Solubilization of histocompatibility and tumour-associated antigens of the P-815 murine mastocytoma cell

Stimulation of different pathways of T-cell functions by syngeneic tumor cells and soluble membrane proteins

Cells from the draining lymph nodes of DBA/2 mice bearing syngeneic intradermal P-815 tumors represent an excellent responding cell population for secondary stimulation in vitro, despite the virtual absence of response by spleen cells of the same animals. Cytotoxicity is a result of stimulation with intact mitomycin-treated tumor cells. Isolated tumor cell membranes, in the form of small vesicles, stimulated cytotoxicity to a very limited extent and inhibited the development of cytotoxic T lymphocytes over a wide range of concentrations. Membrane proteins solubilized with deoxycholate and papain had only a suppressive effect. Soluble proteins exerted their effect during the induction of cytotoxic T lymphocytes and were ineffective when present during the effector phase of cytotoxic T lymphocytes. The suppressive capacity was shown to reside in a cell population which was sensitive to treatment with monoclonal Lyt-2.1 antibody and complement but not with Lyt-1.1 antibody. This phenotype was compatible with a specific rather than a promiscuous type of suppressor effector cell.

The stimulation of a T cell response in the syngeneic host by the P-815 mastocytoma cell and the isolation of a tumor-associated antigen which has some H-2 antigen characteristics

Although not obviously immunogenic when developing intraperitoneally or subcutaneously, the P-815 mastocytoma cell induces a significant immune response when injected intradermally into the syngeneic host. In some animals the immune reaction leads to spontaneous tumor regression and survival of the animals, but in most cases the effectively initiated immune-reaction is abrogated by as yet unknown mechanisms. The T cell is identified as the killer cell both in vivo and in vitro during the described period of immune reactivity. By means of two antibodies from two different species, rendered specific for the P-815 tumor cell by in vivo absorption in DBA/2 mice, two distinct antigens have been identified, isolated and partially purified from P-815 cell membranes. One of them is obviously different from H-2 antigens, the other one shows striking similarities with H-2 antigens (molecular weight, lectin binding properties), but does not coprecipitate with H-2 antigens in an indirect precipitation assay, using Staph. aureus Cowan I as the Fc-binding agent.