if a serum revealed a significantly reduced immobilizing activity on such f ( ab ' ) 2-covered spermatozoa , compared with the effect on spermatozoa treated with f ( ab ' ) 2 fragments from normal human serum , this was taken as evidence that the f ( ab ' ) 2 fragments and the serum antibodies were directed against the same antigen or closely associated antigenic determinants .
C0003320
antigen
C0003316
antigenic determinants