In vivo modulation of thymus-leukemia antigens on mouse leukemia cells and thymocytes: retention of modulating antibody on the cell surface.

Inoculation of RADA1, ASL1, and ERLD murine leukemia cells into the peritoneal cavities of (C57BL/6J x A/TL--)F1 mice hyperimmunized against thymus-leukemia (TL) cell-surface antigens rendered most cells insensitive to lysis in vitro by guinea pig complement even in the presence of TL antiserum. Thymocytes of A/J mice were similarly modulated by passive injection of TL antiserum. In all cases, retention of some modulating antibody on the surfaces of most cells modulated in vivo for 1--27 days was indicated by: 1) acquisition of sensitivity of modulated cells to lysis by absorbed rabbit complement; 2) positive immunofluorescence reactions for mouse IgG on the surfaces of modulated cells; and 3) release of cytolytically active TL antibody from cells into the circulation of unimmunized mice following transfer of modulated cells. Reversal of modulation of RADA1 cells was complete in some experiments within 24 hours after transfer to unimmunized mice, by which time all indications of cell-bound TL antibody were lost. These results indicate that even long-term modulation of TL antigenicity in vivo does not result in a complete loss of modulating antibody (presumably attached to TL antigens) from the cell surface.