Abstract
The phenomenon of in vitro activation of the classical complement pathway at low temperatures (4–21°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.