT
There are no known specific therapies for HUV.
Treatments include systemic corticosteroids, dapsone, colchicine, hydroxychloroquine, and various immunosuppressant medications, such as methotrexate, mycophenolate, and azathioprine.
Newer targeted medications, including omalizumab and belimumab, are also efficacious.