Recombinant tumor necrosis factor alpha does not inhibit the growth of African trypanosomes in axenic cultures

Comparative pathology of mice infected with high and low virulence of Indonesian Trypanosoma evansi isolates

Mice infected with T. evansi cause various clinical manifestations and histopathological changes. The aim of this study was to compare the histopathological lesions of mice infected with T. evansi Bang 87 isolates (high virulence) and Pml 287 isolates (low virulence). A total of 15 susceptible mice (DDY) were divided into three groups (five mice/group): Groups I and II each were infected with 10⁴ T. evansi of high virulence (Bang87) and low virulence (Pml 287), respectively, whereas group III served as a control group. A total of three mice from group I, and one mouse from each group II and III were killed at 4 dpi. A total of two mice from each group II and III were killed at 24 dpi. Two remaining mice from each group were observed until succumb. Mice of group I and group II at 4 dpi showed no gross lesions. However, mice of group I showed very acute animal death at 5 dpi and showed mild to moderate histopathological lesions at 4 dpi, namely non-suppurative encephalitis, non-suppurative pneumonia, hepatitis non-suppurative with intravascular trypanosomiasis, tubular degeneration and necrosis. Group II showed chronic death at 26 dpi with significant gross pathological changes at 24 dpi in spleen (swelling 10 times than normal size) accompanied by severe non-suppurative encephalitis, cholangiohepatitis non-suppurative and bile duct proliferation, diffused splenic necrosis. The result of this study is expected to be used as a basis for improved treatment management in cattle infected with high virulence T. evansi isolates that are need to be handled appropriately to avoid fatal consequences.

Trypanosoma brucei growth control by TNF in mammalian host is independent of the soluble form of the cytokine

Infection of C57Bl/6 mice by pleomorphic African trypanosomes Trypanosoma brucei and T. congolense is characterized by parasitemia waves coupled with the production of systemic levels of TNF. This cytokine is known to control T. brucei growth, but also to contribute to tissue damage, shortening the survival time of infected mice. Using a dominant-negative version of TNF to discriminate between the effects of the membrane-form versus the soluble form of TNF, we show that the second form is involved in neither parasite control nor induction of liver injury. Therefore, soluble TNF is likely not a major contributor to disease outcome. We propose that membrane-bound TNF is responsible for both T. brucei control and host pathology.

TNF-alpha in bulls experimentally infected with Trypanosoma vivax: a pilot study

There are few studies about the immune response during trypanosomosis in cattle. The objective of this research was to evaluate the effect of experimental infection with Trypanosoma vivax (T. vivax) on serum levels of TNF-alpha in bulls and its relationship to hematocrit, body temperature and parasitemia. Two adult crossbred bulls were infected experimentally with T. vivax and two were used as controls. The bulls were evaluated during a 64 day period in terms of temperature, hematocrit, and parasitemia. Serum TNF-alpha levels were determined by ELISA, using an antibody specific for bovine. TNF-alpha in serum began rising on the seventh day after infection and reached a peak on day 40 of post-infection, then dropped. The lowest hematocrit levels corresponded to the upper levels of TNF-alpha, for each animal. In conclusion, the experimental infection of cattle with T. vivax promotes the release of TNF-alpha, demonstrating a pro-inflammatory immune response to this hemotropic parasite. Moreover, the lowest hematocrit levels coincide with high concentrations of TNF-alpha, suggesting that this cytokine can be linked to the observed anemia during the course of infection by T. vivax in cattle.

Unravelling human trypanotolerance: IL8 is associated with infection control whereas IL10 and TNFα are associated with subsequent disease development

In West Africa, Trypanosoma brucei gambiense, causing human African trypanosomiasis (HAT), is associated with a great diversity of infection outcomes. In addition to patients who can be diagnosed in the early hemolymphatic phase (stage 1) or meningoencephalitic phase (stage 2), a number of individuals can mount long-lasting specific serological responses while the results of microscopic investigations are negative (SERO TL+). Evidence is now increasing to indicate that these are asymptomatic subjects with low-grade parasitemia. The goal of our study was to investigate the type of immune response occurring in these “trypanotolerant” subjects. Cytokines levels were measured in healthy endemic controls (n = 40), stage 1 (n = 10), early stage 2 (n = 19), and late stage 2 patients (n = 23) and in a cohort of SERO TL+ individuals (n = 60) who were followed up for two years to assess the evolution of their parasitological and serological status. In contrast to HAT patients which T-cell responses appeared to be activated with increased levels of IL2, IL4, and IL10, SERO TL+ exhibited high levels of proinflammatory cytokines (IL6, IL8 and TNFα) and an almost absence of IL12p70. In SERO TL+, high levels of IL10 and low levels of TNFα were associated with an increased risk of developing HAT whereas high levels of IL8 predicted that serology would become negative. Further studies using high throughput technologies, hopefully will provide a more detailed view of the critical molecules or pathways underlying the trypanotolerant phenotype.

Whereas immunological mechanisms involved in the control of trypanosome infections have been extensively studied in animal models, knowledge of how Trypanosoma brucei gambiense interacts with its human hosts lags far behind. In this study we measured cytokine levels in sleeping sickness patients and individuals who were apparently able to control infection to subdetection levels over long periods of time or who were engaged in a process of self-cure as demonstrated by the disappearance of specific antibodies. In contrast to patients, trypanotolerant subjects were characterized by a strong inflammatory response with elevated levels of IL8, IL6, and TNFα. This study indicates that both protective immune responses and markers of disease development exist in human T. brucei. gambiense infection and constitute an important step forward to identify new diagnostic or therapeutic targets in the fight against sleeping sickness.

Immune evasion strategies of trypanosomes: a review

Trypanosomes are digenetic protozoans that infect domestic and wild animals, as well as humans. They cause important medical and veterinary diseases, making them a major public health concern. There are many species of trypanosomes that infect virtually all vertebrate taxa. They typically cycle between insect or leech vectors and vertebrate hosts, and they undergo biochemical and morphological changes in the process. Trypanosomes have received much attention in the last 4 decades because of the diseases they cause and their remarkable armamentarium of immune evasion mechanisms. The completed genome sequences of trypanosomes have revealed an extensive array of molecules that contribute to various immune evasion mechanisms. The different species interact uniquely with their vertebrate hosts with a wide range of evasion strategies and some of the most fascinating immune evasion mechanisms, including antigenic variation that was first described in the trypanosomes. This review focuses on the variety of strategies that these parasites have evolved to evade or modulate immunity of endothermic and ectothermic vertebrates.

Induction and regulation ofTrypanosoma bruceiVSG-specific antibody responses

The review addresses how infection withTrypanosoma bruceiaffects the development, survival and functions of B lymphocytes in mice. It discusses (1) the contributions of antibodies to trypanosome clearance from the bloodstream, (2) how B lymphocytes, the precursors of antibody producing plasma cells, interact with membrane form variable surface glycoprotein (VSG), i.e. with monovalent antigen that is free to diffuse within the lipid bilayer of the trypanosome plasma membrane and consequently can cross-link B cell antigen specific receptors by indirect processes only and (3) the extent and underlying causes of dysregulation of humoral immune responses in infected mice, focusing on the impact of wild type and GPI-PLC−/−trypanosomes on bone marrow and extramedullary B lymphopoiesis, B cell maturation and survival.

Synthetic nonamer peptides derived from insect defensin mediate the killing of African trypanosomes in axenic culture

Synthetic antimicrobial 9-mer peptides (designated as peptides A and B) designed on the basis of insect defensins and their effects on the growth of African trypanosomes were examined using two isolates of Trypanosoma congolense, IL1180 and IL3338, and two isolates of Trypanosoma brucei brucei, ILTat1.1and GUTat 3.1, under axenic culture conditions. Both peptides inhibited the growth of all bloodstream form (BSF) trypanosomes at 200-400 microg/mL in the complete growth medium, with peptide A being more potent than peptide B. In addition, these peptides exhibited efficient killing at 5-20 microg/mL on BSF trypanosomes suspended in phosphate-buffered saline, whereas procyclic insect forms in the same medium were more refractory to the killing. Electron microscopy revealed that the peptides induced severe defects in the cell membrane integrity of the parasites. The insect defensin-based peptides up to either 200 or 400 microg/mL showed no cell killing or growth inhibition on NIH3T3 murine fibroblasts. The results suggest that the design of suitable synthetic insect defensin-based 9-mer peptides might provide potential novel trypanocidal drugs.

Interleukin-12p70 deficiency increases survival and diminishes pathology in Trypanosoma congolense infection

To determine the immunological role played by interleukin (IL)-12 family members in Trypanosoma congolense infection, IL-12p35(-/-), IL-12p40(-/-), and IL-12p35(-/-)/p40(-/-) mice were used. While the latter 2 strains lack all IL-12 homologues, IL-12p35(-/-) mice still produce IL-12p80 homodimers and IL-23. Compared with wild-type mice, all infected IL-12-deficient mouse strains showed prolonged survival, whereas parasitemia levels were unaltered. Interferon (IFN)-gamma production in IL-12-deficient mice was strikingly reduced during the acute and chronic stages of infection, coinciding with significantly reduced chronic-stage hepatocellular damage, as demonstrated by histological analysis and plasma aspartate transaminase measurements. In contrast, IL-10 production was not affected by the absence of IL-12. Taken together, these results show that, during T. congolense infection, the absence of IL-12, but not the IL-12p80 homodimer or IL-23, leads to a reduction in IFN-gamma production, which reduces hepatic pathology and improves host survival in conjunction with IL-10 without negatively affecting parasitemia control.

Contributions of experimental mouse models to the understanding of African trypanosomiasis

African trypanosomiasis is the collective name for a wide variety of trypanosome infections that affect humans and livestock. In recent years, experimental mice infection models have provided new insights into both human and animal trypanosomiasis. Mouse models seem to be a valuable and versatile tool in trypanosomiasis-associated pathology and immunology research and highlight the variety shown by African trypanosomiases. Indeed, inbred mouse strains have enabled the study of genetic determinants of susceptibility and of the roles of anti-parasite antibodies, inflammatory mediators and anti-inflammatory mediators for each trypanosome species. Remarkable advances relating to the encephalitic stage of sleeping sickness have also been achieved thanks to murine models. The different contributions of murine models to the African trypanosomiases knowledge are presented here. Future search directions are finally proposed, with respect to mouse model opportunities and limitations.

Anti-Trypanosoma brucei activity in Cape buffalo serum during the cryptic phase of parasitemia is mediated by antibodies

Cape buffalo are reservoir hosts of African trypanosomes. They rapidly suppress population growth of the highly antigenically variable extracellular haemoprotozoa and subsequently maintain a cryptic infection. Here we use in vitro cultures of trypanosomes cloned from Cape buffalo blood during cryptic infection, as well as related and unrelated trypanosomes, to identify anti-trypanosome components present in cryptic-phase infection serum. Trypanosome clone-specific complement-dependent trypanolytic IgM and IgG arose after appearance of target trypanosomes during cryptic infection. Serum collected late in the cryptic phase of infection contained complement-independent growth-inhibitory IgG which varied in activity among target trypanosomes. Removal of protein A/G-binding IgG from the serum restored its capacity to support trypanosome growth in vitro. Recovered growth-inhibitory IgG reacted with the variable surface glycoprotein (VSG) of parasites most affected by it, and reacted with trypanosome common antigens, notably the endosome-restricted tomato lectin-binding glycoproteins (TL-antigens). The inclusion of purified TL-antigens in culture medium did not affect the trypanosome growth-inhibitory activity of immune Cape buffalo serum. In addition, hyperimmune rabbit IgG against TL-antigens showed little or no binding to intact trypanosomes and did not affect trypanosome growth in vitro although it did react strongly with TL-antigens and trypanosome endosomes. We conclude that antibodies, particularly clone-specific (putatively VSG-specific) antibodies are responsible for the anti-trypanosome activity of cryptic phase infection serum consistent with a dominant role in parasite control in Cape buffalo.

Human African trypanosomiasis: clinical presentation and immune response

Human African trypanosomiasis or sleeping sickness is caused by infection with two subspecies of the tsetse-fly-vectored haemoflagellate parasite Trypanosoma brucei. Historically, epidemic sleeping sickness has caused massive loss of life, and related animal diseases have had a crucial impact on development in sub-Saharan Africa. After a period of moderately successful control during the mid-part of the 20th century, sleeping sickness incidence is currently rising, and control is hampered by a combination of factors, including civil unrest and the possible development of drug resistance by the parasites. The prevailing view is that the disease is invariably fatal without anti-trypanosomal drug treatment. However, there have also been intriguing reports of wide variations in disease severity as well as evidence of asymptomatic carriers of trypanosomes. These differences in the presentation of the disease will be discussed in the context of our knowledge of the immunology of trypanosomiasis. The impact of dysregulated inflammatory responses in both systemic and CNS pathology will be examined and the potential for host genotype variation in disease severity and control will be discussed.

TNF-alpha mediates the development of anaemia in a murine Trypanosoma brucei rhodesiense infection, but not the anaemia associated with a murine Trypanosoma congolense infection

Development of anaemia in inflammatory diseases is cytokine-mediated. Specifically, the levels of tumour necrosis factor-alpha (TNF-alpha), produced by activated macrophages, are correlated with severity of disease and anaemia in infections and chronic disease. In African trypanosomiasis, anaemia develops very early in infection around the time when parasites become detectable in the blood. Since the anaemia persists after the first waves of parasitaemia when low numbers of trypanosomes are circulating in the blood, it is generally assumed that anaemia is not directly induced by a parasite factor, but might be cytokine-mediated, as in other cases of anaemia accompanying inflammation. To clarify the role of TNF-alpha in the development of anaemia, blood parameters of wild type (TNF-alpha+/+), TNF-alpha-null (TNF-alpha-/-) and TNF-alpha-hemizygous (TNF-alpha-/+) trypanotolerant mice were compared during infections with the cattle parasite Trypanosoma congolense. No differences in PCV, erythrocyte numbers or haemoglobin were observed between TNF-alpha-deficient and wild type mice, suggesting that the decrease in erythrocytes was not mediated by TNF-alpha. Erythropoetin (EPO) levels increased during infection and no significant differences in EPO levels were observed between the three mouse strains. In contrast, during an infection with the human pathogen Trypanosoma brucei rhodesiense, the number of red blood cells in TNF-alpha-deficient mice remained significantly higher than in the wild type mice. These data suggest that more than one mechanism promotes the development of anaemia associated with trypanosomiasis.

Susceptibility of TNF-alpha-deficient mice to Trypanosoma congolense is not due to a defective antibody response

C57BL/6 mice deficient in one or two copies of the gene for tumor necrosis factor alpha (TNF-alpha) were more susceptible to Trypanosoma congolense infection than their resistant, wild-type counterparts. The number of TNF-alpha genes was correlated with the capacity to control parasitaemia and with survival time. Absence of TNF-alpha resulted in a diminished capacity to form germinal centres in lymph nodes and spleen. Since germinal centres are involved in antibody production and affinity maturation, the susceptibility of the TNF-alpha-deficient mice could have been due to this secondary defect. Despite the lack of the germinal centres, the antibody responses to internal and exposed trypanosome antigens and to non-trypanosome antigens were not significantly different. Also the relative avidities measured in infected sera did not significantly differ between the two mouse strains. These data suggest that the role of TNF-alpha in control of T. congolense was not due to its role in the development of an antibody response.

The secretion of acute phase proteins and inflammatory cytokines during Trypanosoma congolense infection is not affected by the absence of the TNF-alpha gene

Tumor necrosis factor-alpha (TNF-alpha) plays a role in the host's defence against infections with African trypanosomes. It helps to control the blood stream form of the parasite and in Trypanosoma congolense infections, it also prolongs survival. The mechanisms by which this cytokine can influence parasitemia and survival are unknown. Therefore, the levels of acute phase proteins and other inflammatory cytokines were monitored in trypano-tolerant wild-type and TNF-alpha-deficient mice during a T. congolense infection. The titres of ceruloplasmin (CP), alpha1-acid glycoprotein (AGP) and serum amyloid P (SAP) increased and reached their peaks at 11 days post-infection, when the first peak of parasitemia was observed. No significant differences were observed in the acute phase protein profiles between the two mouse strains. Also the profiles of serum titres of IFN-gamma, IL-1alpha, IL-6 and IL-10 were not significantly different. Our present results indicate that acute phase protein and cytokine responses can be induced in the absence of TNF-alpha during a T. congolense infection in mice, and that the susceptibility of the TNF-alpha-deficient mice is not due to modulation of expression of these molecules.

Susceptibility of heat shock protein 70.1-deficient C57BL/6 J, wild-type C57BL/6 J and A/J mice to Trypanosoma congolense infection

The heat shock protein (HSP) 70.1 gene lies on mouse chromosome 17 among the candidates for Tir1, the major quantitative trait locus associated with response to Trypanosoma congolense infection. To evaluate whether the HSP70.1 gene is involved in the response, we compared the susceptibility of HSP70.1-deficient C57BL/6 J, resistant wild-type C57BL/6 J and susceptible A/J mice. No differences were observed between HSP70.1-deficient and wild-type C57BL/6 J mice in survival time, levels of parasitemia and anemia, suggesting that there is no involvement of the HSP70.1 gene in control of T. congolense infection. The course of infection was markedly different between A/J and C57BL/6 J mice. A/J mice showed a bi-phasic survival pattern, which seemed to be associated with two waves of high parasitemia, but developed only moderate anemia. C57BL/6 J mice controlled parasitemia well but developed severe anemia in the late stage of infection.

Responses of bovine chimaeras combining trypanosomosis resistant and susceptible genotypes to experimental infection with Trypanosoma congolense

West African N'Dama cattle have developed a genetic capacity to survive, reproduce and remain productive under trypanosomosis risk. The cellular and molecular bases of this so-called trypanotolerance are not known, but the trait is manifested by the N'Dama's greater capacity to control parasitaemia and anaemia development during an infection. In order to examine the role of the haematopoietic system in trypanotolerance, we have exploited the tendency for the placentas of bovine twin embryos to fuse. Placental fusion in cattle results in bone marrow chimaerism in twins. By comparison with the N'Dama, cattle of the East African Boran breed are relatively susceptible. We evaluated the role of the haemopoietic system in trypanotolerance by comparing the performance of five Chimaeric Boran/N'Dama twin calves with that of singletons of the two breeds. Chimaeric Boran/N'Dama pairs of twins were produced in recipient Boran cows by embryo transfer, and the majority of haemopoietic cells in all twinned individuals were of Boran origin. Thus, N'Dama chimaeras differed from N'Dama singletons in that the bulk of their haemopoietic system was derived from their susceptible Boran twins, while Boran chimaeras differed little from Boran control animals. All cattle became parasitaemic and developed anaemia. The N'Dama chimaeras did not manage their anaemia and white blood cell counts effectively. However, they were able to limit parasitaemia development. These results suggest that trypanotolerance is the result of two mechanisms, one that improves parasite control and is independent of the genetic origin of the haemopoietic tissue, and another that is influenced by haemopoietic tissue genotype and which improves control over anaemia. The capacity to maintain growth during infection was similarly dependent on the genetic origin of the haemopoietic tissue.