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.     

Regulation of innate and acquired immunity in African trypanosomiasis

African trypanosomes are well known for their ability to avoid immune elimination by switching the immunodominant variant surface glycoprotein (VSG) coat during infection. However, antigenic variation is only one of several means by which trypanosomes manipulate the immune system of their hosts. In this article, the role of parasite factors such as GPI anchor residues of the shed VSG molecule and the release of CpG DNA, in addition to host factors such as IFN-gamma, in regulating key aspects of innate and acquired immunity during infection is examined. The biological relevance of these immunoregulatory events is discussed in the context of host and parasite survival.     

Polyamine oxidase-mediated killing of African trypanosomes

African trypanosomes, Trypanosoma brucei brucei, T. vivax and T. congolense , were killed when incubated in vitro with ruminant sera in the presence of exogeneous spermidine, and were non-infective for mice. Purified polyamine oxidase in the presence of spermidine-mediated similar killing of trypanosomes. The abundance of polyamine oxidase activity in ruminant sera which can react with polyamines to produce products with cytotoxic properties may explain the trypanosome killing. This system may contribute to non-specific parasite killing in vivo.     

Genetic manipulation of African trypanosomes as a tool to dissect the immunobiology of infection

The variant surface glycoprotein (VSG) coat of African trypanosomes exhibits immunobiological functions distinct from its prominent role as a variant surface antigen. In order to address questions regarding immune stealth effects of VSG switch-variant coats, and the innate immune system activating effects of shed VSG substituents, several groups have genetically modified the ability of trypanosomes to express or release VSG during infection of the mammalian host. The role of mosaic surface coats expressed by VSG switch-variants (VSG double-expressors) in escaping early immune detection, and the role of VSG glycosylphosphatidylinositol (GPI) anchor substituents in regulating host immunity have been revealed, respectively, by stable co-expression of an exogenous VSG gene in trypanosomes expressing an endogenous VSG gene, and by knocking out the genetic locus for GPI-phospholipase C (PLC) that releases VSG from the membrane. Both approaches to genetic modification of African trypanosomes have suggested interesting and unexpected immunobiological effects associated with surface coat molecules.     

Alternative pathway activation of complement by African trypanosomes lacking a glycoprotein coat

An in vitro culture Trypanosoma congolense cell line was established using the mammalian cell feeder layer system. One of the principle characteristics of this parasite was its ability to multiply in culture at 35 degrees C, as an uncoated trypanosome (lacking a glycoprotein surface coat) unlike the original blood stream form from which it was derived. This trypanosome was lysed when incubated in normal human serum in contrast to the parasite which possessed a surface coat. The lytic reaction as inhibited by EDTA but not EGTA and occurred in C2-deficient serum, demonstrating the involvement of the alternative pathway of complement activation. Similar results were obtained with procyclic forms of T. congolense and T. brucei brucei which also lacked surface coats. The results suggest that the glycoprotein surface coat protects the parasite by masking sites on the plasma membrane which are capable of promoting alternative pathway activation.     

活动性肺结核病患者髓系抑制性细胞的检测分析

目的 研究活动性肺结核病患者、潜伏感染者和健康者髓系抑制性细胞(myeloid-derived suppressor cells,MDSCs)的产生及分布特性.方法 活动性肺结核病患者均为确诊的住院患者,潜伏感染者及健康者经ELISPOT检查确定.外周静脉血用CD14、HLA-DR、CD11b、CD33抗体共染色,采用流式细胞术分析.结果 通过对78例活动性肺结核病患者、30例潜伏感染者及66例健康者的对比分析发现,活动性肺结核病患者CD14-HLA-DR-CD33+ CD11bhighMDSCs细胞比例高于潜伏感染者(P=0.0238),也高于健康者( P＜0.001),而潜伏感染者与健康者CD14-HLA-DR- CD33+ CD11bhighMDSCs细胞比例差异无统计学意义;活动性肺结核病患者CD14+ HLA-DR-MDSCs比例与潜伏感染者及健康者比较差异无统计学意义.活动性肺结核病患者外周血转化生长因子β1水平高于健康对照组(P＜0.05).结论 活动性肺结核病患者CD14- HLA-DR- CD33+CD11bhigh MDSCs比例显著增高,提示活动性肺结核病可能诱导特定的MDSCs亚群,发挥免疫抑制作用,促进结核病的发生及发展.     

Differential suppression of experimental allergic diseases in rats infected with trypanosomes

PVG/c rats, infected 3 days previously with 10(3) Trypanosoma brucei brucei S.42 organisms failed to develop adjuvant disease in response to an intradermal inoculation of mycobacterial adjuvant. By contrast, similarly infected rats, immunized with heterologous brain and spinal cord in Freund's complete adjuvant with pertussis vaccine as a secondary adjuvant, developed clinical signs of allergic encephalomyelitis (EAE) at least as severe as those in uninfected rats. Delayed hypersensitivity reactions to PPD were depressed in trypanosome-infected, adjuvant-injected rats, as were the reactions to myelin basic protein in infected rats developing EAE. There appeared to be no cross-reactivity between trypanosomal antigen and myelin basic protein which could account for the lack of suppression of EAE. It is suggested that the different extent to which autoimmunity is involved in these two experimental allergic diseases may account for the differential suppressive activity of trypanosome infections upon them.     

Circulating myeloid-derived suppressor cells in patients with pancreatic cancer

BACKGROUND: Myeloid-derived suppressor cells (MDSCs) are heterogeneous cell types that suppress T-cell responses in cancer patients and animal models, some MDSC subpopula-tions are increased in patients with pancreatic cancer. The present study was to investigate a specific subset of MDSCs in patients with pancreatic cancer and the mechanism of MDSCs increase in these patients.
METHODS: Myeloid cells from whole blood were collected from 37 patients with pancreatic cancer, 17 with cholangiocarcinoma, and 47 healthy controls. Four pancreatic cancer cell lines were co-culturedwithnormalperipheralbloodmononuclearcells(PBMCs) to test the effect of tumor cells on the conversion of PBMCs to MDSCs. Levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and arginase activity in the plasma of cancer patients were analyzed by enzyme-linked immunosorbent assay.
RESULTS: CD14+/CD11b+/HLA-DR- MDSCs were increased in patients with pancreatic or bile duct cancer compared with those in healthy controls, and this increase was correlated with clinical cancer stage. Pancreatic cancer cell lines induced PBMCs to MDSCs in a dose-dependent manner. GM-CSF and arginase activity levels were significantly increased in the se-rum of patients with pancreatic cancer.
CONCLUSIONS: MDSCsweretumorrelated:tumorcellsinduced PBMCs to MDSCs in a dose-dependent manner and circulating CD14+/CD11b+/HLA-DR- MDSCs in pancreatic cancer patients were positively correlated with tumor burden. MDSCs might be useful markers for pancreatic cancer detection and progression.     

二硝基氟苯实验性结肠炎模型的建立及T抑制细胞亚群的研究

目的　探讨CD8+ T细胞亚群尤其是CD8+ CD2 8-T抑制细胞在 2 ,4 二硝基氟苯 (DNFB)大鼠实验性结肠炎模型中的变化及其可能作用。方法　建立DNFB实验性结肠炎大鼠模型 ,流式细胞仪计数检测脾脏和结肠黏膜上皮细胞内CD8+ T细胞、CD8+ CD2 8+ T细胞和CD8+ CD2 8-T抑制细胞的变化。结果　成功地建立了DNFB大鼠实验性结肠炎模型。模型 (n =12 )中脾脏和结肠黏膜上皮细胞内CD8+ T细胞含量与对照组 (n =8)差异无显著性 [脾脏 :(34.6± 7.2 ) %比 (33.5± 9.4 ) % ,结肠 :(14 .0± 8.9) %比 (18.0± 4 .1) % ,P >0 .0 5 ],CD8+ CD2 8-T抑制细胞含量均显著高于对照组 [脾脏 :(11.3± 2 .3) %比 (5 .6± 1.0 ) % ,结肠 :(6 .5± 5 .4 ) %比 (1.1± 0 .6 ) % ,P <0 .0 5 ],而结肠黏膜上皮细胞内CD8+ CD2 8+ T细胞含量显著低于对照组 [(7.5± 4 .2 ) %比 (16 .9± 4 .1) % ,P <0 .0 5 ],脾脏CD8+CD2 8+ T细胞含量亦低于对照组 [(2 3.3± 6 .1) %比 (2 7.8± 9.7) % ,P >0 .0 5 ]。实验性结肠炎模型中脾脏和结肠黏膜上皮细胞内CD8+ CD2 8-T抑制细胞占CD8+ T细胞的比例均显著高于对照组 [脾脏 :(33.3± 5 .5 ) %比 (18.4± 7.3) % ,结肠 :(46 .0± 14 .3) %比 (6 .1± 3.7) % ,P <0 .0 5 ]。结论　DNFB可诱导大鼠实验     

Role of l-arginine and CD11b+Gr-1+ cells in immunosuppression induced by Heligmosomoides polygyrus bakeri

Myeloid-derived suppressor cells (MDSCs) are heterogeneous population of monocyte and granulocyte progenitors that are highly suppressive against T cells. In BALB/c mice infected with a nematode Heligmosomoides polygyrus bakeri, we studied the dynamics of MDSCs, identified as CD11b+Gr-1+, induction in different tissues along with the development of parasite infection. We observed that MDSC-like cells are induced both by larvae and adult stages of H polygyrus bakeri. Gr-1+ cells of suppressive phenotype are recruited in the bone marrow, peripheral blood and peritoneal cavity during histotropic phase of infection and are present at that time in the intestine wall, where worms reside. Later, during intestinal phase, suppressive Gr-1+ cells increased in mesenteric lymph nodes and the spleen. l -arginine metabolism was important for the protective immunity, and parasite-induced Gr-1+ cells showed elevated arginase-1 and iNOS expression. Inhibition of arginase-1 and l -arginine administration caused reduced level of infection that coincided with weaker suppressive phenotype of Gr-1+ cells. We identified that l -arginine pathway activation and induction of MDSC-like cells characterize immunosuppressive state during H polygyrus bakeri infection in mice. Our findings confirm the role of MDSCs in parasitic infections and point l -arginine pathway as a potential target for immunomodulation during nematode infections.     

髓系来源的抑制细胞在肝病发病中的作用研究进展*

髓系来源的抑制细胞来源于骨髓祖细胞和未成熟的髓系细胞。近年来的研究表明,该细胞参与调节多种肝脏疾病的病理变化。本文系统地归纳了髓系来源的抑制细胞的历史、分群、作用机制和当前该细胞在各种肝病发病中的免疫调控作用及其与疾病进展的关系。     

寄生虫感染中髓系抑制性细胞的免疫抑制机制研究

髓系抑制性细胞(myeloid-derived suppressor cells,MDSC)是髓系来源的一群异质细胞,具有强大的免疫抑制功能.在病理情况下可大量扩增,包括各种感染、肿瘤和急慢性炎症等.在肿瘤模型和肿瘤患者体内均发现有MDSC,其促进肿瘤免疫逃避的机制已取得很大进展.寄生虫感染一般都伴随免疫逃避和显著抑制机体免疫应答的现象,而目前较少关注MDSC在寄生虫感染中的免疫抑制功能.该文综述了一些种类的原虫和蠕虫感染中,MDSC的扩增、活化、趋化、表型和功能.     

抑癌基因Mxil在白血病细胞中突变的研究

目的：分析Mxil基因突变在白血病发病中的作用。方法：利用逆转录-聚合酶链反应（RT-PCR）、单链构象多态性（SSCP）分析及DNA序列分析技术检测26例初治急性白血病患者、30名健康对照者和2种髓系白血病细胞株（KG1、K562）Mxil基因表达及突变情况。结果：RT—PCR显示所有标本中均可检测到Mxil基因的表达，在11．5％（3／26）初治急性白血病患者和KG1细胞株中发现四处错义突变，发生突变的3例患者均于确诊后5个月内死亡。结论：首次在急性白血病细胞中发现Mxil基因突变，提示Mxil基因的突变可能与白血病的发病和预后有关。     

Autoreactive erythroid progenitor-T suppressor cells in the pure red cell aplasia associated with thymoma and panhypogammaglobulinemia

In vitro erythroid culture studies and lymphocyte markers were performed in a patient with a spindle cell thymoma who developed red cell aplasia, panhypogammaglobulinemia, and multiple opportunistic infections. At the time of presentation, erythroid progenitor cells (CFUe, BFUe) were markedly reduced when cultured from marrow mononuclear cells. Removal of T cells from bone marrow mononuclear cells by E-rosetting or complement-mediated lysis with OKT3 pan T cell monoclonal antibody increased growth of erythroid progenitor cells in vitro. Readdition of bone marrow or pleural fluid T cells derived from the thymoma suppressed autologous, but not allogenic, erythroid progenitor cell (CFUe, BFUe) proliferation in vitro. The erythroid progenitor suppressor T cells were predominantly OKT11+, OKT3+, OKT8+ and Ia+ consistent with activated suppressor T cells. Treatment of the patient with cyclophosphamide and corticosteroids reduced marrow lymphocytes fourfold, and a prompt reticulocytosis ensued. After recovery, erythroid progenitor cells were easily detectable. These studies provide new evidence for T cell-mediated suppression of erythropoiesis in a unique subset of patients with red cell aplasia associated with thymoma and hypogammaglobulinemia.     

Experimental African trypanosomiasis: lack of effective CD1d-restricted antigen presentation

BALB/c mice are highly susceptible to African trypanosomiasis, whereas C57BL/6 mice are relatively resistant. Other investigators have reported that the synthesis of IgG antibodies to purified membrane form of variant surface glycoprotein (mfVSG) of Trypanosoma brucei is CD1 restricted. In this study, we examine the role of the CD1d/NKT cell pathway in susceptibility and resistance of mice to infection by African trypanosomes. Administration of anti-CD1d antibodies to Trypanosoma congolense-infected BALB/c mice neither affects the parasitemia nor the survival time. Correspondingly, CD1d(-/-) and CD1d(+/+) BALB/c mice infected with T. congolense or T. brucei show no differences in either parasitaemia or survival time. The course of disease in relative resistant C57BL/6 mice infected with T. congolense is also not affected by the absence of CD1d. Parasitaemia, survival time, and plasma levels of IgG2a and IgG3 parasite-specific antibodies in infected CD1d(-/-) C57BL/6 are not different from those of infected CD1d(+/+) C57BL/6 mice. We conclude that CD1d-restricted immune responses do not play an important role in susceptibility/resistance of mice infected with virulent African trypanosomes. We speculate that virulent trypanosomes have an evasion mechanism that prevents the induction of a parasite-specific, CD1d-restricted immune response by the host.     

A subpopulation of suppressor cells in Richter's syndrome with both monocytic and T-lymphocytic characteristics

We evaluated T-lymphocyte functions in the peripheral blood of a patient with B-cell chronic lymphocytic leukemia after transformation to large cell lymphoma (Richter's syndrome). A subpopulation of E-rosette adherent cells were found with T-lymphocytic surface markers (OKT3+/8+/4+), monocytic characteristics (latex ingestion, nonspecific esterase staining), and suppressor activity. In contrast to the patient's nonadherent T-cells, this subpopulation suppressed PHA proliferation of autologous lymphocytes, pokeweed mitogen (PWM)-induced proliferation of normal non-T cells, and a mixed lymphocyte reaction. Further studies are warranted in patients with Richter's syndrome, in order to determine the frequency and significance of our findings.     

髓样抑制细胞在促进肿瘤发生中的作用

总结了髓样抑制细胞(MDSC)在促进炎症发生和肿瘤细胞的免疫逃逸中发挥的作用,以及促进肿瘤发生发展的作用机制。可为以后探讨肝纤维化和肝癌发病的免疫学机制提供一条新的思路,也将有利于未来寻找肝纤维化和肝癌治疗的有效靶点。     

Cellular responses to phase fractions of Trypanosoma lewisi

Infections by Trypanosoma lewisi are characterized by hyporesponsiveness of the immune system during the early phase of parasitaemia. Blastogenic response of normal rat spleen cells to amphiphilic and hydrophilic components of Triton X-114 solubilized epimastigote forms of T. lewisi which characterizes the early phase of infection showed that suppression of responses to mitogens Concanavalin A (Con-A) and lipopolysaccharide (LPS) occurred exclusively with the amphiphilic fraction that consists of integral surface membrane constituents. The Con-A-induced suppression by the amphiphilic constituents was ablated by addition of exogenous IL-2 or by the removal of the adherent cell population in the cultures. This suggests that the integral surface membrane components play an important regulatory role in infections with Trypanosoma lewisi, through complex mechanisms that probably involve the B cells and suppressor macrophages; the suppressor macrophages probably produce a suppressor factor that inhibits the proliferation of T helper cells and subsequently the production of interleukin-2.     

Increased frequency and clinical significance of myeloid-derived suppressor cells in human colorectal carcinoma

AIM: To investigate the frequency and clinical significance of the myeloid-derived suppressor cells (MDSC) in human colorectal carcinoma (CRC).METHODS: Samples of peripheral blood and tumor tissue from 49 CRC patients were analyzed. Mononuclear cells were isolated by Ficoll-Hypaque density gradient centrifugation and were subjected to a flow cytometry-based immunophenotypic analysis.RESULTS: A considerable increase in the percentage of CD33⁺HLA-DR^- MDSCs was observed in the peripheral blood (1.89% ± 0.75%) and tumor tissues (2.99% ± 1.29%) of CRC patients as compared with that in the peripheral blood of healthy controls (0.54% ± 0.35%). This expanded CD33⁺HLA-DR^- subset exhibited immature myeloid cell markers, but not lineage markers, and showed up-regulation of CD18/CD11b expression as compared with the MDSCs from healthy donors. Further studies showed that the MDSC proportion in CRC peripheral blood was correlated with nodal metastasis(P = 0.023), whereas that in tumor tissues was correlated with nodal/distant metastasis (P = 0.016/P = 0.047) and tumor stage (P = 0.028), suggesting the involvement of MDSCs in CRC tumor development.CONCLUSION: Characterization of MDSCs in CRC suggests the clinical significance of circulating and tumor-infiltrating MDSCs and may provide new insights into the CRC immunotherapy targeting MDSCs.