Effects of cellular constituents of mycobacteria on the resistance of mice to heterologous infections I. Protective effects

Immunostimulant effect of heat-inactivated Mycobacterium bovis in mice challenged with vector-borne pathogens

Trained immunity is defined as an enhanced state of the innate system which leads to an improved immune response against related or non-related pathogens. Bacillus Calmette-Guérin (BCG) vaccine, a live attenuated Mycobacterium bovis strain, is currently one of the main inductors of trained immunity. The objective of the present study was to evaluate the protective effects of heat-inactivated M. bovis (HIMB) against Plasmodium berghei and Borrelia burgdorferi and characterize the immunological mechanisms involved. BALB/c and C3H/HeN mice were randomly assigned in similar number to either immunized group receiving two oral doses of HIMB with a 4-week interval, or control group treated with PBS. All the BALB/c mice were intraperitoneally infected with P. berghei while the C3H/HeN mice were subcutaneously infected with B. burgdorferi. Pathogen burden was significantly reduced in both immunized groups when compared to controls. The number of macrophages significantly decreased in the liver or in the spleen of the mice that had been immunized prior to the challenge with P. berghei or B. burgdorferi, respectively. Furthermore, the immunized groups showed an apparent upregulation of IFN-γ, TNF-α and IL-1α in the liver (P. berghei challenge) or a significant increase in IL-1α producing cells in the spleen (B. burgdorferi challenge). Our findings suggest that oral immunization with heat-inactivated mycobacteria limits pathogen burden through stimulation of the innate immune response in two vector-borne diseases in mice.

Deconvoluting the interplay of innate and adaptive immunity in BCG-induced nonspecific and TB-specific host resistance

BCG is the oldest vaccine in continuous use. While current intradermal vaccination regimens confer limited protection outside the context of pediatric extrapulmonary tuberculosis (TB), promising new data indicate that when administered mucosally or intravenously at a higher dose, BCG can induce sterilizing immunity against pulmonary TB in nonhuman primates. BCG is also known to promote nonspecific host resistance against a variety of unrelated infections and is a standard immunotherapy for bladder cancer, suggesting that this innate immune function may contribute to its protective role against TB. Here, we propose that both the mycobacterial-specific and off-target effects of BCG depend on the interplay of adaptive and innate cells and the cytokines they produce, and that the elucidation of this interaction should be a major strategy in the development of more effective BCG-based vaccines and immunotherapies.

Cellular and Molecular Mechanisms of Innate Memory Responses

There has been an increasing effort to understand the memory responses of a complex interplay among innate, adaptive, and structural cells in peripheral organs and bone marrow. Trained immunity is coined as the de facto memory of innate immune cells and their progenitors. These cells acquire epigenetic modifications and shift their metabolism to equip an imprinted signature to a persistent fast-responsive functional state. Recent studies highlight the contribution of noncoding RNAs and modulation of chromatin structures in establishing this epigenetic readiness for potential immune perturbations. In this review, we discuss recent studies that highlight trained immunity-mediated memory responses emerging intrinsically in innate immune cells and as a complex interplay with other cells at the organ level. Lastly, we survey epigenetic contributors to trained immunity phenotypes-specifically, a recently discovered regulatory circuit coordinating the regulation of a key driver of trained immunity.

Heat inactivated mycobacteria, alpha-gal and zebra fish: insights gained from experiences with two promising trained immunity inductors and a validated animal model

Trained immunity (TRAIM) may be defined as a form of memory where innate immune cells such as monocytes, macrophages, dendritic and natural killer (NK) cells undergo an epigenetic reprogramming that enhances their primary defensive capabilities. Cross-pathogen protective TRAIM can be triggered in different hosts by exposure to live microbes or microbe-derived products such as heat-inactivated Mycobacterium bovis or with the glycan α-Gal to elicit protective responses against several pathogens. We review the TRAIM paradigm using two models representing distinct scales of immune sensitization: the whole bacterial cell and one of its building blocks, the polysaccharides or glycans. Observations point out to macrophage lytic capabilities and cytokine regulation as two key components in nonspecific innate immune responses against infections. The study of the TRAIM response deserves attention to better characterize the evolution of host-pathogen cooperation both for identifying the etiology of some diseases and for finding new therapeutic strategies. In this field, the zebrafish provides a convenient and complete biological system that could help to deepen in the knowledge of TRAIM-mediated mechanisms in pathogen-host interactions. This article is protected by copyright. All rights reserved.

Nonspecific protection of heat-inactivated Mycobacterium bovis against Salmonella Choleraesuis infection in pigs

Trained immunity is the capacity of innate immune cells to produce an improved response against a secondary infection after a previous unrelated infection. Salmonellosis represents a public health issue and affects the pig farming industry. In general, vaccination against salmonellosis is still facing problems regarding the control of distinct serovars. Therefore, we hypothesized that an immunostimulant based on heat inactivated Mycobacterium bovis (HIMB) could have an immune training effect in pigs challenged with Salmonella enterica serovar Choleraesuis (S. Choleraesuis) and decided to explore the amplitude of this non-specific immune response. For this purpose, twenty-four 10 days-old female piglets were randomly separated in three groups: immunized group (n = 10) received orally two doses of HIMB prior to the intratracheal S. Choleraesuis-challenge, positive control group (n = 9) that was only challenged with S. Choleraesuis, and negative control group (n = 5) that was neither immunized nor infected. All individuals were necropsied 21 days post-challenge. HIMB improved weight gain and reduced respiratory symptoms and pulmonary lesions caused by S. Choleraesuis in pigs. Pigs immunized with HIMB showed higher cytokine production, especially of serum TNFα and lung CCL28, an important mediator of mucosal trained immunity. Moreover, immunized pigs showed lower levels of the biomarker of lipid oxidation malondialdehyde and higher activity of the antioxidant enzyme superoxide dismutase than untreated challenged pigs. However, the excretion and tissue colonization of S. Choleraesuis remained unaffected. This proof-of-concept study suggests beneficial clinical, pathological, and heterologous immunological effects against bacterial pathogens within the concept of trained immunity, opening avenues for further research.

Non-specific effects of veterinary vaccines: a systematic review

The benefits of vaccines have been centred on their specific effects on subsequent infections by target pathogens. Recent studies, however, have opened up new insights into additional effects of vaccines known as non-specific effects (NSEs) or heterologous effects of vaccines. While several articles have reviewed epidemiological and immunological evidence for NSEs of vaccines in humans, similar works on veterinary vaccines are scarce. The objective of this paper was to review the findings of published studies on NSEs of vaccines developed or repurposed for use in animals. In total 8412 titles were retrieved from PubMed and CABI databases on the 30^th of April 2021. After the final stage of screening, 45 eligible articles were included in the review. Data from these articles were summarised and presented here. In general, most of the vaccines studied in the reviewed articles have beneficial NSEs against multiple pathogens and disease conditions. There were, however, fewe studies reporting detrimental NSEs from both non-live and live vaccines which is in contrast to the currently existing evidence of beneficial NSEs of live vaccines and detrimental NSEs of non-live vaccines. This review may be used as a complement for future review of RCT studies of NSEs of vaccines in animals and provide a useful addition to the evolving understanding of the NSEs of vaccines.

How diseases caused by parasites allowed a wider understanding of disease in general: my encounters with parasitology in Australia and elsewhere over the last 50 years

This is an account of how it can prove possible to carve a reasonable scientific career by following what brought most scientific thrill rather than pursue a safe, institution-directed, path. The fascination began when I noticed, quite unexpectedly, that the normal mouse immune response causes Babesia microti to die, en masse, inside circulating red cells. It eventuated that prior Bacillus Calmette Guerin infection caused the same outcome, even before the protozoal infection became patent. It also rendered mice quite immune, long term. I acquired an obsession about this telling us how little we know. Surrounded by basic immunologists, parasitologists and virologists in London, I had been given, in the days that funding was ample, the opportunity to follow any promising lead with a free hand. Through Bacillus Calmette Guerin, this meant stumbling through a set of phenomena that were in their infancies, and could be explained only through nebulous novel soluble mediators such as TNF, described the following year as causing the in vivo necrosis of tumours in mice. Beginning with malarial disease pathogenesis, I followed TNF wherever it led, into innate immunity, acute and chronic infections, neurophysiology and neurodegenerative diseases, in all of which states awareness of the role of this cytokine is still growing fast. Many of these steps can be illustrated and expanded upon in parasitic diseases. Covering the importance of TNF in the pathogenesis of neurodegenerative disease has proved to be highly illuminating, scientifically and otherwise. But the insights it has given me into understanding the temptations to which patent-owners can succumb when faced with opportunities to put money before people is not for the faint hearted. Clearly, parasitologists inhabit a much more common-good yet science-orientated, civilised, world.

Innate Immunomodulation in Food Animals: Evidence for Trained Immunity?

Antimicrobial resistance (AMR) is a significant problem in health care, animal health, and food safety. To limit AMR, there is a need for alternatives to antibiotics to enhance disease resistance and support judicious antibiotic usage in animals and humans. Immunomodulation is a promising strategy to enhance disease resistance without antibiotics in food animals. One rapidly evolving field of immunomodulation is innate memory in which innate immune cells undergo epigenetic changes of chromatin remodeling and metabolic reprogramming upon a priming event that results in either enhanced or suppressed responsiveness to secondary stimuli (training or tolerance, respectively). Exposure to live agents such as bacille Calmette-Guerin (BCG) or microbe-derived products such as LPS or yeast cell wall ß-glucans can reprogram or "train" the innate immune system. Over the last decade, significant advancements increased our understanding of innate training in humans and rodent models, and strategies are being developed to specifically target or regulate innate memory. In veterinary species, the concept of enhancing the innate immune system is not new; however, there are few available studies which have purposefully investigated innate training as it has been defined in human literature. The development of targeted approaches to engage innate training in food animals, with the practical goal of enhancing the capacity to limit disease without the use of antibiotics, is an area which deserves attention. In this review, we provide an overview of innate immunomodulation and memory, and the mechanisms which regulate this long-term functional reprogramming in other animals (e.g., humans, rodents). We focus on studies describing innate training, or similar phenomenon (often referred to as heterologous or non-specific protection), in cattle, sheep, goats, swine, poultry, and fish species; and discuss the potential benefits and shortcomings of engaging innate training for enhancing disease resistance.

The Effect of Inactivated Mycobacterium Paratuberculosis Vaccine on the Response to a Heterologous Bacterial Challenge in Pigs

Background: Vaccines may have non-specific effects, affecting resistance to heterologous pathogens. Veterinary vaccines have seldom been investigated for their non-specific effects. However, recent observational studies suggest that an inactivated paratuberculosis vaccine reduced all-cause mortality in goats and cattle. Aim: We tested if vaccination with a killed mycobacterial vaccine may have heterologous effects in swine (Sus domesticus), specifically on the pathogenic and clinical effects of a heterologous challenge with Actinobacillus pleuropneumoniae in young pigs. Methods: Newborn piglets were randomized to vaccination s.c. with the inactivated paratuberculosis vaccine Gudair (Zoetis Inc.) (n = 17) or no vaccine (n = 16). At 4-5 weeks after vaccination, all piglets were challenged intra-nasally with a high (Gudair: n = 8; control: n = 8) or a low (Gudair: n = 9; control: n = 8) dose of the gram-negative bacterium A. pleuropneumoniae causing acute porcine pleuropneumonia. The effect and severity of pathogen challenge was evaluated by measuring acute phase proteins C-reactive protein, haptoglobin and Porcine α1-acid glycoprotein, and by gross pathology 1 day post challenge. Specific and non-specific in vitro cytokine responses to vaccination were evaluated in whole blood before bacterial challenge. Results: The vaccine was immunogenic in the pigs as evidenced by increased IFN-γ responses to purified protein derivative of Mycobacterium paratuberculosis. However, Gudair vaccine did not affect IL-6 responses. The gross pathology of the lungs as well as the acute phase protein responses after the high A. pleuropneumoniae dose challenge was slightly increased in the vaccinated animals compared with controls, whereas this was not seen in the animals receiving the low-dose bacterial challenge. Conclusion: The inactivated paratuberculosis vaccine exacerbated the pathological and inflammatory effects of an experimental A. pleuropneumoniae infection in young pigs.

Candida innate immunity at the mucosa

The tremendous diversity in microbial species that colonise the mucosal surfaces of the human body is only now beginning to be fully appreciated. Distinguishing between the behaviour of commensal microbes and harmful pathogens that reside at mucosal sites in the body is a complex, and exquisitely fine-tuned process central to mucosal health. The fungal pathobiont Candida albicans is frequently isolated from mucosal surfaces with an asymptomatic carriage rate of approximately 60% in the human population. While normally a benign member of the microbiota, overgrowth of C. albicans often results in localised mucosal infection causing morbidity in otherwise healthy individuals, and invasive infection that often causes death in the absence of effective immune defence. C. albicans triggers numerous innate immune responses at mucosal surfaces, and detection of C. albicans hyphae in particular, stimulates the production of antimicrobial peptides, danger-associated molecular patterns and cytokines that function to reduce fungal burdens during infection. This review will summarise our current understanding of innate immune responses to C. albicans at mucosal surfaces.

Collagenases in an ether extract of bacterial metabolites used as an immunostimulator induces TNF-α and IFN-γ

Non-specific immunostimulation by bacterial extracts and their components are widely accepted for the prevention and treatment of several infectious diseases. An ether extract of the metabolites of ß-streptococcus, Staphylcoccus albus, Staphylcoccus aureus, Escherichia coli, Haemophilus influenza, Moraxella caterhalis, Salmonella typhi (standard O & H), Salmonella paratyphi (A & B) and Diptheroid bacilli along with bile lipids is used as a licensed drug for immunostimulation. While characterizing the drug, we observed gelatinolytic/collagenolytic activity in the ether extract by zymography. This activity was contributed by each bacterial species as observed by collagen zymography of individual extract. Immuno-blot also confirmed the presence of collagenases in the pooled extract whose activity was estimated to be 0.081 U/ml ± 0.005 by DQ-gelatin assay. The enzyme was purified by immuno-affinity chromatography. Homogeneity of the preparation was demonstrated by SDS-PAGE and SE-HPLC. Degradation of collagen by purified collagenases was visualized by atomic force microscopy and transmission electron microscopy wherein, fragmentation of collagen leading to loss of network structure occurred under physiological conditions. Results indicated that purified collagenases can trigger the release of pro-inflammatory cytokines TNF-α and IFN-γ in-vitro and in-vivo without inducing detectable stress and toxicity on both models. The findings suggest that bacterial collagenases remain stable and biological functional in an organic solvent validating its potential for industrial and medical applications as the enzymes are key regulators of inflammatory and immune responses.

Antiviral memory phenotype T cells in unexposed adults

αβ T cells are an integral part of protective immunity against pathogens. After precursor cells arise in the adult bone marrow or fetal liver, they migrate to the thymus where they rearrange their T-cell receptor genes (TCR) and undergo selection on the basis of their interactions with ligands expressed by thymic stroma and other cells. Those that survive then exit the thymus to populate the peripheral immune compartment, where they patrol the blood and lymphoid systems. The composition of this pre-immune peripheral repertoire is critically important in determining the robustness of an immune response. In both mice and humans, the magnitude and diversity of a response are directly correlated with the frequency of precursor T cells. Equally relevant are the functional characteristics of these lymphocytes. Engagement of a specific antigen to the TCR activates signaling pathways in the naive T cell that result in cellular proliferation and the acquisition of particular effector functions. A portion of these persist following the resolution of infection and become memory cells. These memory cells can mount a faster and stronger response when they encounter the same antigen at a later time. As the molecular basis for TCR ligand interaction has become better defined, it is clear that some T cells can recognize multiple distinct ligands and therefore T-cell memory developed by exposure to one ligand may play a significant role in the response to a different antigen. Thus, there is an increasing focus on understanding how exposure to related or unrelated antigens influences the T-cell repertoire and impacts subsequent immunity. In this review, we discuss the issue of TCR cross-reactivity in the development of memory phenotype CD4(+) T cells and the implications for pathogen-specific responses. We review both the human and mouse data and discuss the therapeutic implications of these findings in the contexts of infection and vaccination.

Mycobacterium tuberculosis infection interferes with HIV vaccination in mice

Tuberculosis (TB) has emerged as the most prominent bacterial disease found in human immunodeficiency virus (HIV)-positive individuals worldwide. Due to high prevalence of asymptomatic Mycobacterium tuberculosis (Mtb) infections, the future HIV vaccine in areas highly endemic for TB will often be administrated to individuals with an ongoing Mtb infection. The impact of concurrent Mtb infection on the immunogenicity of a HIV vaccine candidate, MultiHIV DNA/protein, was investigated in mice. We found that, depending on the vaccination route, mice infected with Mtb before the administration of the HIV vaccine showed impairment in both the magnitude and the quality of antibody and T cell responses to the vaccine components p24Gag and gp160Env. Mice infected with Mtb prior to intranasal HIV vaccination exhibited reduced p24Gag-specific serum IgG and IgA, and suppressed gp160Env-specific serum IgG as compared to respective titers in uninfected HIV-vaccinated controls. Importantly, in Mtb-infected mice that were HIV-vaccinated by the intramuscular route the virus neutralizing activity in serum was significantly decreased, relative to uninfected counterparts. In addition mice concurrently infected with Mtb had fewer p24Gag-specific IFN-γ-expressing T cells and multifunctional T cells in their spleens. These results suggest that Mtb infection might interfere with the outcome of prospective HIV vaccination in humans.

Isolation of a Soluble Resistance-Enhancing Factor from Mycobacterium phlei

Fox, Alfred E. (Warner-Lambert Research Institute, Morris Plains, N.J.), Joachim Anschel, George L. Evans, Raam R. Mohan, and Benjamin S. Schwartz. Isolation of a soluble resistance-enhancing factor from Mycobacterium phlei. J. Bacteriol. 92:285-290. 1966.-Extraction of a crude cell wall preparation from Mycobacterium phlei with 20% urea yielded a fraction which induced a state of enhanced resistance to microbial challenge. The resulting soluble extract, after removal of the urea, represented a 15% yield of solids with the separation of the biologically active component(s) and elimination of toxicity. Single oral or subcutaneous submicrogram doses of this material induced a prolonged state of increased resistance to subsequent challenge with Salmonella enteritidis in mice. This effect appeared as early as 2 hr after oral administration and persisted for at least 30 days. Protection against experimental infection with Staphylococcus aureus was also demonstrated. Resistance to viral challenge with influenza type A was observed after intranasal administration of the M. phlei extract to mice. The isolated material was found to contain carbohydrate, protein, nucleic acids, and lipids. The lipids represented 60% of the total solids, and were all short-chain fatty acids. No toxic effects, including pyrogenicity, could be demonstrated after oral or parenteral administration of this preparation.

Along a TNF-paved road from dead parasites in red cells to cerebral malaria, and beyond

This is a personal account of how tumour necrosis factor (TNF) the prototype of a group of host-origin mediators, often known as pro-inflammatory cytokines, came into parasitology, and was subsequently realised to be central to the pathogenesis of most disease pathology. This contribution summarizes an example of how a curiosity-driven outsider, with initially no intention of heading this way, and no relevant experience, and with no more than the simplest of plans but an ambition to read as widely as it takes, and (most importantly) allowed to follow his head, can be what is required to give fresh insight into understanding a disease. It also gives the author's views on aspects of how the field of malaria disease pathogenesis seems to be developing. The hope is to inspire another generation to follow a similarly original course.

Heterologous immunity revisited

Heterologous immunity, or protection by one invading organism against another across phylogenetic divides, has been recognised for decades. It was initially thought to operate largely through enhancement of phagocytosis, but this explanation became untenable when it was realised it worked extremely well against intraerythrocytic protozoa and killed them while they were free in the circulation. Clearly a soluble mediator was called for. This review summarises the logic that arose from this observation, which led to a wider appreciation of the roles of pro-inflammatory cytokines, and then nitric oxide, in the host's response against invaders, as well as the ability of these mediators to harm the host itself if they are generated too enthusiastically. This has led to a discernable pattern across heterologous immunity as a whole, and its lessons influence a range of areas, including vaccine development.

Proinflammatory Cytokines in the Treatment of Bacterial and Fungal Infections

Mortality due to severe bacterial infections has not been markedly effected by the introduction of new antimicrobial drugs over the last 30-40 years. This has emphasized the need for development of new therapeutic strategies to combat sepsis. The outcome of an infection depends on two factors: the growth of the microorganisms (including the effect of antibacterial drugs), and the host's defensive response to the invading organism. It is known that injection of bacterial products into experimental animals leads to enhanced nonspecific resistance to a variety of microorganisms. The discovery of the specific mediators responsible for modulation of host defense has created new possibilities for the development of alternative treatment strategies. Molecules such as interleukins, interferons, tumor necrosis factors and hematopoietic growth factors have become available in recombinant form, and their therapeutic potential in various infectious diseases has been tested in various experimental models of infections. Initial data in various patient groups indicate that adjunctive therapy with recombinant proinflammatory cytokines may have beneficial effects in the treatment of bacterial and fungal infections.

The pathophysiology of falciparum malaria

Falciparum malaria is a complex disease with no simple explanation, affecting organs where the parasite is rare as well as those organs where it is more common. We continue to argue that it can best be understood in terms of excessive stimulation of normally useful pathways mediated by inflammatory cytokines, the prototype being tumor necrosis factor (TNF). These pathways involve downstream mediators, such as nitric oxide (NO) that the host normally uses to control parasites, but which, when uncontrolled, have bioenergetic failure of patient tissues as their predictable end point. Falciparum malaria is no different from many other infectious diseases that are clinically confused with it. The sequestration of parasitized red blood cells, prominent in some tissues but absent in others with equal functional loss, exacerbates, but does not change, these overriding principles. Recent opportunities to stain a wide range of tissues from African pediatric cases of falciparum malaria and sepsis for the inducible NO synthase (iNOS) and migration inhibitory factor (MIF) have strengthened these arguments considerably. The recent demonstration of bioenergetic failure in tissue removed from sepsis patients being able to predict a fatal outcome fulfils a prediction of these principles, and it is plausible that this will be demonstrable in severe falciparum malaria. Understanding the disease caused by falciparum malaria at a molecular level requires an appreciation of the universality of poly(ADP-ribose) polymerase-1 (PARP-1) and Na(+)/K(+)-ATPase and the protean effects of activation by inflammation of the former that include inactivation of the latter.

Effect of dietary proteins and amino acids on the susceptibility of mice to bacterial infections

Groups of young albino mice were fed continuously four different types of diets and were compared with regard to (1) rate of weight gain; (2) resistance to experimental bacterial infections. The protein content of the four diets was as follows: (a) pellets: a minimum of 21 per cent "crude" protein (according to the manufacturer); (b) diet 20 C: 20 per cent casein; (c) diet 8 C: 8 per cent casein; (d) diet 8 C + AA: 8 per cent casein supplemented with 12 per cent of a mixture of essential amino acids. All diets provided an adequate supply of minerals and vitamins. They were administered ad lib. Three strains of pathogens virulent for mice were used for the infection tests, namely: Staphylococcus aureus, Mycobacterium fortuitum, and Mycobacterium tuberculosis bovis. The bacteria were injected by the intravenous route. The experimental regimens were begun at different times before infection, and were continued until death of the animal, or until termination of the experiment. It was found that mice on the 8 C diet exhibited much greater susceptibility to infection than did mice on the 20 C diet; mice receiving pellets were intermediate between these two groups. The infection-enhancing effect of the 8 C diet could be entirely corrected by amino acid supplementation (diet 8 C + AA). Indeed, mice fed diet 8 C + AA proved the most resistant to infection. The fact that animals fed pellets (which contain a minimum of 21 per cent protein) consistently died faster following infection than did animals fed diets 20 C or 8 C + AA suggests that qualitative characteristics of the protein in the regimen are as important as the quantity of protein fed in determining susceptibility to infection. The differences in susceptibility exhibited by the mice on the four experimental diets were the same whatever the species of bacterial pathogen used for the infection test, the size of the infective dose, and the duration of the disease. There was no apparent relation between the effects of the diets on the weight curves of the animals, and on resistance to infection. Mice on diet 8 C (which were most susceptible) gained weight as rapidly as those on 20 C and more rapidly than those fed 8 C + AA (which were most resistant). All the tests reported in the present paper were carried out with young mice, which were placed on experimental diets within 1 to 2 weeks after weaning. Preliminary experiments suggest that the relation between dietary factors and susceptibility to infection was more difficult to bring out in older animals. There was evidence also that this relation was most apparent during the first weeks that the animals were fed the experimental diets, and became less striking after several weeks.

Studies on tubercle bacillus-monocyte relationship. III. Conditions affecting the action of serum and cells; modification of bacilli in an immune system

Studies of the relationship of protective serum factor to cellular resistance and to tuberculin skin sensitivity have demonstrated that protective serum factor may exist independently of a high level of cellular resistance, and that both protective factor and cellular resistance may be demonstrable without a concomitant hypersensitivity of the delayed type. The experiments with absorbed sera and the globulin fraction of immune serum indicated no specific association of protective serum factor with antibody globulin. The protective factor in immune serum was found to be thermostable and non-dialyzable. In vitro exposure of virulent tubercle bacilli to the immune serum from BCG-immunized animals failed to alter the bacterial capacity for destruction of monocytes and for intracellular proliferation. In vitro cultivation of normal and immune monocytes in normal or immune serum was not effective in changing the native susceptibility or resistance of these cells. Effective manifestation of resistance to virulent tubercle bacilli by immune monocytes was found to require the continuous presence of immune serum. The intracellular passage of virulent tubercle bacilli in an immune system (immune monocytes cultivated in immune serum) resulted in a decreased bacterial potential for destruction of normal monocytes when these were cultivated in the presence of immune serum.

A cellular basis of immunity in experimental Brucella infection

Brucella suis, Brucella abortus, and Brucella melitensis were shown by microscopic and cultural procedures to multiply extensively within normal rat, mouse, and guinea pig monocytes maintained in vitro in cell cultures for 3 days. Intracellular growth of brucellae had no observable toxic effects on most monocytes, although many of the cells became completely engorged with brucellae within 3 days. Non-smooth brucellae and strain 19 multiplied slowly within normal monocytes. In contrast, "immune" monocytes) i.e. those derived from animals previously infected with smooth brucellae, greatly restricted the intracellular growth of smooth and non-smooth brucellae and strain 19. Growth of smooth Brucella, within either normal or "immune" monocytes, was not influenced by addition of Brucella antiserum to the culture medium. Desensitization of immunized guinea pigs did not diminish the refractory state of their monocytes. Cellular resistance did not develop when animals were vaccinated with heat-killed brucellae, though these animals did produce agglutinating antibody. Similarly, vaccination of animals with living, rough B. suis failed to induce a refractory state in their monocytes, even though the vaccinated animals developed delayed hypersensitivity to smooth Brucella antigen. In vivo studies of Brucella survival in the spleens of normal and vaccinated mice (treated with streptomycin to prevent extracellular survival) gave strong support to the in vitro demonstrations of acquired "cellular immunity." Some implications of these results are discussed.

A quantitative study of the kinetics of blood clearance of P32-labelled Escherichia coli and Staphylococci by the reticuloendothelial system

1. The clearance of P³²-labelled heat-killed E. coli and staphylococci from the blood follows an exponential function of the time, and the bacteria are phagocytized principally by the RES of the liver and spleen. 2. The rates of clearance of equivalent number of E. coli from the blood is rapid in rabbits and slow in mice and appears to be related to the level of antibodies in the serum of these animals. 3. Unlike E. coli, staphylococci are cleared rapidly and efficiently by the RES from the blood of mice which have a sufficient level of serum antibody against these bacteria. 4. The numbers of bacteria, phagocytized by the liver or the spleen respectively, depend upon the rate of clearance and the extent of opsonization of the bacteria. Rapidly cleared, well opsonized E. coli are removed almost exclusively by the liver, while less efficiently phagocytized bacteria are also cleared by the spleen in large numbers. 5. The rate of clearance of E. coli and the efficiency with which they are phagocyted by the RES in mice have been shown to be directly related to the level of antibody in the serum. 6. Treatment of mice with S. typhi or Serratia marcescens endotoxins increases the rate of clearance of E. coli from the blood and the level of antibody against E. coli in the serum. The enhanced clearance of E. coli can be transferred to normal mice by the serum of endotoxin-treated mice.

The susceptibility of mice to bacterial endotoxins

Albino mice (Rockefeller NCS strain) raised and maintained free of ordinary bacterial pathogens, as well as of intestinal Escherichia coli and of Proteus bacilli, were found to be highly resistant to the lethal effect of bacterial endotoxins. When newborn mice of this NCS colony were nursed by foster mothers from another colony raised under ordinary conditions (SS colony from which the NCS colony was derived), they acquired the intestinal flora of the latter animals and became susceptible to the lethal effects of endotoxins. NCS adult mice could be rendered susceptible to the lethal effect of endotoxins by vaccination with heat killed Gram-negative bacilli. The susceptibility thus induced exhibited a certain degree of specificity for the bacterial strain used in vaccination. Although untreated NCS mice were resistant to the lethal effect of endotoxins, they proved exquisitively susceptible to the infection-enhancing effect of these materials. For example, 1 µg. or less of endotoxin was found sufficient to help establish a rapidly fatal septicemia with Staphylococcus aureus. Small amounts of endotoxin (1 µg. or less), administered alone, caused a marked but transient loss of weight. Vaccination with heat-killed Gram-negative bacilli or with killed BCG increased the resistance of NCS mice to the infection-enhancing effect of small amounts of endotoxin. This protective effect exhibited a certain degree of specificity for the bacterial strain from which the toxin used in the infection-enhancing test was derived. These various findings can be explained by assuming that the pathological effects of endotoxins involve at least two unrelated mechanisms; (a) a primary toxicity illustrated in this study by the loss of weight and enhancement of infection resulting from the injection of small doses of toxin; (b) an immunological reaction with lethal consequences which became manifest only in animals sensitized to the endotoxin by prior exposure to Gram-negative bacilli.

Studies on fractions of methanol extracts of tubercle bacilli. I. Fractions which increase resistance to infection

Fractionation procedures yielding partially purified vaccine preparations from a 60°C. methanol extract of tubercle bacilli have been described. Some of the preparations have the characteristics of lipopolysaccharides. Certain ones have been found capable of increasing resistance to experimental tuberculosis in albino mice of the Rockefeller Swiss strain. The levels of resistance elicited by these preparations are equivalent to those following vaccination with BCG (Phipps) in this strain of mice as reported by other authors. The admixture of two of the crude fractions in amounts as small as 0.05 mg. each per dose per mouse affords an even greater increase in resistance. Neither of these substances alone in larger doses can approach this degree of efficacy in mouse protection experiments. The protective activity appears to involve the stimulation of two supplementary mechanisms, one providing a peak resistance between 1 and 3 weeks post vaccination but falling off to a lower level thereafter, the other not responding fully until approximately 6 weeks but continuing undiminished through a 12 week post-vaccination period. The first of these peaks corresponds to an increase in resistance against staphylococci as well as tubercle bacilli. The possibility that the term "broad specificity," rather than "non-specificity," might best describe this phenomenon permits the implication of classical immune mechanisms.

Effect of vaccines prepared from Histoplasma capsulatum and other yeasts on experimental tuberculosis

Hedgecock, Loyd W. (Veterans Administration Hospital, Kansas City, Mo.). Effect of vaccines prepared from Histoplasma capsulatum and other yeasts on experimental tuberculosis. J. Bacteriol. 82:115-123. 1961.-Resistance to experimental tuberculosis was enhanced by the injection of a nonviable vaccine prepared from Histoplasma capsulatum in the mycelial phase but not by the organism in the yeast phase. Acquired resistance was established within 7 days or less and usually maintained for at least 29 days. When both mycelium vaccine of H. capsulatum and a vaccine prepared from tubercle bacilli were utilized in vaccination, the results were additive (in terms of acquired resistance) provided that an interval of 3 weeks was maintained between injection of each of the vaccines. Resistance to tuberculosis was also demonstrable 14 days after the injection of nonviable preparations of Brucella abortus and Cryptococcus neoformans, as well as by yeast and mycelial vaccines of Blastomyces dermatitidis and Sporotrichum schenckii. Resistance decreased significantly when the animals were challenged 29 days after vaccination, with the exception of those injected with the yeast phase of B. dermatitidis.

Studies on fractions of methanol extracts of tubercle bacilli. II. Toxic and allergenic properties of fractions employed as antituberculous vaccine

Fractions of methanol extract which had been previously demonstrated to increase the resistance of mice to experimental tuberculosis have been subjected to an examination of their toxic and allergenic properties. The criteria for toxicity were: (a) production of inflammatory skin reactions in guinea pigs; (b) induction of weight loss in mice by intraperitoneal injection; and (c) depression of resistance to staphylococcus infections in mice. Allergenicity of a preparation was investigated by (a) its ability to evoke a hypersensitive skin response in guinea pigs previously sensitized with whole tubercle bacilli; and (b) its capacity to induce hypersensitivity to one or more of its components when injected under appropriate conditions into guinea pigs. Fraction F I, a preparation precipitated from methanol extract by slow concentration at 45°C., was found to possess some toxicity and some allergenicity by all of the criteria employed. Subfraction F I-P, precipitated from aqueous suspensions of F I by 33 per cent ethanol and 0.5 per cent NaCl, was apparently the F I component responsible for these activities. The saline-ethanol-soluble subfraction, F I-S, was neither toxic nor allergenic by the tests performed. These findings were considered of particular interest inasmuch as F I-S, despite its small yield, had been shown earlier to be the most active single substance used as vaccine to increase resistance to experimental tuberculosis in mice.

Interactions between rabbit polymorphonuclear leucocytes and staphylococci

A method has been described for the study in vitro of leucocyte-bacteria interactions which permits the simultaneous evaluation of both phagocytosis and intracellular bacterial inactivation. Employing this technique, the fate and localization of staphylococci in homogeneous suspensions of rabbit polymorphonuclear leucocytes have been studied. Coagulase-positive strains of S. aureus were not efficiently ingested in the presence of normal rabbit serum. In contrast, coagulase-negative strains of S. albus were rapidly engulfed and inactivated. Immune sera prepared against a coagulase-positive strain enhanced the the ingestion of the homologous organism as well as of three heterologous strains of S. aureus. Following phagocytosis, prompt intracellular killing of S. aureus occurred. The thermostable opsonins in immune sera reacted only with strains of S. aureus. A comparison between polymorphonuclear leucocytes obtained from normal and immune animals revealed no differences in their ability either to ingest or kill coagulase-positive staphylococci. Studies with other bacterial species are presented to illustrate: (a) phagocytosis followed by intracellular inactivation; (b) phagocytosis followed by intracellular survival; and (c) the absence of phagocytosis.

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

Virulent strains of Salmonella opsonized with normal mouse plasma are never phagocytosed as well as avirulent strains. The virulent strains of Salmonella phagocytosed after opsonization with normal mouse plasma are able to multiply within normal mouse peritoneal macrophages, whereas under similar experimental conditions the avirulent strains are killed. When virulent strains of Salmonella are opsonized with specific antiserum or plasma from BCG-infected mice, they are treated by normal mouse macrophages as if they were avirulent. Virulent bacteria opsonized with BCG plasma are phagocytosed and killed better by peritoneal macrophages from BCG-infected mice, than peritoneal macrophages from normal mice.

The correlation of a biphasic metabolic response with a biphasic response in resistance to tuberculosis in rabbits

We have found a phase of susceptibility associated with a reduced metabolic activity on the part of peritoneal mononuclear phagocytes taken from BCG-vaccinated rabbits. A second stage of heightened resistance to infection was found to be associated with a heightened metabolic activity. The period of susceptibility in BCG vaccination is primarily concerned with initiation of the infection and not with the progression of the disease, which in both stages is increased. These reactions are discussed in relation to other conditions, such as nonspecific protein therapy and the administration of endotoxin, which also have similiar biphasic stages of resistance. Of incidental interest is the fact that rabbits who received 400 roentgen units are two years later still unable to respond to BCG vaccination with an increase in resistance. We conclude that there is a relationship between the level of certain metabolic activities of reticuloendothelial cells and resistance to tuberculosis.

STUDIES ON THE HETEROLOGOUS IMMUNOGENICITY OF A MENTHANOL-INSOLUBLE FRACTION OF ATTENUATED TUBERCLE BACILLI (BCG). I. ANTIMICROBIAL PROTECTION

Small quantities of the non-toxic residue of phenol-killed, acetone-washed, and methanol-extracted tubercle bacilli of the BCG strain conferred a high degree of resistance on mice against otherwise lethal experimental infection with Klebsiella pneumoniae and with a number of other pathogenic bacteria. The heightened resistance reached a peak within 24 hours after administration of the fraction, but was already discernible immediately thereafter. A period of reduced resistance was not observed. The state of heightened resistance was invariably manifested for at least 10 days, and could frequently still be demonstrated after several weeks or months. The methanol-insoluble fraction was immunogenically active even in experimental circumstances under which living BCG exerted no effect. Its protective effect was more marked in females than in males. The optimum dosage must be determined empirically vis-á-vis the strain of infecting organisms and the experimental parameters of administration and testing. Administration of the fraction to breeding females reduced the incidence of a naturally occurring endemic pneumonitis among their young, and increased considerably the breeding productivity of the mothers. These effects were manifested as late as 11 months after treatment.

INFLUENCE OF ROUTE OF INFECTION AND OTHER FACTORS ON GROWTH AND DISTRIBUTION OF LISTERIA MONOCYTOGENES IN ORGANS OF MICE

Silverman, Sidney J. (U.S. Army Biological Laboratories, Fort Detrick, Frederick, Md.), Lynn P. Elwell, and James F. Drawdy. Influence of route of infection and other factors on growth and distribution of Listeria monocytogenes in organs of mice. J. Bacteriol. 86:355-362. 1963.-The growth of Listeria monocytogenes in the lungs, liver, spleen, brain, and blood of mice was observed after infection by the respiratory, intravenous, and intraperitoneal routes. The lungs of mice exposed to Listeria aerosols contained about 10(6) infected cells per ml within 24 hr, and the number of organisms remained high for at least 9 days. After exposure by the other two routes, fewer organisms appeared in the lungs. The colony counts of organisms in spleen and liver homogenates were similar regardless of the route. Organisms were found sporadically in the brain and blood. When a cell extract of Listeria was injected simultaneously with the organisms, greater numbers of Listeria were found in spleen and liver than when the bacteria were injected alone. On the other hand, the BCG strain of Mycobacterium tuberculosis enhanced the resistance of the mice, as shown by the recovery of fewer organisms from tissues when compared with tissues from mice receiving L. monocytogenes alone. Prior administration of BCG also reversed the effect of the Listeria extract. Mice (5 to 6 weeks old) born of Listeria-infected mothers were infected with the homologous organism by the intraperitoneal route. Fewer organisms were recovered and the gross pathology was less extensive than in infected progeny of healthy females. However, there was no difference in the lt(50) (time to death for 50% of the animals) between the two groups. In a similar experiment, using 7- to 8-week-old mice born of infected and healthy mothers, there was no difference in the bacterial counts, gross pathology, or lt(50) between the two groups.

Immunostimulating agents: what next? A review of their present and potential medical applications

Many chemical entities, either from natural sources or prepared by synthesis, are known to exert stimulating activities on various functions of the immune system, such as antibody production, resistance to infections, rejection of malignant cells, etc. In this review, the origin, chemical structures and main activities of several immunostimulants are described, with special emphasis on their present or potential medical usefulness. An attempt is made to envisage the future of this type of pharmacological agents, excluding however from the presentation the endogenous modulators of the immune system (cytokines), the production and activities of which are influenced by the immunostimulants themselves.

Cytokines in the treatment of fungal infections

The incidence of invasive fungal infections in the immunocompromized host has increased during the past decade. Even the recently developed antifungal drugs are unable to cure these infections in patients with severely impaired host defense mechanisms. Cytokines have great potential to augment host resistance and as adjunctive therapy of invasive mycoses. We discuss the mechanisms of host defense against invasive candidiasis, aspergillosis, and cryptococcosis, and review the use of cytokines and growth factors in this setting. Interleukin-1 has been shown effective in an animal model of disseminated candidiasis, even during severe granulocytopenia. Interferon-gamma has been very effective as a modulator of resistance against a variety of fungal infections in vitro. The effect of interferon-gamma against disseminated candidiasis has been demonstrated in a mouse model. Activation of neutrophils is the main mechanism by which interferon-gamma enhances the elimination of Candida, and consequently the agent is not effective in severely granulocytopenic animals. Data on the role of colony-stimulating factors against fungal pathogens are accumulating, and trials with these agents for hematologic patients with invasive fungal infections are now being performed.

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.

Cellular mechanisms in in vivo production of gamma interferon induced by lipopolysaccharide in mice infected with Mycobacterium bovis BCG

Infection of mice with Mycobacterium bovis BCG sensitizes them for immune induction of interferon (IFN)-gamma by specific antigen. These mice were found also to respond to lipopolysaccharide (LPS) and concanavalin A (Con A) with high level production of IFN-gamma in the circulation, which was not observed in control mice. In this study, we compared the IFN-gamma response to LPS with that to Con A in an attempt to clarify the cellular mechanisms responsible for in vivo LPS-induced IFN-gamma production. Consequently, (i) the responses to LPS and Con A differed in the kinetics, that to LPS having a longer lag period. (ii) Spleen cells taken from infected mice produced little IFN-gamma in response to LPS, but they showed a higher IFN-gamma response to Con A than those from control mice. (iii) By treating infected mice with immunosuppressive drugs or antibodies to T and natural killer cells before challenge with the inducers, it was indicated that different cellular systems are involved in the IFN-gamma responses to LPS and to Con A.