Maintenance of B cells during chronic murine Trypanosoma brucei gambiense infection.

African trypanosomosis is a debilitating parasitic disease occurring in large parts of sub-Saharan Africa. Trypanosoma brucei gambiense accounts for 98% of the reported HAT infections and causes a chronic, gradually progressing disease. Multiple experimental murine models for trypanosomosis have demonstrated inflammation-dependent apoptosis of splenic follicular B (FoB) cells and the destruction of B-cell memory against previously encountered pathogens. Here, we report that during murine infection with a chronic T. b. gambiense field isolate, FoB cells are retained. This coincided with reduced levels of IFN-γ and TNF-α during the acute phase of the infection. This result suggests that in chronic infections with low virulent parasites, less inflammation is elicited and consequently no FoB cell destruction occurs.

In vivo characterization of two additional Leishmania donovani strains using the murine and hamster model.

Leishmania donovani is a protozoan parasite causing the neglected tropical disease visceral leishmaniasis. One difficulty to study the immunopathology upon L. donovani infection is the limited adaptability of the strains to experimental mammalian hosts. Our knowledge about L. donovani infections relies on a restricted number of East African strains (LV9, 1S). Isolated from patients in the 1960s, these strains were described extensively in mice and Syrian hamsters and have consequently become 'reference' laboratory strains. L. donovani strains from the Indian continent display distinct clinical features compared to East African strains. Some reports describing the in vivo immunopathology of strains from the Indian continent exist. This study comprises a comprehensive immunopathological characterization upon infection with two additional strains, the Ethiopian L. donovani L82 strain and the Nepalese L. donovani BPK282 strain in both Syrian hamsters and C57BL/6 mice. Parameters that include parasitaemia levels, weight loss, hepatosplenomegaly and alterations in cellular composition of the spleen and liver, showed that the L82 strain generated an overall more virulent infection compared to the BPK282 strain. Altogether, both L. donovani strains are suitable and interesting for subsequent in vivo investigation of visceral leishmaniasis in the Syrian hamster and the C57BL/6 mouse model.

IFN-γ mediates early B-cell loss in experimental African trypanosomosis.

African trypanosomes infect humans and animals throughout the African continent. These parasites maintain chronic infections by various immune evasion strategies. While antigenic variation of their surface coat is the most studied strategy linked to evading the host humoral response, African trypanosomes also induce impaired B-cell lymphopoiesis, the destruction of the splenic B-cell compartment and abrogation of protective memory responses. Here we investigate the mechanism of follicular B-cell destruction. We show that during infection follicular B cells undergo apoptosis, correlating to enhanced Fas death receptor surface expression. Investigation of various type 1 cytokine knockout mice indicates a crucial role of IFN-γ in the early onset of FoB cell destruction. Indeed, both IFN-γ(-/-) and IFN-γR(-/-) mice are protected from trypanosomosis-associated FoB cell depletion, exhibiting an inhibition of B-cell apoptosis as well as a reduced activation of FoB cells during the first week post-infection. The data presented herein offer new insights into B-cell dysfunctioning during experimental African trypanosome infections.

Curative drug treatment of trypanosomosis leads to the restoration of B-cell lymphopoiesis and splenic B-cell compartments.

African trypanosomosis is a parasitic disease affecting both humans (sleeping sickness) and animals (nagana). In murine trypanosomosis, the B-cell compartment is rapidly destroyed after infection. In addition, B-cell lymphopoiesis in the bone marrow is abrogated, B-cell subsets in the spleen are irreversibly depleted, and B-cell memory is destroyed. Here, we investigated the effect of cure of infection on the B-cell compartment. Suramin and diminazene aceturate were used in this study as these drugs exhibit different modes of uptake and different mechanisms of trypanocidal action. Curative drug treatment of trypanosomosis infection led to the re-initiation of B-cell lymphopoiesis in the bone marrow, and to the repopulation of splenic B-cell subsets, independent of the drug used. Neither of these drugs by itself induced measurable effects on B-cell lymphopoiesis in the bone marrow or B-cell homoeostasis in the spleen in healthy, naïve animals.

Antibody-mediated control of Trypanosoma vivax infection fails in the absence of tumour necrosis factor.

Trypanosoma vivax causes a wasting disease affecting livestock breeding and agriculture in developing countries of sub-Sahara Africa and South America. Being an extracellular parasite, control of T. vivax has been proposed to be mediated by host antibodies. However, the use of a comparative infection model of wild-type (WT) and tumour necrosis factor (TNF) knockout (TNF(-/-) ) mice shows that the latter is unable to control first-peak parasitaemia, despite the presence of specific antitrypanosome antibodies. In contrast, WT mice parasitaemia peak control coincides with a combined early onset of TNF production and induction of specific antibodies. TNF is mainly produced by liver-associated monocytes and neutrophils. In this study, no other correlation between cellular immunomodulations and peak parasitaemia control was observed, underscoring the importance of the role of TNF in the control of T. vivax infections.

Chronic Trypanosoma congolense infections in mice cause a sustained disruption of the B-cell homeostasis in the bone marrow and spleen.

Trypanosoma congolense is one of the main species responsible for Animal African Trypanosomosis (AAT). As preventive vaccination strategies for AAT have been unsuccessful so far, investigating the mechanisms underlying vaccine failure has to be prioritized. In T. brucei and T. vivax infections, recent studies revealed a rapid onset of destruction of the host B-cell compartment, resulting in the loss of memory recall capacity. To assess such effect in experimental T. congolense trypanosomosis, we performed infections with both the cloned Tc13 parasite, which is considered as a standard model system for T. congolense rodent infections and the noncloned TRT55 field isolate. These infections differ in their virulence level in the C57BL/6 mouse model for trypanosomosis. We show that early on, an irreversible depletion of all developmental B cells stages occur. Subsequently, in the spleen, a detrimental decrease in immature B cells is followed by a significant and permanent depletion of Marginal zone B cells and Follicular B cells. The severity of these events later on in infection correlated with the virulence level of the parasite stock. In line with this, it was observed that later-stage infection-induced IgGs were largely nonspecific, in particular in the more virulent TRT55 infection model.

Immunohistowax processing, a new fixation and embedding method for light microscopy, which preserves antigen immunoreactivity and morphological structures: visualisation of dendritic cells in peripheral organs.

AIMS: To describe a new fixation and embedding method for tissue samples, immunohistowax processing, which preserves both morphology and antigen immunoreactivity, and to use this technique to investigate the role of dendritic cells in the immune response in peripheral tissues. METHODS: This technique was used to stain a population of specialised antigen presenting cells (dendritic cells) that have the unique capacity to sensitise naive T cells, and therefore to induce primary immune responses. The numbers of dendritic cells in peripheral organs of mice either untreated or injected with live Escherichia coli were compared. RESULTS: Numbers of dendritic cells were greatly decreased in heart, kidney, and intestine after the inoculation of bacteria. The numbers of dendritic cells in the lung did not seem to be affected by the injection of E coli. However, staining of lung sections revealed that some monocyte like cells acquired morphological and phenotypic features of dendritic cells, and migrated into blood vessles. CONCLUSIONS: These observations suggest that the injection of bacteria induces the activation of dendritic cells in peripheral organs, where they play the role of sentinels, and/or their movement into lymphoid organs, where T cell priming is likely to occur.