Characterization of Anti-Forssman (ANTI-Fs) Antibodies in Human Sera: Their Specificity and Possible Changes in Patients with Cancer

Abstract

The majority of normal human sera hemolyze sheep erythrocytes in the presence of complement (“hemolyzers”), whereas sera of the remaining population do not lyze sheep erythrocytes (“nonhemolyzers”). The antibodies responsible for this lytic activity are now identified as being specific to Forssman (Fs) glycolipid, predominantly of the IgM class, and only weakly cross-reactive with blood group A glycolipid. These conclusions are based on the following observations: 1) “Hemolyzer” sera produced complement-dependent lysis of liposomes containing Fs glycolipid, whereas “nonhemolyzer” sera reacted very weakly with the same Fs liposomes; the level of hemolytic activity generally paralleled the reactivity of the sera with Fs liposomes. 2) Human “anti-Fs” did not cross-react with liposomes containing either globoside, the precursor to Fs, or blood group A glycolipid. 3) The complement-dependent hemolysis of sheep erythrocytes by hemolyzer sera was specifically inhibited by Fs liposomes but not by either A- or globoside liposomes. 4) In five of six cases tested, hemolysin activity was present in the IgM fraction but not the IgG fraction, whereas in the remaining case the activity was present in the IgG fraction.We have previously described the presence of Fs glycolipid in the normal gastrointestinal mucosa of a minor percentage of Taiwanese cancer patients, whereas in the majority of cases Fs was absent in the normal mucosa but present in the tumors derived therefrom. The sera of cancer patients displayed a decreased anti-Fs reactivity as compared with sera of a control group suggesting that Fs-positive tumor tissue may affect serum anti-Fs levels.