Masking of nontumorous antigens for development of human tumor nucleolar antibodies with improved specificity

Nucleoli purified from HeLa cells were spread by homogenization in low ionic strength buffer and by chelation of divalent cations. The antigenic determinants of these tumor nucleoli that are shared by normal liver nucleoli were masked by addition of rabbit anti-liver nucleolar antisera to form immune complexes. New Zealand White rabbits were immunized with these antibody-nucleolar complexes. The resulting antisera produced nucleolar fluorescence in HeLa cells but not in normal human liver or human kidney cells. One- and two-dimensional immunoblots identified a major Mr 58,000/pl 5.8 antigen in HeLa cells, which was not detected on corresponding immunoblots of normal human liver nucleoli. This method offers an improved approach to selection of tumor-associated antigens.