Cell-mediated killing of protozoa

Trypanosoma sp. infection in Boa constrictor snakes: morphological, hematological, clinical biochemistry, molecular, and phylogenetic characteristics

There are few reports of Trypanosoma in snakes, as well as little information about its pathogenicity in these animals. Thus, the present study aimed to characterize Trypanosoma found in Boa constrictor snakes, to verify the influence of the parasitism on hematological and clinical biochemistry parameters, and to perform a phylogenetic study of the isolates. Blood samples from sixty-one boas were analyzed for the presence of trypanosomatids and by hematological and clinical biochemistry assays. The flagellates that were found in this analysis were used for cell culture, morphometry, and molecular analysis. Later, molecular typing phylogenetic studies were performed. Nine positive animals (14.75%) were identified by microscopy analysis. The hematological results showed that parasitized animals presented significantly lower levels of packed cell volume, hemoglobin, mean corpuscular volume, and mean corpuscular hemoglobin. In the leukogram, eosinophils and heterophils counts were higher in parasitized animals. Considering the molecular analyses, the isolates presented a higher identity of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the 18S small subunit ribosomal RNA (SSU rRNA) gene fragments with Trypanosoma serpentis. The phylogenetic tree, using the GAPDH, clustered all isolates with T. serpentis and Trypanosoma cascavelli. This is the first description of T. serpentis parasitizing boas and of the clinical changes caused by trypanosomatid infection in snakes.

Toxoplasma gondii Infection Inhibits Histone Crotonylation to Regulate Immune Response of Porcine Alveolar Macrophages

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite that can infect almost all warm-blooded animals, causing serious public health problems. Lysine crotonylation (Kcr) is a newly discovered posttranslational modification (PTM), which is first identified on histones and has been proved relevant to procreation regulation, transcription activation, and cell signaling pathway. However, the biological functions of histone crotonylation have not yet been reported in macrophages infected with T. gondii. As a result, a total of 1,286 Kcr sites distributed in 414 proteins were identified and quantified, demonstrating the existence of crotonylation in porcine alveolar macrophages. According to our results, identified histones were overall downregulated. HDAC2, a histone decrotonylase, was found to be significantly increased, which might be the executor of histone Kcr after parasite infection. In addition, T. gondii infection inhibited the crotonylation of H2B on K12, contributing on the suppression of epigenetic regulation and NF-κB activation. Nevertheless, the reduction of histone crotonylation induced by parasite infection could promote macrophage proliferation via activating PI3K/Akt signaling pathway. The present findings point to a comprehensive understanding of the biological functions of histone crotonylation in porcine alveolar macrophages, thereby providing a certain research basis for the mechanism research on the immune response of host cells against T. gondii infection.

CD8+ T cell immunity in an encephalitis model of Toxoplasma gondii infection

Toxoplasma gondii infection induces a robust CD8 T cell immunity in the infected host, which is critical for keeping chronic infection under control. IFNγ production and cytolytic activity exhibited by CD8 T cells are critical functions needed to prevent the reactivation of latent infection. Paradoxically, the susceptible mice infected with the parasite develop encephalitis irrespective of the presence of vigorous CD8 T cell immunity. Recent studies from our laboratory have demonstrated that these animals have defect in the memory CD8 T cell population, which become dysfunctional due to exhibition of inhibitory receptors like PD-1. Although the blockade of PD-1-PDL-1 pathway rescues the CD8 response, PD-1(hi) expressing cells are refractory to the treatment. In this review, we discuss the development of CD8 memory response during chronic infection, mechanism responsible for their dysfunctionality, and possible therapeutic measures that can be taken to reverse the process.

The CD8 T-cell road to immunotherapy of toxoplasmosis

Toxoplasma gondii infection induces a robust CD8 T-cell immunity that is critical for keeping chronic infection under control. In studies using animal models, it has been demonstrated that the absence of this response can compromise the host ability to keep chronic infection under check. Therapeutic agents that facilitate the induction and maintenance of CD8 T-cell response against the pathogen need to be developed. In the last decade, major strides in understanding the development of effector and memory response, particularly in viral and tumor models, have been made. However, factors involved in the generation of effector or memory response against T. gondii infection have not been extensively investigated. This information will be invaluable in designing immunotherapeutic regimens needed for combating this intracellular pathogen that poses a severe risk for pregnant women and immunocompromised individuals.

Molecular mechanisms of host cell invasion by Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease, is an obligate intracellular protozoan pathogen. Overlapping mechanisms ensure successful infection, yet the relationship between these cellular events and clinical disease remains obscure. This review explores the process of cell invasion from the perspective of cell surface interactions, intracellular signaling, modulation of the host cytoskeleton and endosomal compartment, and the intracellular innate immune response to infection.

Infection-induced respiratory burst in BALB/c macrophages kills Leishmania guyanensis amastigotes through apoptosis: possible involvement in resistance to cutaneous leishmaniasis

The immune mechanisms that underlie resistance and susceptibility to leishmaniasis are not completely understood for all species of Leishmania. It is becoming clear that the immune response, the parasite elimination by the host and, as a result, the outcome of the disease depend both on the host and on the species of the infecting Leishmania. Here, we analyzed the outcome of the infection of BALB/c mice with L. guyanensis in vivo and in vitro. We showed that BALB/c mice, which are a prototype of susceptible host for most species of Leishmania, dying from these infections, develop insignificant or no cutaneous lesions and eliminate the parasite when infected with promastigotes of L. guyanensis. In vitro, we found that thioglycollate-elicited BALB/c peritoneal macrophages, which are unable to eliminate L. amazonensis without previous activation with cytokines or lipopolysaccharide, can kill L. guyanensis amastigotes. This is the first report showing that infection of peritoneal macrophages with stationary phase promastigotes efficiently triggers innate microbicidal mechanisms that are effective in eliminating the amastigotes, without exogenous activation. We demonstrated that L. guyanensis amastigotes die inside the macrophages through an apoptotic process that is independent of nitric oxide and is mediated by reactive oxygen intermediates generated in the host cell during infection. This innate killing mechanism of macrophages may account for the resistance of BALB/c mice to infection by L. guyanensis.

The involvement of neutrophils in the resistance to Leishmania major infection in susceptible but not in resistant mice

To understand the immunomodulatory roles of neutrophils in Leishmania major infection, we examined the expression of cytokine and chemokine mRNAs from neutrophils of the infected resistant C3H/HeJ and susceptible BALB/c mice. We also examined the effects of neutrophil depletion on the expression of cytokine by peritoneal macrophages and draining lymph node cells and on the footpad lesions and parasite burdens in these mice. Neutrophils from resistant C3H/HeJ but not from susceptible BALB/c mice expressed mRNAs for IL-12p40, IFN-gamma,TNF-alpha and monokine induced by IFN-gamma(MIG). Neutrophil depletion of the resistant mice reduced the expression of IFN-gammaandTNF-alpha in peritoneal macrophages but did not affect the expression of IL-12p40 and IFN-gamma in draining lymph node cells and the growth of footpad lesions. On the other hand, neutrophil depletion of susceptible BALB/c mice did not affect the expression of TNF-alpha and monocyte-derived chemokine (MDC) in peritoneal macrophages but induced the early stage expression of IL-4 in draining lymph node cells and exacerbated the footpad lesions and increased the parasite burden. The exacerbation of footpad lesions induced by neutrophil depletion was abolished by rIL-12 treatment. Our results suggest that even in susceptible BALB/c but not in C3H/HeJ mice there is a certain resistance requiring neutrophils at the early stage of infection.

Respiratory burst responses of rat macrophages to microsporidian spores

This study investigated the respiratory burst responses of rat resident peritoneal macrophages and of peritoneal macrophages stimulated 5 days previously with viable spores of the fish infecting microsporidian Microgemma caulleryi. Nitric oxide production by resident macrophages and prestimulated macrophages in response to viable microsporidian spores was significantly lower than in response to Escherichia coli lipopolysaccharide (LPS) (nitrite concentration in medium 57 +/- 1 microM for resident macrophages stimulated with LPS versus 31 +/- 1 microM for resident macrophages stimulated with microsporidian spores and 36 +/- 4 microM for M. caulleryi prestimulated macrophages; P < 0.05). Extracellular release of reactive oxygen species (ROS) by resident macrophages in response to microsporidian spores was similar to that in response to Kluyveromyces lactis yeast cells and to that in response to phorbol myristate (a stimulator of protein C kinase). Intracellular ROS production by resident macrophages in response to microsporidian spores was similar to that produced in response to yeast cells. Both extracellular ROS production and intracellular ROS production (in response to all stimuli) were significantly lower after in vivo prestimulation of macrophages with microsporidian spores. These results demonstrate that microsporidian spores of species other than those that habitually infect mammals are capable of modulating the respiratory burst of rat peritoneal macrophages. Such modulation may contribute to avoidance by the microsporidian of cytotoxic responses associated with the respiratory burst.

Elevated anti-parasitic activity in peripheral blood monocytes and neutrophils of cattle infected with Babesia bovis

The innate immune response to bovine Babesia bovis infection in vivo has not previously been established. We used assays measuring phagocytosis and oxidative burst to investigate the immune response because they are indicative of the innate antimicrobial capacity of monocytes and neutrophils. Monocyte and neutrophil phagocytosis is thought to be non-specific in nature and so the phagocytosis of either opsonised Zymosan or Escherichia coli was used to indicate the non-specific phagocytic capacity of monocytes and neutrophils ex vivo. The kinetics of both phagocytic and oxidative burst activity in monocytes and neutrophils were followed twice weekly from pre-inoculation (day 0) through to 31 days after inoculation. Peripheral blood monocytes were found to display a pronounced oxidative burst, but a suppressed capacity to phagocytose during a primary infection. On the other hand, neutrophils exhibited an increased phagocytic capacity and reduced oxidative activity during a primary infection. These findings identified considerable antimicrobial activity evident in peripheral blood monocytes and neutrophils from cattle exposed to B. bovis as a primary exposure. This elevated antimicrobial activity was coincident with the time that parasite numbers peaked in the circulation and occurred prior to parasite clearance. These results suggest that peripheral blood monocytes and neutrophils are active mediators in the innate immune response to a primary B. bovis.

Analysis of immunoglobulin classes and subclasses in response to infection of Balb/cJ and C57BL/6J mice with Coxiella burnetii

In order to establish defined immunological parameters for Q fever infection models, a microtitre enzyme-linked immunosorbent fluorescence assay (ELISA) was used for the first time to analyse the humoral immune response of Balb/cJ and C57BL/6J mice after experimental infection with Coxiella burnetii strain 'Nine Mile' in phase I. The experimental infection evoked a seroconversion in all mice within 10 days. Typically, the immune response measured against the whole-cell antigen showed an early increase of immunoglobulin (Ig) M followed by a later increase of the IgG subclasses. The IgA was low during the entire investigation period. Within the IgG subclasses only IgG2a and IgG2b gained higher values, whereby C57BL/6J mice produced high IgG2b titres and significantly lower IgG2a titres. In contrast, Balb/cJ mice developed IgG2a and IgG2b at equal levels. The use of partial antigens of C. burnetii demonstrated that the dominating IgG2b reaction of the C57BL/6J mice was directed against the lipopolysaccharide (LPS) of C. burnetii. This reaction was almost absent in Balb/cJ mice. In contrast, the SP27 protein antigen did not evoke different IgG2b reactions within the two breeds. No significant influence was observed within the two breeds in regard to sex or between hormone synchronized and non-hormone synchronized animals.

Administration of beta-glucan following Leishmania major infection suppresses disease progression in mice

The potential of beta-glucan (glucan) to suppress the progression of lesions caused by virulent strains of Leishmania major in genetically susceptible BALB/c mice when administered post challenge was evaluated. Glucan particles (glucanp) prepared from Saccharomyces cerevisiae were injected i.v. at 7-day intervals starting 7 days after parasite challenge. Four injections gave a more rapid and a higher extent of suppression than 1, 2 or 3 injections. Mice receiving only parasites, a glucose solution, starch particles or glucanp by the i.p. route showed a progressive increase in footpad thickness and developed ulcerating lesions. An alkali solubilized glucan (glucanas) was injected (50 micrograms, 200 micrograms and 400 micrograms/mouse) 4 times at 4 day intervals either i.v. or i.p. starting four days post parasite challenge. Glucanas injection by either route blocked lesion development; the 50 micrograms treatment had already substantial effects and 400 micrograms in the i.p. route prevented even the initial stages of lesion formation. Touch prints from the lesion area and from the liver of mice receiving 200 micrograms glucanas were amastigote free. The anti Leishmania antibody titre of glucanas treated mice was lower and their sera recognized fewer antigens than that of control Leishmania bearing mice.

Interaction of leishmania metacyclics with macrophages

Metacyclics of L. major and putative metacyclics of L. m. mexicana survived better in explanted murine macrophages than promastigotes from mid-log phase cultures. The latter forms, however, attached in greater numbers to macrophages and, in the case of L. major, also more became intracellular. Only a small percentage of the macrophages infected with amastigotes exhibited a respiratory burst (as detected by nitroblue tetrazolium (NBT) reduction), whereas this occurred with most of the macrophages infected with either metacyclic or non-infective promastigotes of L. major. Approximately half of the macrophages infected with L. m. mexicana promastigotes reduced NBT. The results suggest that avoidance of the oxygen metabolite arm of the host cell's microbicidal activity is not the main survival strategy for metacyclics entering macrophages. Metacyclics of L. major, however, were found to be less sensitive than mid-log phase promastigotes to hydrogen peroxide and also human serum; properties which may aid their survival.

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.

Cytochemical localization of plasma membrane enzyme markers during interiorization of tachyzoites of Toxoplasma gondii by macrophages

The enzyme activity of Mg++-ATPase, Na+-K+-ATPase, 5'-nucleotidase and NAD(P)H-oxidase was cytochemically detected at the ultrastructural level in mouse peritoneal macrophages infected with untreated and with specific antibody-coated Toxoplasma gondii tachyzoites. The Mg++-ATPase and 5'-nucleotidase were distributed throughout the macrophages' plasma membrane but were not observed in the membrane lining endocytic vacuoles containing ingested parasites; however, Na+-K+-ATPase activity was detected in the macrophages' plasma membrane as well as in the parasitophorous vacuoles that contained untreated or specific antibody-coated parasites. Reaction product, indicative of NAD(P)H-oxidase, was detected in the parasitophorous vacuoles that contained only specific antibody-coated parasites.

Resistance of leishmanial phosphatases to inactivation by oxygen metabolites

Leishmania donovani promastigotes produce large quantities of two distinct acid phosphatases; a tartrate-resistant enzyme is localized to the external surface of the plasma membrane, and a tartrate-sensitive enzyme is secreted into the growth medium. It was shown previously that preincubation of human neutrophils and macrophages with the tartrate-resistant phosphatase markedly reduced the ability of these host cells to produce superoxide anions in response to stimulation with the activator formyl-methionyl-leucyl-phenylalanine. The possibility that the cell surface acid phosphatase or the phosphatase that is secreted into the extracellular fluid might compromise other host cell functions, especially intracellular ones, depends on the ability of the enzyme to resist exposure to toxic oxygen metabolites (e.g., superoxide anion, hydrogen peroxide, hypochlorite) generated by phagocytic cells. In the present report, we show that both leishmanial acid phosphatases were relatively resistant to inactivation by oxygen metabolites. At pH 5.5, the activity of the tartrate-resistant phosphatase was reduced 50% by incubation for 1 h with each of the following: 30 mM O2-, 500 mM hydrogen peroxide, and 6 mM hypochlorite ion. These concentrations are many fold greater than the concentrations of these substances that are generated by stimulated polymorphonuclear phagocytes. The tartrate-sensitive acid phosphatase differed markedly from the tartrate-resistant phosphatase in that the former was essentially insensitive to even very high concentrations of superoxide anion and hydrogen peroxide. Furthermore, 50% inactivation of the tartrate-sensitive leishmanial phosphatase required exposure to 35 mM hypochlorite for 30 min. These results indicate that the catalytic potential of these two leishmanial acid phosphatases probably survives exposure to toxic oxygen metabolites generated by neutrophils and macrophages.

Electron microscopic studies on the interaction of rat Kupffer cells and Plasmodium berghei sporozoites

The interactions between Plasmodium berghei sporozoites and Kupffer cells in rat liver were studied by transmission electron microscopy. Between 10 and 45 min after inoculation, sporozoites were found in the process of entering Kupffer cells and inside phagolysosomes. The sporozoites entered the Kupffer cells by phagocytosis as determined by the presence of pseudopods and local accumulations of aggregated microfilaments and the resulting exclusion of other organelles in the phagocyte cytoplasm beneath the attached parasite. Sporozoites were taken up either with their anterior end first, or backwards. Scanning electron microscopy of in vitro sporozoite Kupffer cell interaction confirmed these observations. It was concluded that sporozoites are taken up in a normal phagocytic way by the Kupffer cells, regardless of their initial place of contact or position. Thirty min after inoculation sporozoites found in phagolysosomes were still morphologically intact but after 45 min we could encounter completely digested sporozoites.

Cell-mediated damage to helminths

Although it is difficult to draw any sweeping conclusions that would be applicable to all helminth infections, the main features that are emphasized in this review may be summarized briefly. Pathogenic helminths, although extremely diverse in structure and behaviour, have one common feature, namely that they present to the host's defenses large, non-phagocytosable surfaces. Because of this, they are susceptible to a range of effector mechanisms differing either quantitatively or qualitatively from those that are active against other parasites or against normal or abnormal host cells. As an extreme example, the various types of cytotoxic lymphocyte, with one interesting exception, are inactive against helminths. Instead, helminth infections are characterized by high IgE responses and increased numbers of circulating eosinophils. Such eosinophils are activated, and show a marked capacity to kill a variety of target helminths in vitro. Further activation may occur in response to mast cell mediators released as a result of IgE-dependent degranulation; and IgE, as well as IgG and complement, can mediate eosinophil attachment and killing. It may therefore be suggested that the eosinophil/IgE/mast cell axis represents a powerful host defense against helminth infections. IgE can also mediate macrophage-dependent killing of several helminths, a process which involves a functional change in the macrophage, resembling activation. Although eosinophil-mediated and IgE-dependent macrophage-mediated effects are particularly potent, other effector cells are not excluded: in certain circumstances, neutrophils and conventionally activated macrophages may be equally or more effective. Neutrophils appear to act solely by oxidative killing mechanisms, whereas degranulation and the release of toxic granule contents is equally or more important in eosinophil-mediated damage. Different stages of different helminths vary in their degree of susceptibility to different mechanisms. Eosinophils appear to be somewhat less active than neutrophils against ensheathed nematodes, whereas trematodes and exsheathed nematodes are highly susceptible to eosinophil attack. In many experimental helminth infections, studies in vivo suggest a role for antibody-dependent cell-mediated immune effector mechanisms. The identity of the effector cell is difficult to establish because of a lack of techniques for specific manipulation of individual cell types, but histological studies frequently point to a strong eosinophil or macrophage involvement. The development and analysis of in vitro assays allows the study of immune effector mechanisms in man.(ABSTRACT TRUNCATED AT 400 WORDS)