Relation between infection and autoimmunity in mixed cryoglobulinemia

Mixed cryoglobulinemia (MC) is a systemic vasculitis of small to medium-sized vessels due to the vascular deposition of circulating immune-complexes (CIC) and complement. A leukocytoclastic vasculitis is the histologic hallmark of cutaneous manifestations of the disease, while a clonal B lymphocyte expansion in blood, bone marrow, liver, and spleen represents the underlying pathologic alteration responsible for the production of cryo-CIC and non-cryo CIC with rheumatoid factor activity. A causative role of hepatitis C virus (HCV) infection has been demonstrated in the large majority of MC patients. Hepatitis C virus is both a hepatotropic and a lymphotropic virus; due to this latter biological peculiarity, HCV may trigger a constellation of autoimmune-lymphoproliferative disorders. Besides MC, other important HCV-related diseases are porphyria cutanea tarda, autoimmune hepatitis, membranoproliferative glomerulonephritis, and B cell neoplasias. Hepatitis C virus-related MC represents a link between autoimmune and lymphoproliferative disorders; moreover, MC is an important model to study the complex relation between infections and immune system alterations in humans. During the last years many other autoimmune manifestations have been correlated with HCV infection; namely, sicca syndrome, chronic polyarthritis, polydermatomyositis, fibromyalgia, autoimmune thyroiditis, lung fibrosis, and diabetes mellitus. It is often difficult to verify whether the above associations are coincidental or a pathogenetic link actually exists. At least for particular patients’ subsets and in some geographic areas, a causative role of HCV seems to be likely. The geographically heterogeneous distribution of HCVrelated autoimmune diseases suggests the contribution of important environmental and genetic factors in the pathogenesis of such conditions. In clinical practice, patients with recentonset, atypical rheumatic and autoimmune disorders should be carefully investigated for possible HCV infection; this is particularly advisable for correct diagnosis and adequate therapeutic strategy.