Trypanosoma congolense infection in sheep: cellular phenotypes in lymph and lymph nodes associated with skin reactions

Immunohistochemical phenotyping of macrophages and T lymphocytes infiltrating in peripheral nerve lesions of dourine-affected horses

Dourine is a deadly protozoan disease in equids caused by infection with Trypanosoma equiperdum. Neurological signs in the later stage of infection may be caused by peripheral polyneuritis and related axonal degeneration. This neuritis involves T lymphocytes, B lymphocytes, and macrophages, and is observed in cases without obvious neurological signs. However, the pathogenesis of neuritis remains unclear. We identified M2 macrophages and CD8 T cells as the predominant phenotypes in neuritis of dourine-affected horses with or without neurological signs. In contrast, the populations of M1 macrophages and CD4 T cells were small. This result indicates that inflammation was chronic and suggests that dourine-associated neuritis occurs at the early stage of infection.

An Overview of Trypanosoma brucei Infections: An Intense Host-Parasite Interaction

Trypanosoma brucei rhodesiense and T. brucei gambiense, the causative agents of Human African Trypanosomiasis, are transmitted by tsetse flies. Within the vector, the parasite undergoes through transformations that prepares it to infect the human host. Sequentially these developmental stages are the replicative procyclic (in which the parasite surface is covered by procyclins) and trypo-epimastigote forms, as well as the non-replicative, infective, metacyclic form that develops in the vector salivary glands. As a pre-adaptation to their life in humans, metacyclic parasites begin to express and be densely covered by the Variant Surface Glycoprotein (VSG). Once the metacyclic form invades the human host the parasite develops into the bloodstream form. Herein the VSG triggers a humoral immune response. To avoid this humoral response, and essential for survival while in the bloodstream, the parasite changes its cover periodically and sheds into the surroundings the expressed VSG, thus evading the consequences of the immune system activation. Additionally, tools comparable to quorum sensing are used by the parasite for the successful parasite transmission from human to insect. On the other hand, the human host promotes clearance of the parasite triggering innate and adaptive immune responses and stimulating cytokine and chemokine secretion. All in all, the host–parasite interaction is extremely active and leads to responses that need multiple control sites to develop appropriately.

Immunology and immunopathology of African trypanosomiasis

Major modifications of immune system have been observed in African trypanosomiasis. These immune reactions do not lead to protection and are also involved in immunopathology disorders. The major surface component (variable surface glycoprotein,VSG) is associated with escape to immune reactions, cytokine network dysfunctions and autoantibody production. Most of our knowledge result from experimental trypanosomiasis. Innate resistance elements have been characterised. In infected mice, VSG preferentially stimulates a Th 1-cell subset. A response of <FONT FACE=Symbol>gd</FONT> and CD8 T cells to trypanosome antigens was observed in trypanotolerant cattle. An increase in CD5 B cells, responsible for most serum IgM and production of autoantibodies has been noted in infected cattle. Macrophages play important roles in trypanosomiasis, in synergy with antibodies (phagocytosis) and by secreting various molecules (radicals, cytokines, prostaglandins,...). Trypanosomes are highly sensitive to TNF-alpha, reactive oxygen and nitrogen intermediates. TNF-alpha is also involved in cachexia. IFN-gamma acts as a parasite growth factor. These various elements contribute to immunosuppression. Trypanosomes have learnt to use immune mechanisms to its own profit. Recent data show the importance of alternative macrophage activation, including arginase induction. L-ornithine produced by host arginase is essential to parasite growth. All these data reflect the deep insight into the immune system realised by trypanosomes and might suggest interference therapeutic approaches.

Local skin reaction (chancre) induced following inoculation of metacyclic trypanosomes in cattle by tsetse flies is dependent on CD4 T lymphocytes

The first visible response in livestock to the bite of a trypanosome-infected tsetse fly is the formation of a localized skin reaction, also known as a chancre. This is an inflammatory response in the skin associated with swelling and an influx of cells. It is thought to be associated with an acquired immune response to the injected metacyclic trypanosomes. In this study, we examined the role of T lymphocytes in the development of the inflammatory response, by depleting cattle of T cell subpopulations and monitoring the development of chancres. Depletion of CD4 cells, but not CD8 cells, resulted in a significant reduction in chancre formation, confirming that an acquired response mediates the inflammatory response. In addition, it was established that the CD4 T cells mediate the generation of memory for immunity to a homologueous re-challenge. The inflammatory response in the skin did not affect further progress of the infection.

Distribution of Trypanosoma congolense in infected multimammate rats (Mastomys coucha): light and electron microscopical studies

In an attempt to determine whether Trypanosoma congolense occurs both within and outside the blood vessels in an infected animal host, multimammate rats (Mastomys coucha) were infected with T. congolense and samples from spleen, lymph nodes, bone marrow, liver, kidney, lungs, brain, heart, intestines, ovaries and testes were collected. The tissue samples were fixed and processed for light and electron microscopical examination. In all the tissues examined, trypanosomes were found only within the lumen of large and small blood vessels, capillaries and sinuses. It is concluded that following entry into the blood circulation after intra-peritoneal infection of M. coucha, T. congolense remains restricted to the bloodstream.

Proliferative responses of peripheral blood leucocytes of sheep infected with Trypanosoma evansi

The effects of Trypanosoma evansi on the proliferative responses of ovine peripheral blood leucocytes (PBL) were examined in in vitro cell culture systems. Sheep were vaccinated against pneumonic pasteurellosis with a monovalent Pasteurella haemolytica vaccine and then infected with T. evansi TREU 2143. From 1 week post-infection (p.i.), the PBL were separated and stimulated in cultures with either Concanavalin A (Con A), bacterial lipopolysaccharide (LPS), pasteurella antigen (P.ag), or homologous trypanosome antigen (T.ag). The proliferative responses of the cells to Con A and LPS were significantly (P < 0.001) suppressed by the infection. This suppression was associated with active infection, as treatment of the sheep with a trypanocide restored the proliferative ability of the cells to both mitogens. Similarly, active infection significantly (P < 0.001) suppressed specific responses to P.ag and T.ag but although treatment resulted in full specific proliferative responsiveness to the homologous trypanosome antigen, the same was not true of P.ag, in which the responsiveness of cells from uninfected vaccinated sheep to it were still significantly higher (P < 0.001) than those of cells from infected sheep.

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

The effects of Trypanosoma evansi on efferent lymphocyte phenotypes draining from a lymph node primed with Pasteurella haemolytica vaccine were studied in sheep. The prefemoral efferent lymphatic ducts of the infected sheep along with those of two uninfected sheep were surgically cannulated. Lymph was collected and lymphocytes recovered from it analysed by two-colour indirect immunofluorescence staining and cytofluoremetry in a fluorescence activated cell analyser (FACSCAN). The study showed the appearance and persistence of T. evansi in the efferent lymph for a long period of time and the appearance of CD4+CD8+ (double positive, DP) T lymphocytes in the efferent lymph of infected animals. The infection also resulted in increases in CD5+ B cells in the prefemoral efferent lymph. In addition, there were decreases in the output of conventional B cells, CD5+ and CD4+ T cell subsets but large increases in CD8+ cells followed by terminal depletion of all cell subsets. In contrast, inoculation of sheep with pasteurella vaccine antigen alone produced little alterations in the proportions, but large increases in the numbers of all T cell subsets except that of CD8+ cells which also showed little variation; and there was a concurrent increase in the numbers and proportions of efferent B cells. In addition, the abnormal expression of DP and CD5+ B cells did not occur in the uninfected vaccinated sheep. It is concluded that these abnormal changes in the kinetics of efferent lymphocyte phenotypes are likely to play a role in the genesis of the generalized immunosuppression seen in trypanosome-infected hosts.

Effects of Trypanosoma evansi on the output of cells from a lymph node draining the site of Pasteurella haemolytica vaccine administration

The prefemoral efferent lymphatics of sheep infected with Trypanosoma evansi and inoculated with P. haemolytica vaccine and of those given only the vaccine, were surgically cannulated to study the effects of the infection on the total cellular output and output of blast cells from the node in response to the vaccine. T. evansi delayed and depressed the increases in total cell and lymphoblast outputs. In uninfected sheep, the total cellular output increased and peaked at more than twice the prevaccination values on days 4 and 5 after primary vaccination, but the increases were smaller and peaked on days 6 and 8 after primary vaccination in the infected sheep. The output of lymphoblasts mirrored the total cell output, though it was suppressed to a greater degree by T. evansi. The output of blasts peaked at more than 8 and 14 times the prevaccination values in the uninfected animals after primary and secondary (booster) vaccinations, respectively; but in infected animals, it peaked at twice the prevaccination values after the primary vaccination and showed no increase after booster vaccination until 11 days later. It is concluded that the inhibition of total and blast cell outputs by T. evansi may limit the early systemic dissemination of antigen-specific cells, thus playing a role in the induction of immunosuppression by the parasite.