Lymphocyte induced macrophage cytotoxicity: characterization of the macrophage cytotoxicity-inducing lymphocyte

B-cell mitogenic activity of slime products produced from slime-forming, encapsulated Lactococcus lactis ssp. cremoris

The mitogenic activities of whole cell lyophylized preparations, cell-wall components, and slime products obtained from Lactococcus lactis ssp. cremoris KVS20 were examined on murine spleen cells. Whole cell lyophylized preparations and slime products significantly (P < .05) stimulated mitogenic responses of the cells. The highest activity was induced by slime products in which the optimal concentration was 116 microg/ml. The significant (P < .05) increase of mitogenic activity induced by slime products occurred at 24 h, and the peak response was obtained 48 h after the stimulation. The activity was much higher in the fraction enriched with B cells than in the fraction enriched with T cells. In addition, slime products induced mitogenic activity to spleen cells of athymic nu/nu mice. The chemical analysis of lipopolysaccharide and the minimal concentration for mitogenic response eliminated the possibility that the activity of slime products may be due to the contamination of lipopolysaccharide. The data demonstrate that slime products are a potent B-cell-dependent mitogen.

Differences in the induction of macrophage cytotoxicity by the specific T lymphocyte factor, specific macrophage arming factor (SMAF), and the lymphokine, macrophage activating factor (MAF)

Specific T cell factors, such as specific macrophage arming factor (SMAF), are involved in the initiation of the immune response. Induction of SMAF-producing T lymphocytes in vivo and of SMAF production by T lymphocytes in vitro is dependent on the presence of intact tumor cells, and is independent of antigen presentation by macrophages. SMAF renders peritoneal macrophages cytotoxic for tumor cells. The armed peritoneal macrophages expressed a specific cytotoxicity. However, antigen-presenting cells can trigger lymphokine-producing T lymphocytes. These T lymphocytes produce lymphokines (e.g. macrophage activating factor (MAF] that activate macrophages. The MAF-activated macrophages express a non-specific tumoricidal activity. In the present study, we investigated the difference in the induction of macrophage cytotoxicity by SMAF and MAF. The following differences were found: 1) SMAF renders peritoneal resident macrophages cytotoxic, whereas MAF could only render peritoneal exudate macrophages cytotoxic. 2) SMAF requires only a 4-h incubation with macrophages, whereas MAF activates macrophages optimally after 12 h. 3) SMAF-armed macrophages recognize only the specific target cell(s), and thus, the cytotoxicity is specific in its expression. MAF activated macrophages were non-specifically cytotoxic. 4) Lipopolysaccharide (LPS) in the culture medium did not enhance the cytotoxicity of SMAF-armed macrophages. In contrast, MAF induced tumoricidal activity was enhanced by adding LPS to the culture medium. 5) After adsorption chromatography with anti-murine interferon-gamma (IFN-gamma), the arming capacity of SMAF supernatant was not reduced, whereas the activating capacity of the MAF supernatant was significantly reduced or abrogated. After immunization of mice with allogeneic tumor cells, SMAF-producing lymphocytes were detected in the draining lymph nodes already 4 days after immunization and up to 12 days. Lymphocytes with the capacity to produce MAF were present in the draining lymph nodes 14-24 days after immunization. Our data indicate that the T cell factors SMAF and MAF can both render macrophages cytotoxic, but act in a different way and during different stages of the cellular immune response against allogeneic tumor cells.

Initial immunochemical characterization of specific macrophage-arming factor

This paper describes the initial immunochemical characterization of specific macrophage-arming factor (SMAF). SMAF is an antigen-specific factor that is released by (sensitized) T lymphocytes after contact with the specific antigen. It renders macrophages specifically cytotoxic. The specificity is dependent on the tumor-mouse combination. In allogeneic systems the specificity is H-2-directed, whereas in the syngeneic systems the specificity is tumor-specific. SMAF has a molecular mass of 65-85 kDa (established by gel filtration). By affinity chromatography SMAF could not be adsorbed with anti-(kappa + lambda light chain) immunoglobulins or anti-IgG from SMAF-containing supernatants. SMAF could be adsorbed with the monoclonal antibody 14-30 (directed against specific T-cell factors), and could be eluted from columns containing the latter. Furthermore, SMAF could also be adsorbed with and eluted from affinity chromatography columns to which specific tumor cell membranes or KCl extracts of these tumor cell membranes were coupled. Other tumor cell membranes could not adsorb SMAF. Together these data show that SMAF is not an antibody but a T-cell factor with an antigen-specific recognition site.

Production of specific macrophage-arming factor precedes cytotoxic T lymphocyte activity in vivo during tumor rejection

Recently we published a hypothesis on the immunological events occurring during tumor rejection. One of the implications of this hypothesis is that specific macrophage-arming factor (SMAF) is produced early during the initiation of the immune response, whereas the "classical" cell-mediated immune response components, such as cytotoxic T lymphocytes (CTL), are produced later, that is, during the amplifier-effector phase. In this paper we establish the kinetics of the induction of (a) lymphocytes producing SMAF and (b) CTL. Groups of DBA/2 mice were injected i.p. once, twice or three times with irradiated and/or non-irradiated syngeneic SL2 tumor cells, the injections being given at intervals of 10 days. After each of these injections the production of SMAF and the expression of CTL activity were established. The results showed that in the peritoneal cavity SMAF-producing lymphocytes appeared earlier than cytotoxic lymphocytes (CTL). In addition, it was shown (a) that SMAF does not interfere with the in vitro cytotoxicity expressed by CTL and (b) that in addition to CTL memory cells, SMAF-producing memory cells were also induced after injection of syngeneic tumor cells. These data support the hypothesis that SMAF is involved in the early phase of the cellular immune response against tumors, whereas CTL are induced later.

Lack of correlation between in vivo peroxidatic activity patterns and tumoricidal activity in vitro of peritoneal macrophages after intraperitoneal immunization with tumor cells

Immunization of C57BL mice with one inoculum of 10(7) DBA/2-derived SL2 lymphosarcoma cells resulted in a +/- 20-fold increase in the total number of peritoneal cells. The number of macrophages showed a 10-fold increase from 3 x 10(6) (control mice) to 3.4 x 10(7) cells at day 8 after immunization. Within this macrophage population, four different cell types, based on the ultrastructural peroxidatic activity patterns, could be distinguished: exudate macrophages, resident macrophages, resident-exudate macrophages and peroxidatic-activity-negative macrophages. The number of exudate macrophages significantly increased in the peritoneal cavity after immunization: at day 8 after immunization, a peak value of 10(7) cells was observed. At the same time, there were 2.2 x 10(7) peroxidase-activity-negative macrophages present (representing the control value x 50). Significant in vitro tumoricidal activity of the isolated macrophages could not be measured until 8 days after immunization. At that time, a cytotoxicity index of 68 was reached. After immunization of the C57BL mice with 3 injections with allogeneic SL2 cells, there were no dramatic changes in the number of peritoneal cells after the last immunization. Only immediately after the last immunization was a minor increase in peroxidatic-activity-negative macrophages seen. But already at 5 days after the last immunization, the composition of the peritoneal suspension was similar to that of non-immunized mice with predominantly resident macrophages. The cytotoxicity of the peritoneal macrophages from hyperimmunized mice was constantly high during 1-15 days after the last immunization (cytotoxicity index ranged from 66-72). In order to study which type(s) of macrophage(s) (resident, exudate, resident-exudate or peroxidatic-activity-negative) is/are responsible for the cytotoxicity measured in vitro, peritoneal cell suspensions (obtained after immunization) were fractionated according to their affinity to wheat germ agglutinin (WGA) coupled to Sepharose columns. Comparison of the values of cytotoxicity measured before and after separation into "subtypes" of the macrophages revealed that the expression of cytotoxicity is not correlated with any of the "sub-types", especially when the peroxidatic activity pattern is is taken as a criterion.

Spontaneous tumor rejection is not always due to a complete cellular rejection

In this paper we have studied whether there is a correlation between efficacy of hosts to reject tumor cells spontaneously and the induction of cytotoxic macrophages in these recipients due to injection (immunization) with tumor cells. Results show that there is no cause-effect relationship between macrophage cytotoxicity and tumor rejection in vivo. This lack of cause-effect relationship is greatly influenced by differences in immunogenicity between the various tumor cell lines as well as by the release of tumor-factors by some of these tumors.

Lymphocyte-induced macrophage cytotoxicity. III. Induction of specific macrophage cytotoxicity is independent of lipopolysaccharide

The induction of specific macrophage cytotoxicity by allo-sensitized T cells in vitro is shown to be independent of the presence of lipopolysaccharide (LPS). This contrasts with the induction of macrophage cytotoxicity by Macrophage Activating Factor (MAF). The specific macrophage cytotoxicity could be induced in LPS-free medium (less than l ng/ml). Addition of LPS to the macrophages did not increase the cytotoxicity. Addition of LPS-binding polymyxin B to the macrophages before and during the induction of cytotoxicity did not reduce the specific macrophage cytotoxicity. Macrophages obtained from the LPS-unresponsive mouse strain C3H/HeJ were rendered cytotoxic by the allo-sensitized lymphocytes to the same extent as the macrophages from LPS-responsive C3HeB/Fe and C57BL mice. This indicates that the induction of macrophage cytotoxicity by MAF is different from the induction of specific macrophage cytotoxicity by Specific Macrophage Arming Factor (SMAF).

Cells responsible for tumor surveillance in man: effects of radiotherapy, chemotherapy, and biologic response modifiers

Currently, the most probable theory of tumor surveillance is neither the existence of any tumor-specific, antigen-dependent, T-cell-mediated cytotoxic effect that could eliminate spontaneous tumors in man and that could be used for some kind of vaccination against tumors, nor the complete absence of any surveillance or defense systems against tumors. What is probable is the cooperation of a number of antigen-independent, relatively weakly cytotoxic or possibly only cytostatic humoral and cellular effects, including nutritional immunity, tumor necrosis factor, certain cytokines, and the cytotoxic effects mediated by macrophages, NK cells, NK-like cells, and certain stimulated T-cells. One question remaining to be solved is why these antigen-independent effects do not attack normal cells. A number of plausible hypotheses are discussed. The hypothetical surveillance system is modulated both by traditional cancer treatment and by attempts at immunomodulation. Radiotherapy reduced the T-helper cell function for almost a decade, but not those of macrophages or NK cells. T-cell changes have no prognostic implication, supporting, perhaps, the suggestion of a major role for macrophages and NK cells. Cyclic adjuvant chemotherapy reduces the peripheral lymphocyte population and several lymphocyte functions but not NK activity. Most of the parameters were normalized some years following treatment, but NK activity remained elevated and Th/Ts cell ratio was still decreased. This might possibly be taken to support the surveillance role of NK cells. Bestatin increases the frequency of lymphocytes forming rosettes with sheep red blood cells (but not their mitogenic responses), enhances NK activity, and augments the phagocytic capacity of granulocytes and monocytes (but not their cytotoxic activity). Improved survival with Bestatin treatment following chemotherapy has been observed in patients with melanoma Stages 1b and II and in patients with acute nonlymphatic leukemia, where BCG also seems active, although possibly only in patient groups with less than 49% complete remissions.