Detection of thymus leukemia antigens on the surface membranes of murine leukemia cells resistant to thymus leukemia antibodies and guinea pig complement.

The thymus leukemia (TL) antigens of ASL-1 murine leukemia reversibly disappeared from the membranes of cells exposed to TL antisera; the cells acquired resistance to fresh TL antiserum and complement (antigenic modulation). Three independent methods, however, indicated that the acquisition of complement resistance preceded the complete disappearance of TL antigens from the cell surface. Modulated cells reduced known titers of TL antisera by absorption; they stained positively in immunofluorescence studies involving TL antibodies and fluorescence-labeled rabbit anti-mouse immunoglobulin. TL antigens labeled previously with 125I were recovered by immunoprecipitation from cellular extracts prepared with nonionic detergent. Continued exposure of the cells to TL antiserum led to virtually complete disappearance of the antigens. Similar results were obtained for RADA-1 cells, another murine leukemia that forms TL antigens, although in this instance the cells were resistant to the cytolytic effects of TL antisera and guinea pig complement (GPC) without prior exposure to TL antibodies. The density of TL antigens remaining on the surface of different TL(+) cell types failed to correlate with resistance to TL antibodies and GPC. Cells from F, hybrids of TL(+) and TL(-) mouse strains formed TL antigens and were susceptible to TL antibodies and GPC even though the density of TL antigens formed by the susceptible cells was less than the density of TL antigens formed by modulated cells. Stable somatic hybrids of RADA-1 cells and TL(-) cells formed TL antigens at lower density than did RADA-1 cells and lysed in the presence of aliquots of the TL antisera and GPC used in previous tests.