The in vitro inhibition of growth of intracellular Listeria monocytogenes by lymphocyte products

Direct activation of human monocyte-derived macrophages by a bacterial glycoprotein extract inhibits the intracellular multiplication of virulent Legionella pneumophila serogroup 1

Intracellular multiplication of virulent Legionella pneumophila serogroup 1 was inhibited by human monocyte-derived macrophages activated by a glycoprotein extract of Klebsiella pneumoniae, RU 41.740. Macrophage cultures were infected with L. pneumophila in the presence of immune antibodies on day 7 of culture. Extracellular bacteria were removed an hour after infection, and various concentrations of RU 41.740 or an antibiotic, erythromycin, were added. Intracellular multiplication in the presence of RU 41.740 was significantly slowed down compared with that of cultures without RU 41.740. The reduction was, however, significantly less than that effected by erythromycin, which was used as a positive control for inhibition of intracellular multiplication. Cultures incubated with RU 41.740 before infection also demonstrated a significant reduction in the intracellular multiplication of L. pneumophila. In addition, RU 41.740 increased superoxide anion production from human monocytes in suspension in the presence of L. pneumophila. These results show that direct nonspecific activation of macrophages by a bacterial glycoprotein inhibits the intracellular multiplication of L. pneumophila and may suggest a role for activated macrophages in host defense against intracellular pathogens.

Serum amyloid P-component-induced enhancement of macrophage listericidal activity

Purified serum amyloid P component (SAP), the major acute-phase reactant of mice, augmented the in vitro listericidal activity of inflammatory (elicited) macrophages, bone marrow-derived monocytes, and macrophages from a subcutaneous site of inflammation. Monocytes and macrophages from C57BL/B6 mice, which are relatively resistant to Listeria monocytogenes, exhibited a significantly greater enhanced killing capacity for listeria than macrophages from listeria-susceptible A/J mice. SAP did not alter the extent of phagocytosis by macrophages of opsonized L. monocytogenes, nor was SAP opsonic for listeria. Mannose-derived simple sugars inhibited the binding of SAP to macrophages and consequently prevented the enhanced SAP-dependent listericidal activity. Macrophages from lipopolysaccharide-hyporesponsive mice also had increased microbicidal activity following incubation with SAP. SAP activated macrophages independently of lymphokine. Therefore, SAP may serve as a mediator of the heightened nonspecific host defense response that is associated with the acute phase of the systemic inflammatory response.

Requirement of endogenous interferon-gamma production for resolution of Listeria monocytogenes infection

Peritoneal exudate cells and splenic cells of mice infected with Listeria monocytogenes show increased production of interferon-gamma (IFN-gamma) after antigen or mitogen stimulation. When an IFN-gamma-specific enzyme-linked immunosorbent assay was used, increased production was first observed 2 days after infection in peritoneal cells and 4 to 6 days after infection in splenic cells. The increased production of IFN-gamma correlated with the clearance of Listeria from the peritoneal cavity and spleen. Macrophages derived from mice at these times were activated as evidenced by expression of nonspecific tumoricidal activity against 111In-labeled P815 mastocytoma cells. Injection of neutralizing monoclonal anti-IFN-gamma into 1-day-infected mice completely inhibited the generation of activated macrophages. Normal hamster IgG had no effect. In vivo, the monoclonal antibody also abrogated clearance of bacteria from the spleen and peritoneal cavity. Six days after injection of a sublethal dose of Listeria, the peritoneal cavity of control mice treated with normal hamster IgG was devoid of bacteria and the spleen contained less than 10(3) colony-forming units. However, mice treated with anti-IFN-gamma carried more than 8 X 10(6) colony-forming units in either anatomical site at day 6 and exhibited a higher mortality rate. These results indicate that IFN-gamma production is required for the in vivo generation of activated macrophages and the clearance of bacteria during Listeria infection.

Activation of macrophages by lymphokines: enhancement of phagosome-lysosome fusion and killing of Coccidioides immitis

Previously, it was shown that arthroconidia of Coccidioides immitis appear to inhibit phagosome-lysosome fusion and survive within normal mouse peritoneal macrophages. However, when these macrophages are exposed to antigen-stimulated T lymphocytes from immune mice, activation occurs, leading to enhanced phagosome-lysosome fusion and killing of C. immitis. Results indicate that the activation of macrophages can be effected after incubation with soluble lymphocyte product(s) (lymphokines). The activation of macrophages results if the macrophages are exposed to the lymphokine before, but not after, infection. The results indicate that the lymphocyte population responsible for the elaboration of the lymphokine is phenotypically Lyt1+2- and that activation of macrophages by the lymphokine can occur across H-2 histocompatibility barriers.

Time course of antilisterial activity by immunologically activated murine peritoneal macrophages

Murine peritoneal macrophages were rapidly rendered listericidal after exposure to lymphokine-rich supernatants (LRSs) derived from antigen-pulsed Listeria monocytogenes-immune spleen cells. A 6-h incubation period with LRSs was sufficient to induce microbicidal activity in resident macrophages. In vitro induction of macrophage listericidal activity by constant exposure to LRSs persisted for 18 h, after which time spleen cell factors were no longer capable of modifying intracellular inactivation of Listeria. Results obtained by utilizing a short assay indicated that the killing kinetics is extremely rapid, with large numbers of bacteria destroyed during the first 15 min of infection. Intracellular killing at this time appeared to be greatly dependent upon the stage of growth from which the microorganisms were harvested. Induction of bactericidal macrophages by infection of mice with a sublethal dose of virulent Listeria cells and subsequent intraperitoneal elicitation with heat-killed homologous bacteria was similarly a transient event. Macrophages harvested 18 h after antigenic challenge displayed dramatic antibacterial activity during the first 22 h in culture. After 22 h, activity was lost, and stasis was observed during the ensuing 23 h. At 68 h, macrophages were devoid of antilisterial action. Activity, however, could be recalled after incubation with LRSs.

Activated human monocytes inhibit the intracellular multiplication of Legionnaires' disease bacteria

We have examined the interaction between virulent egg yolk-grown L. pneumophila, Philadelphia 1 strain, and in vitro-activated human monocytes, under antibiotic-free conditions. Freshly explanted human monocytes activated by incubation with concanavalin A (Con A) and human lymphocytes inhibited the intracellular multiplication of L. pneumophila. Both Con A and lymphocytes were required for activation. Con A was consistently maximally effective at greater than or equal to 4 mug/ml. Monocytes activated by incubation with cell-free filtered supernatant from Con A-sensitized mononuclear cell cultures also inhibited the intracellular multiplication of L. pneumophil a. The most potent supernatant was obtained from mononuclear cell cultures incubated with greater than or equal to 15 mug/ml Con A for 48 h. The degree of monocyte inhibition of L. pneumophila multiplication was proportional to the length of time monocytes were preincubated with supernatant (48 {greater than} 24 {greater than} 12 h) and to the concentration of supernatant added (40 percent {greater than} 20 percent {greater than} 10 percent {greater than} 5 percent). Monocytes treated with supernatant daily were more inhibitory than monocytes treated initially only. With time in culture, monocytes progressively lost a limited degree of spontaneous inhibitory capacity and also lost their capacity to respond to supernatant with inhibition of L. pneumophila multiplication. Supernatant-activated monocytes inhibited L. pneumophila multiplication in two ways. They phagocytosed fewer bacteria, and they slowed the rate of intracellular multiplication of bacteria that were internalized. As was the case with nonactivated monocytes, antibody had no effect on the rate of intracellular multiplication in supernatant-activated monocytes. Neither supernatant-activated nor nonactivated monocytes killed L. pneumophila in the absence of antibody. Both killed a limited proportion of these bacteria in the presence of antibody and complement. We have previously reported that anti-L, pneumophila antibody and complement neither promote effective killing of L. pneumophila by human polymorphonuclear leukocytes and monocytes nor inhibit the rate of L. pneumophila multiplication in monocytes. These findings and our present report that activated monocytes do inhibit L. pneumophila multiplication indicate that cell-mediated immunity plays a major role in host defense against Legionnaires' disease.

Concanavalin A-induced resistance to Listeria monocytogenes and activation of macrophages: defect in mice treated with 89Sr

89Sr-treated mice injected with concanavalin A (Con A) 24 h prior to infection with Listeria monocytogenes (LM) could not enhance the clearance of LM from the spleen. Adoptive transfer of normal syngeneic spleen cells together with Con A rendered these animals more resistant. Spleen cells of 89Sr-treated or age-matched control mice were stimulated with con A for 24 h, and supernatant fluids were assessed for macrophage-activating factor (MAF), i.e. the ability to activate resident peritoneal macrophages to kill LM intracellularly in vitro. A defective MAF production by spleen cells was observed in 89Sr-treated, 2 week-old, and athymic nude mice. Also, treatment of spleen cells with anti-Thy-1.2 antiserum plus complement inhibited MAF production. Synergism between spleen cells from 89Sr-treated and nude mice did not occur. The cells required for MAF production were relatively resistant to gamma irradiation. Nylon wool filtration did not modify the ability of spleen cells to make MAF. 89Sr-treated mice possess macrophages responsive to MAF derived from normal spleen cells. The data suggest that the failure of 89Sr-treated mice to develop an anti-LM response observed in thi system could be due to a defective capacity to produce protective humoral factors and/or cells in response to Con A.

Mouse spleen cell-derived toxoplasma growth inhibitory factor: its separation from macrophage migration inhibitory factor

Spleen cells from hyperimmunized mice infected with Toxoplasma gondii were cultured in vitro with Toxoplasma specific antigen. The supernatant produced from the cells were termed lymphokines (LKs). The LKs were divided into 4 major fractions, namely: LKs-I, LKs-II, LKs-III and LKs-IV, according to the elution pattern on Sephadex G-100 gel columns. Partially purified LKs contained 2 MIF peaks, namely: MIF-I in LKs-II fraction and MIF-II in LKs-IV fraction. In this study, Toxoplasma growth inhibitory factor (Toxo-GIF), which inhibits the multiplication of Toxoplasma within non-immune macrophages in vitro, was separated by the same method as MIF separation, i.e. Sephadex G-100 gel filtration. Toxo-GIF activity was present in the LKs-II fraction in which MIF-I was also detected with a calculated molecular weight of 30,000 to 40,000. This murine LKs inhibited Toxoplasma multiplication only in murine macrophages but not in guinea pig macrophages or canine monocytes. Cytotoxic substances against macrophages were observed in the LKs-IV fraction, however, no Toxo-GIF was present in this fraction which in addition contained MIF-II with a calculated molecular weight of 3,000 to 5,000.

Legionnaires' disease bacterium (Legionella pneumophila) multiples intracellularly in human monocytes

We have studied the interaction between virulent egg yolk-grown Legionella pneumophila Philadelphia 1 and human blood monocytes in vitro. The leukocytes were cultured in antibiotic-free tissue culture medium supplemented with 15% autologous human serum.L. pneumophila multiplied several logs, as measured by colony-forming units, when incubated with monocytes or mononuclear cells; the mid-log phase doubling time was 2 h. The level to which L. pneumophila multiplied was proportional to the number of mononuclear cells in the culture. L. pneumophila multiplied only in the adherent fraction of the mononuclear cell population indicating that monocytes but not lymphocytes support growth of the bacteria. Peak growth of L. pneumophila was correlated with destruction of the monocyte monolayer. By fluorescence microscopy using fluorescein conjugated rabbit anti-L. pneumophila antiserum, the number of monocytes containing L. pneumophila increased in parallel with bacterial growth in the culture. At the peak of infection, monocytes were packed full with organisms. By electron microscopy, L. pneumophila in such monocytes were found in membrane-bound cytoplasmic vacuoles studded with structures resembling host cell ribosomes. Several lines of evidence indicate that L. pneumophila grows within monocytes. (a) In the absence of leukocytes, L. pneumophila did not grow in tissue culture medium with or without serum even if the medium was conditioned by monocytes. (b) L. pneumophila did not grow in sonicated mononuclear cells. Lysis of these cells at various times during logarithmic growth of L. pneumophila was followed by cessation of bacterial multiplication. Growth resumed when intact mononuclear cells were added back to the culture. (3) In parabiotic chambers separated by 0.1-mum Nuclepore filters, L. pneumophila multiplied only when placed on the same side of the filter as mononuclear cells. These findings indicate that L. pneumophila falls into a select category of bacterial pathogens that evade host defenses by parasitizing monocytes. It remains to be determined whether cell-mediated immunity plays a dominant role in host defense against L. pneumophila as it does against other intracellular pathogens.

Mediation of immunity to intracellular infection (Toxoplasma and Besnoitia) within somatic cells

Antigen-treated lymphocytes from immune hamsters specifically protected not only macrophages, but also cultured fibroblasts and kidney cells infected with Toxoplasma gondii or Besnoitia jellisoni. Macrophages were not necessary for the protection of fibroblasts and kidney cells. A mediator that inhibited the intracellular proliferation of these microbes was obtained from immune lymphocytes in contact with specific antigen. Again, macrophages were not necessary for the elaboration of this mediator or its activity in kidney cells or fibroblasts. The mediator was microbe and host specific, had a molecular weight between 4,000 and 5,000, was resistant to heating at 56 degrees C for 30 min, and was sensitive to chymotrypsin, but resistant to ribonuclease and deoxyribonuclease. A single injection of Besnoitia mediator afforded better protection to hamsters infected with Besnoitia than did antibody. Whereas antibody lysed extracellular organisms, the microbe-specific mediators conferred immunity not only on macrophages, but also on other cells of the body, apparently the first such demonstration.

Studies on production of biologically active substance which inhibits the intracellular multiplication of Toxoplasma within mouse macrophages

In vitro assessments were carried out to study some biological aspects of immune lymphocytes producing a new lymphokine, called by the authors Toxoplasma growth inhibitory factor (Toxo-GIF), which inhibits the intracellular multiplication of Toxoplasma gondii within nonimmune mouse macrophages. Concanavalin A and phytohemagglutinin-P were found to induce vigorous production of Toxo-GIF, whereas bacterial lipopolysaccharide did not. In vitro treatment of splenic lymphocytes with rabbit anti-mouse thymocyte serum plus complement abolished almost completely their ability to produce Toxo-GIF. Treatment of splenic lymphocytes with inhibitors of protein synthesis, cycloheximide or puromycin resulted in a remarkable reduction of the ability of sensitized lymphocytes to produce this lymphokine. Thus the production of Toxo-GIF seems to be dependent on the cellular metabolic events of sensitized T-lymphocytes. The significant activity of Toxo-GIF was demonstrable even in the supernate of lymphocyte cultures incubated in serum-free medium and was also evident after immune lymphocytes and homologous antigen were incubated for the relatively short period of 10 h.

Macrophage proliferation and activation during Toxoplasma gondii infection in mice: relationship to lymphocyte stimulation

Macrophage proliferation and activation as well as lymphocyte stimulation in the peritoneal cavities of mice were investigated during the course of a Toxoplasma gondii (Beverly strain) infection. Macrophage proliferation had started already after day one and reached a first peak on day 2 (3H-thymidine labelling index approximately 6%). This proliferation was not accompanied by any notable lymphocyte stimulation. An equally high L.I. for macrophages was found after injection of 0.9% saline. From day 3-4 and peaking on day 7-11, a considerable blastoid transformation of lymphocytes occurred (maximum L.I. for lymphoid cells approximately 20% on day 7). In parallel with this blastoid response, a substantial macrophage proliferation took place (L.I. approximately 8%). Large numbers of activated macrophages also appeared during this period, DNA synthesizing cells were found even among the most highly activated macrophages. The results indicated that the early and the late macrophage proliferations were stimulated by different mechanisms.

Effects of immune lymphocyte products and serum antibody on the multiplication of Toxoplasma in murine peritoneal macrophages

In vitro studies on cell-mediated immunity against Toxoplasma infection were carried out by estimating the ability of antigenically stimulated lymphocytes. Splenic lymphocytes from normal mice and from hyper-immunized mice were cultured in the presence or absence of Toxoplasma lysate antigen. The cell-free supernatant fluids from the lymphocyte cultures were assassed for their ability to alter the functional capacities of normal macrophages. When glycogen-induced peritoneal macrophages were incubated with the culture supernatant from immune lymphocytes reacting with specific angigen, the intracellular multiplication of the organisms was inhibited remarkably. In contrast, the addition of antitoxoplasma antibody to culture medium had no effect on the enhancement of phagocytic activity of culture macrophages. However, when extra-cellular organisms were exposed to fresh or heat-inactivated immune serum just before infection of the monolayers, the intracellular multiplication of Toxoplasmas was inhibited significantly by either activated or normal macrophages.

Effect of rifampin on immunity to tuberculosis and on delayed hypersensitivity to purified protein derivative

Mice vaccinated with mycobacterial ribonucleic acid (RNA) produced a high immune response and did not develop delayed hypersensitivity to purified protein derivative (PPD), and rifampin had no effect on the immune response. Mice vaccinated with viable H37Ra cells produced a high immune response and did develop delayed hypersensitivity to PPD. Rifampin had no effect on this immune response, but reduced the footpad reactions to PPD. Both mycobacterial RNA and poly(A:U) served as adjuvants for induction of hypersensitivity to PPD. This hypersensitivity was reduced by the administration of rifampin. Rifampin had no effect on the production of mycobacterial growth inhibitory factor, which is produced following vaccination of mice with mycobacterial RNA or viable H37Ra cells. Rifampin had no effect on the nonspecific phase of the granulomatous response, but did inhibit the secondary allergic phase of this response. The action, therefore, of rifampin that inhibits the induction of delayed hypersensitivity but had no effect on the immune responses against tuberculosis leads to a separation of tuberculin hypersensitivity from cellular immunity to tuberculosis.

Phagocytosis and intracellular killing of Staphylococcus aureus by normal mouse peritoneal macrophages

Although Staphylococcus aureus is incapable of intracellular multiplication in cultured mouse peritoneal macrophages, it is killed at a much slower rate than the avirulent Staphylococcus epidermidis. In addition to the presence of capsular material which inhibits phagocytosis of specific strains of S. aureus, the data show that a number of cellular and environmental factors affect the functional capacities of mononuclear phagocytic cells. The data obtained by varying the initial level of infection indicate that the number of ingested bacteria may subsequently alter the kinetics of intracellular killing. In vitro maturation of macrophages in culture was also found to exert a pronounced effect on the kinetics of bacterial death.

Activation of mouse peritoneal cells to kill Listeria monocytogenes by T-lymphocyte products

An in vitro system has been used to demonstrate that glass-adherent mouse peritoneal cells can be activated to kill intracellular Listeria monocytogenes by antigen-stimulated T-lymphocytes derived from immunized mice. The soluble products of such stimulated lymphocyte cultures could only be shown to similarly activate peritoneal cells if the antigen used in both the immunization and lymphocyte stimulation was also present on the target intracellular organism.

Cell-mediated immune phenomena induced by lymphokines from splenic lymphocytes of mice with chronic staphylococcal infection

Splenic lymphocytes from normal mice and from mice displaying delayed hypersensitivity to Staphylococcus aureus were cultured in the presence or absence of specific staphylococcal antigens. The cell-free supernatant fluids from these lymphocyte cultures were assessed for their ability to alter the functional capacities of normal macrophages. It was found that supernatants from staphylococcus-immune cells cultured in vitro with antigen possessed migration inhibitory factor activity and also were capable of stimulating the incorporation of [14C]glucosamine into macrophage membrane glycoproteins. In addition, the lymphokine-containing supernatants were capable of inducing activation of normal macrophages so that they inhibited the multiplication of intracellular Listeria monocytogenes. Although it was not possible to snow any significant enhancement of intracellular killing of S. aureus by the activated macrophages, evidence is presented that suggests that cell-mediated immune responses to S. aureus may significantly enhance pahgocytosis of staphylococci and, thereby, may provide for their rapid clearance from extracellular fluids.

In vitro antilisterial activity of soluble product(s) released from Listeria-immune murine peritoneal macrophages

The importance of macrophages as effector cells in cellular reactions of immunity and hypersensitivity is well established (8). Macrophages activated as a result of specific immunological events exhibit increased microbicidal activity not only for the primary organism used for immunization purposes but also against unrelated intracellular pathogens (7). It is believed that the acquisition of this bactericidal or bacteriostatic activity is conferred on macrophages by materials released during the interaction of specifically immune lymphocytes with the antigen (Fowles et al., 1973; Godal et al., 1971; Jones and Youmans, 1973; Krahenbuhl and Remington, 1971; Mackaness, 1971; Patterson and Youmans, 1970). The antimicrobial activity in these studies refers to the intracellular inhibition and/or killing of the organisms; no attempts were made to assess the effect of activated macrophages on the extracellularly residing organisms. In an earlier study with the pathogenic yeastlike fungus Cryptococcus neoformans, we observed that freshly collected peritoneal macrophages from mice pretreated with a variety of nonspecific agents or from specifically immune mice possessed the capacity to exert anti-cryptococcal effect both on intracellular yeasts as well as those present in the extracellular milieu (Sethi et al., 1971; Sethi and Pelster, in press). Our results suggest that soluble product(s) released from mouse macrophages immune to Listeria monocytogenes can exert antilisterial activity under in vitro conditions.