Characterization of anti-Forssman (anti-Fs) antibodies in human sera: their specificity and possible changes in patients with cancer.

The m a j o r i t y o f n o r m a l h u m a n se ra h e m o l y z e sheep e r y t h r o c y t e s in the p r e s e n c e o f c o m p l e m e n t ( "hemoly zers") , w h e r e a s s e ra o f the r e m a i n i n g populat ion do not lyze sheep e r y t h r o e y t e s C~nonhemolyzers") . The antibodies respons ib le for this lyt ic ac t iv i ty a r e n o w identified as be ing specific to F o r s s m a n (Fs) glycol ipid, p re d o m i n a n t l y of the IgM class , a nd on ly w e a k l y crossreact ive w i t h blood group A glycolipid. These conclus ions are based on the fo l lowing observat ions: 1) "Hem o l y z e r " s e ra produced complement -dependent lys is o f l iposomes conta in ing Fs glycoHpid, w h e r e a s " n o n h e m o l yze r " s e ra r e a c t e d v e r y w e a k l y wi th the same Fs liposomes ; the level o f hemoly t i c act iv i ty gene ra l l y pa ra l le led the react iv i ty o f the se ra w i th Fs l iposomes . 2) H u m a n " a n t i F s " did not cross -react wi th l iposomes conta lning e i the r globoside, the precursor to Fs, o r blood group A glycolipid. 3) The complement -dependent hemo lys i s o f sheep ery throcytes by h e m o l y z e r sera w a s specif ical ly inhibited by Fs l iposomes but not by e i ther Aor g lobos ide l iposomes . 4) In f ive o f six cases tested, h e m o l y s i n act iv i ty w a s present in the IgM f r ac t i on but not the IgG fraction, w h e r e a s in the remain ing case the ac t iv i ty w a s present in the IgG f rac t ion . We h a v e p r e v i o u s l y described the p r e s e n c e o f Fs glycol ipid in the normal gastro intes t inal m u c o s a o f a minor percentage o f T a i w a n e s e cancer pat ients , w h e r e a s in the major i ty o f cases Fs w a s absent in the normal m u c o s a but present in the tumors der ived t he r e f rom. The s e r a o f cancer pat ients displayed a decreased anti-Fs react iv i ty as compared w i t h se ra o f a control group sugges t ing that Fs-pos i t ive tumor t i ssue m a y affect s erum anti-Fs levels .