The liver as a major site of immunological elimination of murine trypanosome infection, demonstrated with the liver perfusion model

Trypanosoma brucei infection protects mice against malaria

Sleeping sickness and malaria are parasitic diseases with overlapping geographical distributions in sub-Saharan Africa. We hypothesized that the immune response elicited by an infection with Trypanosoma brucei, the etiological agent of sleeping sickness, would inhibit a subsequent infection by Plasmodium, the malaria parasite, decreasing the severity of its associated pathology. To investigate this, we established a new co-infection model in which mice were initially infected with T. brucei, followed by administration of P. berghei sporozoites. We observed that a primary infection by T. brucei significantly attenuates a subsequent infection by the malaria parasite, protecting mice from experimental cerebral malaria and prolonging host survival. We further observed that an ongoing T. brucei infection leads to an accumulation of lymphocyte-derived IFN-γ in the liver, limiting the establishment of a subsequent hepatic infection by P. berghei sporozoites. Thus, we identified a novel host-mediated interaction between two parasitic infections, which may be epidemiologically relevant in regions of Trypanosoma/Plasmodium co-endemicity.

Despite the geographical overlap between the parasites that cause sleeping sickness and malaria, the reciprocal impact of a co-infection by T. brucei and Plasmodium had hitherto not been assessed. We hypothesized that the strong immune response elicited by a T. brucei infection could potentially limit the ability of Plasmodium parasites to infect the same host. In this study, we showed that a primary infection by T. brucei significantly attenuates a subsequent infection by the malaria parasite. Importantly, a significant proportion of the co-infected mice do not develop Plasmodium parasitemia, and those few that do, do not display symptoms of severe malaria and survive longer than their singly infected counterparts. We further showed that the prevention or delay in appearance of malaria parasites in the blood results from a dramatic impairment of the preceding liver infection by Plasmodium, which is mediated by the strong immune response mounted against the primary T. brucei infection. Our study provides new insights for a novel inter-pathogen interaction that may bear great epidemiological significance in regions of Trypanosoma/Plasmodium co-endemicity.

Trypanosoma brucei brucei: A comparison of gene expression in the liver and spleen of infected mice utilizing cDNA microarray technology

Trypanosoma brucei brucei, the infectious agent of the disease known as Nagana, is a pathogenic trypanosome occurring in Africa, where it causes significant economic loss to domesticated livestock. Although many studies on the histopathology of organs of mice infected with T. b. brucei have been reported, little work has been done regarding gene expression in these organs in infected mice. In this paper, we describe the use of cDNA microarray to determine gene expression profiles in the liver and spleen of mice infected with T. b. brucei (STIB 920) at peak parasitaemia (12 days after infection). Our results showed that a total of 123 genes in the liver and 389 genes in the spleen were expressed differentially in T. b. brucei infected mice. In contrast, however, in an acute infection in mice caused by Trypanosoma brucei evansi, a species genetically related to T. b. brucei, 336 genes in the liver and 190 genes in the spleen were expressed, differentially, indicating that the liver of mice was more affected by the acute T. b. evansi infection whilst the spleen was more affected by the subacute T. b. brucei infection. Our results provide a number of possible reasons why mice infected with T. b. evansi die sooner than those infected with T. b. brucei: (1) mice infected with T. b. evansi may need more stress response proteins to help them pass through the infection and these are probably excessively consumed; (2) proliferating cell nuclear antigen was more down-regulated in the liver of mice infected with T. b. evansi, which indicated that the inhibition of proliferation of hepatocytes in mice infected with T. b. evansi might be more severe than that in T. b. brucei infection; and (3) more hepatocyte apoptosis occurred in the mice infected with T. b. evansi and this might be probably the most important reason why mice died sooner than those infected with T. b. brucei. Studies of the changes in the gene expression profile in the liver and spleen of mice infected with T. b. brucei may be helpful in understanding the mechanisms of pathogenesis in Nagana disease at the molecular level. By comparing the gene profiles of the liver and spleen of mice infected with T. b. brucei with T. b. evansi, we have identified a number of factors that could explain the differences in pathogenesis in mice infected with these two African trypanosomes.

Analysis of gene expression profiles in the liver and spleen of mice infected with Trypanosoma evansi by using a cDNA microarray

Trypanosoma evansi, the cause of the disease Surra in livestock, is the most widely geographically distributed pathogenic trypanosome occurring in Africa, South and Central America, and Asia, where it causes significant economic loss. Although many studies have described the histopathology induced in the organs of mice infected with T. evansi, few studies have been conducted on gene expression in these organs. Here we used complementary DNA microarray to analyze the gene expression profiles in the liver and spleen of mice infected with T. evansi (STIB 806) at the peak parasitemia (7 days after infection). A total of 14,000 sequences including full length and partial complementary DNAs representing novel, known, and control genes of mouse were analyzed. Results from GeneOntology annotation showed that 158 genes in the liver and 73 genes in the spleen were up-regulated in the infected mice and that 178 genes in the liver and 117 genes in the spleen of infected mice were down-regulated compared with control (non-infected) mice. Most of these genes are metabolism, transport, protein biosynthesis, transcription factors, and nucleic acid binding protein-related genes. The changes of some important genes, such as heat shock protein 70 and proliferating cell nuclear antigen, were confirmed by quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. TdT-mediated dUTP-digoxigenin nick end labeling analysis results revealed that extensive apoptosis occurred in the liver of infected mice at the peak of parasitemia. Our results provide a comprehensive profile of changes in gene expression in the liver and spleen of mice infected with T. evansi and may be helpful in understanding the pathogenesis of Surra at a molecular level.

Rodent trypanosomes: their conflict with the immune system of the host

Rodent trypanosome infections provide the opportunity to study major phenomena that are displayed in many parasite-host combinations and, therefore, the chance to contribute to the elucidation of those phenomena. Here, Julia and Joseph Albright focus on the immune responses to rodent trypanosomes and on the tricks the parasites play to minimize the effects of those responses.

Comparative analysis of antibody responses against HSP60, invariant surface glycoprotein 70, and variant surface glycoprotein reveals a complex antigen-specific pattern of immunoglobulin isotype switching during infection by Trypanosoma brucei

During Trypanosoma brucei infections, the response against the variant surface glycoprotein (VSG) of the parasite represents a major interaction between the mammalian host immune system and the parasite surface. Since immune recognition of other parasite derived factors also occurs, we examined the humoral host response against trypanosome heat shock protein 60 (HSP60), a conserved antigen with an autoimmune character. During experimental T. brucei infection in BALB/c mice, the anti-HSP60 response was induced when parasites differentiated into stumpy forms. This response was characterized by a stage-specific immunoglobulin isotype switching as well as by the induction of an autoimmune response. Specific recognition of trypanosome HSP60 was found to occur during the entire course of infection. Immunoglobulin G2a (IgG2a) and IgG2b antibodies, induced mainly in a T-cell-independent manner, were observed during the first peak of parasitemia, whereas IgG1 and IgG3 antibodies were found at the end of the infection, due to a specific T-cell-mediated response. Comparative analysis of the kinetics of anti-HSP60, anti-invariant surface glycoprotein 70 (ISG70), and anti-VSG antibody responses indicated that the three trypanosome antigens give rise to specific and independent patterns of immunoglobulin isotype switching.

Trypanosoma musculi: tracking parasites and circulating lymphoid cells in host mice

Two aspects of host-parasite relationships that seem worthy of more attention are: (a) the distribution of parasites among host organs in the early course of infection, and (b) the dynamics of host lymphocyte tissue localization and recirculation during the course of infection. We have employed the derivatized aminostyrylpyridinium dye, [125I] I 2P-Di-6-ASP, to provide a relatively stable tag on both a parasite, Trypanosoma musculi, and on host mouse splenocytes, enriched B and T lymphocytes, and natural killer cells. The organ distribution of the parasites, splenocytes, and lymphocytes in recipient, host mice was tracked. Radiolabeled T. musculi localized primarily in the liver with lesser numbers in spleen, lungs, and kidneys. Per unit wet weight, the spleen accumulated parasites most efficiently. When T. musculi were inoculated intraperitoneally, most of them remained in the peritoneal space and the numbers that gained access to liver, lungs, and spleen were significantly smaller than in mice inoculated intravenously. The acquisition of parasites by the spleen (and lungs) of mice with an existing T. musculi infection was markedly inhibited. This was true also of syngeneic splenocytes and lymphocytes. In addition, lymphocytes from infected mice were significantly less likely to take residence in the spleens of normal recipient mice and were especially unlikely to localize in the spleens of infected recipients. These and other findings suggested that the inability of circulating lymphocytes to gain access to lymphoid tissues in infected mice, coupled with the poor ability of those tissues to sequester parasite antigens, could account for the known prolonged delay in the development of curative antibody response characteristic of T. musculi-infected mice. It is likely that the marked disruption of lymphoid tissue histoarchitecture that is typical of T. musculi infection contributes significantly to the failure of the tissues to sequester parasites and lymphocytes. Because lymphoid tissue disruption is seen in many parasitic infections, the findings reported here may have fairly broad relevance. In any case, the procedure described here for labeling parasites and lymphocytes should be of general utility for tracking their disposition in vivo.

Distribution of free and liposome-encapsulated cefoxitin in experimental intra-abdominal sepsis in rats

The distributions of radiolabelled free cefoxitin (FC) and liposome-encapsulated cefoxitin (LC) were compared in an animal model of intra-abdominal sepsis. Intraperitoneally administered LC was initially retained in the peritoneal cavity with subsequent preferential drug targeting to the liver (14% injected LC) and spleen (6% injected LC) by 3 h post-injection. Differing patterns of liposomal drug and lipid retention indicated that drug release from the liposome complex occurred within the peritoneum, liver and spleen. Intraperitoneal FC was rapidly taken up into the systemic circulation, with peak recovery in the blood (9% injected FC) and liver (5% injected FC) at 1 h post-injection. FC was also rapidly eliminated; 7% of the injected drug was recovered in the kidney 1 h post-injection. A negligible amount of FC was recovered in the spleen and very little FC or LC was found in the lungs of treated animals. Unlike FC, LC was found to provide a sustained bactericidal drug level (> 40 micrograms mL-1) in the peritoneal fluid for up to 5 h post-injection. LC also achieved significantly higher drug levels, compared with FC, within the liver at 3 and 5 h post-injection. Since severe intra-abdominal sepsis is often characterized by the presence of intraphagocytic bacteria in hepatic and splenic reticuloendothelial systems, the enhanced delivery of liposome-encapsulated anti-microbial agents, such as cefoxitin, to the liver and spleen may provide a more effective treatment for the septic condition.