Inhibition of cell‐mediated lysis by xenoantibodies reactive with effector T lymphocytes

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Abstract
The aim of the present study was to determine whether rabbit antisera against various murine tissue antigens contain antibodies that affect the activity of cytotoxic T lymphocytes in the absence of complement. Following heat inactivation, the xenoantisera were absorbed with mouse liver and kidney and tested for their capacity to inhibit cell-mediated lysis (CML). In the presence of complement (C), rabbit anti-brain antiserum (RABr), rabbit anti-thymus antiserum (RAT) and rabbit anti-boiled thy- mus antiserum (RABT) lysed effector T cells, and CML was abolished. In the absence of C, RAT maintained its strong inhibitory activity on CML, RABr had no inhibitory effect, whereas only some batches of RABT were effective. Monovalent Fab fragments of RAT inhibited CML as effectively as intact antibody molecules. The activity of RAT could be removed by absorption with T and B lymphocytes of various sources. Inhibitory antibodies could be removed by absorption with C3H B lymphoma cells and upon elution from antibody-coated cells proved again highly effective in inhibiting CML. These results show that RAT contains antibodies which react with determinants shared by T and B lymphocytes and which block the activity of cytotoxic T cells.