MEK5/ERK5 signaling mediates IL-4-induced M2 macrophage differentiation through regulation of c-Myc expression.

Macrophages are highly plastic cells, responding to diverse environmental stimuli to acquire different functional phenotypes. Signaling through MAPKs has been reported to regulate the differentiation of macrophages, but the role of ERK5 in IL-4-mediated M2 macrophage differentiation is still unclear. Here, we showed that the ERK5 signaling pathway plays a critical role in IL-4-induced M2 macrophage differentiation. Pharmacologic inhibition of MEK5, an upstream activator of ERK5, markedly reduced the expression of classical M2 markers, such as Arg-1, Ym-1, and Fizz-1, as well as the production of M2-related chemokines and cytokines, CCL22, CCL17, and IGF-1 in IL-4-stimulated macrophages. Moreover, pharmacologic inhibition of ERK5 also decreased the expression of several M2 markers induced by IL-4. In accordance, myeloid cell-specific Erk5 depletion (Erk5∆mye ), using LysMcre /Erk5f/f mice, confirmed the involvement of ERK5 in IL-4-induced M2 polarization. Mechanistically, the inhibition of ERK5 did not affect STAT3 or STAT6 phosphorylation, suggesting that ERK5 signaling regulates M2 differentiation in a STAT3 and STAT6-independent manner. However, genetic deficiency or pharmacologic inhibition of the MEK5/ERK5 pathway reduced the expression of c-Myc in IL-4-activated macrophages, which is a critical transcription factor involved in M2 differentiation. Our study thus suggests that the MEK5/ERK5 signaling pathway is crucial in IL-4-induced M2 macrophage differentiation through the induction of c-Myc expression.

Multiple functional therapeutic effects of TnP: A small stable synthetic peptide derived from fish venom in a mouse model of multiple sclerosis.

The pathological condition of multiple sclerosis (MS) relies on innate and adaptive immunity. New types of agents that beneficially modify the course of MS, stopping the progression and repairing the damage appear promising. Here, we studied TnP, a small stable synthetic peptide derived from fish venom in the control of inflammation and demyelination in experimental autoimmune encephalomyelitis as prophylactic treatment. TnP decreased the number of the perivascular infiltrates in spinal cord, and the activity of MMP-9 by F4/80+ macrophages were decreased after different regimen treatments. TnP reduces in the central nervous system the infiltration of IFN-γ-producing Th1 and IL-17A-producing Th17 cells. Also, treatment with therapeutic TnP promotes the emergence of functional Treg in the central nervous system entirely dependent on IL-10. Therapeutic TnP treatment accelerates the remyelination process in a cuprizone model of demyelination. These findings support the beneficial effects of TnP and provides a new therapeutic opportunity for the treatment of MS.

Molecular mechanisms and timing of cortical immune activation in schizophrenia.

OBJECTIVE: Immune-related abnormalities are commonly reported in schizophrenia, including higher mRNA levels for the viral restriction factor interferon-induced transmembrane protein (IFITM) in the prefrontal cortex. The authors sought to clarify whether higher IFITM mRNA levels and other immune-related disturbances in the prefrontal cortex are the consequence of an ongoing molecular cascade contributing to immune activation or the reflection of a long-lasting maladaptive response to an in utero immune-related insult. METHOD: Quantitative polymerase chain reaction was employed to measure mRNA levels for immune-related cytokines and transcriptional regulators, including those reported to regulate IFITM expression, in the prefrontal cortex from 62 schizophrenia and 62 healthy subjects and from adult mice exposed prenatally to maternal immune activation or in adulthood to the immune stimulant poly(I:C). RESULTS: Schizophrenia subjects had markedly higher mRNA levels for interleukin 6 (IL-6) (+379%) and interferon-ß (+29%), which induce IFITM expression; lower mRNA levels for Schnurri-2 (-10%), a transcriptional inhibitor that lowers IFITM expression; and higher mRNA levels for nuclear factor-κB (+86%), a critical transcription factor that mediates cytokine regulation of immune-related gene expression. In adult mice that received daily poly(I:C) injections, but not in offspring with prenatal exposure to maternal immune activation, frontal cortex mRNA levels were also markedly elevated for IFITM (+304%), multiple cytokines including IL-6 (+493%), and nuclear factor-κB (+151%). CONCLUSIONS: These data suggest that higher prefrontal cortex IFITM mRNA levels in schizophrenia may be attributable to adult, but not prenatal, activation of multiple immune markers and encourage further investigation into the potential role of these and other immune markers as therapeutic targets in schizophrenia.

Oral lichen planus: focus on etiopathogenesis.

Lichen planus is a chronic mucocutaneous inflammatory disease, which frequently affects the oral mucosa of white females over 40 years old. Its aetiology remains uncertain and the pathogenesis is still the object of much speculation. The present paper presents the most well known antigens, and describes the action of different cells and proteins associated with the development of that disease, as well as the possible agents involved with its malignant transformation. Different external agents, especially virus, and internal agents, like stress, and the heat shock protein antigen expression, associated or not, can alter the basal keratinocytes of the oral mucosa making them susceptible to apoptosis by CD8(+) cytotoxic T cell as well as activate matrix metalloproteinase and mast cell degranulation, which produce a great range of inflammatory mediators and cytokines determining the clinical onset of the disease. Regarding carcinogenesis, since it is a complex process and presents multifactorial origin, it is believed that there may be a synergism between intrinsic, such as inflammation mediators, and extrinsic agents (tobacco, alcohol, viral infections) for the OLP malignant transformation to occur. However, further studies are needed to better understand the origin, pathogenesis and process of malignant transformation of OLP.

Different parasite inocula determine the modulation of the immune response and outcome of experimental Trypanosoma cruzi infection.

During infection, the host response develops effector mechanisms to combat the parasite. However, this response can become uncontrolled or regulated by mechanisms that modulate the inflammatory reaction. The number of parasites that infects the host, such as trypomastigotes in Chagas disease, may also influence immune activation and disease pathology. We evaluated the inflammation and immune regulation that follows Trypanosoma cruzi infection with low (300), intermediate (3000) or high (30000) parasite loads. Our results showed that the load of parasite inoculum influenced disease outcome: the higher the number of parasites in the inoculum, the lower were the survival rates. There was a strong association between parasitism and inflammatory infiltrate in the heart and the parasite inoculum determined cytokine interplay in this tissue, as shown by increased interferon-γ, tumour necrosis factor-α, interleukin-17 (IL-17) and IL-23 in the 300 and 30000 inoculum groups, higher IL-4 and IL-10 in the intermediate-inoculum mice, and elevated IL-6 production in the heart of mice in the 3000 and 30000 groups. The number of T cells and antigen-presenting cells was augmented in the infected groups, especially for the splenic CD4(+) CD25(+) regulatory T cells expressing CD45RB(low) , GITR, PD-1 and FoxP3 in the group with the highest inoculum. Interestingly, these mice also presented an apparent decrease in CD4(+) CD25(+) FoxP3(+) cells in the cardiac infiltrate, in contrast to the intermediate inoculum group, which showed elevated numbers of these regulatory leucocytes in the heart. Finally, our results demonstrated that parasite load during T. cruzi infection is linked to the response pattern that will result in parasite/inflammation control or tissue damage.

IFN-ß, IFN-γ, and TNF-α decrease erythrophagocytosis by human monocytes independent of SIRP-α or SHP-1 expression.

BACKGROUND: Many cases of autoimmune hemolytic anemia have been reported after viral infection. Phagocyte activation and accompanying erythrophagocytosis are thought to result from proinflammatory cytokines released during viral infection. SIRP-α (signal regulatory protein-α), a receptor expressed on phagocytes, inhibits phagocytosis when bound to CD47 on the erythrocyte membrane. Ligation with CD47 results in SHP-1 recruitment to SIRP-α and dephosphorylation of specific downstream substrates involved in phagocytosis. SIRP-α ligation by CD47 may be inhibited by proinflammatory cytokines. OBJECTIVES: The aim of this work was to evaluate the effect of IFN-ß, IFN-γ, and TNF-α on erythrophagocytosis and assess the effect on expression of SIRP-α and SHP-1 in human monocytes. MATERIALS AND METHODS: Monocytes were cultured ex vivo with IFN-ß or IFN-γ/TNF-α. Erythrophagocytosis was determined by flow cytometry. SIRP-α and SHP-1 gene expression was determined by real time-PCR, while SIRP-α and SHP-1 protein expression was determined by western blot. RESULTS: Erythrophagocytosis by monocytes significantly decreased after treatment with either IFN-ß or IFN-γ/TNF-α. Monocytes cultured with IFN-γ/TNF-α showed increased SIRP-α gene and protein expression and SHP-1 gene expression. Monocytes cultured with IFN-ß did not show any alteration in SIRP-α or SHP-1 expression. CONCLUSION: We conclude that IFN-ß and IFN-γ/TNF-α decrease erythrophagocytosis by human monocytes in vitro, and this effect does not apparently require an increase in SIRP-α or SHP-1 expression.

Monocyte dysfunction in Sydenham's chorea patients.

Until now, there are no conclusive data about the mechanisms involved in motor symptoms of Sydenham's chorea (SC). Taking into account the autoreactive antibody-mediated hypothesis of SC pathogenesis, the SC may be associated with uncontrolled immune mechanisms. Besides the antibody hypothesis, the innate immune system has been underappreciated. Hence, we evaluated the activation state of monocytes, cells that are precursors of macrophages, to characterize the inflammation profile of patients. We assessed the surface molecules CD80, CD86, and human leukocyte antigen DR expression in patients with SC by flow cytometry analysis. Our results showed a decreased CD14(+) (monocyte) frequency, with concomitant increased CD14(-) frequency inside monocyte population. Although monocyte population showed a decreased human leukocyte antigen DR and CD86 frequencies, the CD14(-) population showed an increased frequency of CD80(+) monocyte from SC compared with controls. These data suggest that monocytes showed a reduced costimulatory potential in SC.

Estudio inmunohistoquímico del carcinoma de glándula mamaria: en el Hospital Vargas de Caracas / Immunohistochemical study of mammary gland carcinoma: in Hospital Vargas de Caracas

Estudiar la asociación entre diferentes elementos morfológicos con aspectos inmunohistoquímicos y su posible utilidad pronóstica. Estudio descriptivo-retrospectivo, de 651 casos de carcinoma mamario con marcaje inmunohistoquímico en el Hospital Vargas de Caracas desde mayo 2001 a julio 2004. Se analizaron características morfológicas de los diferentes tipos tumorales, aplicando la clasificación de Scarff-Bloom-Richardson modificada, relacionándolos con la expresión de diferentes marcadores inmunohistoquímicos: receptores de estrógeno, receptores de progesterona, c-erbB-2 y Ki-67, realizados mediante la técnica de biotina-estreptavidina. La edad promedio fue 51,72 años. El tumor más frecuente fue el carcinoma ductal infiltrante (88,7 por ciento), seguido del carcinoma lobulillar infiltrante (4,6 por ciento). El 5,5 por ciento de los carcinomas ductales eran bien diferenciados, 42,3 por ciento moderadamente diferenciados, 52,2 por ciento poco diferenciados; de estos, el 77 por ciento tenían receptores de estrógeno y de progesterona ≤ 10 por ciento; los carcinomas bien diferenciados mostraron positividad variable. Los tumores poco diferenciados presentaron c-erbB-2 positivo en 51,36 por ciento, entre los bien diferenciados el 81,84 por ciento fueron negativos, el carcinoma intraductal fue positivo en un 42,86 por ciento, generalmente asociado a comedocarcinoma. El 94,37 por ciento de los tumores poco diferenciados fueron Ki-67 positivos. El carcinoma ductal infiltrante de tipo clásico es el tumor maligno más frecuente de la glándula mamaria, con una edad promedio de 51,5 años, generalmente es poco diferenciado, implicando posiblemente tumores con conducta biológica agresiva. Esto se evidencia por la negatividad para receptores hormonales y la expresión aumentada de c-erbB-2 y Ki-67.

To study and assess the association between different morfhological and pathologic features and immunohistochemistry as a prognostic factor. A retrospective-descriptive study of 651 cases of breast cancer by immunohistochemistry markers was analyzed in the Vargas Hospital of Caracas since may 2001 until july 2004. We evaluate the pathologic features of the different tumor subtypes, and relation this with the expression of immunohistochemistry markers: the estrogen receptor, progesterone receptor, c-erbB-2 and Ki-67, made by the biotin-streptavidin technique. The median patient age was 51.72 years. The most frequent type of tumor was the invasive duct carcinoma (88.7 %), follow by the invasive lobular carcinoma (4.6 %). The 5.5 % of the duct carcinomas were well differentiated tumors, 42.3 % moderate differentiated, and 52.2 % poorly differentiated; in which 77 % had estrogen receptor and progesterone receptor ≤ 10 %, well differentiated tumors show a variable positivity. The poorly differentiated tumors show positive c-erbB-2 in 51.36 %, in the well-differentiated group 81.84 % were negative; the c-erbB-2 on intraductal carcinoma was positive in 42.86 %, generally associated with the comedocarcinoma; the 94.7 % of the poorly differentiated tumors were Ki-67 positives. Classic invasive duct carcinoma is the most frequent malignant tumor, with a median age of 51.5 years, and the poorly differentiated tumors generally show an aggressive biologic conduct, associated to patients with estrogen receptors and progesterone receptors negative tumors and a high expression of the c-erbB-2 y Ki-67.

Frequency of concurrent autoimmune disorders in patients with autoimmune hepatitis: effect of age, gender, and genetic background.

BACKGROUND: Concurrent autoimmune disorders (CAIDs) have been shown to occur in 22% to 34% of the patients with autoimmune hepatitis (AIH). Their presence has been linked to female gender, older age, and to certain HLA antigens, namely HLA-A11, DRB1*04, and DRB4*01. AIMS: To assess the frequency and nature of CAID in Brazilian patients with AIH types 1 (AIH-1) and 2 (AIH-2) and to investigate the influence of age, gender, and genetic background in their occurrence. PATIENTS AND METHODS: The presence and nature of CAID was studied in 143 patients [117 females, median age 11 (1.3 to 69)] with AIH-1 (n=125) and AIH-2 (n=28). HLA typing and tumor necrosis factor alpha gene promoter and exon 1 cytotoxic T lymphocyte associated antigen 4 (CTLA-4) gene polymorphisms were determined by polymerase chain reaction-based techniques. RESULTS: The frequency of CAID was similar in patients with AIH-1 (14%) and AIH-2 (18%), but their nature was shown to vary. Arthritis was seen in half of the patients (n=8) with CAID and AIH-1 and in none of those with AIH-2. Subjects with AIH-1 and CAID were shown to be older [24 (1.3 to 61) vs. 11 (1.3 to 69) y, P=0.02] and to have more often circulating antinuclear antibody (76% vs. 40%, P=0.008) and less frequently antiactin antibodies (33% vs. 75%, P=0.008) when compared with their counterparts without CAID. No particular HLA-DR and DQ alleles, as well as tumor necrosis factor alpha and CTLA-4 genotypes, were associated with CAID. CONCLUSIONS: The nature, but not the frequency, of CAID was shown to vary in AIH-1 and AIH-2. In subjects with AIH-1, CAID was linked to older subjects and to the presence of antinuclear antibody. No predisposition to CAID was associated to HLA-DRB1*04 or DDB4*01 alleles. The observed lower frequency of CAID could be attributed to the lower age of disease onset in Brazilians and to differences in HLA-encoded susceptibility to AIH-1 observed in South America.

Gr-1+ cells play an essential role in an experimental model of disseminated histoplasmosis.

Recent studies have shown the participation of Gr-1(+) cells in many types of infections; however, the role played by these cells in the immune response to fungal pathogens is controversial. In this study we determined whether Gr-1(+) cells are involved in the protective immune response in systemic Histoplasma capsulatum infection. Depletion of Gr-1(+) cells using the monoclonal antibody (MAb) RB6-8C5 increased histoplasmosis severity and inhibited the subsequent development of a protective immune response. In addition to the increased fungal burden in lungs and spleens, the Th1 response was found to be unbalanced in these mice and the suppression of the cellular immune response seemed to be associated with increased nitric oxide production. Taken together, these results indicate that Gr-1(+) cell depletion at the beginning of infection allows yeast multiplication and increases mice mortality. This study improves the understanding of the role of Gr-1(+) cells on the protective immunity in histoplasmosis.

Cytotoxic T lymphocyte antigen 4 heterozygous codon 49 A/G dimorphism is associated to latent autoimmune diabetes in adults (LADA).

Autoimmune diabetes is an organ specific and multifactorial disorder with a classical onset as insulin dependent diabetes mellitus (IDDM) and with another form of onset as latent autoimmune diabetes in adults (LADA), which has a slower onset and a later progress to insulin dependency as a result of the beta cells destruction. The cytotoxic T lymphocyte-antigen 4 (CTLA4) has been identified as a susceptible marker of the disease; it is considered a down regulator of T cell function, playing a key role in autoimmunity. We analyzed CTLA4 codon 49 A/G polymorphism in 123 IDDM patients, 63 LADA patients and 168 healthy non-diabetic control individuals. The frequency of the heterozygous A/G genotype in LADA patients was significantly increased compared to IDDM patients (55.6 vs. 39.8%, p = 0.0415). There was no statistical significant difference in the distribution of the A/G dimorphism between autoimmune diabetes patients (LADA or IDDM) and non-diabetic control individuals. HLA DQ region is responsible for the genetic susceptibility to autoimmune diabetes in IDDM patients in about 50% and it has a lower effect in genetic susceptibility in LADA patients. Several other genetic loci are needed to develop autoimmune diabetes in adult patients. Therefore, LADA may be the result of a combined minor risk loci effect in a major risk haplotype.

Differential expression of function-related antigens on blood monocytes in children with hemolytic uremic syndrome.

Monocytes (Mo) mediate central functions in inflammation and immunity. Different subpopulations of Mo with distinct phenotype and functional properties have been described. Here, we investigate the phenotype and function of peripheral Mo from children with hemolytic uremic syndrome (HUS). For this purpose, blood samples from patients in the acute period of HUS (HUS AP) were obtained on admission before dialysis and/or transfusion. The Mo phenotypic characterization was performed on whole blood by flow cytometry, and markers associated to biological functions were selected: CD14 accounting for lipopolysaccharide (LPS) responsiveness, CD11b for adhesion, Fc receptor for immunoglobulin G type I (FcgammaRI)/CD64 for phagocytosis and cytotoxicity, and human leukocyte antigen (HLA)-DR for antigen presentation. Some of these functions were also determined. Moreover, the percentage of CD14+ CD16+ Mo was evaluated. We found that the entire HUS AP Mo population exhibited reduced CD14, CD64, and CD11b expression and decreased LPS-induced tumor necrosis factor production and Fcgamma-dependent cytotoxicity. HUS AP showed an increased percentage of CD14+ CD16+ Mo with higher CD16 and lower CD14 levels compared with the same subset from healthy children. Moreover, the CD14++ CD16- Mo subpopulation of HUS AP had a decreased HLA-DR expression, which correlated with severity. In conclusion, the Mo population from HUS AP patients presents phenotypic and functional alterations. The contribution to the pathogenesis and the possible scenarios that led to these changes are discussed.

Regulatory role of Toll-like receptor 2 during infection with Trypanosoma cruzi.

Previous studies have emphasized the role of Toll-like receptors (TLRs) and myeloid differentiation factor 88 (MyD88) during infection with protozoan parasites. TLR2 was shown to be important for induction of cytokine synthesis by macrophages exposed to the purified glycosylphosphatidylinositol (GPI)-anchored mucin-like glycoproteins of Trypanosoma cruzi trypomastigotes (tGPIm). On the other hand, MyD88(-/-) mice, but not TLR2(-/-) mice, showed impaired cytokine production and resistance to infection with T. cruzi parasites. Here we evaluate the importance of MyD88 and TLR2 in MAPK activation and cytokine synthesis by macrophages exposed to live T. cruzi parasites and compared to tGPIm. The absence of MAPK phosphorylation in TLR2- and MyD88-deficient macrophages exposed to tGPIm correlated with the incapacity to induce cytokine release in these cells. In contrast, activation of MAPK and synthesis of pro-inflammatory cytokines were not abrogated in TLR2-deficient macrophages exposed to live T. cruzi parasites. We also showed that pretreatment with tGPIm significantly reduces cytokine release by macrophages in response to T. cruzi in a TLR2-dependent manner. Consistently, TLR2(-/-) mice were shown to produce enhanced levels of cytokines upon in vivo challenge with T. cruzi parasites. Together, these results suggest the involvement of additional TLR(s) in the pro-inflammatory response of macrophages to whole parasites, and that, in vivo, TLR2 may have a predominant immunoregulatory role during acute infection with T. cruzi parasites.

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.

Fas-Fas ligand (CD95-CD95L) and cytotoxic T lymphocyte antigen-4 engagement mediate T cell unresponsiveness in patients with paracoccidioidomycosis.

The mechanism that leads to the remarkable T cell unresponsiveness to antigens in paracoccidioidomycosis is unknown. We investigated the involvement of cytokines, of Fas-Fas ligand (Fas-FasL)-induced apoptosis, and of cytotoxic T lymphocyte antigen 4 (CTLA-4) engagement, in the mediation of this phenomenon. T cell unresponsiveness was not associated with imbalanced cytokine production or with absence of CD28 expression. Only patient T cells expressed higher levels of CTLA-4, Annexin V(+), and FasL. The addition of anti-FasL decreased the levels of apoptosis, suggesting an activation-induced cell death triggered through the Fas-FasL pathway. Blockage of CTLA-4 and FasL resulted in increased production of interferon-gamma. Moreover, concomitant inhibition of FasL and of CTLA-4, but not of transforming growth factor-beta, resulted in significant T cell proliferation in patients, in response to phytohemagglutinin. Together, these data show that apoptosis mediated by Fas-FasL and engagement of CTLA-4 are involved in modulation of the immune response in patients infected with Paracoccidioides brasiliensis.

Aplicación del anticuerpo c-kit (CD 117) para diferenciación inmunohistoquímica en tumores estromales gastrointestinales / C-kit (CD 117) antibody application for immunohistochemistry differentiation in gastrointestinal stromal tumours

La interpretación diagnóstica de las lesiones del estroma gastrointestinal, basada en los significativos avances de la inmunohistoquímica, parece indicar que estos tumores previamente considerados como leiomiomas o leiomiosarcomas, tienen un origen y expresión distinta que contrasta con los caracteres histopatológicos de estos. La incorporación del anticuerpo c-kit (CD-117) permitiría efectuar esa diferenciación y darles la designación de tumores estromales gastrointestinales (GIST). En el presente estudio se analizaron 5 casos de tumores gástricos y 3 de origen muscular de otras ubicaciones anatómicas, previamente diagnosticados, a los cuales se aplicaron anticuerpos primarios para Desmina, CD34, ENE y c-kit. Las muestras fueron posteriormente reveladas con complejo avidina-biotina y se evaluaron según su reacción a la inmunotinción como positivas o negativas. Los resultados obtenidos se expresan cualitativamente de acuerdo a la marcación e intensidad de la reacción con los distintos anticuerpos, observándose una manifiesta diferenciación entre los tumores que son de origen gástrico con aquellos provenientes de músculo liso. En consecuencia, la aplicación del anticuerpo c-kit(CD117) en procedimientos inmunohistoquímicos de rutina, es útil y recomendable para definir un diagnóstico diferencial

Galectin-3 modulates carbohydrate-dependent thymocyte interactions with the thymic microenvironment.

The process of thymocyte differentiation occurs within the context of the thymic microenvironment, in which T cell precursors interact with thymic microenvironmental cells and extracellular matrix. Here we studied the expression of galectin-3, a beta-galactoside binding lectin, in the thymus of young adult mice. Galectin-3 was found mainly in the medulla and to a lesser extent in the cortex. We further showed that distinct microenvironmental elements, such as thymic epithelial cells, the epithelial component of thymic nurse complexes and phagocytic cells of the thymic reticulum produce, secrete and accumulate galectin-3 on the cell surface. Functionally, galectin-3-enriched medium inhibited in vitro thymocyte interactions with thymic microenvironmental cells, accelerated the release of thymocytes from thymic nurse cells and inhibited the reconstitution of these lymphoepithelial complexes. These effects were blocked by exogenous lactose (Galbeta1-4Glc), but not melibiose (Galalpha1-6Glc), and by a monospecific anti-galectin-3 antibody. Recombinant galectin-3 also inhibited thymocyte/thymic epithelial cell interactions. Our data indicate that intrathymically produced galectin-3 disrupts thymocyte/microenvironmental cell interactions, thus acting as a de-adhesion molecule.

Susceptible hosts: a resort for parasites right in the eye of the immune response

Trypanosomatid protozoan parasites express an aggressive strategy of parasitism by infecting host macrophages and inducing extensive T-lymphocyte activation. One goal of such strategy is to drive the immune response of genetically susceptible hosts to a state of unresponsiveness regarding parasite killing. Unresponsiveness is achieved through different mechanisms, depending on the parasite species. In this brief review, recent findings on the molecular and cellular bases of the parasites' exploitation of host immune responses are discussed.

TGF-beta mediates CTLA-4 suppression of cellular immunity in murine kalaazar.

Recent studies indicate important roles for CTLA-4 engagement in T cells, and for TGF-beta production in the immunopathogenesis of murine kalaazar or visceral leishmaniasis, but a functional link between these two pathways in helping intracellular parasite growth is unknown. Here we report that Ag or anti-CD3 activation of splenic CD4+ T cells from visceral leishmaniasis leads to intense CTLA-4-mediated TGF-beta1 production, as assessed either by CTLA-4 blockade or by direct CTLA-4 cross-linkage. Production of TGF-beta1 accounted for the reciprocal regulation of IFN-gamma production by CTLA-4 engagement. Following CD4+ T cell activation, intracellular growth of Leishmania chagasi in cocultured splenic macrophages required both CTLA-4 function and TGF-beta1 secretion. Cross-linkage of CTLA-4 markedly increased L. chagasi replication in cocultures of infected macrophages and activated CD4+ T cells, and parasite growth could be completely blocked with neutralizing anti-TGF-beta1 Ab. Exogenous addition of rTGF-beta1 restored parasite growth in cultures protected from parasitism by CTLA-4 blockade. These results indicate that the negative costimulatory receptor CTLA-4 is critically involved in TGF-beta production and in intracellular parasite replication seen in murine kalaazar.