Interferon, induced in lymphocytes either with viruses or cell lines, increases severalfold the natural cytotoxicity of human lymphocytes on target cell lines. Cell separation experiments support the hypothesis that interferon enhances the activity of natural killer cells rather than generating a new population of effector cells. In mixed culture of lymphocytes and cell lines in which endogenous interferon is produced, interferon mediates an enhancement of cytotoxicity that represents up to 70-90% of the observed cytotoxicity. The effect of interferon on target cells is antagonistic to the effect on the lymphocytes: the susceptibility to cell-mediated lysis of various cells upon pretreatment with interferon is decreased and in some cases almost completely suppressed. Interferon renders target cells resistant to natural killer cells acting by an intracellular mechanism which requires RNA and protein synthesis. While normal fibroblasts are protected, virus-infected cells and most tumor cells usually are not protected by interferon. Interferon by stimulating very efficient nonspecific cytotoxic cells and by protecting at the same time normal cells from lysis, might render the natural killer cell system an inducible selective defense mechanism against tumor and virus-infected cells.

https://rupress.org/jem/article-pdf/147/5/1314/1393333/1314.pdf

Anti-viral activity induced by culturing lymphocytes with tumor-derived or virus-transformed cells. Enhancement of human natural killer cell activity by interferon and antagonistic inhibition of susceptibility of target cells to lysis.

Antitumor effects of interferon.

A viral inhibitor(s) is released in the supernate of mixed cultures containing human or mouse lymphocytes and cells from certain lines. The inhibitor is active against a variety of unrelated viruses and is a protein that is not toxic for cells. It does not inactivate viruses directly, but inhibits viral replication through an intracellular mechanism that involves synthesis by the cells of both RNA and protein. These characteristics identify the inhibitor as an interferon. The anti-viral activity is contained in at least two molecular species, of approximately 25,000 and 45,000 daltons, respectively. In addition to the anti-viral activity, the supernates of the mixed cultures display an anti-cellular activity, the inhibition of DNA synthesis and of cell multiplication. The anti-viral and the anti-cellular activities are positively correlated in supernates from various cultures and in partially purified preparations. The human cell population responsible for interferon production is composed mainly of Fc-receptor positive, surface immunoglobulin negative, non-T-cell lymphocytes. The ability of certain cell lines to induce interferon seems to be preferentially associated with tumor origin or with in vitro transformation by certain viruses (Epstein-Barr virus, murine sarcoma virus).

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Anti-viral activity induced by culturing lymphocytes with tumor-derived or virus-transformed cells. Identification of the anti-viral activity as interferon and characterization of the human effector lymphocyte subpopulation.

Host reactivities not requiring immunization in the mouse, especially natural resistance of irradiated animals to accept grafts of normal or malignant hemopoietic cells, were compared with NK activity against the YAC-1 lymphoma. The effects of several independent variables known to influence natural resistance in vivo had a similar effect on the NK system. Figure 12 lists an impressive array of shared properties and positive correlations. In contrast, the distinctions were few and minor. Many of the positive correlations were of particular significance since the experimental variables either have opposing or no effects on conventional induced immunity. The multiplicity and pervasiveness of these correlations suggest that the cellular mechanisms underlying natural reactivities are similar or common. Cytotoxic effectors mediating natural resistance to normal cells, tumors, and cells infected with intracellular pathogens may be distinct in terms of target selectivity, yet belong to a single cell lineage subject to common regulatory influences for differentiation and function. Regulation of reactivity via suppressor cells was studied in the NK system only. The spleens of mice selected for low levels of NK activity (resulting from young age, irradiation, and treatment with the macrophage-active agents l-carrageenan or hydrocortisone acetate) contained cells capable of inhibiting the lytic function of NK effectors taken from untreated adult donors. All the suppressor cells studied were thymus-independent, as judged by their occurrence in spleens of genetically athymic mice; the suppressive function was resistant to 2000 rads of gamma-rays administered in vitro and was not restricted by the major histocompatibility complex, without exception. However, two major classes of suppressors were identified: (a) macrophagelike cells inducible by l-carrageenan or hydrocortisone acetate, and (b) nonadherent cells found in spleens of untreated infants and of irradiated adult mice. It is proposed that the suppression of NK cytolysis demonstrated in vitro was a manifestation of regulatory mechanisms modulating the level of NK activity in vivo. Macrophagelike cells that are induced, activated, or inactivated by bacteria, viruses, hormones, and other agents may act as regulators of differentiation, maturation, and function of cells belonging to the NK lineage. Nonadherent cells could be either a distinct class of suppressors or immature NK cells capable of binding but not lysing target cells. In the latter case, regulation would be achieved via competitive binding of targets by pre-NK cells presumably in dynamic equilibrium with functional (i.e. matured) NK effectors.

Do natural killer cells engage in regulated reactions against self to ensure homeostasis

Publisher Summary This chapter focusses on the study of cell-mediated immunity in vitro, principally in terms of explaining the effector process of the response. To organize the observations in many species and systems, four general assumptions has been made. First, the diversity of information for cell-mediated immunity is carried by lymphocytes, and is of the same order of magnitude and specificity as for circulating antibodies. Second, all cell-mediated immune reactions have a common basis, including the tuberculin-type reaction, contact hypersensitivity, cellular resistance to infection, allograft rejection, and tumor immunity. Third, the increase in responsiveness after a process of sensitization or immunization is consistent with a clonal selection by the antigen of reactive cells. Information for cell-mediated immunity is carried by thymus-dependent lymphocytes, but whether their specificity is generated by genes informational molecules from other cells or antigen itself remains unclear. Fourth, the mechanisms of effector reactions mediated by delayed-type hypersensitivity and humoral antibody are fundamentally different. Explicit discrimination between these two mechanisms must be made wherever possible, not only in vivo but in vitro as well.

In Vitro Approaches to the Mechanism of Cell-Mediated Immune Reactions

INTERFERON induces a cytotoxic effect in normal mouse spleen cells against allogeneic tumour target cells in tissue culture1,2. We here present evidence that syngeneic lymphoid cells may be similarly activated by interferon and that syngeneic lymphoid cells plus interferon suppress the growth of tumour cells in vivo.

Antitumour effect of lymphoid cells activated by interferon.

HELLSTROM et al.1 showed that homogenates of allogeneic spleens caused a greater decrease in the number of tumour cells in tissue culture than did homogenates of syngeneic spleens. They called this phenomenon “syngeneic preference”2,3 in tissue culture. The action of phytohaemagglutinin on target cells plus allogeneic lymphocytes is also caused by “syngeneic preference”4. The extent to which this phenomenon is applicable to other tissue systems is unknown.

Inessa Yu. Chernyakhovskaya

Papers

Antitumour effect of lymphoid cells activated by interferon.

Effect of Syngeneic and Allogeneic Lymphocytes on L-cells and Mouse Embryo Fibroblasts in vitro