In vitro studies on the interaction between mouse peritoneal macrophages and strains of Salmonella and Escherichia coli

BCG-trained macrophages couple LDLR upregulation to type I IFN responses and antiviral immunity

Trained immunity refers to memory-like responses of innate immune cells when they re-encounter pathogenic stimuli. Bacillus Calmette-Guérin (BCG) vaccination implies enhanced antiviral immunity, whereas the underlying mechanisms remain unclear. Herein, we have uncovered elevated expression of low-density lipoprotein receptor (LDLR) on BCG-trained macrophages with robust type I interferon (IFNI) production and antiviral effects both in vivo and in vitro. Consequently, cholesterol is accumulated in BCG-trained macrophages, leading to the augmentation of NFE2L1 expression and the formation of NFE2L1/IRAK1/TRIM25 complex where TRIM25 mediates IRAK1 K63 polyubiquitination to exaggerate IFNI responses in an RIG-I-dependent manner. We have also observed LDLR+ macrophages displaying heightened IFNI responses in BCG-treated human macrophages. To antagonize LDLR degradation by PCSK9 inhibitors increases IFNI responses in the macrophages and accelerated viral clearance. Our study thus couples LDLR upregulation to antiviral activity in BCG-trained macrophages, making commercial PCSK9 inhibitors potential antiviral indications in clinic.

Mg(OH)2 nanoparticles enhance the antibacterial activities of macrophages by activating the reactive oxygen species

Infection often causes disastrous consequences in all fields of clinical medicine, especially orthopedics. Hence, critical efforts are being made to engineer novel nanomaterials for the treatment of orthopedic infections due to the high biocompatibility and antibacterial properties they possess. The purpose of this study was to investigate the antibacterial effects of magnesium hydroxide (Mg(OH)₂ ) nanoparticles (NPs) in vitro and determine their possible mechanisms of action. In this study, Escherichia coli was selected as the pathogenic bacteria and it was found that Mg(OH)₂ NPs significantly inhibited the growth of E. coli by promoting nucleic acid leakage, inhibiting protein synthesis, and suppressing the metabolic activity. The minimum inhibitory concentration for these bacteria was determined to be 4.4 μg/ml. In vitro flow cytometry and immunofluorescence tests indicated that Mg(OH)₂ NPs induced the macrophages to generate reactive oxygen species to kill the bacteria. To understand the mechanisms involved in this process, western blotting was performed and it was found that Mg(OH)₂ NPs activated the phosphatidylinositol-3-kinase/serine-threonine kinase (PI3K/Akt) signaling pathway of macrophages to enhance their phagocytosis with no obvious cytotoxicity. Thus, Mg(OH)₂ NPs are a suitable choice to develop promising agents or coating materials for the treatment of clinically widespread infections in view of their safety, biocompatibility, and powerful antibacterial properties.

The cellular microbiology of Salmonellae interactions with macrophages

Salmonellae are important enteric pathogens that cause gastroenteritis and systemic illnesses. Macrophages are important components of both the innate and acquired immune system, acting as phagocytes with significant antimicrobial killing activities that present antigen to the adaptive immune system. Macrophages can also be cultured from a variety of sites as primary cells, and the study of the survival and interactions of Salmonellae with these cells is a very early model of infection and cellular microbiology. This review traces the history of discoveries made using Salmonellae infection of macrophages and addresses the possibility of future research in this area, in particular with regards to understanding the complexity of individual bacteria and macrophage cell variability and how such heterogeneity may alter the outcome of infection.

Interactions Between Macrophages of Guinea Pigs and Salmonellae II. Phagocytosis of Salmonella typhimurium by Macrophages of Normal Guinea Pigs

Peritoneal macrophages from normal guinea pigs were allowed to phagocytize Salmonella typhimurium in vitro. The extent of phagocytosis was determined by quantitative viable counts of the bacteria released after lysis of the phagocytes with sodium deoxycholate. It was shown that the avirulent strain RIA of salmonellae was more susceptible to ingestion by macrophages than the virulent strain SR-11. The presence of immune serum in the phagocytic mixture greatly enhanced the extent with which strain SR-11 was phagocytized. Also, the virulent bacteria recovered from infected mice exhibited a greater resistance to phagocytosis than those maintained in artificial media.

Uptake of h-dihydrostreptomycin by macrophages in culture

Mouse peritoneal macrophages, in culture, concentrate significant amounts of (3)H-dihydrostreptomycin, provided that the incubation period is sufficiently extended. Macrophages cultured in vitro from both stimulated and unstimulated animals concentrate the antibiotic from growth or maintenance media. The increase in cell-associated radioactivity is linear for almost a week before a plateau is reached. Calculations based on intracellular volumes of the cells indicate that the intracellular concentration of dihydrostreptomycin may attain levels greater than five times that of the external milieu. No uptake is measurable at 4 C, suggesting an active mechanism of transport into the cell. Phagocytosis of killed bacteria during incubation did not increase uptake of the antibiotic nor did the addition of poly-l-ornithine to the medium augment uptake. A nonphagocytic cell line (BHK-21) concentrated (3)H-dihydrostreptomycin to a lesser extent than the macrophages. These observations suggest that a wide variety of mammalian cells may be permeable to the antibiotic, and thus potential bactericidal action on intracellular bacteria cannot be ignored.

Role of cell wall structure of salmonella in the interaction with phagocytes

Wild-type and cell wall mutants of Salmonella were examined for sensitivity to ingestion and intracellular killing in vitro by mouse peritoneal macrophages and guinea pig polymorphonuclear leukocytes. A complete polysaccharide core of the cell wall is important for resisting ingestion and intracellular killing, and the presence of the O-specific side chains contributes further resistance. Uridine diphosphate-gal-4-epimeraseless mutants grown on galactose-supplemented medium, rendering them smooth phenotypes, showed resistance to ingestion and intracellular killing similar to the wild type.

The roles of Nramp1 and Tnfa genes in nitric oxide production and their effect on the growth of Salmonella typhimurium in macrophages from Nramp1 congenic and tumor necrosis factor-alpha-/- mice

The macrophages from Nramp1 congenic mice and tumor necrosis factor (TNF)-alpha(-/-) mice were used to examine the functions of Nramp1 and Tnfa genes in nitric oxide (NO) production and Salmonella typhimurium infection. It was confirmed that the level of inducible NO synthase (iNOS)-mediated NO production in Nramp1(r) peritoneal macrophages was generally higher than that of Nramp1(s) macrophages after stimulation by interferon-gamma (IFN-gamma), lipopolysaccharide (LPS), and tumor necrosis factor-alpha (TNF-alpha) alone or in combination. Nramp1 mRNA expression in both Nramp1 congenic macrophages was constitutive notwithstanding cytokine stimulation. During infection with S. typhimurium strain 6203, Nramp1(r) macrophages produced a lower amount of NO because of an initial strong reaction and unsustained iNOS gene expression as compared with Nramp1(s) macrophages. An inhibitory effect of the Nramp1(r) gene on bacterial replication was also observed during the early stage of S. typhimurium infection, whereas the effect of TNF-alpha occurred later. NO production and iNOS expression in TNF-alpha(-/-) macrophages were not detected from the start of the bacterial infection or at 24 h after infection. We also observed that S. typhimurium strain 6203 grew more profoundly without TNF-alpha, especially in Nramp1(s) macrophages. These data, therefore, demonstrate that there is cooperation of the Nramp1 and Tnfa genes in NO production and a growth inhibitory effect in response to S. typhimurium infection.

Synergistic action of streptomycin with other antibiotics of intracellular Brucella abortus in vitro

Richardson, Marvis (Michigan State University, East Lansing) and Jane N. Holt. Synergistic action of streptomycin with other antibiotics on intracellular Brucella abortus in vitro. J. Bacteriol. 84:638-646. 1962.-It has been found that streptomycin acts synergistically with penicillin and tetracycline to inhibit the growth of Brucella abortus within bovine cells cultured in vitro. Extracellular penicillin at 10 to 50 mug/ml was essentially bacteriostatic for intracellular brucellae. A combination of 5 to 50 mug/ml of streptomycin, which alone did not prevent the multiplication of intracellular brucellae, and 50 mug/ml of penicillin was bactericidal. Tetracycline at 0.5 to 1.0 mug/ml, which permitted growth or was bacteriostatic for brucellae within tissue cells, proved markedly bactericidal when combined with 10 mug/ml of streptomycin. Within certain limits, the synergistic effect of streptomycin and tetracycline did not appear to be a function of concentration. When the addition of streptomycin was delayed until 24 hr after the addition of tetracycline, the antibiotics acted synergistically on intracellular brucellae. To achieve intracellular synergism, five to ten times the effective extracellular concentration of streptomycin was required. Penicillin and tetracycline acted at the same concentration on extracellular and intracellular brucellae. These results suggest that tissue cell systems may prove useful for study of multiple drug therapy to be used in vivo against intracellular bacteria.

An antigenic basis for virulence in strains of Salmonella typhimurium

A study has been made of the antigenic relationships between a virulent and an avirulent strain of Salmonella typhimurium. Evidence is presented which supports the hypothesis that the susceptibility of the mouse to infection by S. typhimurium is due to an antigenic relationship between host and parasite. The antigen shared between host and parasite, appears to be absent or is masked in the avirulent strain.

The role of opsonins in the clearance of living and inert particles by cells of the reticuloendothelial system

An investigation of the clearance of bacteria and colloids from the blood stream of mice has shown that both living and inert particles require serum factors (opsonins) in order that they may be phagocytosed by the macrophages of the reticuloendothelial system. It has been demonstrated that after the injection of a large dose of colloid there is a depletion of these serum opsonins which appears to account for the reduced rate of clearance of a second dose of colloid or living bacteria, since replacement of these factors leads to normal clearance. The significance of these results is discussed and it is suggested that in "blockaded" animals there is a depletion of serum opsonins rather than a saturation of phagocytic cells.

Spacious phagosome formation within mouse macrophages correlates with Salmonella serotype pathogenicity and host susceptibility

Light microscopic studies indicated a correlation between the virulence for mice of different Salmonella serotypes and the ability to form or maintain spacious phagosomes (SP) within mouse macrophages. Although Salmonella typhimurium induced membrane ruffling, macropinocytosis, and SP formation in macrophages from BALB/c mice, serotypes which are nonpathogenic for mice produced markedly fewer SP. SP formation correlated with both serotype survival within mouse macrophages and reported lethality for mice. Time-lapse video microscopy demonstrated that the human pathogen S. typhi induced generalized macropinocytosis and SP formation in human monocyte-derived macrophages, indicating a similar morphology for the initial phases of this host-pathogen interaction. In contrast to bone marrow-derived macrophages from BALB/c mice, macrophages from S. typhimurium-resistant outbred (CD-1) and inbred (CBA/HN) mice did not initiate generalized macropinocytosis after bacterial infection and formed markedly fewer SP. These deficiencies were not due to the Ihy resistance genotype of these mice, as macrophages from mice that were congenic except for the Ihy locus demonstrated equal SP formation in response to S. typhimurium. The observation that S. typhimurium-resistant CD-1 and CBA/HN mice are deficient in the ability to form and/or maintain SP indicates that a variable host component is important for SP formation and suggests that the ability to induce or form SP affects susceptibility to S. typhimurium. When serotypes nonpathogenic for mice were used to infect BALB/c macrophages, or when CD-1 or CBA/HN mouse macrophages were infected by S. typhimurium, some of the SP that formed shrank within seconds. This rapid shrinkage suggests that SP maintenance is also important for S. typhimurium survival within macrophages. These studies indicate that both host and bacterial factors contribute to SP formation and maintenance, which correlate with Salmonella intracellular survival and the ability to cause lethal enteric (typhoid) fever.

Salmonella stimulate macrophage macropinocytosis and persist within spacious phagosomes

Light microscopic studies of phagocytosis showed that Salmonella typhimurium entered mouse macrophages enclosed in spacious phagosomes (SP). Viewed by time-lapse video microscopy, bone marrow-derived macrophages exposed to S. typhimurium displayed generalized plasma membrane ruffling and macropinocytosis. Phagosomes containing Salmonella were morphologically indistinguishable from macropinosomes. SP formation was observed after several methods of bacterial opsonization, although bacteria opsonized with specific IgG appeared initially in small phagosomes that later enlarged. In contrast to macropinosomes induced by growth factors, which shrink completely within 15 min, SP persisted in the cytoplasm, enlarging often by fusion with macropinosomes or other SP. A Salmonella strain containing a constitutive mutation in the phoP virulence regulatory locus (PhoPc) induced significantly fewer SP. Similar to Yersinia enterocolitica, PhoPc bacteria entered macrophages in close-fitting phagosomes, consistent with that expected for conventional receptor-mediated phagocytosis. These results suggest that formation of SP contributes to Salmonella survival and virulence.

Contemporary adhesion prevention

OBJECTIVE

To (1) review the events leading to peritoneal adhesion formation; (2) review traditional adhesion prevention adjuvants; (3) overview studies for adhesion prevention barriers including a perspective for their use; and (4) look toward the future of adhesion prevention.

RESULTS

A great deal of effort has been dedicated to reduce adhesion formation because of the morbidity associated with adhesions and the associated economic burden, which considering only hospital costs and surgeons' fees, was $1,180 million in the United States. To understand the role of adhesion barriers in gynecological surgery, an appreciation of the cellular cascade and temporal nature of peritoneal repair is necessary. Evidence indicates that areas denuded of peritoneum will heal satisfactorily and that suturing of the peritoneum may increase adhesion formation. Physical barriers, including both mechanical and viscous solutions, are widely used to prevent adhesion formation by limiting tissue apposition during the critical stages of mesothelial repair. Clinical studies do not support the use of intraperitoneal, dextran for adhesion prevention. Theoretical considerations of peritoneal fluid dynamics indicate that crystalloid instillates should not prevent adhesion formation because of their short intraperitoneal residence. This prediction is consistent with clinical observation. The availability of Interceed (Johnson and Johnson Medical, Inc., Arlington, TX) and Gore-Tex Surgical Membrane (W.L. Gore, Flagstaff, Arizona) barriers provides substantial progress in postsurgical adhesion prevention.

CONCLUSIONS

Although many investigators are incorporating adhesion prevention barriers into their routine clinical situations, physician acceptance is constrained by technical difficulties.

Intracellular distribution and activity of antibiotics

Intracellular penetration, accumulation and disposition are important parameters governing the activity of antibiotics against intracellular bacteria. Beta-lactams diffuse into but do not accumulate in phagocytes, probably because of their acidic character. Aminoglycosides are too polar to pass across membranes and are therefore only taken up slowly by endocytosis, which results in an exclusively lysosomal localization. Lincosaminides, macrolides and fluoroquinolones all accumulate in phagocytes, the two former classes of drugs showing both a cytosolic and a lysosomal localization. Fluoroquinolones appear to be entirely soluble in cells. Analysis of their activity in a model of Staphylococcus aureus-infected J774 macrophages has revealed low activity of clindamycin, whereas macrolides, and even more so fluoroquinolones, easily reduce the original inoculum.

Activity of antibiotics against microorganisms ingested by mononuclear phagocytes

The data available on the activity of antibiotics against microorganisms ingested by mononuclear phagocytes are reviewed. The antibacterial activity of penicillins against Staphylococcus aureus is enhanced by human monocytes. This enhancement is possibly brought about by a peptidoglycan-degrading enzyme that is produced and secreted by monocytes. Aminoglycosides affect bacteria ingested by mononuclear phagocytes, but their intracellular activity is limited as compared with that of non-phagocytosed bacteria. Clindamycin, erythromycin, ciprofloxacin and rifampicin are effective against intracellular bacteria. The first three of these antibiotics do not show enhanced activity against phagocytosed bacteria, contrary to what might be expected from their high cell-associated concentrations.

Ability of mononuclear phagocytes from cattle naturally resistant or susceptible to brucellosis to control in vitro intracellular survival of Brucella abortus

The role of bovine mammary macrophages and peripheral blood monocyte-derived macrophages in natural resistance to bovine brucellosis was evaluated. A group of 11 naturally resistant and 10 chronically infected susceptible cows was studied following challenge with Brucella abortus. Macrophages from a greater proportion (P less than 0.026) of naturally resistant cows were significantly superior to macrophages from susceptible cows in their ability to inhibit the in vitro intracellular replication of B. abortus after challenge exposure. Studies of a second group of cows used mammary macrophages from 12 heifers and blood monocyte-derived macrophages from 22 bulls and heifers. These tests were completed before exposure to B. abortus, using mammary macrophages (P less than 0.039) and blood monocyte-derived macrophages (P less than 0.045), and also showed that macrophages from naturally resistant cattle were significantly superior in their ability to control the in vitro intracellular replication of B. abortus. Our data indicate that the mononuclear phagocytes from more than 80% of the resistant cattle controlled intracellular replication of B. abortus significantly better than did mononuclear phagocytes from susceptible cattle. Mononuclear phagocyte function appears to be an important factor in determining natural resistance to bovine brucellosis.

Porcine neutrophil function in the presence of virulent and avirulent Salmonella choleraesuis

Porcine polymorphonuclear leukocytes (PMNLs) may be activated by bacteria to begin phagocytosis followed by oxidative and non-oxidative mechanisms of killing. The purpose of this study was to identify differences between virulent and avirulent Salmonella choleraesuis (S. choleraesuis) strains, 38 and 9 respectively, in their interactions with porcine PMNLs using five different assays. (1) Staphylococcus aureus (S. aureus) ingestion was determined by exposure of porcine PMNLs to a mixture of S. choleraesuis and 125I labeled S. aureus. There was a 2.98% and 22.20% decrease in S. aureus ingestion by mouse-avirulent S. choleraesuis 9 and mouse-virulent S. choleraesuis 38 respectively. (2) Iodination of proteins was done by exposing zymosan stimulated porcine PMNLs to S. choleraesuis in the presence of 125I and measuring its incorporation into porcine PMNL proteins. This assay indicated a 73.7% and 74.7% decrease in iodination by S. choleraesuis 9 and S. choleraesuis 38, respectively. (3) Cytochrome c reduction was performed by using porcine PMNLs, zymosan, and S. choleraesuis to determine the bacterial effect on superoxide anion production. S. choleraesuis 9 and S. choleraesuis 38 inhibited superoxide anion production by 78.0% and 92.6%, respectively. (4) Lactoferrin release from porcine PMNLs was measured by an ELISA using the supernatant from the cytochrome c assay. Results indicate a 52.0% and 61.0% increase in lactoferrin release by S. choleraesuis 9 and 38 respectively. (5) The bactericidal assay was performed by counting cfus of S. choleraesuis after preliminary incubation with porcine PMNLs, followed by killing of extracellular S. choleraesuis and lysis of porcine PMNLs. Survival of S. choleraesuis 9 and E. coli (control) were 7.50% and 1.37%, respectively, in contrast to 52.62% survival of the virulent S. choleraesuis 38. These results indicate that both strains inhibited protein iodination and caused a slight increase in lactoferrin release, but the virulent S. choleraesuis 38 inhibited S. aureus ingestion, cytochrome c reduction, and survived porcine PMNL killing more effectively than the avirulent S. choleraesuis 9.

Role of resident macrophages, peripheral neutrophils, and translymphatic absorption in bacterial clearance from the peritoneal cavity

Microbial pathogens within the peritoneal cavity are thought to encounter three categories of host defense mechanisms: (i) removal mechanisms, which occur via diaphragmatic lymphatic absorption; (ii) killing mechanisms, in which host phagocytes act as effector cells; and (iii) sequestration mechanisms due to fibrin trapping and the formation of adhesions between visceral surfaces. We sought to define and quantitate the relative role of the first two components in an experimental rat model of Escherichia coli peritonitis in which fibrinous adhesions do not form. Intraperitoneal challenge with greater than or equal to 2 X 10(8) CFU of viable E. coli led to an initial decline in bacterial numbers followed by ongoing proliferation and greater than 50% mortality. With inocula of less than or equal to 5 X 10(7) CFU, elimination of bacteria occurred after moderate initial proliferation, and no mortality ensued. Nonviable, radiolabeled E. coli organisms were utilized to examine bacterial clearance via translymphatic absorption and phagocytosis. Both processes were extremely rapid, serving to eliminate free bacteria rapidly within the peritoneal cavity. Although macrophages and polymorphonuclear leukocytes within the peritoneal cavity demonstrated similar phagocytic capacities, the predominance of macrophages at the time of the initial bacterial insult led to the conclusion that these cells, in addition to translymphatic absorption, represent the first line of host defenses, acting to eliminate bacteria in the incipient stages of infection.

The influence of antimicrobial agents on macrophage-associated Staphylococcus aureus

Macrophages obtained by culturing human blood monocytes were incubated with Staphylococcus aureus for phagocytosis to occur and exposed to gentamicin, rifampin, clindamycin or trimethoprim/sulphamethoxazole. The macrophage-associated bacteria were protected against gentamicin at low concentrations (1 mg/l) and trimethoprim/sulphamethoxazole. However, high concentrations of gentamicin and clindamycin reduced the number of bacteria, indicating that these drugs penetrated into human macrophages and killed phagocytosed bacteria. Rifampin, even at low concentrations (0.5 mg/l), caused a marked reduction in macrophage-associated bacteria, implying that the drug penetrated into the phagocytes and retained its effect in the cells most effectively.

The adjuvant effect of peritoneal fluid in experimental peritonitis. Mechanism and clinical implications

At laparotomy, many surgeons routinely instill crystalloid solutions into the peritoneal cavity, presumably to dilute out necrotic debris, bacteria, and adjuvant substances which foster bacterial growth. We examined the effect on mortality, bacterial growth, clearance, and phagocytosis of various volumes of saline instilled into the peritoneal cavity of rats during Escherichia coli peritonitis. Minimal intraperitoneal bacterial growth was seen after the introduction of a nonlethal inoculum of viable E. coli in 1 ml of saline, while administration of an identical inoculum in 30 ml of saline intraperitoneally (i.p.) led to increased 48-hour mortality (p less than 0.01), and associated rapid bacterial proliferation (p less than 0.01). Clearance of nonviable radiolabelled E. coli from the peritoneal cavity was delayed, bacterial association with host peritoneal leukocytes was decreased, and blood uptake of radiolabelled bacteria was diminished in animals receiving 30 ml of saline i.p., compared to controls which received the identical inoculum in 1 ml of saline i.p. The clinical relevance of these studies is manifold: (1) they provide a possible explanation why patients with ascites due to cirrhosis or the nephrotic syndrome, or those patients undergoing peritoneal dialysis are more susceptible to primary and secondary bacterial peritonitis, possibly on the basis of impaired peritoneal clearance or diminished phagocytosis and, (2) although irrigation of the peritoneal cavity with crystalloid solution would seem prudent during laparotomy, these solutions must be removed prior to closure to prevent interference with normal peritoneal host defense mechanisms.

Fate of Listeria monocytogenes in murine peritoneal macrophage subpopulations

Peritoneal macrophages derived from CD-1 and C57BL/6 mice were separated into distinct groups based on their buoyant densities on discontinuous gradients of Percoll and assayed for antibacterial activity against Listeria monocytogenes. Subpopulations of peritoneal macrophages derived from Listeria-immune mice present a wide variation in their ability to control intracellular infection. Distinct subsets were found which exhibited bacteriostatic and listericidal activity. The fractionation procedure yielded a population of peroxidase-positive macrophages which were devoid of antilisterial action. Subpopulations of resident and elicited macrophages were also functionally heterogeneous in their ability to restrict intracellular growth of bacterial. In some experiments, subclasses were examined for secretion of plasminogen activator and phagocytosis of latex particles. These activities varied considerably with the status of activation of the macrophages, but failed to correlate with antimicrobial activity within given subpopulations.

Phagocytosis and killing of salmonella typhimurium by peritoneal exudate cells

Normal peritoneal cells from conventional, germfree, or nu/nu mice readily killed opsonized salmonellae, an observation that suggests that this activity in the normal peritoneal cavity may not be dependent on either environmental antigenic stimulation or T-cell mediation. In contrast, peritoneal cells elicited 4 days after injection with thioglycolate medium failed to kill opsonized salmonellae but appeared to be highly phagocytic. Peritoneal cells from thioglycolate-treated mice could be induced to kill opsonized salmonellae by giving the mice a primary footpad injection and a secondary intraperitoneal injection of Corynebacterium parvum. This activation by C. parvum appeared to be thymus dependent, since it did not occur in nu/nu mice.

Hydrogen peroxide-releasing function of chemically elicited and immunologically activated macrophages: differential response to wheat germ lectin and concanavalin A

Various types of mouse peritoneal macrophages were studied for H(2)O(2) release in the presence of wheat germ lectin or phorbol myristate acetate. Macrophages elicited 3 days before harvest by a single injection of thioglycolate, zymosan A, or a streptococcal preparation (OK-432) were highly responsive to wheat germ lectin, resulting in a marked increase in H(2)O(2) release. However, immunologically activated macrophages induced by double injections of live and heat-killed BCG at 15 and 3 days before harvest or by double injections of zymosan A or OK-432 at 20 and 3 days before harvest did not show any significant response to wheat germ lectin. On the other hand, all macrophages tested responded well to phorbol myristate acetate by augmentation of H(2)O(2) release. Concanavalin A inhibited wheat germ lectin- and phorbol myristate acetate-triggered H(2)O(2) release from all types of macrophages, but inhibition was much more marked in the case of wheat germ lectin-stimulated H(2)O(2) release. Succinylated concanavalin A (divalent concanavalin A) showed only slight suppressive action against macrophage H(2)O(2) release, and prostaglandin E(1) and dibutyryl cyclic adenosine 3', 5'-monophosphate caused depression of H(2)O(2) release from OK-432-induced macrophages.

Enhanced phagocytosis and bactericidal activity of hepatic reticuloendothelial system during endotoxin tolerance

The effects of tolerance to Escherichia coli endotoxin on the phagocytic and bactericidal activity of the hepatic reticuloendothelial system against viable E. coli were examined using ex vivo perfused rat livers. Livers were isolated from control and endotoxin-tolerant rats and perfused with a medium containing 5% homologous serum from either control or tolerant rats. After the addition of the E. coli (2 x 10(7) cells per ml) to the perfusate, the hepatic clearance of the bacteria was followed for 30 min. The highest activation of the hepatic reticuloendothelial system was observed when serum from tolerant animals was added to the perfusate. Under these conditions phagocytosis was 47% (12% in controls), and 37 to 38% of the bacteria were killed (5% in controls). This activation was less when livers obtained from tolerant rats were perfused with serum from controls or with saline only. The data suggests that, during endotoxin tolerance, humoral factors play an important role in the activation of the hepatic reticulendothelial system, although a direct stimulation of Kupffer cells also occurs. The enhancement of phagocytosis by tolerant serum did not require the presence of homologous antibodies and involved the activation of the alternative complement pathway, since it was lost after removal of factor B activity. On the other hand, stimulation of intracellular killing required both complement and specific antibodies. The data suggest a role of endotoxin in the activation of humoral and cellular mechanisms involved in the host resistance to gram-negative bacterial infection.

Macrophage heterogeneity

Macrophages are a mobile, functionally diverse group of cells which may be recruited and stimulated to a high degree of metabolic activity. Heterogeneity may be detected from one site to another and result from local influences, e.g. lung v. peritoneal cells, or occur within a population and arise dur to different stages of differentiation, maturation or activation or possibly from distinct cell lines. Recruitment and turnover are important determinants of the diversity of cells at any one site. In addition, anti-tumour, anti-microbial and secretory capacities of macrophages are greatly influenced by the degree and nature of stimulation possibly affecting only a subpopulation of the cells. Accessory cell activity is also a function of a minor population of macrophages which have distinct surface antigens. The sources of the heterogeneity and the interrelationship between the macrophages subpopulations remain to be determined.

Interferon and cytotoxic factor (cytotoxin) released in the blood of mice infected with Mycobacterium bovis BCG. II. Influence of time after BCG inoculation on production of interferon and cytotoxin by capsular polysaccharide of Klebsiella pneumoniae or by bacterial lipopolysaccharide and on hyperreactivity to their lethal effects

The time course of the occurrence of hyperreactivity in interferon and cytotoxin responses to the active substance (neutral fraction) of the capsular polysaccharide of Klebsiella pneumoniae (neutral CPS-K) and bacterial lipopolysaccharide (LPS) and of the hyperreactivity to their lethal effects was followed after infection with BCG in SMA and ICR strains of mice. The duration of these hyperreactivities of BCG-infected mice depended on the inoculum doses of BCG. The time patterns of the hyperreactivity to the lethal effects of neutral CPS-K and LPS were similar in both strains of mice, although the maximum toxicity of LPS by the intraperitoneal route in BCG-infected mice on a weight basis was stronger than that of neutral CPS-K. Irrespective of inducer and mouse strain, the time pattern of the hyperreactivity to produce cytotoxin was similar to that of the hyperreactivity to produce interferon. The patterns for these phenomena when neutral CPS-K was used as an inducer were also similar to those when LPS was used. In ICR mice the hyperreactivity in interferon and cytotoxin responses to either neutral CPS-K or LPS decayed significantly earlier than the hyperreactivity to their lethal effects, whereas in SMA mice the occurrence of both types of hyperreactivities seemed to be associated. Therefore, it is suggested that the mechanism for the hyperreactivity in interferon and cytotoxin responses to neutral CPS-K or LPS in BCG-infected mice is not necessarily the same as that for the hyperreactivity to their lethal effects.

Immunity to antigenically related salmonellae: effects of humoral factors on the bactericidal activity of normal and immune peritoneal exudate cells

Immunity against Salmonella enteritidis and Listeria monocytogenes was studied by measuring in vitro the bactericidal activity of peritoneal exudate cells (PEC) of control (normal PEC) and S. typhi Ty2-immune (immune PEC) mice. Specific immune serum, anti-S. tyhphi Ty2, heat inactivated at 56 degrees C for 30 min, significantly inhibited the growth of S. enteritidis only with immune PEC. These opsonic factors had no effect upon the activity of normal PEC. That such inhibition could not be demonstrated in Listeria experiments, either with immune or normal PEC, suggests that S. enteritidis was specifically recognized, in vitro, by the thermostable opsonin anti-S. typhi Ty2 and that macrophages from immune PEC were more efficient in inhibiting bacterial growth than those from normal PEC. Thus, the interaction between macrophages and the microorganism seems to play an essential role in cell-mediated as well as humoral immunity.

Effect of growth environment on Pseudomonas aeruginosa killing by rabbit polymorphonuclear leudocytes and cationic proteins

Pseudomonas aeruginosa grown in a chemostat under carbon- and magnesium-limited conditions showed varying resistance to killing by rabbit peritoneal exudate polymorphonuclear leukocytes. Slow-growing (D = 0.05 h-1), magnesium-limited cells were significantly more resistant to the lethal effects of the phagocytes than were fast-growing magnesium-limited cells and carbon-limited cells (D = 0.05 h-1 and D = 0.5 h-1, respectively). The resistance of magnesium-limited cells to killing by cationic proteins isolated from the leukocytes was shown to be growth-rate dependent, the slowest-growing (D = 0.05 h-1) cells being the most resistant. Carbon-limited cells were sensitive to killing by the cationic proteins at all growth rates tested. Antisera raised in rabbits to all types of cells and commercial anti-Pseudomonas serum rapidly agglutinated magnesium-limited cells but failed to agglutinate carbon-limited cells. There was some indication that slow-growing (D = 0.05 h-1), magnesium-limited cells agglutinated most readily with both types of antisera. No difference was detected in the mouse toxicity of heat-killed cells grown under the various conditions.

Anomalous high native resistance to athymic mice to bacterial pathogens

Congenitally athymic (nude) mice exhibited an anomalous high resistance against infections with the facultative intracellular parasite Listeria monocytogenes and other bacterial pathogens. Protection against lethal infection was demonstrated to result from the presence of naturally occurring activated macrophages in the reticuloendothelial organs of the nude mice. This was exemplified after intravenous challenge by enhanced bacterial clearance from the blood and augmented bacterial killing in the spleens and livers of nude mice as compared with immunologically competent control mice. Resident peritoneal macrophages of nude mice were not activated in terms of phagocytic, bactericidal, or tumoricidal potential. The development of activated fixed tissue macrophages appears to arise as a result of the T-lymphocyte deficiency since thymus implantation abrogated the enhanced resistance of nude mice. Antibiotic elimination of intestinal bacteria also modified resistance to bacterial infection, indicating a role of environmental factors on macrophage activation. Several possible mechanisms leading to macrophage activation and heightened resistance to infection in nude mice are offered.

Mechanisms of resistance to Corynebacterium kutscheri in mice

Involvement of the mononuclear phagocyte system in the mechanism of resistance to Corynebacterium kutscheri was studied in C57B1/6 and Swiss Lynch mice. A major difference between the two mouse strains was that the phagocytic cells of the livers of C57B1/6 mice destroyed the bacteria with much greater efficiency. There was no evidence of serum factors which might have led to this greater bacterial killing observed in the C57B1/6 mice, and in vivo phagocytosis of C. kutscheri was identical in both mouse strains. Resistance to C. kutscheri could be transferred with spleen and/or bone marrow cells from resistant (Swiss Lynch X C57B1/6) F1 mice to 650-rad irradiated susceptible Swiss Lynch mice. Nonspecific and acquired mechanisms of resistance to C. kutscheri are discussed.

Phagosome-lysosome interactions in cultured macrophages infected with virulent tubercle bacilli. Reversal of the usual nonfusion pattern and observations on bacterial survival

Tubercle bacilli of the pathogenic human strain H37Rv had previously been shown to multiply, after ingestion by cultured mouse peritoneal macrophages, within phagosomes that tended to remain unfused with secondary lysosomes. Means were sought therefore for promoting experimentally a modification of the host response so as to attain a high level of phagolysosome formation, enabling tests to be made of any effects on the course and outcome of the intracellular infection. This was achieved by exposing viable bacilli to specific rabbit antiserum before their ingestion. Quantitative assessments, using electron microscopy, now showed that a majority of the phagosomes containing intact bacilli had fused with ferritin-labeled lysosomes, and frequently the fusion was massive. Bacterial viability studies established that the serum pretreatment was not itsel bactericidal. In the course of progressive infections with strain H37Rv, monitored by counts both of viable bacterial units and of intracellular acid-fast organisms, no appreciable difference was found between the intracellular growth rates of control and antiserum-treated bacilli. Concurrent electron microscopy showed that bacilli could remain intact and multiply both in phaagolysosomes and in unfused phagosomes, ruling out the possibility of selective growth of antiserum-pretreated bacilli within the minority of phagosomes that remained unfused. It was concluded that "turning on" phagosome-lysosome fusion in normal macrophages did not influence the outcome of infection with virulent M. tuberculosis; lysosome contents manifestly failed to exercise an antibacterial effect on this organism. Nevertheless, the possibility remains that the lysosomes of specific immune macrophages have antituberculous potentiality. In that case the experimental "turning on or off" of fusion could be a decisive factor in the outcome of a virulent challenge. Should it not be, the antibacterial capabilities of immune cells would need to be ascribed to factors other than lysosomal attack, the latter being essentially for disposal of the dead organisms.

Intraleukocytic bactericidal activity in patients receiving corticosteroid and radiation therapy, and in patients with diabetes mellitus

Bactericidal activities of peripheral white blood cells obtained from patients and from healthy persons were examined in vitro. The results obtained are summarized as follows. 1. Peripheral white blood cells from patients receiving corticosteroid and radiation therapy showed decreased levels of intracellular bactericidal activities against Staphylococcus aureus. The leukocytes from almost all patients examined displayed intense activities of intracellular bacterial killing against Streptococcus pyogenes. 2. Only polymorphonuclear leukocytes (PMNs) and macrophages obtained from patients in severe stages of diabetes mellitus exhibited decreased levels of intracellular bactericidal activities against S. aureus. 3. The leukocytes from all patients examined exhibited the same levels of intracellular bactericidal effects against S. pyogenes as leukocytes from healthy persons. 4. Pseudomonas aeruginosa, which was phagocytized by PMNs obtained from healthy persons, demonstrated a remarkable degree of resistance to any intracellular bactericidal effect.

Enhanced in vitro phagocytic power of macrophages from PPD-stimulated skin sites in human subjects hypersensitive to PPD

By a quantitative Rebuck's skin-window technique human macrophages were collected from individuals either unreactive or hypersensitive to PPD, the latter having recovered from tuberculous infection.

In vitro testing of macrophages with a strain of Paracolonbacter aerogenoides proved that cells from hypersensitive convalescents were provided with increased pagocytic and bactericidal activities. An even higher degree of macrophage activation was attained when cells from hypersensitive individuals had previously been stimulated in vitro with PPD. Changes of macrophage functions such as those mentioned above might well result from the action on macrophages of lympho-kine-like agents released by sensitized lymphocytes coming in contact with PPD.

Interaction of virulent and avirulent Listeria monocytogenes with cultured mouse peritoneal macrophages

The interaction between smooth and rough Listeria monocytogenes and mouse peritoneal macrophages in culture was investigated. Initially, antibiotics were deleted from the culture medium, and no attempt other than the removal of unphagocytized bacteria by extensive washings was made to control extracellular growth. Under these conditions the monolayers were rapidly destroyed within an 8-h period, and this was associated with increases in the intracellular population of both strains. Extracellular viability counts revealed that washings failed to reduce the bacteria in the medium to less than 10% of the original inoculum. Continuous phagocytosis of Listeria which grew logarithmically in the maintenance media appears to account for the observed changes in the number of intracellular bacteria. The data also indicate that it is primarily the free bacteria in the culture medium which are responsible for the cytotoxic effects. In other experiments streptomycin-penicillin solutions were added to the maintenance media after an initial period of phagocytosis. In the presence of antibiotics, the total number of macrophages per field remained relatively constant, and no morphological alterations in the leukocyte cultures were observable. Extensive intracellular multiplication of either strain was not evident in fixed and stained cover slips. Viable intracellular counts reveal that after 24 h there is almost total killing of the rough variant, whereas the smooth strain tended towards complete survival.

Role of the macrophage in natural resistance to salmonellosis in mice

In vitro, macrophages from normal strain BRVR mice killed Salmonella more quickly than did macrophages from normal strain BSVS mice. Salmonella injected intraperitoneally multiplied more quickly in BSVS mice than in BRVR mice. BRVR macrophages injected intraperitoneally into BSVS mice protected against Salmonella multiplication better than did BSVS macrophages. The populations of peritoneal cells that could be washed from the peritoneal cavity of normal BRVR and BSVS mice were morphologically and numerically identical. In vitro, BSVS macrophages were as efficient as BRVR macrophages in phagocytizing virulent Salmonella. These findings all support the concept that the greater natural resistance of BRVR mice to Salmonella infection may be explained by the greater ability of normal BRVR macrophages to kill ingested Salmonella.