Cell-mediated Immunosuppression Research Articles

Species Variation in the Mechanisms of Mesenchymal Stem Cell-Mediated Immunosuppression (141.45)

Abstract Bone marrow derived mesenchymal stem cells (MSCs) hold great promise for treating immune disorders, although the immunoregulatory mechanisms remain largely controversial. Here we show that the mechanisms of MSC-mediated immunosuppression vary in different species. Under the same culture conditions, immunosuppression by MSCs derived from human or monkey was mediated by indoleamine 2, 3 dioxygenase (IDO), while immunosuppression by mouse MSCs depended on nitric oxide (NO). When the expression levels of inducible nitric oxide synthase (iNOS) and IDO were examined in mouse and human MSCs stimulated with their respective inflammatory cytokines, we found that human MSCs expressed high levels of IDO, but very low levels of iNOS, while mouse MSCs expressed high levels of iNOS and very little IDO. Except the executor molecules, moreover, the human and mouse MSCs shared some similarities. Like in mouse MSCs, immunosuppression by human MSCs was not intrinsic, but inducible by inflammatory cytokines. Additionally, IDO-mediated immunosuppression by human MSCs is also chemokine-dependent. These findings help to explain the apparently conflicting reports in the literatures and provide critical information to allow better application of human MSCs in treating immune disorders.

Laparoscopy or fast-track surgery, or both?

There is no doubt that the laparoscopic revolution could beconsidered one of the major improvements for the man-agement of colorectal diseases. Since its introduction in the1990s, several meta-analyses have clearly demonstrated itsfeasibility and efficacy [1, 2]. It is becoming the new ‘‘goldstandard’’ for the care of colonic diseases with a high levelof evidence [3] because of its mini-invasiveness and betterpostoperative comfort for surgical patients. At the sametime, another improvement in colorectal surgery, initiatedby Kehlet and coworkers, the so-called enhanced recoveryprotocol or the fast-track surgery (FTS) approach [4, 5],initially less recognized, has gradually gained worldwideacceptance [6]. This new paradigm, a parallel revolution inthe care of surgical patients (based on a multimodalapproach of patients), was initiated in the field of opensurgery. However, the evidence-based literature showswith a high level of evidence that FTS is feasible, safe, andoffers a better postoperative recovery compared with tra-ditional care [5], even for laparoscopic surgery.Generally speaking, beside the field of colorectal sur-gery, one of the most important lessons learned from thelaparoscopic revolution has been that some of the olddogma has to be questioned: this has sparked a review ofseveral practices in open surgery. As an example, surgicalstress and inflammatory response to surgery have beenbetter evaluated and cell-mediated immunosuppression hasbeen highlighted as an important component in this setting[7]. Thanks to the laparoscopic approach, ‘‘modern open’’surgery also has become less ‘‘aggressive.’’Two alternatives for colorectal surgeryWe are now faced with two alternative options, bothdesigned to improve perioperative surgical care: ‘‘tradi-tional’’ laparoscopic surgery and ‘‘open’’ FTS.It is noteworthy that in the major, randomized trials [8–11] that served to establish the superiority of laparoscopiccolon surgery compared with its open counterpart, the con-trol patients underwent open traditional approach withoutFTS—the standard when those trials were initiated. There-fore, from anevidence-basedpoint ofview, one can only saythat laparoscopic surgery is superior to open surgery as itwas conceptualized in the 1990s. Without trials comparingtraditional laparoscopic surgery to open FTS, whether thereis sound evidence that the traditional laparoscopic surgery issuperior to open FTS remains to be shown.When we consider the respective results of these twoapproaches and compare for example the length of post-operative hospital stay (LOS), the results of randomizedtrials on conventional laparoscopic surgery (without amultimodal perioperative approach) were never superior tothose of FTS. Indeed, LOS is an outcome subjected tovariations related to socioeconomic factors, but all pub-lished large trials showed concordant results with a meanLOS exceeding 5 days in all cases [8–11], whereas in mostrandomized trials on ‘‘open’’ FTS, the mean LOS did notexceed 5 days [references on request to KS].

The Role of Treg Cells in the Cancer Immunological Response

Problem statement: T cell-mediated immunosuppression has been observed for decades without clarification as to which factor was responsible for this observation. The identification of CD4+CD25+ regulatory T (Treg) cells represents a milestone in the filed of immunology and provides an explanation for T-cell-mediated immunosuppression. Although Treg cells were originally identified for their ability to prevent organ-specific autoimmune disease in mice, emerging evidence suggests that Treg cells play a pivotal role in tumor immunity and contribute to tumor growth and progression, thereby having an important impact on the outcome of cancer patients. Approach: This article reviewed the medical literature to describe how Treg cells affect anti-tumor immunity. Results: Treg cells suppressed anti-tumor immunity by inhibiting the effector functions of tumor-specific T cells and NK cells. Importantly, tumor cells played an active role in recruiting and generating Treg cells and creating a suppressive tumor microenvironment. Strategies to deplete Treg cells or inhibit their function had yielded promising results by enhancing anti-tumor immunity in experimental studies as well as clinical practice. Conclusion: A better understanding of the pathophysiology of Treg cells not only increased our knowledge in a variety of aspects of immunology but also potentially benefited cancer patients.

Reversal of Myeloid Cell–Mediated Immunosuppression in Patients with Metastatic Renal Cell Carcinoma

Tumor-induced immunosuppression remains a significant obstacle that limits the efficacy of biological therapy for renal cell carcinoma. Here we evaluate the role of CD33 myeloid-derived suppressor cells (MDSC) in the regulation of T-cell responses in renal cell carcinoma patients. We also examine effect of all-trans-retinoic acid (ATRA) on MDSC-mediated immune suppression. CD33-positive myeloid cells were isolated from the peripheral blood of renal cell carcinoma patients with magnetic beads and tested in vitro for their ability to inhibit T-cell responses. T-cell function was evaluated using ELISPOT and CTL assays. MDSC isolated from renal cell carcinoma patients, but not from healthy donors, were capable of suppressing antigen-specific T-cell responses in vitro through the secretion of reactive oxygen species and nitric oxide upon interaction with CTL. MDSC-mediated immune suppression and IFN-gamma down-regulation was reversible in vitro by exposing cells to the reactive oxygen species inhibitors. Moreover, ATRA was capable of abrogating MDSC-mediated immunosuppression and improving T-cell function by direct differentiation into antigen-presenting cell precursors. These results may have significant implications regarding the future design of active immunotherapy protocols that may include differentiation agents as part of a multimodal approach to renal cell carcinoma immunotherapy.

In vitro evaluations of innate and acquired immune responses to electrospun polydioxanone–elastin blends

Immune response testing of biomaterials is an essential component of biocompatibility assessment, particularly when the materials of interest are used to design bioresorbable scaffolds with the potential to promote in situ regeneration. Current trends in immune response testing of biomaterials typically examine few elements of the immune system, and they often undertake a mechanistic approach without first determining if material exposure results in physiologically relevant modulation of both innate and acquired immunity. Here, we present a comprehensive in vitro evaluation of biomaterial-induced modulation of acquired (i.e. cell-mediated and humoral) and innate immune responses following exposure to electrospun blends of polydioxanone (PDO) and elastin (ELAS). Results indicated that in vitro exposure of murine spleen cells to PDO–ELAS blends produced statistically significant immunosuppression in multiple cell-mediated and humoral endpoints. Results suggested that ELAS is the primary cause of cell-mediated immunosuppression. In contrast, PDO and ELAS were equally suppressive of humoral immune responses, while blends of the two were more immunosuppressive than either pure polymer alone. Evaluations of innate immune responses demonstrated few significant effects, with statistically significant immunosuppression observed in natural killer cell activity but not in macrophage functional assays. This work presents an approach for assessing potential modulation of immune responses resulting from exposure to biomaterials, and such evaluations are essential to obtaining comprehensive assessments of biocompatibility.

Apoptotic Cells Induce Immunosuppression through Dendritic Cells: Critical Roles of IFN-γ and Nitric Oxide

Apoptotic cells induce immunosuppression through unknown mechanisms. To identify the underlying molecular mediators, we examined how apoptotic cells induce immunoregulation by dendritic cells (DC). We found that administration of DC exposed to apoptotic cells (DC(ap)) strongly inhibited the expansion of lymphocytes in draining lymph nodes in vivo and the subsequent Ag-specific activation of these lymphocytes ex vivo. Unexpectedly, DC(ap) supported T cell activation to a similar extent as normal DC in vitro, leading to proliferation and IL-2 production, except that DC(ap) did not support T cell production of IFN-gamma. Surprisingly, when DC(ap) were cocultured with normal DC, they completely lost their ability to support T cell activation, an effect reversed by anti-IFN-gamma or inhibitors of inducible NO synthase (iNOS). As expected, exposure to apoptotic cells rendered DC(ap) capable of producing much more NO in response to exogenous IFN-gamma than normal DC. Furthermore, DC(ap) from iNOS(-/-) or IFN-gammaR1(-/-) mice were not inhibitory in vitro or in vivo. Therefore, the IFN-gamma-induced production of NO by apoptotic cell-sensitized DC plays a key role in apoptotic cell-mediated immunosuppression.

Foxp3 +CD4 + T cell-mediated immunosuppression involves extracellular nucleotide catabolism

Foxp3(+)CD4(+) T cells represent a population of naturally arising suppressor T cells that are crucial for the control of autoimmune responses. The suppressive activity of this T cell subset relies on multiple mechanisms that include secretion of anti-inflammatory factors such as TGF-beta or IL-10. Novel studies now establish that, through the generation of the immunosuppressive factor adenosine, the ectoenzymes CD39 and CD73 are important contributors to the regulatory activity of Foxp3(+)CD4(+) T cells.

Mesenchymal Stem Cell-Mediated Immunosuppression Occurs via Concerted Action of Chemokines and Nitric Oxide

Mesenchymal stem cells (MSCs) can become potently immunosuppressive through unknown mechanisms. We found that the immunosuppressive function of MSCs is elicited by IFNgamma and the concomitant presence of any of three other proinflammatory cytokines, TNFalpha, IL-1alpha, or IL-1beta. These cytokine combinations provoke the expression of high levels of several chemokines and inducible nitric oxide synthase (iNOS) by MSCs. Chemokines drive T cell migration into proximity with MSCs, where T cell responsiveness is suppressed by nitric oxide (NO). This cytokine-induced immunosuppression was absent in MSCs derived from iNOS(-/-) or IFNgammaR1(-/-) mice. Blockade of chemokine receptors also abolished the immunosuppression. Administration of wild-type MSCs, but not IFNgammaR1(-/-) or iNOS(-/-) MSCs, prevented graft-versus-host disease in mice, an effect reversed by anti-IFNgamma or iNOS inhibitors. Wild-type MSCs also inhibited delayed-type hypersensitivity, while iNOS(-/-) MSCs aggravated it. Therefore, proinflammatory cytokines are required to induce immunosuppression by MSCs through the concerted action of chemokines and NO.

Oncologic Impact of Surgery in the Early Postoperative Period

Surgical intervention represents a deliberate form of tissue injury producing the acute phase response. The response to injury is also associated with a period of relative immune suppression and the magnitude of the response is proportional to the degree of surgical trauma. The proinflammatory cascade of events produced by the response to injury coupled with a impairment of postoperative cell-mediated immune function may provide a stimulus for the progression of neoplastic disease. There is strong evidence from animal studies that all types of abdominal surgical procedures are associated with increased rates of systemic tumor establishment and growth postoperatively. In preclinical models, minimally invasive techniques have been shown to ameliorate the effects of surgically induced tumor progression. This pattern of tumor behavior was noted following sham operations and after bowel resections. The precise mechanism of these changes remains unclear; however, both an increased rate of tumor cell proliferation and a decreased apoptosis have been noted after open surgery. There is also evidence that the cell-mediated immunosuppression that has been documented to occur after surgery accounts for some of the differences in tumor growth after open versus laparoscopic surgery. Systemic plasma factors elaborated following laparotomy have also been associated with increased tumor cell proliferation in vitro, suggesting that it may prove possible to pharmacologically protect patients from the deleterious side effects of surgery on postoperative tumor proliferation.

Regulatory T Cells: Potential Target in Anticancer Immunotherapy

The concept of regulatory T cells was first described in the early 1970s, and regulatory T cells were called suppressive T cells at that time. Studies that followed have demonstrated that these suppressive T cells negatively regulated tumor immunity and contributed to tumor growth in mice. Despite the importance of these studies, there was extensive skepticism about the existence of these cells, and the concept of suppressive T cells left the center stage of immunologic research for decades. Interleukin-2 receptor alpha-chain, CD25, was first demonstrated in 1995 to serve as a phenotypic marker for CD4+ regulatory cells. Henceforth, research of regulatory T cells boomed. Regulatory T cells are involved in the pathogenesis of cancer, autoimmune disease, transplantation immunology, and immune tolerance in pregnancy. Recent evidence has demonstrated that regulatory T cell-mediated immunosuppression is one of the crucial tumor immune evasion mechanisms and the main obstacle of successful cancer immunotherapy. The mechanism and the potential clinical application of regulatory T cells in cancer immunotherapy are discussed.

Cutting Edge: CNS CD11c+ Cells from Mice with Encephalomyelitis Polarize Th17 cells and Support CD25+CD4+ T cell-Mediated Immunosuppression, Suggesting Dual Roles in the Disease Process

CD11c(+) dendritic cells (DCs) are a prominent component of CNS infiltrates in mice with experimental autoimmune encephalomyelitis. However, their role in immunopathogenesis is controversial. In this study, we report that they originate from peripheral hemopoietic cells and exhibit diverse functions that change during the course of acute disease. CNS DCs stimulate naive T cells to proliferate and polarize Th(17) responses when harvested shortly following disease onset but are relatively inefficient APC by the time of peak disability. Conversely, they can support CD4(+)CD25(+) T cell-mediated immunosuppression early during experimental autoimmune encephalomyelitis. Such paradoxical functions might reflect dual roles of CNS DCs in promoting local inflammation while setting the stage for remission.

Cutting Edge: Induction of B7-H4 on APCs through IL-10: Novel Suppressive Mode for Regulatory T Cells

Multiple modes of suppressive mechanisms including IL-10 are thought to be implicated in CD4+CD25+ regulatory T (Treg) cell-mediated suppression. However, the cellular source, role, and molecular mechanism of IL-10 in Treg cell biology remain controversial. We now studied the interaction between Treg cells and APCs. We demonstrate that Treg cells, but not conventional T cells, trigger high levels of IL-10 production by APCs, stimulate APC B7-H4 expression, and render APCs immunosuppressive. Initial blockade of B7-H4 reduces the suppressive activity mediated by Treg cell-conditioned APCs. Further, APC-derived, rather than Treg cell-derived, IL-10 is responsible for APC B7-H4 induction. Therefore, Treg cells convey suppressive activity to APCs by stimulating B7-H4 expression through IL-10. Altogether, our data provide a novel cellular and molecular mechanism for Treg cell-mediated immunosuppression at the level of APCs, and suggest a plausible mechanism for the suppressive effect of IL-10 in Treg cell-mediated suppression.

Treatment of human bone marrow with recombinant placenta immunoregulator ferritin results in myelopoiesis and T-cell suppression through modulation of the cytokine-chemokine networks

Placenta immunomodulator ferritin (PLIF) is a cloned human chimeric ferritin H chain with a novel non-ferritin C-terminal 48 amino acid sequence (C48). Recombinant PLIF-C48 exhibited cell-mediated immunosuppression. The aim of the current study was to investigate the regulatory effects of native placental ferritin (PLF), recombinant PLIF, and C48 on hematopoiesis of human bone marrow (BM). BM mononuclear cells (BM-MNCs) and CD34(+) selected cells were treated in vitro with either PLF, PLIF, or C48 without and in combination with granulocyte (G)-monocyte (M) colony-stimulating factor (GM-CSF) and subjected to hematopoietic progenitor cell assay. Cytokines and chemokines secreted by the treated cells were evaluated in culture supernatant using antibody array assays to determine mechanism of action. In vitro treatment of BM-MNCs with PLF, PLIF, or C48 induced significant growth of myeloid colonies and when mixed with GM-CSF or Granulocyte-Colony Stimulating Factor (G-CSF) exhibited additive enhanced colony forming units-granulocyte monocyte growth. Yet, C48 treatment of selected CD34(+) cells did not yield colony formation and did not affect their response to GM-CSF. Treatment of BM-MNCs with C48 for 48 hours induced secretion of marked levels of GM-CSF, interleukin (IL)-6, IL-1, and IL-10. These cytokines were secreted primarily by C48-treated BM adherent cells and partly by nonadherent cells, whereas the CD34(+) selected cells secreted IL-6 only. C48-PLIF enhancement of myelopoiesis resulted from cross talk between BM accessory cells and progenitor cells. The differential PLIF-C48 effects (i.e., myeloid progenitor cell growth and T-cell suppression) are due to their effect on the cytokine-chemokine networks.

Reversal of immature myeloid cell-mediated immunosuppression

2563 Background Tumor-bearing animals and cancer patients exhibit defects in myelopoiesis, resulting in the accumulation of immature myeloid cells (ImC). ImC have shown to induce a profound state of immune suppression by interfering with the function of tumor-specific T cells through several mechanisms, including the production of reactive oxygen species, or increased arginine activity. Thus, there is increased interest in developing strategies that allow the elimination of ImC in cancer immunotherapy protocols. Methods In this study we sought to develop accurate and reliable methods for the isolation of ImC in the peripheral blood of RCC patients and functionally validate their immunosuppressive action in vitro. In order to reverse ImC-mediated immunosuppressive activity, we used various differentiation agents, including all-trans retinoic acid to differentiate ImC to a mature, non-suppressive phenotype. Results We show that patients with advanced RCC possess significantly elevated levels of ImC in their...

<I>Bacillus subtilis</I> DB9011 菌株による犬の外科的侵襲後の細胞性免疫能低下の防御効果

<I>Bacillus subtilis</I> DB9011 菌株による犬の外科的侵襲後の細胞性免疫能低下の防御効果

Surgical trauma: hyperinflammation versus immunosuppression?

Experimental and clinical studies have brought evidence that surgical trauma markedly affects the immune system, including both the specific and the non-specific immune response. This report reviews the present knowledge on the mechanisms of surgical trauma-induced immune dysfunction and outlines experimental and clinical approaches to find effective treatment strategies. Major surgical trauma induces an early hyperinflammatory response, which is characterized by (1) pro-inflammatory tumour necrosis factor alpha (TNF), interleukin (IL)-1, and IL-6 cytokine release and (2) neutrophil activation and microvascular adherence, as well as (3) uncontrolled polymorphonuclear (PMN) and macrophage oxidative burst. The massive and continuous IL-6 release induces an acute phase response, but, more importantly, also accounts for the up-regulation of major anti-inflammatory mediators, such as prostaglandin (PG) E2, IL-10 and transforming growth factor (TGF)-ss. This results in surgical, trauma-induced, immunosuppression, as indicated by (1) monocyte deactivation, reflected by the lack of monocytic TNF- production upon lipopolysaccharide (LPS) stimulation, and (2) a shift of the Th1/Th2 ratio towards a Th2-dominated cytokine pattern. The imbalance between pro-inflammatory and anti-inflammatory cytokines and immuno-competent cells determines the phenotype of disease and should help the physician to compose the therapeutic strategy. In fact, recent clinical studies have shown that both the initial uncontrolled hyperinflammation and the continued cell-mediated immunosuppression represent primary targets to counteract post-surgery immune dysfunction. The balance between inflammatory and anti-inflammatory forces may be restored by interferon gamma (IFN-gamma) to counteract monocyte deactivation; the anti-inflammatory PGE2 may be inhibited by indomethacin to attenuate immunosuppression; or the initial hyperinflammation may be targeted by administration of anti-inflammatory substances, such as granulocyte colony-stimulating factor (G-CSF), hydoxyethyl starch, or pentoxifylline. When drawing up the therapeutic regimen the physician should not consider hyperinflammation versus immunosuppression, but hyperinflammation and immunosuppression, aiming at restoring an appropriate mediator- and immune cell-associated balance.

Timed ablation of regulatory CD4+ T cells can prevent murine AIDS progression.

We describe successful immunotherapy of murine AIDS (MAIDS) in C57BL/6J mice based on the elimination of replicating CD4(+) regulator T cells. We demonstrate that a single injection of the antimitotic drug vinblastine (Vb) given 14 days postinfection (p.i.) with LP-BM5 can prevent MAIDS progression. Treatment with anti-CD4 mAb at 14 days p.i. is similarly able to prevent MAIDS. Treatment at other time points with Vb or anti-CD4 mAb is ineffective. The effect is based on ablation of a replicating dominantly suppressive CD4(+) T cell population, as indicated by adoptive transfer and in vivo depletion experiments using mAbs against CD4 as well as combinations of mAbs against the known regulatory cell surface markers CD25, GITR, and CTLA-4. Cell surface marker analysis shows a population of CD4(+)CD25(+) cells arising shortly before day 14 p.i. Cytokine analyses show a peak in IL-10 production from day 12 to day 16 p.i. MAIDS-infected mice also have CD4(+) T cells with significantly higher expression levels of CD38 and particularly CD69, which have been demonstrated to be regulator T cell markers in the Friend retroviral model. The immunotherapy appears to prevent disease progression, although no protection against reinfection with LP-BM5 is generated. These data define a new therapy for murine retroviral infection, which has potential for use in other diseases where T regulator cell-mediated immunosuppression plays a role in the disease process.

TGF-β: the missing link in CD4 +CD25 + regulatory T cell-mediated immunosuppression

A unique population of CD4 + T lymphocytes that constitutively express CD25 has been recognized as anergic/suppressor cells. While the immunosuppressive activity of these CD4 +CD25 + cells has been validated and implicated in tolerance, autoimmunity, transplantation, cancer and infectious diseases, the mechanism(s) by which they function still remains controversial. Although the involvement of TGF-β was initially discounted, emerging evidence now links this cytokine with CD4 +CD25 + T cell-mediated suppression of antigen-activated T cells. In this perspective, we summarize recently published studies, as well as our own data, which shed light on how cell membrane-bound TGF-β can deliver a regulatory signal to target cells via a contact-dependent process. Moreover, suppressor T cell function is a complex process, tightly regulated by multiple factors, including IL-2, cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and glucocorticoid induced TNF receptor (GITR). Collectively, multiple previously unconnected puzzle pieces are beginning to be linked into a more coherent, albeit incomplete picture of CD4 +CD25 + T cell-mediated suppression.

Immunosuppression in specific-pathogen-free broilers administered infectious bursal disease virus vaccines by in ovo route.

The effect of two infectious bursal disease virus (IBDV) vaccines (IBDV-immune complex [Icx] and IBDV-2512), administered in ovo, on the cell-mediated immunity of specific-pathogen-free (SPF) broilers was examined. A decrease (P < 0.05) in the T-cell mitogenic response occurred in birds vaccinated with both vaccines on days 9 and 21 post in ovo vaccination (PIOV), but an increase (P < 0.05) occurred on day 15 PIOV. The T cells from birds given the IBDV-2512 were less responsive. There were no significant differences in proportions of lymphocytes expressing CT4+CT8 and CT8+CT4- except on day 21 PIOV, where an increase (P < 0.05) in IBDV-2512-vaccinated birds and a decrease (P < 0.05) in percentage of CT4+CT8- in IBDV-Icx-vaccinated birds was observed. There was an increase (P < 0.05) in percentage of CT8+CT4- T cells on day 21 PIOV in both vaccinated groups. A decrease (P < 0.05) in B-cell percentage was observed on day 21 PIOV in birds given both vaccines. Results indicated that although humoral immunosuppression is associated with destruction of B cells (bursal atrophy), cell-mediated immunosuppression induced by these two IBDV vaccines in SPF birds was not associated with altered helper (CT4+CT8-) or cytotoxic (CT8+CT4-) subpopulations of T lymphocytes.

Cytokine expression during the outcome of canine experimental infection by Leishmania infantum

In this study, the cytokines, interferon-gamma (IFN-γ), interleukin-2 (IL-2), IL-12 p40, IL-6 and IL-10, expressed by peripheral blood mononuclear cells of 13 beagle dogs inoculated with Leishmania infantum amastigotes, were analysed during a period of up to 23 months. The course of infection was monitored through clinical and parasitological examinations, haematological alterations and serum antileishmania antibody levels. Dogs developed symptomatic infections with haematological alterations, humoral immune response and reduced specific lymphoproliferative response. Parasite presence was detected in bone marrow, popliteal lymph node and skin. Specifically stimulated cytokine transcripts were generally observed in a low proportion of dogs, except at months 9, 10 and 11 post-infection where there was a considerable increase in the proportion of dogs expressing IFN-γ and IL-2 mRNA. IL-12 p40 and IL-10 transcripts were sporadically detected in few animals. In non-infected animals, IFN-γ mRNA was the only detectable cytokine but only in cells cultured in the presence of concanavalin A (ConA). The low proportion of animals expressing specific cytokines, during the first 8 months of infection associated with evidences of parasite dispersion without clinical signs of disease, suggests the occurrence of a relatively “silent establishment” of the parasite avoiding adverse host-cell-mediated immunological reactions. The humoral immune response displayed in these animals, the cell-mediated immunosuppression, nor the disease severity could be related with the expression of IL-10. The predominance of a Th1 type response for a relatively short period indicates that these cytokines are required to control the infection delaying the appearance of progressive disease.