Prognostic relevance of topoisomerase II α and minichromosome maintenance protein 6 expression in colorectal cancer.

BACKGROUND: Despite rising incidence rates of colorectal malignancies, only a few prognostic tools have been implemented in proven clinical routine. Cell division and proliferation play a significant role in malignancies. In terms of colorectal cancer, the impact of proliferation associated proteins is controversially debated. The aim of our study was to examine the expression of topoisomerase II α and minichromosome maintenance protein 6 and to correlate these findings with the clinical data. METHODS: Tissue samples of 619 patients in total were stained using the antibodies Ki-S4 and Ki-MCM6 targeting topoisomerase II α as well as minichromosome maintenance protein 6. The median rate of proliferation was correlated with clinical and follow up data. RESULTS: The expression rate of minichromosome maintenance protein 6 is significantly higher than the proportion of topoisomerase II α in tumour cells (p < 0.001). A high expression of both proteins coincides with a beneficial outcome for the patient, indicating a favourable prognostic marker (p < 0.001 and p = 0.008). CONCLUSIONS: We have demonstrated that high expression rates of proliferative markers is linked to a beneficial patient outcome. According to the general opinion, a high expression rate correlates with a poor patient outcome. In this study, we were able to refute this assertion.

Mechanical resistance of the periorbita and the orbital floor complex--are isolated orbital floor fractures only a soft tissue problem?

The primary aims of orbital floor reconstruction are to prevent enophthalmos and herniation of the orbital contents in order to achieve correct globe position. Theoretically, the mechanical load of the orbital floor is approximately 0.0005N/mm(2) (30g orbital content onto 600mm(2) of orbital floor area). Therefore, low mechanical stress from orbital floor reconstruction materials is expected. The periorbita and orbital floor complex (bony orbital floor with periorbita) of 12 human cadavers were investigated for their mechanical resistance to distortion and compared to different absorbable pliable reconstruction materials after modification with pores (Bio-Gide, Creos, and PDS). The human periorbita resistance (approximately 1.4N/mm(2)) was comparable to that of the absorbable membranes (Creos, Bio-Gide), and the resistance of PDS (approximately 2.3N/mm(2)) was comparable to that of the orbital floor complex. The periorbita has a higher stability than the bony orbital floor. Therefore, in isolated orbital floor fractures with a traumatized bony orbital floor and periorbita, reconstruction of the soft tissue as a periorbita equivalent with a resorbable membrane appears to be adequate to prevent enophthalmos and herniation of the orbital contents.

Detection of the genial spinal canal in atrophic mandibles with a CBCT: a cadaver study.

OBJECTIVES: The use of a single midline implant to retain a complete mandibular denture when more implants cannot be used is an incipient treatment modality. However, in the mandibular symphysis, the genial spinal canal (GSC) is an anatomical structure with neurovascular content that can be harmed during dental implant surgery. The purpose of the present study was to use CBCT of edentulous atrophic cadaver mandibles and evaluate how often the simulated placement of a single midline implant would contact the GSC if present. METHODS: CBCT scans of 47 edentulous cadaver mandibles were performed. A digital simulation of the placement of a single midline implant (3.8 × 11.0 mm) was performed, and the implant-GSC contact was evaluated. RESULTS: A GSC was detected in the CBCT scan of all atrophic mandibles. In 42 cases (89.4%), the single midline implant contacted the GSC. On average, the five cases without GSC contact had a higher alveolar ridge (4.1 mm) and a lower GSC (0.79 mm) than did the cases with GSC contact. CONCLUSIONS: CBCT scans can adequately detect the GSC during pre-surgical diagnostics. There is a high risk of implant-GSC contact during surgery of the anterior mandible. However, the clinical relevance of such a contact is not known yet, because none of the clinical studies evaluating a single midline implant has reported any implant-GSC contact-related complications.

Therapeutic potential of larval excretory/secretory proteins of the pig whipworm Trichuris suis in allergic disease.

BACKGROUND: Gastrointestinal nematodes are currently being evaluated as a novel therapeutic in the treatment of chronic human inflammatory disorders, due to their unique ability to induce immunoregulatory pathways in their hosts. In particular, administration of ova from the pig whipworm Trichuris suis (T. suis; TSO) has been proposed for the treatment of allergic, inflammatory and autoimmune disorders. Despite these advances, the biological pathways through which TSO therapy modulates the host immune system in the context of human disease remain undefined. METHODS: We characterized the dominant proteins present in the excretory/secretory (E/S) products of first-stage (L1) T. suis larvae (Ts E/S) using LC-MS/MS analysis and examined the immunosuppressive properties of whole larval Ts E/S in vitro and in a murine model of allergic airway disease. RESULTS: Administration of larval Ts E/S proteins in vivo during the allergen sensitization phase was sufficient to suppress airway hyperreactivity, bronchiolar inflammatory infiltrate and allergen-specific IgE production. Three proteins in larval Ts E/S were unambiguously identified. The immunomodulatory function of larval Ts E/S was found to be partially dependent on the immunoregulatory cytokine IL-10. CONCLUSIONS: Taken together, these data demonstrate that the released proteins of larval T. suis have significant immunomodulatory capacities and efficiently dampen allergic airway hyperreactivity. Thus, the therapeutic potential of defined larval E/S proteins should be exploited for the treatment of human allergic disorders.

Poly(A) tail shortening correlates with mRNA repression in tropoelastin regulation.

BACKGROUND: It has been shown for various organisms that expression of tropoelastin (TE) is high during fetal and neonatal growth and that it is reduced in adulthood by an unknown mechanism. OBJECTIVE: To highlight the process of TE mRNA repression in vivo, total RNA from human skin biopsies was analyzed and TE mRNA expression was compared in fetal and adult donors. METHODS: TaqMan Real-Time PCR, Poly(A) tail length assay, immunoblot. RESULTS: In this study a more than 30-fold reduction of mature TE mRNA was detected whereas the decline on pre-mRNA level was not pronounced. This finding supports the hypothesis that the repression of mature TE mRNA is for the most part due to posttranscriptional mechanisms. Since deadenylation-dependent mRNA destabilization is the major decay pathway for most mRNAs, poly(A) tail length of mature TE mRNA was analyzed in fetal and adult human skin, lung and uterus, showing a profound reduction of poly(A) tail length in the adult samples. While TE mRNA is repressed in adult tissues in vivo, TGF-ß(1) has been shown to induce expression of TE mRNA in vitro on the posttranscriptional level. To analyze the underlying mechanism, TE mRNA poly(A) tail length was analyzed in human dermal fibroblasts after treatment with TGF-ß(1)in vitro. Besides the expected increase in TE expression, TGF-ß(1) treatment resulted in a significant stabilization of TE mRNA poly(A) tail length. CONCLUSION: Our findings correlate for the first time TE expression level with poly(A) tail length and suggest that maintenance of poly(A) tail and deadenylation of TE mRNA might be general mechanisms involved in the regulation of TE expression.

Involvement of formyl-peptide-receptor-like-1 and phospholipase D in the internalization and signal transduction of amyloid beta 1-42 in glial cells.

Recent studies suggest that the formyl-peptide-receptor-like-1 (FPRL1) plays an essential role in the inflammatory responses of host defense mechanisms and neurodegenerative disorders such as Alzheimer's disease (AD). We therefore analyzed whether amyloid beta1-42 (Abeta1-42) increased the activity of phospholipase D (PLD) via FPRL1, which is an enzyme involved in the secretion, endocytosis and receptor signaling. PLD activity was determined using a transphosphatidylation assay. The internalization of Abeta1-42 via FPRL1 was visualized using fluorescence microscopy and quantified by ELISA (Enzyme Linked Immunosorbent Assay). Determining receptor activity by extracellular-signal regulated kinases 1/2 (ERK1/2) phosphorylation and cAMP level measurement verified the Abeta1-42-induced activation of FPRL1. We were able to show that Abeta1-42 is rapidly internalized via FPRL1 in astrocytes and microglia. PLD was additionally activated by Abeta1-42 and via FPRL1 in rat glial cells. Furthermore, the ERK1/2 phosphorylation by FPRL1 agonists was dependent on the PLD product phosphatidic acid (PA). Together, these data suggest that PLD plays an important role in the regulation of Abeta1-42-induced endocytosis and FPRL1 receptor signaling.

Vaccination of eels (Anguilla japonica and Anguilla anguilla) against Anguillicola crassus with irradiated L3.

The original host of the swimbladder nematode Anguillicola crassus, the Japanese eel (Anguilla japonica) and the recently colonized European eel (Anguilla anguilla) were immunized with 40 irradiated (500 Gy) 3rd-stage larvae (L3) of this parasite and challenged with an infection of 40 normal L3. The immunization induced a significant reduction of the number of adult worms developing from the challenge infection in A. japonica, but not in A. anguilla. The induced resistance (calculated using the relation of the number of adult worms in immunized eels and in non-immunized control eels) in A. japonica was 87.3%+/-30.4%. Following a single infection, the percentage of adult worms found in A. japonica was lower as compared to A. anguilla, and the few adult worms were much smaller, revealing a lower susceptibility of A. japonica to A. crassus in comparison to A. anguilla. Both eel species developed an antibody response against A. crassus, but the level of antibody responses was not positively correlated with the protection against infection, suggesting that the antibody response is not a key element in resistance of eels against A. crassus. This study suggests that the original host of A. crassus is able to mount efficient protective immune responses against its parasite, whereas the newly acquired host seems to lack this ability.

Involvement of benzodiazepine receptors in neuroinflammatory and neurodegenerative diseases: evidence from activated microglial cells in vitro.

Increased binding of a ligand for the peripheral benzodiazepine binding receptor is currently used in PET studies as an in vivo measurement of inflammation in diseases like multiple sclerosis and Alzheimer's disease. Although peripheral-type benzodiazepin receptors (PBRs) are abundant in many cell types and expressed in the CNS physiologically only at low levels, previous reports suggest that after experimental lesions in animal models and in human neurodegenerative/-inflammatory diseases upregulated PBR expression with increased binding of its ligand PK11195 is confined mainly to activated microglia in vivo/in situ. Because the functional role of the PBR is unknown, we confirm by immunohistochemistry and PCR (I) that this receptor is expressed on microglia in vitro and (II) that benzodiazepines modulate proliferation of microglial cells and the release of the inflammatory molecules nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) in cell culture supernatants of primary rat microglia. Compared to lipopolysaccharide-activated controls the release of NO was markedly decreased in cultures treated with benzodiazepines (clonazepam, midazolam, diazepam) and the PBR ligand PK11195. Moreover, release of TNF-alpha and proliferation was significantly inhibited in the benzodiazepine-treated groups. These findings link the in vivo data of elevated PBR levels in neurodegenerative/-inflammatory diseases to a functional role and opens up possible therapeutic intervention targeting the PBR in microglia.

Modulation of host immune responses by nematode cystatins.

Parasitic nematodes, living in the intestinal tract or within tissues of theirs hosts, are constantly exposed to an array of immune effector mechanisms. One strategy to cope with the immune response is the release of immunomodulatory components that block effector mechanisms or interact with the cytokine network. Among the secreted nematode immunomodulators, cysteine protease inhibitors (cystatins) are shown to be of major importance. Nematode cystatins inhibit, among others, proteases involved in antigen processing and presentation, which leads to a reduction of T cell responses. At the same time nematode cystatins modulate cytokine responses, the most prominent trait being the upregulation of IL-10, a Th2 cytokine, by macrophages. In this situation, IL-10 leads among others to downregulation of costimulatory surface molecules of macrophages. These properties contribute to induction of an anti-inflammatory environment, concomitant with a strong inhibition of cellular proliferation. This setting is believed to favour the survival of worms. An opposite activity of nematode cystatins is the upregulation of production of inducible nitric oxide by IFN-gamma activated macrophages, an intrinsic property of natural cysteine protease inhibitors. This shows that these proteins can act as proinflammatory molecules under certain circumstances. A comparison of the immunomodulatory effects of cystatins of filarial nematodes with homologous proteins of the free-living nematode Caenorhabditis elegans revealed distinct differences. Caenorhabditis elegans cystatins induce the production of the Th1 cytokine IL-12, in contrast to filarial cystatins that upregulate IL-10. Caenorhabditis elegans cystatins hardly inhibit cellular proliferation. These data suggest that cystatins of parasitic nematodes have multiple, specific capacities for immunomodulation, acting in parallel on different immune effector mechanisms. Elucidation of the mechanisms involved might be useful in the development of immunotherapeutic reagents in the future.

Cerebrospinal fluid from patients with neurodegenerative and neuroinflammatory diseases: no evidence for rat glial activation in vitro.

To determine the possible contribution of glial cells via oxidative stress/cytokine secretion in the pathogenesis of Parkinson's disease (PD), Alzheimer disease (AD), amyotrophic lateral sclerosis (ALS) or multiple sclerosis (MS) the concentration of nitric oxide (NO) (by the Griess method) and Interleukin-6 (IL-6) (by enzyme-linked immunosorbent assay) were measured in resting rat microglial and astrocytic cell culture supernatants stimulated by cerebrospinal fluid (CSF) (dilution 1:4, 1:10) from patients with the aforementioned diseases. Neither the concentration of NO (optical density at 450 nm: control, 0.036+/-0.006; MS, 0.034+/-0.008; AD, 0.031+/-0.006; PD, 0.02+/-0.01; lipopolysaccharide (LPS), 0.26+/-0.018) nor the amount of IL-6 (ng/ml: control, 0.112+/-0.026; PD, 0.12+/-0.027; MS, 0.123+/-0.008; ALS, 0.137+/-0.01; LPS, 1.81+/-0.11) differed in any disease group from those of unaffected controls. These findings suggest that the stimuli for inflammatory activation of glia are quite localized and not present in sufficient concentrations in the CSF of affected patients.

Immunisation with Salmonella typhimurium-delivered glyceraldehyde-3-phosphate dehydrogenase protects mice against challenge infection with Echinococcus multilocularis eggs.

Recombinant glyceraldehyde-3-phosphate dehydrogenase of the cestode parasite Echinococcus multilocularis was expressed in Escherichia coli and in Salmonella typhimurium. The potential of different forms of the recombinant antigen to protect BALB/c mice against oral challenge infections with E. multilocularis eggs was evaluated. Oral or intraperitoneal immunisation with live attenuated S. typhimurium as a carrier for recombinant glyceraldehyde-3-phosphate dehydrogenase of the E. multilocularis resulted in significant protection, reducing the number of developing metacestodes up to 79.8%. The sera of protected animals did not contain detectable amounts of antibody against glyceraldehyde-3-phosphate dehydrogenase of E. multilocularis. By contrast, although anti-glyceraldehyde-3-phosphate dehydrogenase of E. multilocularis antibodies were detectable in the sera, immunisation with E. coli-expressed recombinant glutathione-S-transferase-fusion protein or with glyceraldehyde-3-phosphate dehydrogenase of E. multilocularis fused to a 6HIS-tag failed to protect the animals against oral challenge infections. These data emphasise that antigen delivery systems play a critical role in vaccination and the induction of protective immunity against helminth parasites.

Modulation of human T cell responses and macrophage functions by onchocystatin, a secreted protein of the filarial nematode Onchocerca volvulus.

Immune responses of individuals infected with filarial nematodes are characterized by a marked cellular hyporesponsiveness and a shift of the cytokine balance toward a Th2/Th3 response. This modulation of cellular immune responses is considered as an important mechanism to avoid inflammatory immune responses that could eliminate the parasites. We investigated the immunomodulatory potential of a secreted cysteine protease inhibitor (onchocystatin) of the human pathogenic filaria Onchocerca volvulus. Recombinant onchocystatin (rOv17), a biologically active cysteine protease inhibitor that inhibited among others the human cysteine proteases cathepsins L and S, suppressed the polyclonally stimulated and the Ag-driven proliferation of human PBMC. Stimulated as well as unstimulated PBMC in the presence of rOv17 produced significantly more IL-10, which was paralleled in some situations by a decrease of IL-12p40 and preceded by an increase of TNF-alpha. At the same time, rOv17 reduced the expression of HLA-DR proteins and of the costimulatory molecule CD86 on human monocytes. Neutralization of IL-10 by specific Abs restored the expression of HLA-DR and CD86, whereas the proliferative block remained unaffected. Depletion of monocytes from the PBMC reversed the rOv17-induced cellular hyporeactivity, indicating monocytes to be the target cells of immunomodulation. Therefore, onchocystatin has the potential to contribute to a state of cellular hyporesponsiveness and is a possible pathogenicity factor essential for the persistence of O. volvulus within its human host.

From theory to therapy: implications from an in vitro model of ramified microglia.

Microglia are the principal immune cells in the central nervous system (CNS), characterized by a highly specific morphology and unusual antigenic phenotype. An increasing number of studies have focused on the role of microglia in the pathogenesis of neurodegenerative diseases. To elucidate the function of microglial cells under several neuropathological conditions, we have studied and established a cell culture model that allows us to cultivate microglial cells in their inactive, resting (ramified) phenotype. In the first part of this work, we describe the interaction of microglia cells with their epithelial (astrocytic) microenvironment. The second part reviews experiments with microglia cell cultures to elucidate underlying signalling pathways and summarizes recent advances of our knowledge in microglial molecular pathways that may ultimately lead to neurodegeneration.

ATP and adenosine induce ramification of microglia in vitro.

Microglial cells in the healthy adult brain possess a characteristic ramified morphology with multiple branched processes, small somata and down-regulated inflammatory properties. In contrast, microglial cells isolated from new-born rat brain inevitably show a non-ramified amoeboid phenotype, which is observed in vivo after pathologic activation or during development. To identify factors that control microglial morphology we investigated the effects of purines alone or in combination with astrocyte-conditioned medium (ACM). Under optimized culture conditions postnatal rat microglial cells developed an amoeboid to ovoid phenotype. Addition of 0.6-1 mM ATP or adenosine induced the outgrowth of numerous processes after 2-3 days that could be observed also in the presence of ACM as previously reported. Culture in ACM plus ATP or adenosine yielded an optimized ramified phenotype. ATP or adenosine, but not ACM alone, also prevented the formation of a flat, amoeboid morphology induced by lipopolysaccharide (LPS); however, at 0.6-1 mM they did not reduce the initial LPS-induced activation of the transcription factor NF-kappaB. By using specific agonists or antagonists the morphological transformations could not be confined to a distinct purinoreceptor subtype, but appeared to be mediated by long-term presence of adenosine in the medium to which phosphorylated purines were rapidly hydrolyzed by microglial cells. Since ACM did not contain sufficient concentrations of ATP or adenosine, purines are not the only ramification-inducing factors present in ACM; however, they are a valuable tool to induce microglial ramification in vitro.

An epidemiologic survey of human alveolar echinococcosis in southwestern Germany. Römerstein Study Group.

The inhabitants of a rural community in southwestern Germany were examined for alveolar echinococcosis (AE). The study was prompted by the recent increase of the prevalence of the parasite in foxes and the increase of fox populations: in the study area, 75% of the foxes carried Echinococcus multilocularis. The human population was screened using hepatic ultrasound and serology. All participants were interviewed for demographic and potential risk factors. Of 2,560 participants, one was identified with active AE, while 3 others had suspicious liver lesions. Another 9 participants were seropositive for specific antibodies without detectable lesions. Demographic and behavioral factors were not correlated with active or suspected cases nor with seropositivity. If the prevalence of 40/100,000 (95% confidence interval = 15-295/100,000) for active cases would be representative for the rural population in high endemicity areas, the current number of AE cases in southwestern Germany is considerably higher than previously suspected.

Toxoplasma infection and cell free extract of the parasites are able to reverse multidrug resistance of mouse lymphoma and human gastric cancer cells in vitro.

A large number of compounds are known to reduce the ATP-dependent efflux pump activity of multidrug resistant (mdr) tumor cells. Here we report that an infection of cancer cells with T. gondii reduced the multidrug resistance of the tumour cells against cytostatic drugs. Two mouse lymphoma cell lines (Mdr L 5718 and Par 5718) were infected with Toxoplasma gondii in vitro and the reduction of efflux pump activity of the cells was measured. The drug accumulation (Rhodamin-123) was increased in the infected mdr cell lines compared with non- infected mdr-cells, and no effect was shown after infection of the parental cell line. The same effect was also achieved by incubation of Mdr-tumor cells with cell lysate of Toxoplasma gondii. Mdr-1-gene expression was reduced in the infected cell lines 48 hours after infection. Co-cultivation of Toxoplasma gondii with mdr cell lines separated by a microfilter from tumor cells was performed, but this cocultivation did not change the mdr efflux activity. The effect of Toxoplasma gondii infection on the efflux pump activity and mdr-1 gene expression was also examined in the human gastric cancer cells. A sensitization of resistant gastric cancer cells was also achieved by parasite infection. This phenomenon is an evidence that a reduction of resistance in tumor cells can be achieved by a natural parasite infection. It is as yet unclear whether an active infection or another substance of T. gondii is responsible for this phenomenon.

Detection of Echinococcus multilocularis in the definitive host: coprodiagnosis by PCR as an alternative to necropsy.

Recently, extensions of the range of Echinococcus multilocularis in Europe and North America and drastic increases in fox populations in Europe put an increasing proportion of the human population at risk of alveolar echinococcosis. To obtain data on the local infection pressure, studies of the prevalence of the parasite in the animals that transmit the parasite, foxes, dogs, and cats, are urgently required. Such investigations, however, have been hampered by the need for necropsy of the host animal to specifically diagnose infection with the parasite. In this study, a nested PCR and an improved method for DNA extraction were developed to allow the sensitive and specific diagnosis of E. multilocularis infections directly from diluted fecal samples from foxes. The target sequence for amplification is part of the E. multilocularis mitochondrial 12S rRNA gene. The specificity of the method was 100% when it was tested against 18 isolates (metacestodes and adult worms) of 11 cestode species, including E. granulosus. The sensitivity of the method was evaluated by adding egg suspensions and individual eggs to samples of diluted feces from uninfected foxes. The presence of one egg was sufficient to give a specific signal. To confirm the PCR results, an internal probe which hybridized only with E. multilocularis amplification products but not with the DNA of other cestodes was constructed. In order to investigate the applicability of this method for epidemiological studies, 250 wild foxes from a area in southern Germany where echinococcosis is highly endemic were examined by both necropsy and PCR of rectal contents. The sensitivity correlated with the parasites' number and stage of maturity. It ranged from 100% (>1,000 gravid worms) to 70% (<10 nongravid worms). On the basis of positive PCR results for 165 foxes, the sensitivity of the traditional and widely used necropsy method was found to be not higher than 76%. We therefore present this PCR system as an alternative method for the routine diagnosis of E. multilocularis in carnivores.

Cutaneous malignant melanoma and oculodermal melanocytosis (nevus of Ota): report of a case and review of the literature.

A 29-year-old white man, with oculodermal melanocytosis, had a rapidly enlarging, erythematous, painful nodule over his left brow, within the nevus. The lesion was excised and diagnosed as a malignant melanoma. Systemic evaluation showed no evidence of distant disease. This is the tenth case reported of a cutaneous melanoma developing in a nevus of Ota. Melanoma arising in the choroid, brain, orbit, iris, ciliary body, or optic nerve in association with a nevus of Ota is well documented. Careful observation is necessary in patients with a nevus of Ota, particularly in white patients, in whom malignant degeneration seems to occur with a disproportionate frequency.

Localization of T and B cell stimulating domains of the immunodominant 33-kDa protein of Onchocerca volvulus (Ov33).

The localization of T and B cell epitopes on a well characterized 33-kDa protein of the filarial nematode Onchocerca volvulus (Ov33) was studied using peripheral blood mononuclear cells (PBMC) and sera from a total of 52 onchocerciasis patients with the generalized form of infection. A proportion of the PBMC samples proliferated in response to recombinant Ov33-GST fusion protein and to fusion free Ov33-6xHis. Proliferative responses of patient PBMC to seven truncated Ov33-6xHis polypeptides and to three synthetic peptides revealed at least one major and two minor T cell epitopes in the protein. The dominant T cell stimulating domain was localized between amino acids 113 and 143. ELISA studies with the Ov33-GST fusion protein revealed that patient sera contained Ov33-specific IgG1, IgG4, IgE, and IgM antibodies. Analysis of the IgG4 response with 10 truncated Ov33 polypeptides identified four B cell stimulating domains in the N-terminal, central, and C-terminal region of the molecule. The B cell domain recognized by the majority of sera was localized between amino acids 113 and 143. The data indicate that this region of the protein is the major T and B cell stimulating domain of Ov33 and might be relevant for vaccine development and for improved immunodiagnosis of onchocerciasis.

A filarial cysteine protease inhibitor down-regulates T cell proliferation and enhances interleukin-10 production.

Filarial nematodes are a cause of chronic debilitating diseases in the tropics. A hallmark of filariasis is the marked down-regulation and polarization of host immune responses, yet molecular constituents of parasites causing this state have remained undefined. We describe a 17-kDa antigen (Av17) of the rodent filarial parasite Acanthocheilonema viteae, which shows amino acid homologies to cystatin C, a major cysteine protease inhibitor belonging to family 2 of the cystatin superfamily. Av17 is released by filariae in vitro. Exported molecules of A. viteae worms are shown to markedly suppress mitogen-induced T cell proliferation of mice and jirds. Av17 accounts for 45.5% of this suppressive activity in the murine system. Recombinant Av17 (rAv17), expressed in Escherichia coli, exhibits biological activity as a cysteine protease inhibitor and was used to examine the immunomodulatory effects, rAv17 induces down-regulation of murine T cell responses to mitogens, to T cell receptor cross-linking by anti-CD3 antibodies and to specific antigens, and at the same time up-regulation of interleukin-10. Hence, this filarial cystatin is a likely effector molecule of immunomodulation and a potential target for antifilarial intervention.