Cellular requirements for the in vitro induction of specific suppression of antibody responses by immune spleen cells

Abstract Feedback regulatory signals to an intermediary suppressor cell may provide the mechanism of the suppression of antibody responses which has been described in cocultures of primed (immune) and unprimed (normal) spleen cells. The active cell(s) in the unprimed spleen population is nonadherent to nylon wool, Sephadex G‐10 and glass beads. Lymph node cells and cortisone‐resistant thymocytes from normal animals act similarly to normal spleen cells in this coculture system. Spleen cells from homozygous nude mice, unlike their heterozygous thymus‐bearing littermates, do not produce a high degree of suppression in coculture with immune spleen cells. These data strongly suggest that the normal cell which interacts with primed cells in the cocultures to produce suppression is of thymic origin. However, spleen cells from neonatally thymectomized mice are suppressive in the presence of spleen cells immune to sheep red blood cells. The unprimed cell(s) active in the suppression are sensitive (in the presence of complement) to antisera directed against the surface markers, Thy‐1, Qa‐1, Lyt‐1, Lyt‐2, and Ia. Most of the antiserum treatments abrogated the suppressive capacity of the normal spleen cells only partially. Only treatment with anti‐Qa‐1 and complement routinely eliminated the ability of these cells to suppress in the cocultures suggesting either low concentration of or inaccessible surface alloantigen on the active cells. Alternatively, more than one Qa‐1‐positive cell set from the unprimed population may be involved. It is postulated that there is at least one subset of Qa‐1‐positive T lymphocytes present in unprimed spleen and lymph node cell populations capable of participating in the suppression of specific secondary antibody responses when cocultured with spleen cells from specifically primed animals.