By immunization of a rabbit with purified gs-antigen from mouse leukemia virus (MLV) a potent antiserum (R-gs-serum) was obtained, which reacts specifically with gs-antigen of MLV.In cat leukemia virus (KLV) two types of antigens, probably both group specific, could be demonstrated with anti-KLV-sera by Ouchterlony test. One of these was shown with MLV-sera to be identical with a MLV-gs-antigen component. This antigen occurring in both viruses is called gsinterspecies (interspec.) antigen.R-gs-serum allowed to detect gs-interspec. antigen also by the more sensitive CF-test. [Lispa (leukemia virus interspec. antigen) CF-test]. Preliminary experiments with this test indicated that bovine leukosis as well as human cancer cells can produce an agent in tissue culture which is serologically related to MLV.
