Effects of Dextran Sulfate 500 on Cell-Mediated Resistance to Infection with Listeria monocytogenes in Mice

Acquired resistance to Listeria monocytogenes during a secondary infection in a murine model fed dietary lipids

OBJECTIVE

The ω-3 polyunsaturated fatty acids can suppress immune system functions. This property may cause adverse effects by impairing host resistance to infection. The present study focused on estimating the impact of different dietary lipids on the immune system of mice after a secondary infection with Listeria monocytogenes.

METHODS

BALB/c mice were divided into five dietary groups of olive oil, fish oil, sunflower oil, high-oleic sunflower oil, or low fat that was administered for 8 wk. The mice were immunized with 10(3) colony-forming units. Thirty-eight days later, each mouse was challenged with 10(4) colony-forming units. Mice survival and bacterial clearance from livers and spleens were determined. In addition, cytokine, chemokine, and adhesion molecule productions were quantified from the sera.

RESULTS

Survival percentage in mice fed a fish oil diet was 100% and bacterial numbers from spleen were decreased at 72 h. Interleukin-12, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 productions were decreased. Levels of tumor necrosis factor-α and interferon-γ were increased, whereas macrophage inflammatory protein-1α (MIP-1α) production was unaltered.

CONCLUSION

Immune defense in mice fed a fish oil diet was improved after secondary exposure, acquiring an adequate resistance. This result could be attributable to an increase of a T-helper type 1 response.

Morphological changes induced by dextran sulfate 500 in mononuclear phagocytes of listeria-infected mice

Morphological changes involving mononuclear phagocytes in Listeria-infected mice after treatment with dextran sulfate 500 were investigated. Mononuclear phagocytes in livers and spleens, both circulating monocytes and fixed macrophages, showed uptake of electron-dense material. Mononuclear phagocyte changes were most pronounced within granulomatous lesions, where many phagocytes showed large membrane-bound inclusions and extensive cellular damage. It is concluded that dextran sulfate 500 selectively damages mononuclear phagocytes and that, in listerial infection, dextran sulfate 500 renders mononuclear phagocytes unable to express cellular resistance.

Protection of mice against SV40 tumours by Pam3Cys, MTP-PE and Pam3Cys conjugated with the SV40 T antigen-derived peptide, K(698)-T(708)

The intraperitoneal injection of Balb/c mice with synthetic analogues of adjuvants S-[2,3-bis(palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-R-cysteine (Pam3Cys) or muramyltripeptide phosphatidylethanolamine (MTP-PE) inhibited the tumourigenic growth of subcutaneously injected VLM cells, a syngeneic simian virus 40 (SV40)-transformed cell line. Furthermore, the Pam3Cys conjugate of K698-T708 (KT), which represents the C-terminal undecapeptide of the SV40 large tumour (T) antigen, was tumour-protective. Also syngeneic spleen cells, preincubated in vitro with this Pam3Cys-KT derivative, which anchores spontaneously at the cell membrane, were, through SV40 tumour mimicry, tumour-protective. The protection was impaired by treatment of the mice with either anti-CD4, anti-CD8 IgG, anti asialo GM1 antiserum or dextrane sulfate, which deplete the CD4+, CD8+ and NK cells or the macrophages, respectively. In summary, SV40 tumour transplantation resistance can be experimentally elicited by a tumour-epitope-specific vaccine. In the absence of an immunogenic epitope protection was obtained by administration of biological response modifiers. Protection is effected by SV40-T-antigen-specific cytotoxic lymphocytes in cooperation with NK cells and macrophages.

The consequences of the intracellular retention of pathogen-derived T-cell-independent antigens on protein presentation to T cells

Intracellular pathogens can be considered as particulate antigens chemically composed of a complex mixture of T-cell-dependent antigens (TD) (peptides and proteins) and T-cell-independent antigens (TI) (glycolipids and complex polysaccharides). A large range of saccharides (from oligosaccharides to complex polysaccharides) derived from pathogenic microorganisms are being isolated and characterized. They are currently implicated in signaling systems and concomitant host-parasite relationships. However, there are not many structure-function relationships described for these pathogens. This is particularly true of polysaccharides. In this report we have reviewed the role of defined TI antigens in the processing and presentation of defined TD antigens to specific T cells by antigen-presenting cells (APC). We also considered the importance of some of the chemical characteristics shared by different carbohydrates implicated in the inhibition of antigen presentation. These findings are discussed in relation to the clear immunopathological consequences of long retention periods of complex carbohydrate molecules derived from intracellular parasites inside certain APC and the absence of antigen presentation impairment in physiological situations such as the removal of senescent or damaged red blood cells by splenic macrophages or intracellular accumulation of carbohydrates in colostrum and milk macrophages during lactation.

Elimination of resident macrophages from the livers and spleens of immune mice impairs acquired resistance against a secondary Listeria monocytogenes infection

During a secondary Listeria monocytogenes infection in mice, the bacteria are eliminated more rapidly from the liver and spleen than during a primary infection. This acquired resistance against a secondary infection is dependent on T lymphocytes, which induce enhanced elimination of bacteria via stimulation of effector cells such as neutrophils, resident macrophages, exudate macrophages, and hepatocytes. The aim of the present study was to determine the role of the resident macrophages in acquired resistance against a secondary L. monocytogenes infection in mice. Mice which had recovered from a sublethal primary infection with 0.1 50% lethal dose (LD50) of L. monocytogenes intravenously (i.v.), i.e., immune mice, received a challenge of 1 LD50 of L. monocytogenes i.v. to induce a secondary infection. At 2 days prior to challenge, immune mice were given an i.v. injection of liposomes containing dichloromethylene-diphosphonate (L-Cl2MDP) to selectively eliminate resident macrophages from the liver and spleen. Control immune mice received either phosphate-buffered saline (PBS) or liposomes containing PBS (L-PBS). Treatment of mice with L-Cl2MDP effectively eliminated resident macrophages from the liver and spleen but did not affect the number of granulocytes, monocytes, or lymphocytes in peripheral blood or their migration to a site of inflammation. Phagocytosis and killing of L. monocytogenes by peritoneal exudate cells elicited with heat-killed L. monocytogenes were similar in all groups of immune mice. On day 3 of a secondary infection, the number of L. monocytogenes organisms in the livers and spleens of L-Cl2MDP-treated immune mice was 4 log10 units higher than in immune mice treated with PBS or L-PBS. The concentration of reactive nitrogen intermediates in plasma, a measure of the severity of infection, was 70-fold higher for L-Cl2MDP-treated immune mice than for PBS- or L-PBS-treated immune mice. Treatment with L-Cl2MDP significantly increased the number of inflammatory foci in the liver and spleen, decreased their size, and affected their structure. From these results, we conclude that resident macrophages are required for the expression of acquired resistance against a secondary L. monocytogenes infection in mice.

Failure of FK 506 to suppress the T cell-mediated immunity of mice to Listeria monocytogenes

Listeria monocytogenes belongs to the group of intracellular bacteria, which means that they reside and multiply within host cells. The protective immunity against such an infection is mediated by cellular immune mechanisms. Whereas the CD8+ T cell population plays a major role therein, the CD4+ T cells are held to be of minor importance in this defence system. Consequently, one can understand that immune suppression with FK 506 which acts primarily on this latter T cell subset, does not interfere with protective immunity of mice infected with L. monocytogenes. We have demonstrated that the drug blocks neither curing of primary infection, nor formation of granulomas, nor induction of cell populations capable of mediating adoptive transfer of immunity, nor expression of pre-existing immunity.

Is any strain of Listeria monocytogenes detected in food a health risk?

Listeria spp. have been isolated from various food items. This fact does not mean in any case a true health risk. A balanced appraisal should be based on quantitative as well as qualitative aspects. Actually, there is still an open debate whether a limited number of Listeria has to be tolerated at least in certain food items. In addition, the pathogenic potency of an isolate may be put into account. Pathogenicity of various Listeria spp. definitely varies. Most Listeria spp., except Listeria monocytogenes, can be regarded as harmless to man. Also, not all strains of L. monocytogenes are pathogenic: rough variants possess only reduced virulence; non-hemolytic mutants have completely lost their pathogenic potency. Furthermore, several other virulence factors may be lost under natural conditions, so that among the majority of hemolytic, pathogenic isolates there may be others which are non-pathogenic or of low virulence only. Unfortunately, these strains actually cannot be recognized and characterized by common laboratory tests, so that animal pathogenicity seems to be the only way to get a final conclusion on the health risk of an isolate of L. monocytogenes from any food. The problem raised by this is which animal test is able to predict a true health risk either for normal hosts or for immunocompromised patients?

Humoral and cellular defense against intestinal murine infection with Yersinia enterocolitica

The role of phagocytes and the complement system as potential host defense mechanisms against bacterial infection were studied in mice with two isogenic strains of Yersinia enterocolitica serotype O8 differing in pathogenicity because of differences in plasmid content. Complement depletion in mice by intraperitoneal injection of cobra venom factor did not affect the course of colonization of the intestinal tissue by each strain, indicating that in mice complement is not essential for the elimination of these bacteria. This conclusion is supported by the fact that fresh murine serum had no bactericidal effect in vitro either on the pathogenic or on the nonpathogenic strain. However, in the intestinal tissue as well as in the peritoneal cavity, only the pathogenic, plasmid-bearing Y. enterocolitica strain survived, while the nonpathogenic, plasmidless strain was rapidly eliminated. Since elimination from the peritoneal cavity is due to phagocytosis by polymorphonuclear leukocytes and macrophages, resistance to phagocytosis in vivo seems to be the decisive factor determining the virulence of pathogenic Y. enterocolitica strains.

Application of purified polysaccharides from cell cultures of the plant Echinacea purpurea to mice mediates protection against systemic infections with Listeria monocytogenes and Candida albicans

Purified polysaccharides from cell cultures of the plant Echinacea purpurea were investigated for their ability to enhance phagocytes' activities regarding nonspecific immunity in vitro and in vivo. Macrophages (M phi) from different organ origin could be activated to produce IL-1, TNF alpha and IL-6, to produce elevated amounts of reactive oxygen intermediates and to inhibit growth of Candida albicans in vitro. Furthermore, in vivo the substances could induce increased proliferation of phagocytes in spleen and bone marrow and migration of granulocytes to the peripheral blood. These effects indeed resulted in excellent protection of mice against the consequences of lethal infections with one predominantly M phi dependent and one predominantly granulocyte dependent pathogen, Listeria monocytogenes and C. albicans, respectively. Specific immune responses to sheep red blood cells (antibody production) and to listeria (DTH) were not affected by the polysaccharides. The possibility of clinical use is discussed.

Enhancement of natural resistance of mice to Rhodococcus equi infection by Dextran Sulfate 500

The effect of intraperitoneal injection of Dextran Sulfate 500 (DS-500, 500,000 Mr) on the intravenous clearance and host resistance to Rhodococcus equi in mice was studied. Contrary to the results seen with Listeria monocytogenes, DS-500 enhanced murine resistance to R. equi and altered organ distribution and clearance.

Mechanisms of antigen processing

Using MAb and monovalent Fab probes and saponin permeabilization we have demonstrated that PEC and TA3 B lymphoma-hybridoma cells contain a significant intracellular pool of Ia. At least in TA3 cells, this intracellular pool was independent of protein synthesis. In PEC, adherence caused redistribution of Ia with disappearance of the intracellular pool. Endocytosis of Ia occurred in both TA3 and PEC, and internalized Ia reached a plateau level corresponding in size to the total intracellular Ia pool revealed by saponin treatment. These results suggest that intracellular Ia is largely in a recycling pool derived from the plasma membrane by endocytosis. Subcellular fractionation studies suggest that Ia processing occurs in endosomes similar to those involved in transferrin processing. Antigen processing by TA3 cells was found to be unaffected by cycloheximide. In contrast, antigen processing by adherent PEC was markedly inhibited by cycloheximide, despite the fact that they maintained surface Ia and were still capable of presenting antigen peptides. This suggests that an important intracellular Ia processing step or antigen processing step was blocked in these cells. Adherent PEC may contain less recycling Ia, making protein synthesis the major source for intracellular Ia and the availability of intracellular Ia sensitive to cycloheximide. Alternatively, the inhibition of antigen processing by cycloheximide in PEC may reflect depletion of enzymes or other factors involved in antigen processing. Proteins and polysaccharides may interfere with the events that result in the formation of an immunogenic Ia-peptide complex. We had previously documented that peptides compete for the binding site of Ia molecules. We discussed here a second form of interference by polysaccharides and microbial products. These materials did not compete or interfere with the binding and presentation of processed peptides by Ia. Rather, their presence inside the macrophage inhibited MHC-dependent presentation of immunogenic proteins by inhibiting intracellular steps in antigen processing. This intracellular interference with antigen presentation can be of major importance in the presentation of complex mixtures of protein and carbohydrates.

The role of T cell subpopulations in cell mediated immunity to facultative intracellular bacteria

This brief review summarizes the experimental data which underly the classic concept of antibacterial cell mediated immunity and will integrate recent developments focusing on results obtained by in vivo studies in the model of rodent listeriosis.

Alteration of non-specific resistance to infection with Listeria monocytogenes

The experimental infection of murine hosts with Listeria monocytogenes is often used as a model for cell-mediated immunity. However, the natural immunity or non-specific resistance to listeriosis can be influenced by the parasite itself and also by a wide array of endogenous and exogenous host factors. The most important host factor in inbred mouse strains is their genetically determined susceptibility or resistance to Listeria monocytogenes. Secondly, the age of the mice is crucial for the outcome of infection. Resistance is only slowly developed by newborn mice, while aged mice possess an increased non-specific resistance as compared to young adult animals. Resistance is further influenced by the nutritional status, by pregnancy or by a simultaneous second antigenic stimulation. Regarding exogenous factors, macrophage blocking agents can totally abolish the resistance to listeriosis, while a lot of immunomodulating agents, such as BCG, killed Bordetella pertussis or Propionibacterium acnes organisms, lipopolysaccharides, suramin etc., can either increase or decrease the resistance. The mononuclear phagocyte system seems to be the main target of all these immunomodifiers. The timing between listeria infection and application of the immunomodulator determines the effect on non-specific resistance. A simultaneous injection of parasite and immunomodulator results in a decrease of resistance, while the application of immunoadjuvants several days before infection can dramatically increase the resistance to listeriosis. The delicate equilibrium of the mononuclear phagocyte system must therefore be taken into account, when infection with Listeria monocytogenes is used to test for immune-modifying agents, which are intended for use in humans or animals.

Inhibitory effect of tetracycline and doxycycline on resistance of mice to infection with a tetracycline-resistant strain of Listeria monocytogenes

By transposon mutagenesis a tetracycline-susceptible strain of Listeria monocytogenes (MIC 1 mg/l. for tetracycline and 0.25 mg/l. for doxycycline) was rendered resistant (MIC 64 mg/l. for tetracycline and 16 mg/l. for doxycycline). Infection of mice with this resistant strain led to an acute infection. Treatment with 2 x 2 mg tetracycline per day did not influence the course of infection during the first 3 days, indicating that the nonspecific resistance, mediated mainly by macrophages and granulocytes, was not affected by this treatment. The second phase of infection, characterized by a continuous resistance to infection due to macrophages activated by T-lymphocytes was, however, definitely hampered. Even acquired immunity to a secondary infection was impaired by treatment with tetracycline, indicating that cell-mediated immunity can be blocked. The course of infection of athymic, nude mice which are unable to build up a cell-mediated immune response, was not affected by tetracycline treatment. Doxycycline expressed the same activities as tetracycline.

Effect of silica on the genetic regulation of antibody responsiveness

The high (H) and low (L) antibody responder lines of mice produced by selective breeding are characterized by different modifications in immunocompetent cell potentialities, according to the immunization procedure used for the selection process. In selections I and II, the difference in antibody responsiveness between H and L lines was clearly shown to depend mainly on macrophage function: the more rapid catabolism of antigens in L mice was the main cause of the low antibody production. In contrast, up to now, no difference has been observed between H and L mice of selections III and IV in terms of the macrophage accessory role. The administration of silica particles has a well known impairment effect on macrophage activity. Therefore, the effect of silica injection on the kinetics of antibody responses to selection antigens was compared in H and L mice of the four selections. Silica was given either intravenously or locally in one hind footpad 6 or 24 h before immunization by the same route. Silica treatment consistently improved antibody responsiveness in the L mice of selections I and II, but had no effect in the L mice of selections III and IV. The antibody responses of the H lines of the four selections were not substantially modified by silica injections. Therefore, the silica treatment reduced the interline difference in antibody responses in selections I and II only, by interfering with the expression of the genetic modification of macrophage activity. However, a similar effect was not obtained with other substances known to affect macrophages, including dextran sulphate or carrageenan. The results reported here are in agreement with the above-mentioned statement that the genetic modification of macrophage function plays a major role in the interline difference in selections I and II and is not involved in selections III and IV.

[Virulence of Listeria welshimeri]

The species L. welshimeri consists of non-pathogenic bacteria. 16 different strains which were characterized biochemically were unable to multiply within adult NMRI mice after injection of a high dose of about 10(7) bacteria. Even macrophage depleted animals, which were obtained by treatment with highmolecular dextran sulfate, could eliminate L. welshimeri. 5 day old baby mice were resistant against L. welshimeri. L. innocua was as avirulent as L. welshimeri, whereas L. monocytogenes was virulent, since these bacteria multiplied in adult animals, killed macrophage depleted adult mice as well as baby mice after injection of low doses.

Effects of suramin on the immune responses to sheep red blood cells in mice. I. In vivo studies

The effect of Suramin on the cell-mediated delayed-type hypersensitivity (DTH) and the humoral immune responses elicited in mice by sheep erythrocytes was studied. The results show that administration of Suramin, at various times before or after antigenic sensitization, results in a profound inhibition of cell-mediated responses but has no adverse effect on antibody production. Suramin was particularly effective when given during the effector phase of DTH: mice which were treated with this drug, 4 days after immunization, at the time of skin testing, exhibit negative or low DTH responses compared to control mice. Evidence is presented that this short-term Suramin-induced suppressive effect on the expression of DTH is related to a defective recruitment, by sensitized T lymphocytes, of phagocytic cells at the site of the inflammatory reaction. In addition, when treatment with Suramin precedes by 8 days (Day -8) or by 1 hr sensitization with sheep erythrocytes for DTH, decreased DTH reactions over controls were observed. The inhibitory effect exerted by Suramin administered on Day -8 can be reversed by increasing the dose, from 10(6) to 10(8) sheep erythrocytes, of the sensitizing antigen. The possibility is discussed that, in this case, Suramin may interfere with the generation of DTH-mediating cells through a rapid degradation of antigen related to the Suramin-induced hyperplasia of the mononuclear phagocyte system. In contrast, DTH anergy in mice treated with Suramin 1 hr before sensitization is maintained regardless of the sensitizing antigen dose. Analysis of the sensitized lymphocyte population in these mice indicates that Suramin does not prevent the induction of DTH-mediating cells and suggests that the expression of these latter is inhibited by suppressive cells which are generated as a result of drug treatment.

Dextran sulfate-induced peritoneal lysophospholipase activity varies among mouse strains

Lysophospholipase (LPL) activity resulting from the intraperitoneal injection of dextran sulfate (DS) was studied in different mouse strains. AKR/J and BALB/cByJ mouse strains showed decreased LPL levels when a low molecular weight DS was injected but increased LPL activity when high molecular weight DS was injected intraperitoneally. C57BL/6 mice had increased LPL activity with low molecular weight DS but decreased LPL activity with high molecular weight DS. All three mouse strains showed increased peritoneal-cell changes when injected with DS of a molecular weight of 79,000.

Virulence of different strains of Listeria monocytogenes serovar 1/2a

Different strains of Listeria monocytogenes serovar 1/2a were used to infect mice. A smooth, haemolytic strain multiplied in the spleen of normal adult mice and induced a long-lasting immunity to subsequent challenge infection. When the animals were treated with dextran sulphate (DS) Listeriae multiplied more rapidly and death followed within a few days. When normal baby mice were infected with this organism, fatal infection occurred. In nude mice a chronic infection developed. Secondly, a rough, haemolytic strain was used to infect mice. In normal adult mice no multiplication of this strain was observed. This holds true also for DS-treated animals. In nude mice the bacteria were eliminated slowly. Normal baby mice could only be killed if the infective dose was increased. This strain was considered to be intermediate in virulence. The infection stimulated a considerable immune response in mice, although to a lesser degree than the smooth, haemolytic Listeria strain. Thirdly, a smooth, non-haemolytic strain of L. monocytogenes serovar 1/2a was used. The bacteria were rapidly eliminated in normal, in DS-treated and in nude animals. Normal baby mice did not develop fatal disease, so it was considered that this strain of L. monocytogenes serovar 1/2a was avirulent. This variant was found to be non-immunogenic. A boosting of immunity of animals by this avirulent Listeria strain was, however, found to be possible. A reasonable explanation for the rapid elimination of avirulent L. monocytogenes serovar 1/2a from mice cannot be presented at this time. Whereas it is known that the macrophage system and the T-lymphocytes play an essential role in the resistance to virulent Listeriae, there is no increased susceptibility of the avirulent bacteria to these defence mechanisms. Other bacterial properties, such as serum sensitivity and lysozyme susceptibility, are likewise considered to be unimportant.

Studies of immune function and host resistance in B6C3F1 mice exposed to formaldehyde

A series of immune function and host resistance parameters were examined in female B6C3F1 mice following a 21-day (6 hr/day) inhalation exposure to 15 ppm of formaldehyde (HCHO). Immune parameters examined included delayed hypersensitivity to keyhole limpet hemocyanin, antibody plaque-forming cell response to sheep erythrocytes (T-lymphocyte-dependent antigen) and TNP-Ficoll (T-lymphocyte-independent antigen), lymphoid organ weights and histopathology, routine hematology, bone marrow cellularity and CFU progenitor cell enumeration, lymphocyte subpopulation quantitation by cell surface markers, mitogen-induced lymphocyte blastogenesis, macrophage function parameters, and host resistance to challenge with the bacterium Listeria monocytogenes and transplantable tumor cells. Lymphoid organ weight, bone marrow cellularity, and hematology parameters were unchanged in HCHO exposed mice. Similarly, the percentage of T and B lymphocytes and their proliferative responses to mitogens were not significantly altered. Antibody (IgM) plaque-forming cell response following antigen challenge was unchanged. Macrophage function was normal although some evidence of enhanced H2O2 production associated with elevated bactericidal activity was observed in resident macrophages. Resistance to challenge with the bacteria Listeria monocytogenes was significantly enhanced, while resistance to tumor challenge remained unchanged. No evidence of immunosuppression following short-term exposure to HCHO was observed.

Suppression of liver uptake of liposomes by dextran sulfate 500

The effect of dextran sulfate (DS, 500,000 Mr) and multilamellar vesicles (MLV) as liver blockade agents has been investigated in mice. Intravenous injection of unlabeled MLV prior to radioactive MLV caused moderate reduction in the liver uptake and increased tibia, lung, and spleen uptake. More drastic differences were observed with intraperitoneal injection of DS. When tested in the range of 0-50 mg of DS per kg of body weight, maximal liver blockade occurred at a dose of 50 mg. By using 50 mg of DS per kg, maximal liver blockade occurred at 12 hr after DS injection. The liver blockade was temporary, ending within 48 hr. The intraperitoneal route of injection for DS was more effective for liver blockade than the intravenous route.

The role of macrophages in acquired cell-mediated immunity to Toxoplasma gondii

Mice immunized by primary infection with an avirulent strain of Toxoplasma gondii were protected against challenge infection with a highly virulent strain, even though macrophages were eliminated either by dextran sulfate or by carbon ink. This findings differs strikingly from previous results obtained in similar experiments with other intracellular pathogens such as Listeria monocytogenes and Salmonella typhimurium. It is therefore concluded that the macrophage population, which plays an essential role in the cell-mediated immunity to reinfection with L. monocytogenes and S. typhimurium, is not of primary importance in cell-mediated immunity to reinfection with T. gondii.

Delayed hypersensitivity to nonviable Mycoplasma pulmonis in mice is enhanced by dextran sulfate

The enhancing effect of dextran sulfate (DS) on delayed hypersensitivity to nonviable Mycoplasma pulmonis in mice was evaluated by means of delayed footpad swelling. Mice pretreated subcutaneously with nonviable M. pulmonis and DS had significantly increased delayed footpad swelling when the mice were injected subcutaneously in the footpad with the same antigen 7 days later. Delayed footpad swelling was not detected in mice pretreated only with nonviable M. pulmonis or DS followed by footpad injection with nonviable M. pulmonis. Subcutaneous pretreatment in the scruff of the neck with nonviable M. pulmonis and DS was more effective in eliciting delayed footpad swelling than intravenous or intraperitoneal pretreatment. Delayed footpad swelling did not develop when mice were injected in the footpad with nonviable Mycoplasma hyopneumoniae, M. gallisepticum, M. dispar, or M. bovis on day 7 after pretreatment with M. pulmonis and DS. Injection of nonviable M. pulmonis in the footpad on day 3 after pretreatment with M. pulmonis and DS resulted in no significant footpad swelling, but injection in the footpad on days 7, 14, 21, and 28 resulted in significant footpad swelling. Delayed footpad swelling was transferred by intravenous injection with spleen cells of mice which were pretreated with nonviable M. pulmonis and DS into nontreated recipient mice. Intravenous injection with anti-mouse thymus cell rabbit serum into the mice which were previously pretreated with nonviable M. pulmonis and DS reduced the delayed footpad swelling significantly.

Two steps in the generation of acquired cellular resistance against Listeria monocytogenes: accumulation and activation of macrophages

Mice were immunized with 1 X 10(3) viable Listeria monocytogenes, and the mechanism of the acquired resistance against challenge infection with 5 X 10(4) L. monocytogenes was studied by the use of the peritoneal cavity of mice as the site of challenge. An enhanced elimination of bacteria from the peritoneal cavity became detectable on day 5 after immunization, and lasted thereafter. Before day 10 postimmunization, a marked accumulation of macrophages was observed after the challenge but the in vitro listericidal activity of macrophages was not so enhanced. After day 15 postimmunization, peritoneal macrophages did not increase in number after the challenge but the in vitro listericidal activity of macrophages was the stronger. Accumulation of non-activated macrophages seemed to contribute mainly to the expression of acquired resistance against challenge in the early stage of immunization. So-called activated macrophages appeared to be generated only in the later stage of immunization. Thus it was suggested that there may be at least two steps in the expression of acquired listerial resistance.

The role of macrophages in primary and secondary infection of mice with Salmonella typhimurium

Elimination of macrophages with high-molecular dextran sulphate (DS) markedly impairs resistance of mice to primary infection with smooth, virulent strains of Salmonella typhimurium, whereas stimulation of this system by killed Bordetella pertussis organisms increases resistance. In infection with rough, avirulent strains of S. typhimurium the elimination of macrophages was not followed by an essential loss of resistance, and it appears that other non-specific defence mechanisms, for example the complement system, may have compensated for the lack of macrophages. Macrophages, therefore, play an important role in defence during primary infection with virulent strains. In immunity to challenge infection with S. typhimurium, macrophages play an even more significant role. Treatment with DS completely removes immunity, and both humoral and cell-mediated immune mechanisms seem to require the participation of macrophages.

Comparative effects of carrageenan on systemic candidiasis and listeriosis in mice

Carrageenan, a toxic substance for the mononuclear phagocyte system (MPS), increase drastically the susceptibility of mice against Listeria monocytogenes challenge but induces concurrently an increasing resistance against systemic candidiasis and granulocytosis. These results corroborate the minor role played by MPS and suggest that polymorphonuclear cells play a major role in non-specific resistance of mice against systemic candidiasis.

Effects of dextran sulfate 500 on protective responses to sublethal Trichomonas foetus infection in mice

In order to analyze the host-parasite interactions in experimental trichomoniasis, the growth of Trichomonas foetus in the peritoneal cavity and changes in the peritoneal exudate cells were followed in mice treated with dextran sulfate 500 (DS 500), a known macrophage-toxic agent. Light microscopic observation showed that DS 500 treatment induced degeneration of peritoneal macrophages within about 48 hr after the treatment and the damaged macrophages did not phagocytize the parasites, whereas peritoneal neutrophils and lymphocytes were not affected by the drug. In the DS 500-treated mice, growth of parasites in the peritoneal cavity was accelerated and a high susceptibility of the mice to T. foetus infection was observed. These results indicate that macrophages play the most important role among the peritoneal exudate cells in resistance to T. foetus infection, especially during the early stage of infection.

Relationship between non-specific activity of macrophages and immune responses to Listeria monocytogenes

Delayed footpad reactions and acquired cellular resistance to Listeria monocytogenes were studied in mice whose mononuclear phagocyte system (MPS) had been blocked or stimulated. Colloidal carbon was used for the blockade of MPS and Corynebacterium parvum used for the stimulation. Strong delayed footpad reactions. On the other hand, the i.v. injection of 3 X 10(1) listeria induced an appreciable level mice, while in MPS-stimulated mice, i.v. injection with even 4 X 10(3) listeria could not induce such strong delayed footpad reaction. On the other hand, the i.v. injection of 3 X 10(1) listeria induced an appreciable level of delayed footpad reaction only in MPS-blocked mice. Acquired cellular resistance was depressed by MPS stimulation, whereas it was augmented by MPS blockade. These results suggested that non-specific activity of MPS modulates subsequent immune responses after inoculation of listeria.

Cellular basis for genetically determined enhanced resistance of certain mouse strains to listeriosis

The characteristics of the mononuclear phagocytes mediating resistance to infection with Listeria during the early phase (0 to 48 h) of the response have been investigated in genetically determined susceptible (A/J) and resistant (C57BL/6, B10.A/SgSn) strains of mice. Irradiation immediately before infection profoundly enhanced the bacterial growth in the resistant strain, while having no effect in the susceptible strain, over a wide range (3 x 10(3) to 10(5)) of infective doses. This effect of irradiation is demonstrable at low-dose radiation (200 roentgens) and can be reversed by repopulation with 20 x 10(6) syngeneic nucleated bone marrow cells. Administration of dextran sulfate 500 24 h before infection profoundly enhanced the bacterial growth in the susceptible strain, while having much less effect in the resistant strain. Thus, the genetic advantage of the resistant mouse strains to listerial infection, at least during the early phase of the response, appears to be due to a cellular mechanism that is highly radiosensitive and relatively insensitive to dextran sulfate 500. In the susceptible strain, the early protective cellular mechanism is radioresistant and highly dextran sulfate 500 sensitive.

Thioglycolate medium decreases resistance to bacterial infection in mice

Brewer thioglycolate medium, a bacterial culture medium which is widely used as a nonspecific in vivo macrophage stimulant, was tested for its effect on mouse resistance to bacterial infection. Mice which did or did not receive thioglycolate medium were challenged with Listeria monocytogenes. Injection of thioglycolate medium significantly decreased the ability of the host to resist infection. This decreased resistance occurred whether thioglycolate medium was injected 0 to 9 days before, or 1 to 2 h after Listeria challenge. Bacteria grew considerably better in washed adherent peritoneal cells from thioglycolate medium-injected mice than in washed adherent peritoneal cells from normal mice. Thus, thioglycolate medium may ultimately cause a decrease in macrophage function.

Failure of synthetic muramyl dipeptide to increase antibacterial resistance

Synthetic muranyl dipeptide, which potentiates antibody production and cellular immune responses at a dosage of 100 to 500 micrograms, did not enhance resistance to intravenous infection with a sublethal dose of 2 X 10(3) to 4 X 10(3) viable Listeria monocytogenes cells in mice when intraperitoneally injected either 20 min or 5 days before infection. Similarly, blockade of the mononuclear phagocyte system by dextran sulfate 500 could not be overcome by pretreatment with muramyl dipeptide. In contrast, dextran sulfate 500-induced loss of antibacterial resistance was found to be completely abolished by intraperitoneal injection of 3 X 10(9) killed Bordetella pertussis organisms when given 4 days before injection of dextran sulfate 500, i.e., 5 days before infection. B. pertussis were also effective in enhancing antibacterial resistance when administered 5 days before infection. The different behavior of the two adjuvants tested is assumed to be due to their different nonspecific proliferative capacities. Thus, B. pertussis are assumed to act by direct stimulation of the mononuclear phagocyte system whereas muramyl dipeptide does not.

Resistance to listeriosis in mice that are deficient in the fifth component of complement

Infection with Listeria monocytogenes was studied in strains of mice with genetic absence of the fifth component of complement (C5). Mice deficient in C5 consistently showed an increased growth of Listeria in their spleens as compared to normal mice. This increased growth was not corrected by administration of plasma containing C5. Furthermore, depletion of C5 and terminal complement components by administration of cobra venom factor did not impair the resistance to Listeria infection of normal mice. No phagocytic defect could be detected in macrophages from strains lacking C5. Transfer of bone marrow cells from C5+ but not from C5- mice corrected the marked increase of Listeria growth in mice having blockade of the reticuloendothelial system. We hypothesize that the defect of mice lacking C5 lies not in the absence of serum C5 but somewhere at the level of the macrophage.

[Cellular antibacterial immunity (author's transl)]

Facultatively intracellular bacteria (Mycobacteria, Brucellae, Listeria monocytogenes, Salmonella typhi etc.) may not necessarily be killed after having being phagocytosed by polymorphonuclear leucocytes or macrophages, cellular immunity having first to be built up. This results in the formation of specifically committed T-lymphocytes, which in turn release lymphokines after restimulation by homologous antigen. Under the effect of lymphokines, mononuclear phagocytes are chemotactically attracted to the site of infection, granulomas are formed and macrophages within the granuloma are activated. The granuloma represents the tissue reaction within which the interaction between facultatively intracellular bacteria and defence factors takes place. The experimental details underlying this concept are reviewed.

Phenotypic expression of genetically controlled host resistance to Listeria monocytogenes

Several inbred mouse strains, all of them derived from the C57BL background, have genetically determined increased resistance to infection with Listeria monocytogenes, whereas a variety of other strains are relatively sensitive to this infection. Comparison of the host response to L. monocytogenes in the sensitive A strain and the resistant C57BL/6 (B6) strain revealed that the B6 mice were superior to A mice both in the T-cell-independent and in the T-cell-dependent phase of the response. Although animals of both strains had equal ability to clear their circulation of intravenously administered Listeria and to take up comparable amounts of bacteria in their livers and spleens, already 24 to 48 h after infection the genetic advantage of B6 strain mice to suppress bacterial proliferation was apparent. Both the primary (early and late) and the secondary responses as well as the ability to inactivate the bacterial load after adoptive protection by syngeneic immune lymphocytes were more efficient in the B6 animals, suggesting that the common effector macrophage arm of the antilisterial resistance rather than the lymphocyte arm (mediating the T-cell-dependent phase of response) is genetically controlled.

The effect of dextransulfate 500 on the pathogenesis of herpes simplex virus infections in weanling mice

Intraperitoneal (i.p.) injection of Dextran Sulfate (D.S.) 500 during a limited period of time influences the course of herpes simplex-virus-infections. D.S.500 was found to reduce the resistance of mice for some herpes simplex-virus strains (Len, L3--2s, Haase) if given between 16 hours and 2 hours after i.p. infection. The decrease of resistance could be correlated with an increase of the virus content of liver, spleen, brain and spinal cord. Injection of herpes simplex-virus-specific immune serum counteracted the effect of D.S.500 on the course of infections. Conversely, D.S.500 increased the resistance of mice to another group of herpes simplex-viruses (strains D-316, Thea, DD), if given 3 to 8 hours before infection. These effects are ascribed to a special interaction of D.S.500 with macrophages and probably other virus-susceptible cells of the peritoneal cavity and elsewhere with a resulting counteraction to the virus infection.

Comparison of various macrophage-inhibitory agents on vaginal and systemic herpes simplex virus type 2 infections

Pretreatment of mice intraperitoneally with silica, trypan blue, or dextran sulfate to inhibit macrophage function markedly increased the lethality of a systemic intravenous infection with herpes simplex virus type 2, but did not affect the lethality or local virus growth after vaginal infection of mice with herpes simplex virus type 2. Agents which inhibit macrophage function by different mechanisms decreased host resistance to herpes simplex virus type 2, but the effects of macrophage-inhibitory agents may vary according to the route of virus infection.

Listeria monocytogenes cell walls induce decreased resistance to infection

A significant decrease in murine resistance to Listeria monocytogenes was induced by using crude Listeria cell wall fraction (LCWF) and purified Listeria cell walls (PF). When equal amounts of these materials were injected, PF was more effective than LCWF in decreasing resistance. The PF effect was dose dependent when measured either as a decrease in 50% lethal dose of the Listeria challenge or as a decrease in survival time of the infected mice. PF apparently does not act directly on the Listeria since it (i) did not cause a change in in vitro growth of Listeria and (ii) did not increase the virulence of Listeria passaged in vivo or in vitro. The greatest decrease in resistance was observed when both PF and the Listeria challenge were injected intraperitoneally, which may suggest a localized effect. A decrease in resistance was seen when PF was given as early as 3 days before challenge. There was little or no decrease in resistance when PF was given 2 days after the Listeria challenge. Mice previously immunized with live Listeria were immune to Listeria challenge. However, after PF injection the immune mice showed a decreased resistance which was of the same order of magnitude as that seen in unimmunized mice. The effect of PF seems to be at least partially nonspecific, since a decrease in resistance to Salmonella typhimurium could also be demonstrated in PF-treated mice. Phagocytosis of Listeria both in vivo and in vitro did not appear to be inhibited by PF, although the ability of PF-treated mice to kill Listeria in the peritoneal cavity was inhibited.

Reversion of dextran sulfate-induced loss of antibacterial resistance by Bordetella pertussis

Parenteral injection of dextran sulfate 500 (DS 500; 50 mg/kg of body weight) into mice caused a complete loss of resistance to a sublethal (2 X 10(3) to 5 X 10(3)) infection with Listeria monocytogenes. Such loss could be prevented by pretreatment of animals with 3 X 10(9) heat-killed Bordetella pertussis organisms (PO) 5 to 30 days before the administration of DS 500. The increased phagocytic capcity induced by PO was only exhausted when a fourfold dose of DS 500, effecting complete loss of antibacterial resistance (50 mg/kg ob body weight), was administered. Listeriosis in mice treated with DS 500 is characterized by rapid-progressive necro-purulent inflammation of liver and spleen, lack of mononuclear phagocyte response, and 100% lethality within 72 h after infection. In contrast, the time course, extent, and morphological characteristics of listeriosis in animals pretreated with PO before the DS 500 application were not significantly different from those of nonpretreated controls. Evidence is presented that the protective effect of PO is due to activation of the mononuclear phagocyte system, which without such treatment is blocked by the DS 500 administration. The data presented indicate that the protective effect of PO is due only in part to the endotoxic moiety of these bacteria. Differences in the course and morphology of listeriosis in animals with dysfunction of the mononuclear phagocyte system and in animals with deficiency of the cellular immune system are discussed.

Cellular elements in the resistance to candida infection in mice. I. Contribution of T lymphocytes and phagocytes at various stages of infection

Live organisms (cfu) of Candida albicans per organ were counted 1 hr and 1 to 20 days after an intravenous inoculation into various groups of mice which had distinct levels of immunologic or non-immunologic defense mechanisms. a) The number of cfu in the liver decreased progressively in normal mice, but those in the kidney maintained a constant level during the observation period. b) The number of cfu in the liver decreased progressively also in nude mice. In their kidneys, however, cfu increased progressively at a late stage of infection. c) In lethally irradiated AKR of nude mice in which phagocyte functions were severely depressed, the number of cfu increased progressively in both liver and kidney from the initial stage of infection. d) In immunized AKR mice, growth of C. albicans was suppressed at late stages of infection. Such protective immunity could be transferred partly with immune lymphoid cells but not with hyperimmune serum in the experimental system employed. In protection against candida infection, non-immune phagocytosis and T cell-mediated immunity appear to be required at the early and late stages of infection, respectively.

Suppression of cell-mediated immune responses by dextran sulphate

The effect of high molecular weight dextran sulphate (DS) on cell-mediated immune responses was studied. Two criteria were used to assess cell-mediated responses, skin graft rejection and intra-dermal (i.d.) skin tests. Mice receiving allografts and DS displayed a significant increase in graft survival time compared with untreated control animals. Similar results were obtained when the grafted animals differed at only the H-Y locus. Guinea-pigs sensitized with Mycobacterium tuberculosis and treated with DS showed a greatly reduced delayed skin test response when challenged with purified protein derivative. DS was capable of suppressing this response even though, by the same route, dosage, and time of administration, it was previously shown to enhance a cell-mediated response in guinea-pigs sensitized with a different antigen. The results of this study indicate that the adjuvant DS is capable of suppressing cell-mediated immune responses in mice and guinea-pigs.