Serum IgM antibodies to hepatitis C virus in acute and chronic hepatitis C.

A standardized commercially available immunoassay is not available for detection of IgM antibodies against hepatitis C virus antigens (IgM anti-HCV). Therefore, different "in-house" enzyme immunoassays have been assessed. These assays vary greatly in sensitivity, but specificity seems satisfactory in all of them. A typical IgM antibody response to HCV antigens is usually found in nearly all patients with acute hepatitis C. This antibody response rarely precedes the appearance of IgG anti-HCV, and it persists for a few months at high titer. Low titers of IgM anti-HCV are detectable in 50-80% of cases with chronic hepatitis C. IgM anti-HCV reactivity is typically found during acute exacerbation of chronic hepatitis C. Furthermore, many patients with chronic active hepatitis C without acute exacerbation also have IgM anti-HCV. In these patients a correlation exists between the titer of IgM anti-HCV and the biochemical parameters of liver disease. When alpha interferon therapy induces a sustained remission of liver disease activity, positivity for IgM anti-HCV disappears in more than 70% of cases. In contrast, patients who do not respond to therapy rarely loose IgM anti-HCV. In conclusion, serum IgM antibodies to HCV antigens are reliable markers of active HCV-induced liver disease both in acute and in chronic HCV infection.