[Rheumatoid factor and cryoglobulin are not efficiently related to cold activation of complement]

Cold activation of complement (CA) is a phenomenon characterized by a low hemolytic complement activity in chilled serum. Cryoglobulin and RF have been reported as main causes of CA, and we previously reported the close association between CA and HCV infection in 21 CA patients. Therefore, we assayed CA, RF, cryoglobulin and anti-HCV antibody titers in 304 randomly selected patients with unknown diseases. CA was positive in 26 of the 304 patients, and among them, RF and/or cryoglobulin were found positive in 20 patients, and anti-HCV antibody were positive in all of them. RF was positive in 41 of the 304 patients. 37% of them were anti-HCV antibody positive and 63% were negative. Cryoglobulin was positive in 61 out of 304 patients. Anti-HCV antibody positivity was observed in 59 out of 304 patients, and all CA-positive cases were included in the anti-HCV antibody-titer-positive group. However, either RF or cryoglobulin positive patients were observed in the same degree in both anti-HCV antibody titer positive and negative groups. Therefore, RF or cryoglobulin is not considered the main cause of CA.