Use of concanavalin A to analyse the mechanism of memory cell differentiation into killer cells.

The renewing by ConA of the cytolytic activity evaluated in a short-term chromium release assay in a population of memory cells obtained in a long-term mixed lymphocyte culture is shown to be largely dependent upon the dose of ConA used; a three staged phenomenon in terms of dose response and kinetics is analysed and suggests that at least for low concentration of ConA (0.5 micrograms/ml) the lectin acts on the same subpopulation and through the same mechanism as the specific antigen, as shown by DNA-synthesis inhibition experiments. Preincubation with ConA at doses giving the best secondary-like response strongly inhibits further response to the primary alloantigen. Experiments using mixtures of ConA and alloantigens as stimulators show that both agents can compete in differentiating memory cells into killer cells. All these data suggest an important overlap of the structures on memory cells which are triggered by ConA or specific antigen.

[Immunosuppressive phenomena in experimental tumor systems (author's transl)]. / Phénomènes d'immunosuppression dans les systèmes tumoraux expérimentaux.

During the growth of spontaneous or chemically-induced tumors in animals, it has been reported that T lymphocytes are present in the spleen and/or the thymus which are able (i) to specifically block tumor rejection by syngeneic immunized animals in in vivo transfer experiments, and (ii) to specifically inhibit the in vitro cell-mediated immune reactions. The relationship between both types of suppressor cells is unclear. On the other hand, mitogen insensitive cells, acting in vitro in a non specific way on normal cell mitosis and cell-mediated cytotoxicity induction, and having macrophage characteristics, are described in viral and non viral tumor bearing hosts as well as in non tumoral animals after hematopoietic hypoplasia. The various suppressor cells types and their possible mechanisms of action are discussed along with soluble factors when present in experimental tumor systems, but the role of these cells in tumor pathogenesis is not yet clear.