Trypanosoma cruzi: regulation of mitogenic responses during infection in genetically resistant and susceptible inbred mouse strains

The outcome of Trypanosoma cruzi infection in inbred strains of mice is under genetic control. The lymphocyte responses to T-cell mitogens and their regulation were investigated in strains of mice resistant or susceptible to T. cruzi. Six to eight days after the inoculation of T. cruzi, resistant and susceptible mice had depressed responses to T-cell mitogens. In resistant B6 mice, suppression was maximal 18 days after infection and it persisted for at least 320 days. The duration of immunosuppression correlated with the persistence of a subpatent parasitemia. In cell mixing experiments, it was determined that the concanavalin A (Con A) responses in the resistant B6 and B6C3F1 mouse strains were suppressed by highly active T-suppressor cells. In the susceptible C3H mice, intense suppression of the Con A responses was detected 14 days after inoculation of T. cruzi. Nevertheless, only weak suppressor cell activity was detected in the infected C3H mice, and suppression was not abrogated by passage through a nylon wool column nor by treatment with antitheta antibodies and complement. Thus, it was suggested that, during the course of infection with T. cruzi, splenic T cells from C3H mice acquired a block in the metabolic pathway for cellular activation by Con A. The influences of T. cruzi epimastigotes on the Con A responses of spleen cells from uninfected mice were then studied. The Con A responses of spleen cells from C3H mice were depressed in the presence of epimastigotes, whereas they were either unaffected or enhanced in spleen cells from B6 mice. Hence, the immunoregulatory events provoked by T. cruzi infection differed in genetically resistant and susceptible mice, and lymphocytes from C3H mice were predisposed to a parasite-induced block in the responses to Con A. Thus, the gene(s) determining the outcome of infection with T. cruzi may be phenotypically expressed through an influence on immunoregulatory events.     

Trypanosoma cruzi: acute infection affects expression of alpha-2-macroglobulin and A2MR/LRP receptor differently in C3H and C57BL/6 mice

Although a complete cellular and humoral immune response is elicited in Chagas' disease, recent data suggest that other natural elements of innate immunity may also contribute to the initial host primary defense. alpha-Macroglobulins are a family of plasma proteinase inhibitors that are acute-phase reactants in Trypanosoma cruzi-infected mice and humans. Mice contain a tetrameric alpha-2-macroglobulin (MAM) and a monomeric murinoglobulin (MUG). Heterogeneity in their reactions was observed in murine T. cruzi-infected plasma A2M levels despite an overall increase. In addition, up-regulation of the A2M receptor (A2MR/LRP) was observed in peritoneal macrophages during T. cruzi infection. Here, we show that during T. cruzi infection (Y strain), the MAM and MUG hepatic mRNA levels and the corresponding plasma protein levels were up-regulated in C3H and C57BL/6 (B6) mice, but with different kinetics. On the contrary, A2MR/LRP mRNA levels increased in acutely infected C3H mice, but decreased in B6 mice, in both liver and heart. Immunocytochemistry of infected B6 heart cryosections confirmed a less intense endothelium labeling by the fluoresceinated ligand for A2MR/LRP. On the other hand, infected B6 spleen cells displayed higher F-A2M-FITC binding and MAC1 expression, confirming higher A2MR/LRP expression in macrophages. In uninfected mice, as well as after T. cruzi infection, higher A2M plasma levels were measured in C3H mice than in B6 mice. The lower tissue T. cruzi parasitism found in C3H-infected mice could reflect an inhibitory effect of A2M on parasite invasion. Our present data further contribute to clarifying aspects of the role of A2MR/LRP in a model of acute Chagas' disease in different mouse strains.     

Trypanosoma cruzi: the expansion of NK, T, and NKT cells in the experimental infection

T and NK cells play a key role in resistance to Trypanosoma cruzi infections, mainly through IFN-gamma production. The expression of T and NK cells surface markers was studied in NWNA spleen cells of resistant C3H and susceptible BALB/c mice that release IFN-gamma in the early and late acute infection, respectively. In the progressively enlarged spleens, we found: (a) an increased percentage and number of NK blast cells as early as at 2 days post-infection (pi), (b) an enrichment of T and NK cells, in both the total and blast populations, during the late acute phase. At 17 days pi, there was also an accumulation of TCR- alphabeta+DX5+, NKT cells, mainly in resistant mice. At 21 days pi, the enrichment of NK cells ceased, while spleen cells and the T cell compartment continued their expansion. In the chronic stage, TCR-alphabeta+ blasts were expanded in both mouse strains, but NK blasts increased only in BALB/c that, unlike C3H mice, release IFN-gamma. As T and NK cell proliferation is not always associated to IFN-gamma release the experimental downregulation of their expansion to avoid tissue damage could be explored.     

Indiscriminate representation of VH-gene families in the murine B lymphocyte responses to Trypanosoma cruzi

The utilization of the nine major homology families of VH-genes was quantitated in the B lymphocyte response to Trypanosoma cruzi infection of C57BL/6 mice. Normal and infected mice at various times after parasite inoculation were compared for VH-gene distribution of CFU-B produced by activated blasts recovered from spleen and lymph nodes, and for relative hybridization of total spleen RNA with each of the family probes. T. cruzi infection results in large increases of splenic RNA in the various homology families, and the numbers of activated CFU-B, reflecting the massive B lymphocyte responses. In acute phase, all nine families are expressed in roughly the same proportions as in normal mice, whereas in chronic infection, B cells expressing S107 and 7183 VH-genes might be preferentially stimulated. These results establish the polyclonal nature of the host response to T. cruzi infection.     

Comparison of the production of eicosanoids by human and rat peritoneal macrophages and rat Kupffer cells

Human and rat peritoneal macrophages and rat Kupffer cells were labelled with [1-14C] arachidonic acid and stimulated with the calcium ionophore A23187. The metabolites formed were separated by high pressure liquid chromatography (HPLC). Human peritoneal macrophages formed especially leukotriene B4, 5-hydroxy-6,8,11,14 eicosatetraenoic acid and small amounts of leukotriene C4 and thromboxane B2, 12-hydroxy-5,8,10 heptadecatrienoic acid and 6-keto-prostaglandin F1 alpha, whereas rat peritoneal macrophages mainly produced cyclooxygenase products and in particular thromboxane B2 and 12-hydroxy-5,8,10 heptadecatrienoic acid. Rat Kupffer cells synthesized mainly cyclooxygenase products such as prostaglandin F2 alpha, prostaglandin D2 and prostaglandin E2. These results indicate that the profile of eicosanoids production by macrophages is dependent both on the species and on the tissue from which the macrophage is derived.     

Heterologous antibody responses in mice with chronic T. cruzi infection: depressed T helper function restored with supernatants containing interleukin 2

Antibody production to sheep erythrocytes (SRBC) or hapten-conjugated SRBC (TNP-SRBC) was studied in mice with chronic Trypanosoma cruzi infections. Studies in vivo demonstrated that both IgM and IgG anti-SRBC responses were suppressed during chronic infection. Secondary IgG responses were suppressed regardless of whether the primary immunization was given before or after infection. The ability of cells from infected mice to provide help for antibody production was examined in vitro. Anti-SRBC responses were restored to cultures of whole spleen cells from infected mice by the addition of interleukin 2 (IL 2)-rich supernatants, indicating that these cells were capable of antibody production when sufficient help was provided. T cells from SRBC-primed infected mice were unable to provide significant help to normal B cell/M phi cultures for in vitro anti-TNP or anti-SRBC responses. The percentages of Thy-1+, Lyt-1+, and Lyt-2+ spleen cells were not significantly different between normal and infected mice. Anti-TNP and anti-SRBC responses were restored to cultures that contained T cells from infected mice and normal B cell/M phi by the addition of IL 2-rich spleen cell supernatants. The suppression of in vitro antibody responses in mice with chronic T. cruzi infections was associated with a lack of T cell help, which was provided by exogenous spleen cell supernatant.     

Trypanosoma cruzi: explant organ cultures from mice with chronic Chagas' disease

Explants of 13 different organs obtained from C3H/HEN, Swiss-Webster, and C57Bl/6 mice chronically infected with Trypanosoma cruzi (Y strain) were cocultivated with mouse embryo fibroblasts to determine the organs that contain T. cruzi during the chronic infection. Explant cultures frequently yielded T. cruzi as late as 12 months after infection. Spleen and skeletal muscle were most frequently positive; heart cultures were rarely positive in any mouse strain. C3H/HEN mice had significantly more cultures positive than Swiss-Webster mice, as expected from relative susceptibility of C3H/HEN mice to acute infection. In contrast, C57Bl/6 mice, relatively resistant to acute infection, had significantly more cultures positive at 12 months of infection than Swiss-Webster mice. Also, C57Bl/6 mice had a significant increase in the number of positive cultures at 12 months of infection compared to 6 months of infection. These results show that organisms can be recovered routinely from some tissues during the chronic infection, that murine susceptibility to infection should differentiate between acute and chronic infection, and that C57Bl/6 mice may lose control of infection during the chronic infection.     

Effects of ozone on lung mechanics and cyclooxygenase metabolites in dogs.

To determine if acute exposure to ozone can cause changes in the production of cyclooxygenase metabolites of arachidonic acid (AA) in the lung which are associated with changes in lung mechanics, we exposed mongrel dogs to 0.5 ppm ozone for two hours. We measured pulmonary resistance (RL) and dynamic compliance (Cdyn) and obtained methacholine dose response curves and bronchoalveolar lavagate (BAL) before and after the exposures. We calculated the provocative dose of methacholine necessary to increase RL 50% (PD50) and analyzed the BAL for four cyclooxygenase metabolites of AA: a stable hydrolysis product of prostacyclin, 6-keto-prostaglandin F1 alpha (6-keto-PgF1 alpha); prostaglandin E2 (PgE2); a stable hydrolysis product of thromboxane A2, thromboxane B2 (TxB2); and prostaglandin F2 alpha (PgF2 alpha). Following ozone exposure, RL increased from 4.75 +/- 1.06 to 6.08 +/- 1.3 cm H2O/L/sec (SEM) (p less than 0.05), Cdyn decreased from 0.0348 +/- 0.0109 TO .0217 +/- .0101 L/cm H2O (p less than 0.05), and PD50 decreased from 4.32 +/- 2.41 to 0.81 +/- 0.49 mg/cc (p less than 0.05). The baseline metabolite levels were as follows: 6-keto PgF1 alpha: 96.1 +/- 28.8 pg/ml; PgE2: 395.8 +/- 67.1 pg/ml; TxB2: 48.5 +/- 11.1 pg/ml; PgF2 alpha: 101.5 +/- 22.6 pg/ml. Ozone had no effect on any of these prostanoids. These studies quantify the magnitude of cyclooxygenase products of AA metabolism in BAL from dog lungs and demonstrate that changes in their levels are not prerequisites for ozone-induced changes in lung mechanics or airway reactivity.     

Isotype determination of anti-Trypanosoma cruzi antibody in murine Chagas' disease.

Isotypic analysis of anti-parasite humoral responses of C57B1/6 and C3H (He) mice surviving acute Trypanosoma cruzi infection showed that both mouse strains demonstrate IgG1, IgG2a, IgG2b, and IgM enzyme-linked immunosorbent assay titers from days 21 to 300 of infection. Using the western blot technique to determine the antigen specificity of the isotypic responses, 100-day infected C3H mice showed strong IgG1, IgG2a, and IgG2b responses to many antigens, whereas C57B1/6 mice showed weak responses to fewer antigens. Isotype western blots showed that reactivity to the T. cruzi antigen of 75-77 kDa is present in the humoral response of day 21-infected mice that will survive and missing in those that will not survive. In general, surviving immunized C3H mice respond with IgG1, IgG2a, and IgG2b reactions to the 75-77-kDa and other antigens, whereas resistant B6 mice concentrate their anti-T. cruzi response in the IgG2b isotype to the 75-77-kDa antigen. Perhaps induction of ineffective antibody responses to nonprotective antigens is beneficial to the parasite and detrimental to the host.     

Changes in cell populations and immunoglobulin-producing cells in the spleens of mice infected with Trypanosoma cruzi: correlations with parasite-specific antibody response

Infection of mice with Trypanosoma cruzi elicits the production of parasite-specific antibodies which reach high levels and remain elevated for at least 105 days of infection. The more susceptible C3H(He) mouse actually has a higher level of "natural" antibodies for T. cruzi but may show a greater lag time in the production of antibodies in response to infection than the more resistant C57BL/6 mouse. Comparison of the kinetics of antibody production against T. cruzi and the numbers of immunoglobulin-producing cells in the spleen during the course of infection suggests that a large number of the immunoglobulin-producing cells are probably producing antibodies directed against the parasite and are not the result of an exhaustive polyclonal B-cell activation. Cell numbers in the spleen change dramatically both in total numbers and in the percentage of different cell types during infection with T. cruzi. The percentage of T cells in the spleen remains relatively unchanged throughout infection in both mouse strains tested but numbers of Ig-positive cells decrease markedly during the acute phase of infection while macrophage numbers increase up to sixfold. Cell numbers and proportions of B cells, T cells, and macrophages return to near normal values by 105 days of infection in the C57BL/6 mouse.     

Trypanosoma cruzi: cross-reactive anti-heart autoantibodies produced during infection in mice

Preimmunization with attenuated Corpus Christi stain Trypanosoma cruzi provides survival to C3H mice and enhances resistance of C57 mice to Brazil strain infection. C3H(He) and C57 B1/6 mice surviving acute infection of T. cruzi are shown to have heart specific autoantibodies through acute and chronic infection. ELISA assays were performed using nondenatured extract of hearts from normal syngeneic mice as target antigen reacted with sera from immunized and/or infected mice. Surviving C3H mice developed a specific anti-heart response as early as Day 21 of infection and this response continued at a high level to Day 300. The response in C57 mice, both immunized-infected and infected only, increased to Day 100 followed by a decline in intensity. The heart specificity of the response in mice was suggested by negligible reaction of sera with smooth muscle preparations and a reduced autoreactivity with skeletal muscle. Laminin, a suggested target of autoimmunity in Chagas' disease, was shown not to be the target of the responses in these mice. Immunoaffinity-purified heart specific antibodies show strong cross-reactivity with parasite antigen and like purified parasite specific antibodies, reacted with heart antigen.     

Non-antibody-mediated control of parasitemia in acute experimental Chagas' disease

There appear to be two phases in the control of parasitemia in acute Chagas' disease in the mouse. The first phase occurs during the first few weeks after infection and control is achieved through a thymus-dependent, antibody-independent mechanism. Challenge of B cell-suppressed C3H and F1 (C57BL/6 X C3H) mice with the Brazil strain of Trypanosoma cruzi led to a course of parasitemia for the first 3 wk after infection similar to that seen in normal C3H or F1 mice and markedly lower than the parasite levels observed in the blood of nu/nu mice. Challenge of BXH-2 recombinant inbred mice resulted in a course of parasitemia similar to that seen in nu/nu mice up to day 16 despite the production of normal levels of antibody. The BXH-2 mice lack the ability to effect the early control of parasitemia. The second phase begins several weeks after infection with the rise in antibody titer, and the control is exerted through an antibody-mediated mechanism. In all B cell-suppressed mice, an inexorable rise in parasitemia occurred up to the time of death, which suggests that antibody is important for the eventual clearance of parasites from the blood. A comparison of the IgM and IgG antibody titers to T. cruzi in a series of resistant and susceptible strains showed that there was no correlation between the appearance of specific antibody or antibody titers and the levels of parasitemia observed. The level of parasitemia attained in the late acute phase may be primarily determined by the extent of parasite proliferation in the early acute phase.     

CTLA-4 blockage increases resistance to infection with the intracellular protozoan Trypanosoma cruzi

Recent studies have revealed an important role for CTLA-4 as a negative regulator of T cell activation. In the present study, we evaluated the importance of CTLA-4 to the immune response against the intracellular protozoan, Trypanosoma cruzi, the causative agent of Chagas' disease. We observed that the expression of CTLA-4 in spleen cells from naive mice cultured in the presence of live trypomastigote forms of T. cruzi increases over time of exposure. Furthermore, spleen cells harvested from recently infected mice showed a significant increase in the expression of CTLA-4 when compared with spleen cells from noninfected mice. Blockage of CTLA-4 in vitro and/or in vivo did not restore the lymphoproliferative response decreased during the acute phase of infection, but it resulted in a significant increase of NO production in vivo and in vitro. Moreover, the production of IFN-gamma in response to parasite Ags was significantly increased in spleen cells from anti-CTLA-4-treated infected mice when compared with the production found in cells from IgG-treated infected mice. CTLA-4 blockade in vivo also resulted in increased resistance to infection with the Y and Colombian strains of T. cruzi. Taken together these results indicate that CTLA-4 engagement is implicated in the modulation of the immune response against T. cruzi by acting in the mechanisms that control IFN-gamma and NO production during the acute phase of the infection.     

Type I IFNs stimulate nitric oxide production and resistance to Trypanosoma cruzi infection

The participation of type I IFNs (IFN-I) in NO production and resistance to Trypanosoma cruzi infection was investigated. Adherent cells obtained from the peritoneal cavity of mice infected by the i.p. route produced NO and IFN-I. Synthesis of NO by these cells was partially inhibited by treatment with anti-IFN-alphabeta or anti-TNF-alpha Abs. Compared with susceptible BALB/c mice, peritoneal cells from parasite-infected resistant C57BL/6 mice produced more NO (2-fold), IFN-I (10-fold), and TNF-alpha (3.5-fold). Later in the infection, IFN-I levels measured in spleen cell (SC) cultures from 8-day infected mice were greater in C57BL/6 than in infected BALB/c mice, and treatment of the cultures with anti-IFN-alphabeta Ab reduced NO production. IFN-gamma or IL-10 production by SCs was not different between the two mouse strains; IL-4 was not detectable. Treatment of C57BL/6 mice with IFN-I reduced parasitemia levels in the acute phase of infection. Mice deprived of the IFN-alphabetaR gene developed 3-fold higher parasitemia levels in the acute phase in comparison with control 129Sv mice. Production of NO by peritoneal macrophages and SCs was reduced in mice that lacked signaling by IFN-alphabeta, whereas parasitism of macrophages was heavier than in control wild-type mice. We conclude that IFN-I costimulate NO synthesis early in T. cruzi infection, which contributes to a better control of the parasitemia in resistant mice.     

Increase in the formation of leukotriene B4 and other lipoxygenase products in peritoneal macrophages of adrenalectomized rats

The effect of adrenalectomy on the formation of cyclooxygenase and lipoxygenase products by activated peritoneal rat macrophages was determined. After isolation, the cells were incubated with [1-14C]arachidonic acid and the calcium ionophore A23187 and the metabolites isolated by HPLC chromatography. The main components formed in the controls are 6-keto-prostaglandin F1 alpha, thromboxane B2 and 12-HETE. One peak represents 5,12-di-HETE. Smaller amounts of prostaglandin F2 alpha, prostaglandin E2, prostaglandin D2, leukotriene B4 and 15-HETE are also present. After adrenalectomy, a considerable increase occurs in the amounts of leukotriene B4, 15-HETE and 12-HETE. The increase in the prostaglandins is smaller. The compounds formed from endogenous arachidonic acid are also determined. In the cells of the controls, 6-keto-prostaglandin F1 alpha and thromboxane B2 are produced in higher amounts than leukotriene B4. After adrenalectomy, the formation of leukotriene B4 is much more increased than that of 6-keto-prostaglandin F1 alpha. These effects are most probably related to a diminished amount or inactivation of lipocortin, a glucocorticosteroid-induced peptide with phospholipase A2 inhibitory activity in adrenalectomized animals.     

Appearance of the arachidonic acid metabolic pathway in human promyelocytic leukemia (HL-60) cells during monocytic differentiation: enhancement of thromboxane synthesis by 1 alpha,25-dihydroxyvitamin D-3

The appearance of the arachidonic acid metabolic pathway in human promyelocytic leukemia (HL-60) cells was investigated during 1 alpha,25-dihydroxyvitamin D-3-induced monocytic differentiation. 1 alpha,25-Dihydroxyvitamin D-3-treated HL-60 cells acquired the ability to convert [1-14C]arachidonic acid to thromboxane B2 and prostaglandin E2 during monocytic differentiation. The major cyclooxygenase product synthesized by the HL-60 cells after 3-4 days exposure to 1 alpha,25- dihydroxyvitamin D-3 (48 nM) was thromboxane B2 and its production was about 19-25-times higher than that of untreated HL-60 cells. The percent conversion of thromboxane B2 from [1-14C]arachidonic acid in the 1 alpha,25-dihydroxyvitamin D-3 (48 nM, 3 day exposure)-treated HL-60 cells was about 4.4% as compared to that (about 0.3%) of the untreated cells, whereas the percent conversion of thromboxane B2 from [1-14C]prostaglandin H2 in the 1 alpha,25-dihydroxyvitamin D-3-treated cell homogenate was about 22.4% as compared to that (about 13.6%) of the untreated cell homogenate. The stimulatory effect of 1 alpha,25-dihydroxyvitamin D-3 on thromboxane B2 production from [1-14C]arachidonic acid and from [1-14C]prostaglandin H2 in HL-60 cells was inhibited by the addition of cycloheximide (1 microgram/ml). However, 1 alpha,25-dihydroxyvitamin D-3 (48 nM) did not significantly stimulate the arachidonic acid release either in HL-60 cells or in 1 alpha,25-dihydroxyvitamin D-3-induced cells. These results suggest that the stimulatory effect of 1 alpha,25-dihydroxyvitamin D-3 on the thromboxane production in HL-60 cells was not due to the activation of phospholipase A2 but due to the induction of fatty acid cyclooxygenase and thromboxane synthetase activities. Thromboxane A2 actively produced during the monocytic differentiation of HL-60 cells could influence the cell adhesiveness of the monocyte-macrophage-differentiated cells.     

Relation of prostanoids to strength of hypoxic vasoconstriction in dogs with lobar atelectasis

In dogs with acute lobar atelectasis, meclofenamate administration decreases shunt fraction uniformly and moderately without abolishing the wide variation of strength of hypoxic vasoconstriction and resultant variability of shunt fraction (J. Appl. Physiol. 54: 284-289, 1983). To further assess the role of prostanoids, we measured prostanoid metabolites as well as shunt fraction and pressor response to alveolar hypoxia. In six intact anesthetized dogs with acute left lower lobe atelectasis, shunt fraction during normoxia was measured with SF6. Levels of 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 in arterial, mixed venous, and left lower lobe venous blood were measured with the double antibody radioimmunoassay technique. Ten percent O2 was administered to assess pressor response. Twenty-one percent O2 was restarted, meclofenamate was administered, and measurements were repeated 30 min later. Atelectasis did not elevate levels of prostanoid metabolites. 6-Keto-PGF1 alpha averaged 88 +/- 65 pg/ml prior to atelectasis and 81 +/- 73 pg/ml after atelectasis (F = 0.7, P = NS). Likewise, thromboxane B2 values were normal. No transpulmonary concentration differences were found. 6-Keto-PGF1 alpha did not correlate with shunt values, which ranged from 14 to 35% (mean 21%). Meclofenamate effectively blocked cyclooxygenase, as demonstrated by decreases in prostanoid metabolite levels. It seems likely that in dogs with acute atelectasis prostacyclin localized in the pulmonary vasculature decreases strength of hypoxic vasoconstriction modestly and uniformly without raising blood levels of prostacyclin metabolite.     

IL-10 limits parasite burden and protects against fatal myocarditis in a mouse model of Trypanosoma cruzi infection

Chagas' disease is a zoonosis prevalent in Latin America that is caused by the protozoan Trypanosoma cruzi. The immunopathogenesis of cardiomyopathy, the main clinical problem in Chagas' disease, has been extensively studied but is still poorly understood. In this study, we systematically compared clinical, microbiologic, pathologic, immunologic, and molecular parameters in two mouse models with opposite susceptibility to acute myocarditis caused by the myotropic Colombiana strain of T. cruzi: C3H/HeSnJ (100% mortality, uncontrolled parasitism) and C57BL/6J (<10% mortality, controlled parasitism). T. cruzi induced differential polarization of immunoregulatory cytokine mRNA expression in the hearts of C57BL/6J versus C3H/HeSnJ mice; however, most differences were small. The difference in IL-10 expression was exceptional (C57BL/6J 8.7-fold greater than C3H/HeSnJ). Consistent with this, hearts from infected C57BL/6J mice, but not C3H/HeSnJ mice, had a high frequency of total IL-10-producing CD8(+) T cells and both CD4(+) and CD8(+) subsets of IFN-γ(+)IL-10(+) double-producing T cells. Furthermore, T. cruzi infection of IL-10(-/-) C57BL/6J mice phenocopied fatal infection in wild-type C3H/HeSnJ mice with complete loss of parasite control. Adoptive transfer experiments indicated that T cells were a source of protective IL-10. Thus, in this system, IL-10 production by T cells promotes T. cruzi control and protection from fatal acute myocarditis.     

Trypanosoma cruzi: maintenance of parasite-specific T cell responses in lymph nodes during the acute phase of the infection

Mice infected with 5 x 10(3) forms of Trypanosoma cruzi showed a transient, but severe impairment of in vitro spleen cell responses to parasite antigens and to Concanavalin A (Con A). In contrast, inguinal and periaortic lymph node (LN) cells displayed high parasite-specific proliferative responses and only a partial reduction of the Con A-induced proliferation during the acute and chronic phases of infection. Lymphocytes that underwent blastic transformation in T. cruzi-stimulated cell cultures were of the L3T4+ phenotype. Suppression of spleen cell responses occurred in the acute phase whether mice were infected with high (3 x 10(5] or low (5 x 10(3] doses of T. cruzi by intraperitoneal or subcutaneous route. Suppression of the T. cruzi-specific proliferative response of LN cells was only observed in mice infected with high subcutaneous inocula. This suppression, however, was restricted to the LNs draining the site of inoculation without affecting distant LNs. Supernatants from parasite-stimulated proliferating LN cells displayed low or undetectable T cell growth factor (TCGF) activity, in contrast with the high TCGF levels found in supernatants of the same cells stimulated with Con A. Low levels of TCGF were also detected in cultures of LN cells from mice immunized with T. cruzi extracts. Neither the T. cruzi antigen used for in vitro stimulation nor the LN cell supernatants from infected mice inhibited TCGF activity. These findings indicate that (1) parasite-specific responses are present in the LN compartment throughout the acute phase of T. cruzi infection in mice and (2) the proliferative response of L3T4+ LN cells from infected mice to T. cruzi antigens is not associated with a high TCGF secretory response.     

Autoimmune CD4+ T cells interfere with immune tolerance to a thymic-independent antigen

The ability of autoimmune T cell subsets to interfere with tolerization of B cells can be studied by using thymic-independent Ag. We have defined an abnormality within the CD4+ T cell compartment in young NZB and MRL-lpr/lpr mice by studying tolerance of spleen and B cells to the thymic independent Ag, fluorescein-Brucella abortus. Tolerization of spleen cells is defective in MRL-lpr/lpr mice, but not MRL-+/+ or C3H.lpr mice, suggesting that the defect requires both the autosomal MRL background and the lpr gene to be present. T enriched cells from NZB mice and from MRL-lpr/lpr mice (but not MRL-+/+ or C3H.lpr mice) reverse tolerance in spleen cells from [NZB X DBA/2]F1 and C3H/HeJ mice, respectively. This interference is removed by treatment with anti-CD4 antibody and C. Supernatants from cultured T cells of NZB and MRL-lpr/lpr mice also prevent tolerance in spleen cells of [NZB X DBA/2]F1 and MRL-+/+ mice, respectively, unless CD4+ cells are removed prior to T cell culture. Removal of T cells from NZB and MRL-lpr/lpr spleen cells allows normal tolerization of B cells, which is abrogated by the addition of syngeneic T cells or cultured T cell supernatants. This effect also depends on the presence of CD4+ T cells. These studies show that in MRL-lpr/lpr mice, through interaction of the lpr and MRL background genes in a T cell subset, and in NZB mice, CD4+ T cells interfere with B cell tolerance to a thymic-independent Ag.