Lymphocyte function in experimental african trypanosomiasis: mitogenic effects of trypanosome extracts in vitro

Innate resistance to experimental African trypanosomiasis: differences in cytokine (TNF-alpha, IL-6, IL-10 and IL-12) production by bone marrow-derived macrophages from resistant and susceptible mice

Resistance to African trypanosomiasis is under multigenic control. BALB/c mice are highly susceptible while C57Bl/6 mice are relatively resistant. Macrophages eliminate opsonized trypanosomes from the bloodstream and are involved in immunosuppression. We therefore investigated the production of a number of cytokines (IL-10, IL-6, TNF-alpha and IL-12) by bone marrow-derived macrophages (BMDM) from C57Bl/6 and BALB/c mice following challenge with either Trypanosoma congolense or Trypanosoma brucei. BMDM from C57Bl/6 mice, upon challenge with whole cell extracts (WCE) of T. congolense or T. brucei, produced significantly more TNF-alpha and IL-12 than those from BALB/c mice. The production of these cytokines was significantly enhanced by pretreatment of the cells with IFN-gamma. BMDM from BALB/c mice, however, produced significantly more IL-6 and IL-10 than those from C57Bl/6 mice. In contrast to LPS stimulation, simultaneous treatment of cells with WCE and IFN-gamma enhanced IL-10 synthesis by BMDM from BALB/c mice. These results indicate that cytokine genes are differentially regulated in macrophages from trypanosome-susceptible and -resistant mice and are consistent with our previous findings wherein retrovirus-immortalized macrophage cell lines from BALB/c and C57Bl/6 mice produce differential amounts of cytokines after phagocytosis of trypanosomes.

Innate resistance to Trypanosoma congolense infections: differential production of nitric oxide by macrophages from susceptible BALB/c and resistant C57Bl/6 mice

BALB/c and C57B1/6 mice differ in resistance to Trypanosoma congolense infections. Evidence suggests that macrophages play a central role in the resistance to trypanosomiasis. Nitric oxide (NO) produced by macrophages in response to various stimuli or pathogens is one of the important arms of nonspecific immunity. We investigated the production of NO by the peritoneal macrophages and bone marrow-derived macrophages (BMDM) from trypanosome-resistant C57B1/6 and -susceptible BALB/c mice following stimulation with T. congolense whole cell extract (WCE) or following phagocytosis of T. congolense mediated by anti-variant surface glycoprotein (VSG) antibodies of IgM or IgG2a isotype. C57B1/6 peritoneal macrophages as well as BMDM produced significantly more NO than similar BALB/c macrophages in response to T. congolense lysate and IFN-gamma. In both BALB/c and C57B1/6 BMDM cultures, phagocytosis of T. congolense mediated by anti-VSG antibodies of IgG2a isotype in the presence of IFNgamma induced two- to ninefold more NO than phagocytosis mediated by IgM antibodies and C57B1/6 BMDM produced significantly higher amounts of NO than BALB/c BMDM under these conditions. NO produced by BMDM was found to exert trypanostatic effect on T. congolense in vitro, but was not found to influence the in vivo infectivity of these treated parasites under the conditions used in this study.

Identification of rabbit immunoglobulin latent Ckappa1 allotype genes alters the concept of allelic inheritance

In the rabbit, expression of immunoglobulin Ckappa1 light chain genes is believed to be under allelic control. Conventionally, four nominal allotypic variants, b4, b5, b6 and b9 have been shown to be co-dominantly expressed at the Ckappa1 gene locus. Analogously, the heavy chain allotypes, VHa1, VHa2 and VHa3, found in the V region, are also believed to be inherited co-dominantly. However, after our earlier discovery of non-allelic or latent allotypes in the serum and on cell surfaces. we subsequently reported that cDNA sequences for latent b5 and b6 were identical to nominal b5 and b6, respectively (Ishaq et al., 1990). The latent b5 cDNAs were from two homozygous b4,b4 rabbits; the latent b6 cDNA was found in a heterozygous b4,b9 rabbit. The cDNA sequences had been obtained from lymph nodes and spleens of rabbits which had been infected with Trypanosoma brucei in order to induce latent allotypes more consistently. In this article, employing spleen DNA from three different T. brucei-infected rabbits, (one, heterozygous b4,b9; two others, homozygous, b4,b4), we initially detected two bands by Southern analysis after Hind III digestion using a 624 base pair Ckappa1 b4 probe derived from a b4,b4 rabbit. However, the probe was non-specific allotypically as it hybridized to b5, b6 and b9 Ckappa1 DNA. Therefore, in order to search for the latent genes, we used allotype-specific oligonucleotides for b5, b6 and b9 to probe DNAs from both normal and T. brucei-infected rabbits by Southern blotting. At the outset, employing a b4 oligonucleotide probe, we detected a single 5.8 Kb segment in two b4,b4 rabbit DNAs after Bg1 II digestion. The findings, using the 624 base pair Ckappa1 b4 probe and the b4 oligomer, agreed with earlier data reported by others. Subsequently, we tested kidney, liver and spleen DNAs from one of these and other rabbits for genomic latent b5, b6 and b9 using these specific oligomeric probes. For each latent allotype, Southern analysis revealed latent-allotype specific DNA segments in the genome. After cosmid cloning and sequencing, latent kappa1, b5, b6 and b9 genes were found to be identical in their coding regions with their nominal counterparts. The genes contained at the 5' end the PyPyXPyAG RNA splice acceptor site found in immunoglobulin and many eukaryotic genes. as well as the termination codon TAG, together with AATAAA and the T-rich sites responsible for cleavage-polyadenylation in the untranslated region downstream from the 3' end. Single cosmid clones representing the b5, b6 and b9 genes were mapped for restriction sites which resulted in identifying putative Jk and enhancer regions. The results thus indicate that latent allotype genes are potentially functional. The data provide evidence that allotypes are not strictly controlled by allelic genes but must be regulated by an hierarchical mechanism which provides for synthesis of allelic allotypes mainly (10-20 mg/ml) together with non-allelic allotypes at lower concentrations (2-20 microg/ml) following activation of the latent genes. These results lay to rest the belief that Ckappa1 latent allotypes are the products of scrambled genes or idiotypic mimicry. Importantly, we now have the possibility of investigating the factors leading to latent allotype gene expression, the Vk and Jk regions associated with the genes, and therefore whether antibody diversity is expanded. We do not know, nor do we imply, that latent allotypes are present in all rabbits. However, since the four conventional Ckappa1 allotypes are present in the genome of several of our tested rabbits, and are presumably functional. we are faced with the probability that rabbit allotypes under certain conditions may in fact behave as isotypes and not allotypes.

Interleukin-4-dependent immunoglobulin G1 isotype switch in the presence of a polarized antigen-specific Th1-cell response to the trypanosome variant surface glycoprotein

This study examines B-cell immunoglobulin (Ig) class-switching events in the context of parasite antigen-specific Th-cell responses in experimental African trypanosomiasis. Inbred mice were infected with Trypanosoma brucei rhodesiense, and the coordinate stimulation of Th-cell cytokine responses and B-cell responses to the trypanosome variant surface glycoprotein (VSG) was measured. The cytokines produced by T cells in response to VSG, at both the transcript and protein levels, were gamma interferon and interleukin-2 (IL-2) but not IL-4 or IL-5. Isotype profiles of antibodies specific for VSG showed that IgG1, IgG2a, and IgG3 switch responses predominated; no VSG-specific IgE responses were detected. To determine whether cryptic IL-4 responses played a role in promoting the unexpected IgG1 switch response, IL-4 knockout mice were infected; the cytokine responses and Ig isotype profiles of IL-4 knockout mice were identical to those of the wild-type control mice except for dramatically reduced IgG1 levels in response to VSG. Thus, these results revealed an IL-4-dependent component of the VSG-driven B-cell Cmu-to-Cgamma1 switch. We speculate that an IL-4 response is mediated primarily by cells other than T lymphocytes since IL-4-secreting but parasite antigen-unresponsive, "background" cells were detected in all infected mice and since infected nude mice also displayed a detectable IgG1 switch response. Overall, our results suggest that B-cell clonal stimulation, maturation, and Ig class switching in African trypanosomiasis may be partially regulated by unusual mechanisms that do not include antigen-specific Th1 or Th2 cells.

CD5+ B lymphocytes are the main source of antibodies reactive with non-parasite antigens in Trypanosoma congolense-infected cattle

Mice infected with African trypanosomes produce exceptionally large amounts of serum IgM, a major part of which binds to non-trypanosome antigens such as trinitrophenol and single-strand DNA. In this paper, we describe that in cattle infected with Trypanosoma congolense and T. vivax, similar antibodies are found, although they bind mainly to protein antigens, such as beta-galactosidase, ovalbumin and ferritin. The parasite non-specific IgM antibodies appear around the same time as the parasite-specific antibodies, but their origin and function are not clear. We tested the hypothesis that CD5+ B cells (or B-1 cells), which increase during trypanosome infections in cattle, are responsible for production of antibodies to non-trypanosome antigens. Splenic CD5+ and CD5- B cells from infected cattle were sorted and tested in a single cell blot assay. The numbers of immunoglobulin-secreting cells were similar in both B-cell populations. However, antibodies with reactivity for non-trypanosome antigens were significantly more prevalent in the CD5+ B-cell fraction and were exclusively IgM. The preference for production of these antibodies by CD5+ B cells and the expansion of this subpopulation during infections in cattle, strongly suggest that CD5+ B cells are the main source of trypanosome non-specific antibodies. We propose that these antibodies are natural, polyreactive antibodies that are predominantly secreted by CD5+ B cells. Since B-1 cells are up-regulated in many states of immune insufficiency, the immunosuppression associated with trypanosome infections may be responsible for the increase of this subset and the concomitant increase in trypanosome non-specific antibodies.

Immunohistology of lymph nodes draining local skin reactions (chancres) in sheep infected with Trypanosoma congolense

Marked enlargement of lymph nodes draining local skin reactions (chancres) occurred in sheep following intradermal inoculation of cultured metacyclic forms of Trypanosoma congolense. Histologically, these lymph nodes were characterized by follicular hypertrophy and hyperplasia, compression and relative reduction of the paracortical areas and expansion of the medullary regions. Immunohistochemical staining with monoclonal antibodies to ovine lymphocyte subsets and Fc receptor (FcR) bearing macrophages, revealed increased expression of B cells (CD45R+), major histocompatibility complex (MHC) Class II, FcR+ macrophages, and CD1+ cells in the cortical and paracortical areas. The paracortical areas were found to be sparsely populated by CD5+, CD4+ and CD8+ cells, while the medullary areas contained numerous CD8+ cells and FcR+ macrophages. FcR+ macrophages were also present in cortical trabecular and subcapsular sinuses. As the chancre regressed, lymph node reactivity also subsided and fewer B cell follicles were observed and there was decreased expression of CD45R+ and MHC Class II+ cells.

Immunomodulation by Histoplasma capsulatum products; polyclonal activation and mitogenic effects

The presence of reactive spleen cells to sheep red blood cells (SRBC) in nonimmunized BALB/c mice injected with histoplasmin, the culture filtrate of Histoplasma capsulatum, was monitored for 21 days following inoculation. Polyclonal activation, as evidenced by a sharp increase in the number of anti-SRBC rosette-forming cells (RFC), as well as an enhanced response to heterologous non-cross-reactive erythrocytes from other species, was found in the spleens of these rodents on Days 11 to 13. Elimination of B-cell-derived RFC by the addition of complement indicated that the erythrocyte-binding cells consisted of both T- and B-lymphocytes. An immunosuppressive effect was detected if histoplasmin was injected 2 days before the antigen (SRBC), but could be reversed by injecting the filtrate 30 min prior to the antigen, as is found with polyclonal activators displaying immunosuppressive activity. Histoplasmin also had a mitogenic effect on lymphocyte obtained from the spleen, bone marrow, and thymus similar in magnitude to that produced by lipopolysaccharide (LPS) and concanaval in A. The biological significance of these findings is discussed.

Trypanosoma musculi: population dynamics of erythrocytes and leukocytes during the course of murine infections

Cells of the hemocytic and lymphoreticular series located in the blood, bone marrow, spleen, and peritoneal space have been analyzed throughout the course of Trypanosoma musculi infections of intact and splenectomized C3H female mice. Following an early (within 2 days after trypanosome inoculation intraperitoneally) shift of leukocytes from the blood to the peritoneal space, there occurred a more gradual, prolonged infusion of leukocytes into the peritoneal space, the primary site of infection, that continued until the infection was terminated. There was intense cytogeneractive activity in the spleen that included erythrocytes, lymphocytes, myelocytes, and megakaryocytes. The marrow became primarily a site of monocytopoiesis and, to some extent, of lymphopoiesis. During the first 8 days (approximately) of infection, there was a decline in mature erythrocytes in the blood (the well-known anemia) and development of a profound thrombocytopenia. In splenectomized mice, the depletion of these elements continued unabated until the mice died; the marrow of infected, splenectomized mice failed to provide these elements, as was also the case in intact mice. In the peritoneal space, the intense battle between leukocytes and trypanosomes was reflected in a gradual, impressive rise in the number of dead and fatigued cells and, late in infection, in the development of ascites. Both of these abnormal conditions disappeared shortly after cure of the infection. We conclude that infections of mice with T. musculi result in dedication of the entire lymphoreticular system to the generation of cells that are exported to the peritoneal space to combat the major infection the occurs in that locale. This is consistent with the evidence that the belated immune elimination of T. musculi is a cell-mediated (probably antibody-dependent) process. The disruption of the normal histoarchitecture, the shift in the normal proportions of cells and in cells of different degrees of maturity, and probably, a block imposed on precursor cell maturation, account to a large extent for the well-known failure of immune responses commonly associated with trypanosome infections.

High and low responsiveness of bovine lymphocytes to Trypanosoma brucei in vitro: lack of correlation with resistance to trypanosomiasis

Bovine peripheral blood lymphocytes (PBL) were stimulated to proliferate in vitro by live, irradiated or freeze-thawed Trypanosoma brucei, but not by the isolated variant surface glycoprotein. The optimal dose was 10(5) trypanosomes per 5 X 10(5) lymphocytes in 0.2 ml. Maximal proliferation was at day 5. Of the 98 cattle tested, 36 were high-responders (stimulation indexes 20-104), 49 were low or non-responders (SI 1-10) and 13 were intermediate. The responder status of individual animals did not change over a period of 1 year, nor did it alter following deliberate trypanosome infection. The stimulation was dependent on macrophage/monocyte type accessory cells, and this co-operation did not seem to be MHC restricted. Lack of stimulation of non-responder PBL did not appear to be due to the activation of suppressor cells. Accessory cells from non-responder animals could complement PBL from responders, but accessory cells from responders could not complement non-responder PBL. Responsiveness is therefore a characteristic of lymphocytes. Analysis of the surface markers of these lymphocytes or the blast cells generated in culture showed that they were a subpopulation of T cells, possibly TH cells. Analysis of PBL from 98 animals, which had been selected for trypanoresistance or trypanosensitivity under natural tsetse fly challenge, failed to establish a correlation between resistance and level of lymphocyte stimulation by trypanosomes in vitro.

In vitro induction of lymphocyte responsiveness by a Strongylus vulgaris-derived mitogen

Proliferation in vitro of peripheral blood lymphocytes both from horses infected with Strongylus vulgaris and from helminth-free ponies was observed in the presence of extracts of the fourth and fifth stage larvae and adults of S. vulgaris. In addition, S. vulgaris extracts induced transformation in cultures of peripheral blood lymphocytes from sheep and dogs and in mouse spleen cell cultures. Nylon wool non-adherent, T cell enriched fractions of lymphocytes from both mice and horses were stimulated by the S. vulgaris larval mitogen while no proliferation was observed in cultures containing nylon wool adherent, B cell enriched fractions. Macrophage co-operation appeared not to be necessary for S. vulgaris mitogen-induced transformation of spleen cells. The S. vulgaris mitogen stimulated a subpopulation of mouse spleen cells different from those responsive to PHA, Con A and LPS. These cells might be T helper cells since B cells were stimulated to proliferate in the presence of both T cells and S. vulgaris larval mitogen. In addition, the supernatant of in vitro cultured larvae of S. vulgaris induced slight, but significant transformation of equine peripheral blood lymphocytes. Therefore, it is possible that the S. vulgaris mitogen released by both viable parasites and degenerating larvae might induce T cell dependent production of immunoglobulin in vivo and account for the beta-globulinaemia, of which IgG(T) is a major component, in S vulgaris infected horses.

Induction of T cell activity in athymic (nu/nu) mice infected with Trypanosoma rhodesiense

Infection of C57BL/10 (B10)3 nu/nu mice with Trypanosoma rhodesiense results in the development of significant T-cell reactivity in spleen and lymph nodes. The proliferative responses to mitogens, such as concanavalin A (Con A) and phytohemagglutinin (PHA), and in mixed-lymphocyte reactions (MLR) to alloantigens are enhanced compared with control uninfected nu/nu mice. These results serve to emphasize the stimulatory nature of trypanosomes on the immune system.

Schistosoma mansoni: autoantibodies and polyclonal B cell activation in infected mice

The appearance of autoantibodies was investigated during the course of Schistosoma mansoni infection in C57Bl/6 mice. Anti-liver autoantibodies or lymphocyte-reactive alloantibodies were detected respectively without cell-mediated immunity against liver antigen or lymphocytotoxic activity. Anti-liver, anti-DNA, anti-Ig and anti-lymphocyte antibodies were shown 6-7 weeks after the beginning of the infection concomitantly with the increase of immunoglobulin levels and circulating immune complexes. At this period, the antibody response to polyvinylpyrrolidone (PVP) was increased and the injection of spleen cells from day-45-infected mice to uninfected recipients increased the anti-PVP antibody response. Conversely, the injection of spleen cells from uninfected to infected mice did not modify the anti-PVP Ab response. After 6 weeks of infection, the basal thymidine incorporation of spleen cells was increased contrasting with the marked inhibition of spleen cell response to PHA. The present data are consistent with the induction of a polyclonal non-specific B cell activation by S. mansoni.

Activation of human peripheral blood lymphocytes by a trypanosome-derived mitogen

Activation of human peripheral blood lymphocytes from unsensitized donors by fractions of T.b rhodesiense has been demonstrated in vitro. Both T and B cells were stimulated to differentiate into blast cells. Purified T cells failed to proliferate, but did so when mitomycin C-treated non-T cells were added. Non-T cell proliferation (weak in comparison to the T cell response) was shown to be T-dependent. In unseparated cell cultures. cultures, IgM synthesis was enhanced, whilst IgG synthesis was unaltered. However, reconstitution of non-T cells with equal number of irradiated T cells resulted in enhanced IgG synthesis. Thus neither T nor B cells were activated directly, but required the co-operation of accessory cells to proliferate. The role of monocytes in the regulation of this response requires further assessment.

Evidence for depletion of Ia+ macrophages and associated immunosuppression in African trypanosomiasis

The percentage of Ia antigen-bearing (Ia+) macrophages was significantly lower in mice infected with Trypanosoma rhodesiense than in normal controls. The degree of difference varied with the source of macrophages and time course of infection. The percentage of Ia+ macrophages isolated from spleens 10 days after infection was 71% of that in the controls, and depletion continued until Ia+ macrophages were almost undetectable 30 days after infection. The rate of depletion was slower in the peritoneal cavity. In contrast, Ia+ macrophages were not significantly depleted from the lymph nodes until 30 days after infection. The ability of macrophages from trypanosome-infected mice to present listerial antigen to sensitized T cells was significantly lower than in controls. Immune T cells had significantly less ability (43% of controls) to incorporate thymidine when exposed to splenic macrophages from infected mice during the early stage of disease. This loss of antigen presentation increased during the course of infection. Peritoneal macrophages also exhibited an early loss of ability to present antigen, but no significant decline occurred thereafter. No significant loss of antigen had occurred in the lymph node macrophages 10 days after infection, but during the later stages of the disease a significant loss was detected. Treatment of macrophages from infected and control mice with anti-Iab serum and complement inhibited their ability to present antigen. Our results demonstrate that Ia+ macrophages and their distribution can influence the ability of infected animals to process antigens and may therefore account in part for the immunosuppression observed in trypanosomiasis.

Murine T lymphocyte specificity for African trypanosomes. I. Induction of a T lymphocyte-dependent proliferative response to Trypanosoma brucei

A procedure which results in the specific activation of primed murine T lymphocytes was adapted for the study of T lymphocyte activation by the African trypanosome: Trypanosoma brucei. The assay calls for the in vivo priming of lymphocytes by the subcutaneous administration of parasites, followed by the co-cultivation in vitro of cells taken from the regional draining lymph nodes and the parasite. This co-cultivation results in a marked proliferation of lymphoid cells. The proliferation was shown to be specific for the parasite, and to be dependent on the presence of T lymphocytes and macrophages. Both the in vivo priming and the in vitro activation were shown to require the presence of living parasites. Various factors influencing the magnitude of the proliferative response were analysed. Of special interest is the observation that the time interval between in vivo priming and in vitro culture which results in a substantial proliferative response is quite short when compared to that seen with other antigens. Although lymph node cells from mice primed with T. brucei 1 to 2 weeks previously are able to mount a secondary proliferative response upon stimulation with T. brucei, cells taken 3 weeks after priming are unresponsive to an in vitro challenge with T. brucei. This unresponsiveness may be a result of the generalized immunosuppression seen in African trypanosomiasis. Thus, this method offers the potential for the study of specific T cell responsiveness in African trypanosome infections.

Anti-immunoglobulins and heterophil agglutinins in experimental trypanosomiasis

Rheumatoid factor (RF)-like substances and heterophil agglutinins (HA) were induced in rabbits by infection with a strain of Trypanosoma equiperdum. Infection with a T. gambiense strain produced HA, but no RF. RFs appeared usually before immunoglobulin G (IgG) levels started to increase. They disappeared spontaneously after 4 to 6 weeks. HA were of the IgM class, appeared within 1 to 2 weeks after infection, and usually remained at high levels afterwards. They could not be absorbed out with lyophilized whole trypanosomes. Therapy suppressed the formation of RF as well as of HA, but IgG complexes as well as antibodies against trypanosomal antigens remained present for considerable periods after the installment of therapy. It is concluded that RFs are not induced by IgG complexes. The results suggest that HA are probably not cross-reacting antibodies induced by trypanosomal antigens.

Humoral suppression in Trypanosoma cruzi infection in relation to the timing of antigen presentation

(CBA x C57 B1/10)F1 mice infected intraperitoneally with 100 parasites of Trypanosoma cruzi strain Y developed an infection with acute and chronic phases. Humoral suppression to sheep red blood cells was evident in both phases but enhancement of the response was achieved only at the beginning of the infection. A mitogen secreted by the parasite could explain both phenomenons.

The pathogenesis of sleeping sickness

Although the clinical and pathological features of sleeping sickness have been well recognized since the beginning of the century, we still have very little idea about how these changes are brought about. A convincing role for a trypanosome-derived toxin has yet to be established and it is probable that most tissue damage results from an immunopathological reaction. An immediate type hypersensitivity reaction might account for the pruritus and urticaria sometimes encountered in patients with the infection. Autoantibodies are produced by patients with sleeping sickness but it has not been established that these can cause tissue damage. Similarly, although high levels of immune complexes are found in patients with sleeping sickness, it has yet to be clearly established that these damage the brain or heart. The dominant pathological event in sleeping sickness is B lymphocyte proliferation, first within the lymph nodes and then within the brain and meninges, and this response may lead to tissue damage in some way which has not yet been identified. B lymphocyte proliferation could result from the action of a trypanosome-derived mitogen or from interference with T lymphocyte control over B lymphocyte function.

Membrane fractions of trypanosomes mimic the immunosuppressive and mitogenic effects of living parasites on the host

African trypanosomiasis in mice leads to profound changes in lymphoid tissues. In an attempt to define the nature of the trypanosome stimulus, we have studied the effect of radio-attenuated trypanosomes and their subcellular fractions in vivo. We find that relatively low doses of irradiated Trypanosoma brucei S42 injected into (CBA/H x C57B1/6)F1 mice mimicked the previously reported effects of infective parasites. 2 x 10(7) irradiated trypanosomes caused a greater than two-fold increase in spleen weight accompanied by a roughly 10-fold increase in background plaque forming cells (PFC) to sheep red blood cells (SRBC). The primary response to SRBC was significantly enhanced when priming was carried out on the day of trypanosome injection, but significantly suppressed when carried out 3 days later. Disruption of trypanosomes by freeze-thawing did not destroy their mitogenic or immunosuppressive activities. A membrane fraction collected by high speed centrifugation (150 000 x g) after removal of larger organelles at 12 000 x g retained both mitogenic and suppressive activities. The high speed supernatant lost the ability to enhance background PFC, but still caused partial immunosuppression with a much lower potency than the membrane pellet. Whether immunosuppression and enhanced PFC levels relate to the same parasite product is not clear as yet, but both effects can be ascribed to a membrane fraction of the parasite.

Trypanosoma brucei infection in nude mice: B lymphocyte function is suppressed in the absence of T lymphocytes

B lymphocyte function was assessed in outbred nude mice and nu/+controls infected with Trypanosoma brucei brucei. On day 10 of the infection in outbred nu/nu mice in which the initial wave of parasites was strongly controlled, B cell function was unaltered on enhanced compared with uninfected animals or infected nu/+. In other nu/nu mice unable to control the initial parasitaemia, thymidine incorporation and Ig secretion by spleen cells were increased on day 10 and their response to lipopolysaccharide in vitro negated. By day 15 however, even the spleen cells of infected nu/nu which controlled the initial wave of parasites were proliferating and secreting Ig on removal from the mice and they were unable to respond to LPS in vitro. These experiments confirm results of a previous study of B cell function in T cell-depleted mice (Askonas et al. 1979). T. b. brucei infection of mice causes both enhanced Ig production and suppression of the ability of B cells to respond to mitogen even in the absence of T cells, but the presence of T cells may accelerate the changes which occur in B lymphocytes following this infection.

Lectin analysis of Trypanosoma congolense bloodstream trypomastigote and culture procyclic surface saccharides by agglutination and electron microscopic technics

Living, intact bloodstream trypomastigotes and culture procyclic forms of Trypanosoma congolense were tested for aggulination with the lectins concanavalin A (Con A), phytohemagglutinin P (PP), wheat germ agglutinin (WGA), soybean agglutinin (SBA), and fucose binding protein (FBP). Similar experiments were conducted with living bloodstream and culture forms treated with trypsin or dextranase. Parasites were incubated for 30 min at 25 C in various concentrations of each lectin, then examined for agglutination by dark-field microscopy. Control preparations consisted of parasites incubated alone or with 0.5 M of the specific competing sugar, with or without the corresponding lectin. Electron-microscopic localization of lectin binding sites on the surface of intact and dextranase-treated bloodstream and intact culture forms was accomplished with Con A, reacted with horseradish peroxidase (HRP) and then diaminobenzidine (DAB). In addition, FBP and SBA were coupled to HRP, then utilized for the localization of binding saccharides on the surface of bloodstream forms by the DAB technic. Similar studies were conducted with culture procyclics incubated with WGA-, SBA-, PP- or FBP-HRP conjugates and then reacted with DAB. Controls were utilized to confirm the sugar specificity of all positive reactions. Intact living bloodstream forms were agglutinated in a concentration-dependent manner with all the lectins tested. Agglutination levels were scored as Con A greater than FBP greater than WGA = PP = SBA. Sugars resembling alpha-D-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and alpha-L-fucose are evidently present on the surface of the parasites. No agglutination was noted in any control preparations. Identical lectin-induced agglutinations were obtained with trypsin- or dextranase-treated bloodstream forms. Trypsin disrupted but did not entirely remove the surface coat of bloodstream forms, while dextranase did not alter the ultrastructure of the parasites. Con A-, SBA- and FBP-binding saccharides were distributed uniformly on the surface coat of intact bloodstream forms; a similar distribution of Con A receptors was noted also on the surface of dextranase-treated cells. No lectin-binding saccharides were visualized by electron microscopy on any control preparations. Intact, trypsin- or dextranase-treated, procyclics were agglutinated in a concentration-dependent fashion by Con A and WGA, but not by the other lectins tested. Control preparations did not agglutinate and the enzymes did not affect the ultrastructure of the parasites. Con A- and WGA-specifically binding saccharides were uniformly distributed on intact procyclics and control preparations were lectin-negative. Thus, T. congolense procyclics retained surface saccharides resembling alpha-D-mannose and N-acetyl-D-glucosamine but lost sugars resembling N-acetyl-D-galactosamine (or D-galactose) and alpha-L-fucose...

The immunosuppressive and mitogenic effects of Trypanosoma musculi

In CD-1 mice infected with Trypanosoma musculi, the production of IgM and IgG antibodies in response to sheep erythrocytes (SRBC) was significantly suppressed when mice were immunized with SRBC once high parasitaemias had developed. In infected mice which were not immunized with SRBC, background plaque-forming responses of spleen cells to SRBC were significantly higher than in uninfected, unimmunized mice. Factors derived from T. musculi were found to be mitogenic in vitro for spleen cells taken from CD-1 mice. The mitogenic response to these factors by spleen cells from athymic mice was highly significant, whereas the response of spleen cells taken from CD-1 mice which had been pre-treated with cyclophosphamide was much less, suggesting that the B cell was the major target of the trypanosome-derived mitogen. In this paper we discuss the possible relationship of T. musculi-induced mitogenesis to the immunosuppression and non-specific antibody formation associated with T. musculi infections.

Mitogenic activity of an extract of Trypanosoma gambiense

An extract obtained by repeated freeze/thawing of a freshly isolated strain of Trypanosoma gambiense caused stimulation of lymphocytes obtained from healthy adult donors and from cord blood. The active factor had some stimulatory effect on purified B and T lymphocytes and in two of five subjects increased IgM production by lymphocytes cultured in vitro. A trypanosome-derived mitogenic factor may play some part in the pathogenesis of the hypergammaglobulinaemia characteristic of African trypanosomiasis.

Free fatty acids, complement activation, and polyclonal B-cell stimulation as factors in the immunopathogenesis of African trypanosomiasis

Human and animal forms of African trypanosomiasis are characterised by sustained hypocomplementaemia, gross hypergammaglobulinaemia M, and profound immunosuppression. It is suggested that this hypocomplementaemia is probably due to the action of a trypanosome-derived complement-activating factor and that the elevated IgM levels may be the combined result of this decomplementation, together with a subsequent failure of the normal IgM-to-IgG antibody switch mechanism and polyclonal B-lymphocyte activation by a trypanosome-generated mitogen. The immunosuppression in this disease may be a result of the collective immunosuppressive effects of trypanosome-derived immune-modulating free fatty acids, polyclonally stimulating B-cell mitogen, and complement-activating factors.