T-cell-mediated immune responses induced in vitro: a probe for allograft and tumor immunity

Cells mediating graft rejection in the mouse. I. Lyt-1 cells mediate skin graft rejection

The Ly phenotype of cells mediating skin graft rejection was determined using monoclonal anti-Lyt-1.1 and Lyt-2.1 antibodies in CBA mice that received CBA lymphoid cells from mice sensitized to C57BL/6; i.e., alloantigenic differences arising from the H-2 and non-H-2 loci. It was clear that graft rejection was due wholly to the presence of Lyt-1 cells in the inoculum and that Lyt-123 or Lyt-23 cells had no effect. Furthermore, no synergism was noted between Lyt-1 and Lyt-2 cells. In this model, both the cytotoxic T cell and cytotoxic lymphocyte precursors were shown to be Lyt-123 and these could be depleted from sensitized Lyt-1 populations that mediated graft rejection. Thus cytotoxic T cells are not responsible for skin graft rejection, but rather, this is mediated by an Lyt-1 cell. Whether this T cell is distinct from other Lyt-1 cells (T helper, T cells mediating delayed hypersensitivity) is not clear at present, but other evidence, and traditional concepts, link graft rejection and delayed type hypersensitivity as being different manifestations of the same mechanism.

Induction of the immune response to cell surface antigens in vitro

Two tissue culture incubation systems are described in which immune responses to cell surface antigens have been demonstrated. In the one-way "mixed lymphocyte interaction" system, a specific stimulation of thymidine uptake was induced by a particulate membrane antigen fraction, the microsomal lipoproteins (MLP), when low levels (0.01 to 0.001 mug per ml) were incubated with spleen or lymph node cells from nonsensitized mice. No stimulation was seen when allogeneic MLP was used at high levels, 10 mug per ml, nor at any level with syngeneic MLP. Specific effectors were demonstrated after 72-hr incubation with stimulatory levels of allogeneic MLP in three separate in vitro assays, a plaque-forming cell reduction assay, a tumor target assay, and an antigen-binding cell assay. In the latter assay, [125I]MLP was used as the source of antigen. This system has limited potential inasmuch as mouse spleen cells do not survive in it beyond the 4th day of culture. The second tissue culture system, the Marbrook system, has much greater possibilities because at least 25% of the inoculum is recovered 7 days later. In this culture system a cell-free sheep erythrocyte membrane preparation can induce plaque-forming cells in the absence of macrophages. Using a sensitive radioimmunoassay, free specific antibody was detected in culture supernatant fluids. With the same culture system, allogeneic lymphocytotoxic cells (killer) have been induced with spleen cells from unprimed mice in strains differing at the major histocompatibility locus (H-2). Allogeneic MLP induced very significant "killer" cell activity with spleen cells from primed mice. In a syngeneic tumor system, significant amounts of killer cell activity were induced with unprimed spleen cell inocula, and much larger amounts induced with spleen cells from immunized mice.