Specific anti-tumor responses of cultured immune spleen cells III. Further characterization of cells which synthesize factors with blocking and antiserum-dependent cellular cytotoxic (ADC) activities.
Spleen cells from BALB/c mice bearing syngeneic, methylcholanthrene-induced sarcomas were cultured in vitro. In agreement with previous observations, two tumor-specific activities could be demonstrated in the culture supernatants: the supernatants suppressed (blocked) specific lymph-node cell-mediated cytotoxicity directed against the respective neoplasm and they induced specific antibody-dependent-cellular cytotoxicity (ADC) mediated by lymph-node cells from non-immune mice. In the present study, the effects of specific depletion or enrichment of different celltypes on the ability to synthesize the blocking and ADC activities was explored. Spleen cells passed through columns of Sephadex G-10, which removed plasma cells and macrophages, no longer synthesized factors with ADC activity though synthesis of blocking factors continued. However, lysis of Thy-1-positive cells with antiserum and complement did abolish the synthesis of blocking factors. Spleen cells from tumor-bearing mice were then enriched for Thy-1-positive cells by selective removal of macrophages and plasma cells on G-10 columns and of immunoglobulin-bearing cells on anti-mouse immunoglobulin affinity columns. This T-cell-enriched population synthesized blocking factors and restored blocking factor synthesis in cultures depleted of Thy-1-positive cells. Simiarly enriched spleen cells from normal control mice did not synthesize tumor-specific blocking factors but partially restored synthesis of blocking factor in tumor-bearer spleen cultures depleted of Thy-1-positive cells.