IDENTIFICATION OF A TARGET-CELL ANTIGEN RECOGNIZED BY NONSPECIFIC CYTOTOXIC-CELLS USING AN ANTIIDIOTYPE MONOCLONAL-ANTIBODY

Nonspecific cytotoxic cells (NCC) are the teleost equivalent of mammal ian natural killer (NK) cells. In the present study an anti-idiotypic monoclonal antibody (mAb 7D12) was generated against idiotopes on an m Ab (mAb 6D3.2) that recognizes a putative receptor on NCC. The idiotyp ic specificity of mAb 7D12 was determined in competition assays by inc ubating biotinylated mAb 7D12 with mAb 6D3.2 hybridoma cells following preincubation with combinations of biotinylated 7D12 with either nonb iotinylated homologous or heterologous mAb. The ligand recognized by m Ab 7D12 (determined by flow cytometry) was found on cells from the ant erior kidney, spleen, thymus, PBL, liver, and brain. NCC lysis of IM-9 targets was inhibited 76% following preincubation of the target cells with different concentrations of mAb 7D12. The involvement of the lig and recognized by mAb 7D12 in the NCC lytic cycle was determined by sh owing that this mAb produced 50% inhibition of NCC conjugate formation with NC-37 target cells. Biochemical analysis using SDS-PAGE and West ern blotting revealed that mAb 7D12 recognized 54 and 65 M(r) proteins in IM-9 target cell lysates. These studies demonstrated that an idiot ope on a NCC specific anti-receptor mAb was an ''internal image'' of a target cell ligand. The anti-id mAb generated against this image (idi otope) inhibited NCC cytotoxicity and thus was equivalent to an NCC re ceptor that binds to a target cell ligand involved in NCC recognition.