Requirement for the location of both appropriate and irrelevant H-2 antigens on the same stimulator cell for unspecific DNA-synthesis inhibition by the H-2-antigen-primed, specific suppressor T cells.

Specific suppressor T cells (SSTC), primed in vivo with H-2 antigens, have been shown previously to inhibit DNA synthesis in the one-way, three-cell mixed lymphocyte reaction (MLR) provided that (a) the stimulator cells bear the priming H-2 antigens, and (b) the responder cells possess IC + S regions homologous to those of the SSTC. Anti-B10.A B10.A(2R) SSTC (anti-Dd) and anti-A.AL A.TL SSTC (anti-Kk) are shown here to be able to inhibit the DNA synthesis triggered in MLR, not only by the corresponding antigens, Dd and Kk, respectively, but also by irrelevant, third-party H-2 and Mls products provided that the corresponding and third-party antigens are presented on the same stimulator cell. If stimulator H-2 regions, whose products interact with SSTC and responders, are located on different stimulator cells within the particular MLR, SSTC activity is not elicited. Participation of cytotoxic T lymphocytes in DNA-synthesis suppression is ruled out. Direct contact or location of the inhibited responder cell very close to SSTC is considered to be required for the development of SSTC activity.