Protection of mice against Babesia microti with cord factor, COAM, zymosan, glucan, Salmonella and Listeria

Amyloid β: one of three danger-associated molecules that are secondary inducers of the proinflammatory cytokines that mediate Alzheimer's disease

This review concerns how the primary inflammation preceding the generation of certain key damage-associated molecular patterns (DAMPs) arises in Alzheimer's disease (AD). In doing so, it places soluble amyloid β (Aβ), a protein hitherto considered as a primary initiator of AD, in a novel perspective. We note here that increased soluble Aβ is one of the proinflammatory cytokine-induced DAMPs recognized by at least one of the toll-like receptors on and in various cell types. Moreover, Aβ is best regarded as belonging to a class of DAMPs, as do the S100 proteins and HMBG1, that further exacerbate production of these same proinflammatory cytokines, which are already enhanced, and induces them further. Moreover, variation in levels of other DAMPs of this same class in AD may explain why normal elderly patients can exhibit high Aβ plaque levels, and why removing Aβ or its plaque does not retard disease progression. It may also explain why mouse transgenic models, having been designed to generate high Aβ, can be treated successfully by this approach.

Mycobacterial trehalose dimycolate reprograms macrophage global gene expression and activates matrix metalloproteinases

Trehalose 6,6'-dimycolate (TDM) is a cell wall glycolipid and an important virulence factor of mycobacteria. In order to study the role of TDM in the innate immune response to Mycobacterium tuberculosis, microarray analysis was used to examine gene regulation in murine bone marrow-derived macrophages in response to 90-μm-diameter polystyrene microspheres coated with TDM. A large number of genes, particularly those involved in the immune response and macrophage function, were up- or downregulated in response to these TDM-coated beads compared to control beads. Genes involved in the immune response were specifically upregulated in a myeloid differentiation primary response gene 88 (MyD88)-dependent manner. The complexity of the transcriptional response also increased greatly between 2 and 24 h. Matrix metalloproteinases (MMPs) were significantly upregulated at both time points, and this was confirmed by quantitative real-time reverse transcription-PCR (RT-PCR). Using an in vivo Matrigel granuloma model, the presence and activity of MMP-9 were examined by immunohistochemistry and in situ zymography (ISZ), respectively. We found that TDM-coated beads induced MMP-9 expression and activity in Matrigel granulomas. Macrophages were primarily responsible for MMP-9 expression, as granulomas from neutrophil-depleted mice showed staining patterns similar to that for wild-type mice. The relevance of these observations to human disease is supported by the similar induction of MMP-9 in human caseous tuberculosis (TB) granulomas. Given that MMPs likely play an important role in both the construction and breakdown of tuberculous granulomas, our results suggest that TDM may drive MMP expression during TB pathogenesis.

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.

Understanding the role of inflammatory cytokines in malaria and related diseases

It is now broadly accepted for infectious disease in general that it is not the invading organism, but the body's unbridled response to it--the "cytokine storm"--that causes illness and pathology. Nevertheless, many researchers still regard the harmful effects of falciparum malaria as being governed by oligaemic hypoxia arising from parasitised erythrocytes obstructing blood flow through vulnerable organs, particularly the brain, and we summarise why these notions are no longer tenable. In our view, this harmful sequestration is readily accommodated within the cytokine storm perspective as one of its secondary effects. We approach these issues by examining aspects of malaria, sepsis and influenza in parallel, and discuss the insights that comparisons of the literature can provide on the validity of possible anti-disease therapies.

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.

Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficiency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease.

Genetic Analysis of Innate Immunity

The inflammatory response to microbes--and host perception of microbes in general--is largely initiated by a single class of receptors, named for their similarity to the prototypic Toll receptor of Drosophila. The mammalian Toll-like receptors (TLRs) are ultimately responsible for most phenomena associated with infection. This includes both "good" effects of infection (e.g., the induction of lasting specific immunity to an infectious agent) and "bad" effects of infection (systemic inflammation and shock). Although they are essential for host defense, no other endogenous proteins can match their lethal potential. The TLR complexes transduce the toxicity of lipopolysaccharide (LPS), cysteinyl lipopeptides, and many other molecules of microbial origin. The identification of the TLRs as the key conduit to host awareness of microbial infection was a victory for reductionism, proving that the complexity of infectious inflammation as a phenomenon belies the simplicity of its origins. It was achieved by a classical genetic approach, proceeding from phenotype to gene. Further analysis of the signaling pathways activated by the TLRs has depended on both classical and reverse genetic methods. Additional work will ultimately disclose the extent to which sterile inflammatory diseases are mediated by aberrations in these pathways.

The treatment of mice with Lactobacillus casei induces protection against Babesia microti infection

In this study, we report that administration of Lactobacillus casei confers protection to mice against the intracellular protozoan Babesia microti. Mice treated with L. casei orally or intraperitoneally were inoculated 7 days later with an infectious dose of B. microti. Mice treated with lactobacilli showed significant reduction in the percentage of parasitized erythrocytes (PPE) compared to untreated mice. When mice were inoculated intraperitoneally with L. casei 3 or 0 days before challenge with B. microti, the PPE was significantly lower compared to untreated mice and there were no differences between treated mice and mice immune to B. microti infection. When mice treated with live or dead L. casei were compared to mice inoculated with Freund Complete Adjuvant before a B. microti infection, a significant reduction of PPE was observed. These results show the protective effect of L. casei administered to mice against a B. microti infection and suggest that it might act by stimulating the innate immune system.

Interactions between worm infections and malaria

Helminths are the most prevalent parasitic infections and malaria is the deadliest parasitic disease. Helminths have been reported to be protective against the severe forms of malaria but they were also possibly linked to increased malaria-incidence and gametocyte carriage. Connecting the dots between observations suggests that statistical regularities throughout the evolution of worms and malaria parasites in the same hosts, may have led to the emergence of non-zero interactions as observed in iterated prisoners dilemma games. Thus by protecting the host, helminths protect themselves and their reproductive potential, but also favor the dissemination and reproduction of Plasmodium falciparum. The proximate causes of this evolutionarily stable strategy might be mediated by IgE and the CD23/NO pathway, the protective role of IL10 in helminth-infected patients, and possibly the hematological consequences of worms. The chronic activation of the CD23/NO pathway might be instrumental in downregulating the expression of cytoadherence receptors thus reducing sequestration of parasitized red blood cells in the deep organs. Mild anemia in helminth-infected patients might favor gametocytogenesis and send attractive cues to the vector. This framework leads to numerous testable hypotheses and could explain certain singularities regarding the double edged role of IgE and NO. Among these hypotheses, there are 2 practical ones: the impact of helminths on malaria vaccine candidates, and the theoretical risk of increasing the severity of malaria after anthelmintics. The capacity for increased IgE responses could thus have been vital in our ancestor's wormy and malarious past. Allergies may be what remains of it in the modern world.

Pathogenesis of malaria and clinically similar conditions

There is now wide acceptance of the concept that the similarity between many acute infectious diseases, be they viral, bacterial, or parasitic in origin, is caused by the overproduction of inflammatory cytokines initiated when the organism interacts with the innate immune system. This is also true of certain noninfectious states, such as the tissue injury syndromes. This review discusses the historical origins of these ideas, which began with tumor necrosis factor (TNF) and spread from their origins in malaria research to other fields. As well the more established proinflammatory mediators, such as TNF, interleukin-1, and lymphotoxin, the roles of nitric oxide and carbon monoxide, which are chiefly inhibitory, are discussed. The established and potential roles of two more recently recognized contributors, overactivity of the enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the escape of high-mobility-group box 1 (HMGB1) protein from its normal location into the circulation, are also put in context. The pathogenesis of the disease caused by falciparum malaria is then considered in the light of what has been learned about the roles of these mediators in these other diseases, as well as in malaria itself.

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.

The effect of BCG, zymosan and Coxiella burnetti extract on Eimeria infections

Infection of animals with species of Eimeria induces a hyper-reactivity to endotoxin as manifest by a greatly increased capacity of infected animals to produce TNF in response to LPS in vivo compared with uninfected animals. This finding indicates priming for hyperactivation of macrophages by Eimeria infection and raises the possibility that non-specific triggering of macrophages by agents such as Bacille Calmette-Guerin (BCG), zymosan or Coxiella burnetti extract may be a simple means of control for coccidiosis. However, all of these agents enhanced oocyst excretion in mice, rats or chickens infected with Eimeria vermiformis, Eimeria nieschulzi or Eimeria tenella, respectively, without affecting the patent period.

Reactive oxygen and nitrogen intermediates and products from polyamine degradation are Babesiacidal in vitro

Products released from activated macrophages have been demonstrated to have microbicidal activity against a variety of microorganisms. Reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) have been shown to affect the induction of degenerate (crisis) forms of Plasmodium spp. Polyamines are degraded into acrolein which has also been shown to be toxic to Plasmodium spp. We have investigated the possibility that these products act similarly with Babesia bovis. Crisis forms of B. bovis developed in erythrocyte cultures after the introduction of supernatants containing ROI, RNI, and acrolein. Xanthine degradation by xanthine oxidase leads to the formation of superoxide anion, hydrogen peroxide, and hydroxyl radicals. The degradation in the presence of B. bovis was toxic to the parasite. The toxicity was partially reversed by the addition of the ROI scavenger catalase. However, H2O2 added directly had little effect, suggesting a role for the other ROI products. Spermine degradation by polyamine oxidase and direct addition of acrolein was toxic in a dose-dependent manner. Finally, spontaneous generation of nitric oxide from sodium nitroprusside or S-nitroso-N-acetyl-penicillamine was also toxic in a dose-dependent manner. These data lead us to suggest a role for activated macrophages in the primary immune response against B. bovis.

Effect of Mycobacterium phlei on the development of immunity to Babesia bigemina

The immunomodulatory role of Mycobacterium phlei against intracellular blood protozoan Babesia bigemina was demonstrated following experimental immunisation and challenge in bovine calves. A lysate of erythrocytes infected (6 x 10(9)) with B. bigemina was used as a source of dead antigen either with Freund's complete adjuvant (FCA) or with a trypsinised culture of M. phlei as a non-specific immunomodulation (NSI) agent with appropriate controls. Following virulent challenge with B. bigemina infected erythrocytes (1 x 10(7)), the NSI printed calves showed 100% protection, while the dead antigen alone with FCA afforded 75% protection. The protective status of the immunising regimes was studied by clinicopathological parameters and assessment of humoral and cell-mediated immune responses. The role of babesial dead antigen and the effects of M. phlei on the development of immunity to B. bigemina is discussed.

Cytokines and immunological control of Eimeria spp

Protozoan parasites belonging to the genus Eimeria cause considerable losses in livestock production in which stocking densities are high or environments restricted. The ability of hosts to mount immunological responses which limit parasite reproduction vary according to the particular species of Eimeria. Typically though, immune responses restrict parasite reproduction during primary infection and limit, if not prevent, subsequent infections. Although mechanisms of immunity are unknown, host immune responses have been exploited in the development of a method to control coccidiosis-immunisation with attenuated strains of Eimeria. Limitations of this control method, predominantly the cost of producing the attenuated parasites, necessitates identification of protective immune responses to facilitate selection of antigens for use in non-living vaccines. As in immune responses to many other parasitic infections of the gastrointestinal tract, the role of antibodies is at best minor, whereas T-cells are crucial. Numerous studies have shown that the intestinal mucosal T-cell population is dynamic; the number and phenotype of T-cells changes in response to Eimeria-infection. Specific changes in the intestinal T-cell population have not, however, been correlated with limitation of parasite reproduction. Experiments involving adoptive transfer of T-cell sub-populations and in vivo depletion of specific T-cells have shown that CD4+ T-cells and to a lesser extent CD8+ T-cells are important in immune responses which limit primary infection. In contrast, CD8+ T-cells are more important in subsequent infections with CD4+ T-cells having a lesser role. The effects of T-cells on Eimeria are partially mediated by the cytokines they release. Most attention has concentrated on interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) because these cytokines have been shown to limit other protozoan infections. IFN-gamma is produced in Eimeria-infected hosts but evidence that it is present at the site of infection is limited. Intestinal levels of IFN-gamma increase earlier in response to primary Eimeria-infection in mice which are relatively resistant, than in mice which are relatively susceptible. Neutralisation of endogenously produced IFN-gamma has shown that this cytokine limits oocyst production in either primary or secondary infections depending on the species of Eimeria. Production of TNF-alpha is also increased in infected hosts. In comparison with relatively susceptible mice, TNF-alpha is produced earlier and to a greater extent in the intestines of relatively resistant mice. Unexpectedly, injections of TNF-alpha into infected mice increased oocyst production. It remains to be determined whether the effects of endogenous TNF-alpha are the same as those of exogenous TNF-alpha. Mechanisms by which IFN-gamma and TNF-alpha modulate parasite reproduction have not been identified. A number of lines of experimentation have suggested that it is unlikely that IFN-gamma limits parasite reproduction through induction of the synthesis of reactive oxygen or reactive nitrogen intermediates, since both of these reactive intermediates have the capacity to exacerbate Eimeria-infection.

Cellular immune responsiveness in rabbits with Setaria digitata filarial antigen and TDM adjuvant

The purified surface antigens of the bovine filarial parasite Setaria digitata were used as an antigen to immunize rabbits. The aqueous suspensions of trehalose 6-6' dimycolate (TDM) has been successfully used as an effective immunomodulator in experimental studies on filariasis. The effectiveness of such an antigen-TDM combination was demonstrated by enhanced humoral and cellular immunity. Administration of antigen alone shows only humoral immunity. The detectable cellular immune responses further confirm the effect of filarial antigen-TDM combination. The cell-mediated immunity was expressed in vivo by delayed skin reaction and in vitro by leukocyte and macrophage migration inhibition tests.

Inverse age resistance to experimental Babesia divergens infection in cattle

Two groups of calves, 1.5-2 and 7-11 months old respectively, and dairy cows were inoculated i.v. with 3 x 10(7) erythrocytes infected with Babesia divergens. High parasitaemia, fever and other clinical signs of babesiosis occurred among adult animals. A very low parasitaemia and a slightly increased body temperature but no other symptoms occurred in calves. these findings substantiate the conclusion that there exists an inverse age resistance against Babesia divergens. The kinetics of B. divergens IgG antibody formation were similar in all age groups. Consequently this antibody response was not the factor determining the development of the primary parasitaemia and thus the inverse age resistance phenomenon. However, age is not necessarily the only factor involved in the clinical expression of babesiosis. The kinetics of antibody formation was not associated with the intensity of the parasitaemia. In fact only about half the animals had a demonstrable parasitaemia although the antibody responses were similar in all age groups.

Non-specific resistance to Babesia divergens in the Mongolian gerbil (Meriones unguiculatus)

Inoculation of mature gerbils with BCG gave protection to subsequent infection with B. divergens when inoculated by the intracardiac and intraperitoneal routes, the latter showing a dose dependent relationship. BCG vaccination was most effective in immature gerbils (less than 4 weeks old), which are innately resistant to B. divergens. Vaccination of gerbils with killed Propionesbacterium acne and zymosan A failed to elicit a protective response, which contrasts conspicuously with rodent babesia studies. Incubation of B. divergens-infected gerbil blood with hydrogen peroxide produced parasite inhibition only at the highest concentration and treatment of parasitized gerbils with the oxidative radical inducer, alloxan monohydrate, gave equivocal results so it is evident that, unlike Plasmodium spp., B. divergens is not significantly susceptible to the action of reactive oxygen forms.

Protection of mice against intestinal amoebiasis with BCG, Corynebacterium parvum and Listeria monocytogenes

Treatment with Corynebacterium parvum or BCG, or infection with live Listeria monocytogenes was found to protect mice against subsequent infection with Entamoeba histolytica. Complete protection was obtained in mice treated with 10(7) (colony forming units) of BCG but not with 10(5). Partial protection was achieved with 10(6) of BCG. These data provide evidence that non-specific immunity plays an important role in the host defense against amoebic infection.

Effects of splenectomy on antibody-independent immunity to Plasmodium chabaudi adami malaria

Splenectomy of B-cell-deficient mice and immunologically intact mice before infection with Plasmodium chabaudi adami led to the development of significant parasitemias which eventually resolved in the latter mice. Whereas both eusplenic B-cell-deficient mice and immunologically intact mice resolved their acute P. chabaudi adami infection, only B-cell-deficient mice subsequently developed chronic low-grade malaria. Splenectomy of B-cell-deficient mice with chronic malaria led to recrudescing infections, suggesting that the expression of antibody-independent immunity to reinfection was spleen dependent. When dispersed spleen cells were injected into splenectomized mice before challenge with P. chabaudi adami, the kinetics of the resulting infection resembled that seen in splenectomized mice which had not been grafted with normal spleen cells. This finding indicates that immunity to P. chabaudi adami requires the presence of an architecturally intact spleen.

Immunity to Babesia in mice. III. The effects of corticosteroids and anti-thymocyte serum on mice immune to Babesia rodhaini

BALB/c mice, immunized against Babesia rodhaini by an amicarbalide controlled infection, were exposed to selective immunosuppressive treatment with corticosteroids and anti-thymocyte serum (ATS) respectively. Hydrocortisone acetate, 100 mg/kg, given i.p. six times during the three weeks after challenge inoculation caused a rising parasitaemia and high mortality (6/7). Dexamethasone in the drinking water at 20 mg/l or 10 mg/l for 22 days had a similar suppressive effect on the protection against B. rodhaini. Mortality, 100% at the dose rate of 20 mg/l and 50% at 10 mg/l, occurred both in challenged and in carrier animals after the reappearance of parasites in the bloodstream. All the ATS-treated immune mice demonstrated parasitaemia after challenge, although at a lower level than did the corticosteroid treated mice. Seven out of 9 animals died. Corticosteroid-sensitive macrophages together with T-lymphocytes are considered to play an important role in protection against B. rodhaini in specifically induced immunity in mice.

Vaccination of rabbits against Entamoeba histolytica with aqueous suspensions of trehalose-dimycolate as the adjuvant

Rabbits were immunized with soluble Entamoeba histolytica antigen with an aqueous suspension of trehalose-6,6'-dimycolate used as the adjuvant. Induction of protective immunity in the immunized animals was demonstrated by enhanced humoral and cell-mediated immune responses and 100% survival after challenge. Administration of soluble antigen only failed to induce a similar degree of protective immunity. Trehalose-6,6'-dimycolate alone produced only a slight increase in nonspecific resistance.

Macrophages from Babesia and malaria infected mice are primed for monokine release

Serum from mice infected with Babesia microti or Plasmodium vinckei petteri and given lipopolysaccharide (LPS) contained appreciable amounts of tumour necrosis factor (TNF) and lymphocyte-activating factor (LAF; Interleukin I) activity. These monokines were not noted in serum from uninfected mice given the same dose of LPS. This pattern was repeated when adherent peritoneal cells from normal or infected mice were exposed to LPS in vitro and the supernatants assayed for LAF. This indicates that the hyper-reactivity of malaria and Babesia-infected mice to LPS resides in their macrophages, and that infection with these haemoprotozoa provides the host's macrophages with the same priming stimulus for subsequent triggering of monokine release as does an injection of Bacillus Calmette Guerin.

Immunity to Babesia in mice. I. Adoptive transfer of immunity to Babesia rodhaini with immune spleen cells and the effect of irradiation on the protection of immune mice

Immunisation of Balb/c mice against Babesia rodhaini by an amicarbalide-controlled infection resulted in a solid immunity which lasted for 216 days. With spleen cells of immune mice protection could be transferred both to naive mice pretreated with cyclophosphamide. Treatment of naive mice with cyclophosphamide (300 mg/kg) five days before a lethal B. rodhaini inoculation resulted in over 50% survival. This protective effect of cyclophosphamide is explained by its inhibiting effect on suppressor T-cells. The protection against B. rodhaini challenge infection afforded to immune Balb/c mice was completely resistant to a sublethal irradiation of 400 rad. Since B-lymphocyte function in antibody production is suppressed by this dose, the role of antibodies in the effector phase of the immunity appears to be of minor if any importance. A considerable degree of protection was still preserved after irradiation of immune animals with 875 rad. Sensitivity to this irradiation dose of all immunocompetent cells except macrophages and a small fraction of T-lymphocytes indicates the involvement of these cell types in the effector phase of the specific immunity. Highly radioresistant macrophages are therefore considered to play the major role but T-lymphocytes are also required for complete protection.

Immunity to Babesia in mice. II. Cross protection between various Babesia and Plasmodium species and its relevance to the nature of Babesia immunity

Mice immunized against B. rodhaini by means of a drug-controlled infection were subsequently resistant to infection with B. microti and B. ratti. In the reciprocal experiments the protection against B. rodhaini was less effective. B. rodhaini immunized mice were also considerably protected against P. vinckei infection, whereas protection against P. berghei did not occur. Antibody determinations indicated that the heterologous protection cannot be explained by the occurrence of cross-reacting antibodies. Because of similarity with the non-specific suppression of babesiosis in BCG-infected mice, the same effector mechanism is postulated to explain the infection-induced homologous and heterologous protection. Unlike non-specifically induced protection, the induction of acquired resistance by means of a drug-controlled B. rodhaini infection is thymus-dependent.

The immunomodulatory effect of yeast glucan on delayed hypersensitivity

The effect of yeast beta-1, 3-glucan as an immunopotentiator of delayed type-hypersensitivity reactions (DHR) was studied. Delayed-type-hypersensitivity reactions in mice sensitized intraperitoneally (IP) with sheep red blood cells (SRBC) and pretreated three days previously with glucan given IP were significantly increased. However, mice sensitized IP with SRBC three days after the subcutaneous (SC) administration of glucan showed depressed DHR. Glucan given at the same site but not at distance strongly potentiated the DHR induced by SC sensitization with SRBC. Subcutaneous injection of glucan and SRBC given together also resulted in a sustained DHR which persisted twelve days after sensitization when DHR of control mice had waned.

Macrophage mediated resistance toBabesia microti inNematospiroides dubius ? infected mice

Infection with the gastrointestinal nematode, Nematospiroides dubius, induced resistance to a concurrent infection with Babesia microti in mice. This enhanced resistance to B. microti occurred during infection with the larval, rather than the adult stages of N. dubius. Splenectomy or the injection of carrageenan or silica abrogated the protective effect against B. microti induced by infection with N. dubius. Peritoneal macrophages harvested from infected mice produced inhibition of the development of B. microti in vitro. This inhibition was greatest using macrophages harvested from mice recovered from infection with B. microti and from mice infected with the larval stages of N. dubius. Also, supernatants harvested from cultures of macrophages from N. dubius-infected mice suppressed B. microti development in vitro.

Polyamine oxidase mediates intra-erythrocytic death of Plasmodium falciparum

Using a number of established culture strains of Plasmodium falciparum, the effects of the addition of polyamine oxidase and spermine on the intra-erythrocytic forms were studied. Cultures to which polyamine oxidase and polyamines were added contained only degenerate parasites but if one or other were added alone the cultures were similar to the controls. The effects were confirmed by 35S-methionine incorporation.

Immunopotentiation against internal parasites

The economic importance of livestock losses attributed to internal parasites has led to the need of developing and successfully employing effective antiparasitic vaccines. An increasingly important strategy in the development of more effective vaccines is the preparation and use of immunopotentiators or adjuvants. Immunopotentiators or adjuvants have been used effectively in combination with antigen(s) or alone to protect animals against internal parasites. The use of immunopotentiators for specific and nonspecific stimulation of protective immunity against internal parasites is reviewed.

Immunity to Plasmodium chabaudi adami in the B-cell-deficient mouse

Immunity to malaria has a multicomponent basis which requires the participation of both T- and B-lymphocyte systems. Previous studies have suggested that the T-lymphocyte system has an essential role in 're-infection immunity' to malaria, but that B cells and/or their products are necessary for the host to survive acute infection and to clear the blood of parasites during chronic malaria. Thus, B-cell-deficient mice and chickens died of fulminant malaria when infected with Plasmodium yoelii and Plasmodium gallinaceum, respectively, but when their acute infections were controlled with subcurative chemotherapy, B-cell-deficient host developed chronic low-grade infections and resisted challenge with homologous parasites. In contrast, athymic nude mice failed to control their endogenous P. yoelii infection after the termination of drug therapy unless they had been thymus grafted before initiation of acute infection. We now report that Plasmodium chabaudi adami (556KA) infection in B-cell-deficient mice results in an activation of a T-cell-dependent immune mechanism which terminates acute malaria in a similar way to that seen in immunologically intact mice. Furthermore, these immunized B-cell-deficient mice were resistant to homologous challenge infection as well as infections initiated with Plasmodium vinckei, but not with P. yoelii and Plasmodium berghei.

Differences in susceptibility of various mouse strains to haemoprotozoan infections: possible correlation with natural killer activity

Striking differences in the susceptibility to P. chabaudi and B. microti infections among different strains of mice are described. In most of the strains, both parasites induce a moderate, transient parasitaemia, followed by recovery. However, in the A strain P. chabaudi is rapidly lethal and B. microti induces a parasitaemia which persists for life in most animals. In contrast B10.A mice, which have the same H-2q haplotype as the A strain, recover from both infections. In first crosses (A X B10.A)F1 mice are uniformly resistant. Among other correlates, NK cells activity may be relevant. This activity is known to be high in strain of mice which are resistant to both of the parasites studied, such as C57B1 and CBA mice, and low in the susceptible A strain. We have examined the spleen weight, total cell number and NK activity at different times after infection. In the resistant strains there is a rapid increase in size and cell number which is still more marked during recovery. NK activity increases greatly during the infection; this is especially remarkable considering the dilution of nucleated cells with erythrocytes precursors. In contrast, in A mice cell numbers of NK activity remain almost unchanged. Thus, marked activation of NK cells occur, in resistant strains but not in susceptible ones. Possible mechanisms of activation of these cells and their effect in haemoprotozoan infections are discussed.