concanavalin-a and Trypanosomiasis

It is well recognized that zinc is an essential trace element for all organisms, influencing growth and affecting the development and integrity of the immune system. It is also well known that the protective response against Trypanosoma cruzi depends on both innate and acquired immunity and for the control of the parasite load and host survival, the participation of special cells such natural killer (NK), T and B lymphocytes and macrophages are required. So the aims of this study were to evaluate the effects of zinc supplementation on the host's immune response infected with T. cruzi. Our data point in the direction that zinc supplementation triggered enhanced thymocyte and splenocyte proliferation as compared to unsupplied group of animals. It is also important to emphasize that interleukin-12 (IL-12) participates in the resistance to several intracellular pathogens including T. cruzi. Our findings demonstrate an enhanced production of IL-12 during the acute phase of infection in zinc-supplied groups. So we conclude that zinc supplementation leads to an effective host's immune response by up-modulating the host's immune response, thus contributing in the reduction of blood parasites and the harmful pathogenic effects of the experimental Chagas' disease.

Topics: Animals; Concanavalin A; Interleukin-12; Male; Parasitemia; Rats; Rats, Wistar; Spleen; Thymus Gland; Time Factors; Trypanosoma cruzi; Trypanosomiasis; Zinc

Antigen variation is a successful defense system adopted by several infectious agents to evade the host immune response. The principle of this defense strategy in the African trypanosome paradigm involves a dense packing of variant surface glycoproteins (VSG) exposing only highly variable and immuno-dominant epitopes to the immune system, whereas conserved epitopes become inaccessible for large molecules. Reducing the size of binders that target the conserved, less-immunogenic, cryptic VSG epitopes forms an obvious solution to combat these parasites. This goal was achieved by introducing dromedary Heavy-chain antibodies. We found that only these unique antibodies recognize epitopes common to multiple VSG classes. After phage display of their antigen-binding repertoire, we isolated a single domain antibody fragment with high specificity for the conserved Asn-linked carbohydrate of VSG. In sharp contrast to labeled concanavalin-A that stains only the flagellar pocket where carbohydrates are accessible because of less dense VSG packing, the single domain binder stains the entire surface of viable parasites, irrespective of the VSG type expressed. This corroborates the idea that small antibody fragments, but not larger lectins or conventional antibody fragments, are able to penetrate the dense VSG coat to target their epitope. The diagnostic potential of this fluorescently labeled binder was proven by the direct, selective, and sensitive detection of parasites in blood smears. The employment of this binder as a molecular recognition unit in immuno-toxins designed for trypanosomosis therapy becomes feasible as well. This was illustrated by the specific trypanolysis induced by an antibody::beta-lactamase fusion activating a prodrug.

Topics: Animals; Antigenic Variation; Antigens; Antigens, Protozoan; beta-Lactamases; Carbohydrates; Concanavalin A; Dose-Response Relationship, Drug; Enzyme-Linked Immunosorbent Assay; Epitopes; Flow Cytometry; Gene Library; Microscopy, Fluorescence; Peptide Library; Prodrugs; Protein Structure, Tertiary; Time Factors; Trypanosoma; Trypanosomiasis; Variant Surface Glycoproteins, Trypanosoma

Infections with African trypanosomes are known to suppress immune responses to vaccines and to gastrointestinal nematode infections in livestock. Experimental infections with Trypanosoma brucei (Tb) and the gastrointestinal nematode Nippostrongylus brasiliensis (Nb) in mice were used to identify possible mechanisms involved in interference with anti-worm responses and to examine the effects of host genotype on the extent of suppression seen. Concurrent infections with T. brucei resulted in a prolongation of worm survival and a dramatic increase in faecal egg output. Infection also resulted in a marked suppression of the proliferative response of mesenteric lymphocytes (MLNC) to in vitro mitogenic stimulation. When MLNC from concurrently infected mice were stimulated in vitro with the mitogen ConA they released more IFN-gamma and less IL-5 than cells from mice infected only with N. brasiliensis. These data are interpreted in terms of a trypanosome-mediated influence on the development of host-protective type-2 T helper cell responses against N. brasiliensis. The degree to which T. brucei altered the kinetics of the nematode infection was influenced by the particular mouse strain concerned.

Topics: Animals; Concanavalin A; Feces; Genotype; Host-Parasite Interactions; Interferon-gamma; Interleukin-5; Lymphocytes; Male; Mice; Mice, Inbred C57BL; Nippostrongylus; Parasite Egg Count; Strongylida Infections; Time Factors; Trypanosoma brucei brucei; Trypanosomiasis

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.

Topics: Animals; Antigens, Bacterial; Antigens, Protozoan; CD8-Positive T-Lymphocytes; Cell Division; Cells, Cultured; Concanavalin A; Lipopolysaccharides; Lymphocyte Activation; Monocytes; Sheep; Sheep Diseases; Trypanosomiasis

Mitogen stimulation of cells from various lymphoid organs of C3H/He mice chronically infected with an isolate of Trypanosoma congolense was studied at different time intervals after infection, using concanavalin A (Con A) and lipopolysaccharide (LPS). At the same time, changes in the percentages of T, B and null lymphocytes in these organs were determined by immunofluorescence staining. The responses of T and B lymphocytes in the spleen were totally depressed, and the cellular composition was drastically altered by day 14 after infection. Unlike the spleen, the lymph nodes showed minor changes in their T and B lymphocyte responses and cell composition during the course of the infection, except the B cell response and composition which were altered late in the infection. The thymus and bone marrow did not show any appreciable changes in their mitogen responses and cell composition throughout the infection. The peripheral blood lymphocytes showed reduced B cell responses. Spleen cells from chronically infected mice suppressed lymphocyte stimulation induced in normal spleen and lymph node cell populations by Con A, LPS and allogeneic stimulator cells. Lymph node cells from the same group of mice did not exhibit any such suppressor activity. In the experimental system used here, the spleen is the primary site of immune depression, and other lymphoid organs such as the lymph nodes and thymus are very little affected.

Topics: Animals; B-Lymphocytes; Bone Marrow; Concanavalin A; Female; Immunity, Cellular; Lipopolysaccharides; Lymphocyte Culture Test, Mixed; Lymphoid Tissue; Male; Mice; Mice, Inbred C3H; T-Lymphocytes; Thymus Gland; Trypanosomiasis

Spleen cells from trypanosome-infected mice strongly suppressed lymphocyte stimulation induced in normal spleen cell populations by lipopolysaccharide, concanavalin A or allogeneic (H-2-different) stimulator cells. This suppression was not H-2-restricted, as responses of spleen lymphocytes both allogeneic and syngeneic to the suppressors were inhibited. Irradiation or mitomycin C treatment of suppressor populations markedly reduced but did not eliminate suppressor activity. Suppressor populations were effective when present in very low numbers. Addition of suppressor cells to mixed lymphocyte cultures at various intervals after initiation of the cultures showed that the suppressors require 48 h to manifest their activity. Cell depletion or enrichment experiments indicate that the mechanism of suppression is complex and involves more than one cell type.

Topics: Animals; Antilymphocyte Serum; Cell Separation; Concanavalin A; Female; Immunosuppression Therapy; Lipopolysaccharides; Lymphocyte Culture Test, Mixed; Mice; Mice, Inbred BALB C; Mice, Inbred C3H; Mice, Inbred CBA; Spleen; T-Lymphocytes; Trypanosomiasis

Using a wide range of experimental conditions, several kinds of T lymphocyte responses in spleen cell populations from trypanosome-infected mice were studied. Lymphocyte stimulation after culture with the mitogen concanavalin A or with histoincompatible cells differing at H-2 or minor lymphocyte-stimulating loci was reduced or abolished in spleen cells from infected mice when compared with responses of spleen cells from uninfected controls. In addition, cytotoxic lymphocytes were not generated in mixed lymphocyte cultures which contained spleen cells from infected animals. Allogeneic skin grafting experiments performed with normal and infected mice showed that a decreased T lymphocyte response also occurs in vivo. The depressed immune responses were not simply due to low numbers of T lymphocytes in spleens of infected animals, but reflected a generalized immune depression which was not antigen-specific.

Topics: Animals; Concanavalin A; Cytotoxicity, Immunologic; Graft Rejection; Immunity, Cellular; Immunosuppression Therapy; Lipopolysaccharides; Lymphocyte Activation; Lymphocyte Culture Test, Mixed; Mice; T-Lymphocytes; Trypanosomiasis

Topics: Animals; Antilymphocyte Serum; Cell Adhesion; Cell Separation; Concanavalin A; DNA; Glass; Histocompatibility Antigens; Immunosuppression Therapy; Lectins; Lipopolysaccharides; Lymphocyte Activation; Lymphocytes; Mice; Polysaccharides, Bacterial; Spleen; T-Lymphocytes; Trypanosoma brucei brucei; Trypanosomiasis

Topics: Animals; Antibody Formation; Antigens; Cell Division; Cells, Cultured; Concanavalin A; Erythrocytes; Escherichia coli; Immunosuppression Therapy; Lectins; Lipopolysaccharides; Lymphocytes; Mice; Mitogens; Polysaccharides, Bacterial; Sheep; Spleen; Splenomegaly; Trypanosoma; Trypanosomiasis