Presence of lower temperature-dependent antibody with low avidity to C100-3 (HCV) antigen in voluntary blood donors

The association of complement activation at a low temperature with hepatitis C virus infection in comparison with cryoglobulin

Complement activation at a low temperature in vitro and cryoglobulinaemia are associated with hepatitis C virus (HCV) infection. The frequency of HCV antibody positivity determined in serum specimens that showed the cold-dependent activation of complement was 100%, whereas it was 48% among sera with cryoglobulin. On the other hand, the frequency of cold activation among HCV-infected sera was 41%, and that of cryoglobulin 48%. Cold activation was not found in any HCV- sera studied, whereas cryoglobulin was found at a frequency of 14% in HCV- sera. Cold activation was also absent among hepatitis B virus (HBV) S antigen or antibody-positive sera, except a few that were both HBV+ and HCV+. Rheumatoid factor was also frequently detected in sera with cold activation or cryoglobulin. Cold activation and cryoglobulin may be generated by common mechanisms in which a low avidity, low temperature-preferring antibody may function. In sera with cold activation, fine particles of immune complexes, which do not form precipitates, may activate the complement system. HCV is a unique virus that coexists with antibody in the serum, therefore the avidity of the antibody for the virus antigen may be low, and occasionally react only at a low temperature. This may be why the in vitro phenomenon related to immune complexes occurs specifically in HCV-infected sera.

The association between hepatitis C virus infection and in vitro activation of the complement system

The phenomenon of in vitro activation of the classical complement pathway at low temperatures (4-21 degrees C) is known as cold activation, and has been suggested to be associated with non-A, non-B hepatitis. We re-examined the association by using newly developed markers of hepatitis C virus (HCV) infection. Twenty-one cases randomly selected from those fulfilling the screening criteria of complement cold activation all showed evidence of HCV infection. More than half of 55 HCV antibody-positive cases selected randomly from our laboratory samples showed a tendency towards cold activation, whereas none of the HCV antibody-negative sera showed cold activation. All the HCV antibody-positive cases were negative in cold activation when CH50 was assayed with plasma. These results, taken together, indicate that cold activation of the complement system is strongly associated with HCV infection.