Induction of CD4+CD8+ double positive T cells and increase in CD5+ B cells in efferent lymph in sheep infected with Trypanosoma evansi

Enterovirus E infects bovine peripheral blood mononuclear cells. Implications for pathogenesis?

Introduction

Enterovirus E (EV-E) is a common viral pathogen endemic in cattle worldwide. Little is known, however, about its potential interactions with bovine immune cells.

Material and Methods

The EV-E-permissiveness of bovine peripheral blood mononuclear cells (PBMCs) was evaluated. The infectious titres of extracellular virus were measured and the intracellular viral RNA levels were determined by reverse transcription quantitative PCR after cell inoculation. The effects of EV-E on cell viability and proliferative response were investigated with a methyl thiazolyl tetrazolium bromide reduction assay, the percentages of main lymphocyte subsets and oxidative burst activity of blood phagocytes were determined with flow cytometry, and pro-inflammatory cytokine secretion was measured with an ELISA.

Results

Enterovirus E productively infected bovine PBMCs. The highest infectious dose of EV-E decreased cell viability and T-cell proliferation. All of the tested doses of virus inhibited the proliferation of high responding to lipopolysaccharide B cells and stimulated the secretion of interleukin 1β, interleukin 6 and tumour necrosis factor α pro-inflammatory cytokines.

Conclusion

Interactions of EV-E with bovine immune cells may indicate potential evasion mechanisms of the virus. There is also a risk that an infection with this virus can predispose the organism to secondary infections, especially bacterial ones.

Low Dose Gamma Irradiation of Trypanosoma evansi Parasites Identifies Molecular Changes That Occur to Repair Radiation Damage and Gene Transcripts That May Be Involved in Establishing Disease in Mice Post-Irradiation

The protozoan parasite Trypanosoma evansi is responsible for causing surra in a variety of mammalian hosts and is spread by many vectors over a wide geographical area making it an ideal target for irradiation as a tool to study the initial events that occur during infection. Parasites irradiated at the representative doses 100Gy, 140Gy, and 200Gy were used to inoculate BALB/c mice revealing that parasites irradiated at 200Gy were unable to establish disease in all mice. Cytokine analysis of mice inoculated with 200Gy of irradiated parasites showed significantly lower levels of interleukins when compared to mice inoculated with non-irradiated and 100Gy irradiated parasites. Irradiation also differentially affected the abundance of gene transcripts in a dose-dependent trend measured at 6- and 20-hours post-irradiation with 234, 325, and 484 gene transcripts affected 6 hours post-irradiation for 100Gy-, 140Gy- and 200Gy-irradiated parasites, respectively. At 20 hours post-irradiation, 422, 381, and 457 gene transcripts were affected by irradiation at 100Gy, 140Gy, and 200Gy, respectively. A gene ontology (GO) term analysis was carried out for the three representative doses at 6 hours and 20 hours post-irradiation revealing different processes occurring at 20 hours when compared to 6 hours for 100Gy irradiation. The top ten most significant processes had a negative Z score. These processes fall in significance at 140Gy and even further at 200Gy, revealing that they were least likely to occur at 200Gy, and thus may have been responsible for infection in mice by 100Gy and 140Gy irradiated parasites. When looking at 100Gy irradiated parasites 20 hours post-irradiation processes with a positive Z score, we identified genes that were involved in multiple processes and compared their fold change values at 6 hours and 20 hours. We present these genes as possibly necessary for repair from irradiation damage at 6 hours and suggestive of being involved in the establishment of disease in mice at 20 hours post-irradiation. A potential strategy using this information to develop a whole parasite vaccine is also postulated.

Single-cell transcriptome profiling and the use of AID deficient mice reveal that B cell activation combined with antibody class switch recombination and somatic hypermutation do not benefit the control of experimental trypanosomosis

Salivarian trypanosomes are extracellular protozoan parasites causing infections in a wide range of mammalian hosts, with Trypanosoma evansi having the widest geographic distribution, reaching territories far outside Africa and occasionally even Europe. Besides causing the animal diseases, T. evansi can cause atypical Human Trypanosomosis. The success of this parasite is attributed to its capacity to evade and disable the mammalian defense response. To unravel the latter, we applied here for the first time a scRNA-seq analysis on splenocytes from trypanosome infected mice, at two time points during infection, i.e. just after control of the first parasitemia peak (day 14) and a late chronic time point during infection (day 42). This analysis was combined with flow cytometry and ELISA, revealing that T. evansi induces prompt activation of splenic IgM⁺CD1d⁺ Marginal Zone and IgM^IntIgD⁺ Follicular B cells, coinciding with an increase in plasma IgG2c Ab levels. Despite the absence of follicles, a rapid accumulation of Aicda⁺ GC-like B cells followed first parasitemia peak clearance, accompanied by the occurrence of Xbp1⁺ expressing CD138⁺ plasma B cells and Tbx21⁺ atypical CD11c⁺ memory B cells. Ablation of immature CD93⁺ bone marrow and Vpreb3⁺Ly6d⁺Ighm⁺ expressing transitional spleen B cells prevented mature peripheral B cell replenishment. Interestingly, AID^-/- mice that lack the capacity to mount anti-parasite IgG responses, exhibited a superior defense level against T. evansi infections. Here, elevated natural IgMs were able to exert in vivo and in vitro trypanocidal activity. Hence, we conclude that in immune competent mice, trypanosomosis associated B cell activation and switched IgG production is rapidly induced by T. evansi, facilitating an escape from the detrimental natural IgM killing activity, and resulting in increased host susceptibility. This unique role of IgM and its anti-trypanosome activity are discussed in the context of the dilemma this causes for the future development of anti-trypanosome vaccines.

Trypanosoma evansi parasites can infect mammals, occasionally also humans, by evading the humoral immune response. In this study, cellular and transcriptomic profiling reveals that T. evansi induces rapid activation of mature splenic B cells, followed by differentiation into Aicda⁺ GC-like B cells, Tbx21⁺ atypical memory B cells and Sdc1⁺Xbp1⁺ plasma B cells. The process triggers early-stage Ighg2c expression in Follicular B cells. Simultaneous ablation of the bone marrow early B cell lineage prevents B cell replenishment, causing loss of the host’s parasitemia control capacity. Surprisingly, AID^-/- mice lacking anti-parasite IgGs, exhibit a superior defense level against T. evansi infections, with elevated natural IgMs being able to exert trypanocidal activity. Hence, we conclude that in immune competent mice, trypanosomosis associated B cell Aicda activation and IgG2c production is rapidly induced by T. evansi in order to evade natural IgM mediated killing, resulting in increased host susceptibility.

Trypanosoma evansi and surra: a review and perspectives on origin, history, distribution, taxonomy, morphology, hosts, and pathogenic effects

Trypanosoma evansi, the agent of "surra," is a salivarian trypanosome, originating from Africa. It is thought to derive from Trypanosoma brucei by deletion of the maxicircle kinetoplastic DNA (genetic material required for cyclical development in tsetse flies). It is mostly mechanically transmitted by tabanids and stomoxes, initially to camels, in sub-Saharan area. The disease spread from North Africa towards the Middle East, Turkey, India, up to 53° North in Russia, across all South-East Asia, down to Indonesia and the Philippines, and it was also introduced by the conquistadores into Latin America. It can affect a very large range of domestic and wild hosts including camelids, equines, cattle, buffaloes, sheep, goats, pigs, dogs and other carnivores, deer, gazelles, and elephants. It found a new large range of wild and domestic hosts in Latin America, including reservoirs (capybaras) and biological vectors (vampire bats). Surra is a major disease in camels, equines, and dogs, in which it can often be fatal in the absence of treatment, and exhibits nonspecific clinical signs (anaemia, loss of weight, abortion, and death), which are variable from one host and one place to another; however, its immunosuppressive effects interfering with intercurrent diseases or vaccination campaigns might be its most significant and questionable aspect.

Trypanosoma vivax infections: pushing ahead with mouse models for the study of Nagana. II. Immunobiological dysfunctions

Trypanosoma vivax is the main species involved in trypanosomosis, but very little is known about the immunobiology of the infective process caused by this parasite. Recently we undertook to further characterize the main parasitological, haematological and pathological characteristics of mouse models of T. vivax infection and noted severe anemia and thrombocytopenia coincident with rising parasitemia. To gain more insight into the organism's immunobiology, we studied lymphocyte populations in central (bone marrow) and peripherical (spleen and blood) tissues following mouse infection with T. vivax and showed that the immune system apparatus is affected both quantitatively and qualitatively. More precisely, after an initial increase that primarily involves CD4⁺ T cells and macrophages, the number of splenic B cells decreases in a step-wise manner. Our results show that while infection triggers the activation and proliferation of Hematopoietic Stem Cells, Granulocyte-Monocyte, Common Myeloid and Megacaryocyte Erythrocyte progenitors decrease in number in the course of the infection. An in-depth analysis of B-cell progenitors also indicated that maturation of pro-B into pre-B precursors seems to be compromised. This interferes with the mature B cell dynamics and renewal in the periphery. Altogether, our results show that T. vivax induces profound immunological alterations in myeloid and lymphoid progenitors which may prevent adequate control of T. vivax trypanosomosis.

Trypanosoma vivax is responsible for animal trypanosomosis, or Nagana, in cattle and small ruminants. Under experimental conditions, the outbred mouse model infected with a well studied West African T. vivax isolate reproduces the main characteristics of the infection and pathology observed in livestock. Anemia and non-specific (parasite-directed) polyclonal hypergammaglobulinemia are the most common disorders coincident with the rise in parasitemia. Our results presented here show that the decrease in peripheral B cell populations does not seem to be compensated by newly arriving B cells from the bone marrow. The infection nevertheless prompts intense production of stem cells that mature into myeloid and lymphoid precursors. In spite of this, B cell numbers are specifically reduced in the periphery as the infection progresses. Thus, negative feedback seems to be set in motion by the infection in the bone marrow, more precisely affecting the maturation of B precursors and consequently the output of mature B cells. The origin of these phenomena is unclear but this doubtless creates a homeostatic imbalance that contributes to the inefficient immune response against T. vivax infection.

Immune responses to haemorrhagic septicaemia (HS) vaccination in Trypanosoma evansi infected buffalo-calves

To assess the immunosuppressive effect of Trypanosoma evansi infection in buffalo-calves on immune responses to heterologous antigen, the study was planned to examine the responses of haemorrhagic septicaemia vaccination in simultaneously and previously (80 days before vaccination) T. evansi-infected buffalo-calves. Eight buffalo-calves were divided into three groups. Buffalo-calves of group A (n = 3) were previously (80 days before primary vaccination with haemorrhagic septicaemia [HS] vaccine) infected with T. evansi (1 x 10(7) tryps.calf(-1); sc) and that of group B (n = 3) were infected with T. evansi (1 x 10(7) tryps.calf(-1); sc) on the day of primary vaccination with HS vaccine. Two healthy uninfected control calves given only HS vaccine were kept in group C. All the buffalo-calves were given a booster dose of vaccine 21 days post-primary vaccination (PPV). Twenty eight days PPV, animals of group A were given trypanocidal quinapyramine prosalt at 6.66 mg kg(-1). Immunosuppressive effect of T. evansi infection was evident from day 7 PPV with HS vaccine. The effect was more pronounced in previously T. evansi-infected buffalo-calves as compared with simultaneously infected buffalo-calves. Group A buffalo-calves appeared to have recovered from the immunosuppressive effect after 28 days post-trypanocidal treatment as observed by humoral and cell-mediated immune responses. Immunosuppressive effect to HS vaccination was observed in T. evansi-infected buffalo-calves, and trypanocidal therapy enabled the calves to mount the responses similar to uninfected controls.

Trypanosome microtubule-associated protein p15 as a vaccine for the prevention of African sleeping sickness

Trypanosomes cause African sleeping sickness, affecting millions of humans and animals. We tested trypanosome microtubule-associate protein (MAP p15) as a vaccine in mice, and show that p15 (native or recombinant) generated up to 100% protection from an otherwise lethal challenge of a heterologous strain of Trypanosoma brucei. We also tested the adenovirus as a vaccine delivery system and show that both adenoviral vector containing p15 gene or control adenovirus containing lacZ gene generated a protective response and exhibited strong CD8+ T-cell proliferation. These results suggest that the p15 protein itself is an effective vaccine and that the adenovirus may be used to mount a non-specific cellular immune response.

Mucosal memory--maintenance and recruitment

The maintenance of IgA antibody responses at mucosal surfaces is the outcome of influences on IgA precursor cell dissemination from the mucosal inductive sites, such as the intestinal Peyer's patches, their selective extravasation at mucosal effector sites and the retention and local proliferation of these cell populations under local influences. Examination of these local post-extravasational effects has implicated cytokines as major regulatory elements in this process. This paper will address the role of cytokines in induction and expression of IgA responses and the differential requirements for cytokine signals among IgA-committed B cell subsets in both rodent and domestic livestock species. The way in which cytokines influence local immunity in the gut with respect to microbial and parasitic challenge and comparative cytokine effects in extra-intestinal sites, particularly the eye, will be presented, and opportunities for therapeutic interventions to modify cytokine expression will be discussed.

Histopathology of Trypanosoma (Trypanozoon) evansi infection in bandicoot rat. I. visceral organs

Experimental infection of Trypanosoma (Trypanozoon) evansi in Bandicota bengalensis produces an acute disease course leading to untimely death of the bandicoot rat. The sequential alteration of liver, spleen, lung, kidney, and heart was studied on the 5th, 8th, 12th, and 14th days postinoculation. The rats showed inflammatory, degenerative, and necrotic changes in these organs. In liver, pseudolobule formation, necrosis and hemorrhage within the sinusoids, and fatty degeneration of hepatic cells were the predominant histopathological changes. The changes were destructive and irreversible. In spleen giant cells aggregation and granulomatous lesion, i.e., accumulation of histiocytes, were the protective changes, whereas tissue and cell damage indicated irreversible degeneration. The gradual development of intrabronchus inflammation, aggregation of inflammatory cells around the alveoli, congestion of bronchioles, septal edema, atrophy of alveolar walls, migration of macrophages, and emphysema were the histopathological changes noticed in the lungs of the infected rats. The affected kidney showed infiltration of lymphocytes, hemorrhage in the interlobular space, and glomerulitis as the irreversible and destructive changes in the rats. There was degeneration of myocardium in the hearts of the rats. The histopathological changes in these organs are compared with those studied in surra, human sleeping sickness disease, and African trypanosomiasis. Possible mechanisms for these histological changes in the visceral organs are discussed.

Effects of the depletion of CD8(+) T cells and monocytes on the proliferative responses of peripheral blood leucocytes from Trypanosoma evansi-infected sheep

Sheep peripheral blood mononuclear cells and those depleted of CD8(+) T cells and/or monocytes were stimulated with polyclonal mitogens and specific antigens, and analysed by means of cell proliferation assay procedure to examine whether these cell populations are involved in Trypanosoma evansi-induced immunosuppression. The removal of CD8(+) T cells failed to normalize the proliferative responses of peripheral blood mononuclear cells from infected sheep to concanavalin A stimulation while the depletion of monocytes resulted in full and enhanced response, showing that macrophages are mainly responsible for the suppression. Although the depletion of CD8(+) T cells, monocytes or both restored the responses of the cells to lipopolysaccharide stimulation, the responsiveness of the undepleted cells to this mitogen was significantly higher from day 24 post infection (p<0.01). The results were discussed in relation to current known mechanisms of depressed lymphocyte proliferation in tsetse-transmitted African trypanosome infections.