Genetics of Biomphalaria glabrata and its effect on the outcome of Schistosoma mansoni infection

The genetics of the snail Biomphalaria glabrata is better characterized than that of any other intermediate host of schistosomes of humans. Using techniques of selective breeding, several snail stocks have been developed that consistently display resistant or susceptible phenotypes. Investigators using these stocks have learned that several snail and parasite genes influence the course of parasite development. Here, Charles Richards, Matty Knight and Fred Lewis discuss the importance of the snail's genetics in categorizing resistance in this complex invertebrate, some recent molecular evidence that may help us understand several of the problems that still remain, and some challenges lying ahead for investigators in this field.

Distribution of schistosome infections in molluscan hosts at different levels of parasite prevalence

Biomphalaria glabrata snails infected with Schistosoma mansoni were collected during consecutive seasons from a site in Brazil known to have a very high percentage of infected snails. Schistosoma mansoni cercariae from single snails were used to infect individual mice, and the recovered adult worms were genetically assessed using a mtVNTR marker. The number of unique parasite genotypes found per snail was compared to expected abundance values, based on the infection prevalence at the site, to determine the distribution of S. mansoni infections within the snail population. The observed distributions and those from previous studies were used to examine the relationship between schistosome prevalence and aggregation across a wide range of prevalence values. Our analysis showed that prevalence was inversely related to the degree of parasite overdispersion, and at high prevalence, S. mansoni infections were randomly distributed among snails.

The relationship between Schistosoma mansoni and Biomphalaria glabrata: genetic and molecular approaches

Biomphalaria glabrata is a major intermediate host for the helminth parasite Schistosoma mansoni. Beginning in the mid-20th century, studies were carried out with this snail species to identify the immunological and genetic components that might be involved in controlling schistosome development. A number of genetically well-defined snail stocks were derived as a direct result of these studies and have since played major roles in helping investigators to identify important cellular and humoral components in the snail/schistosome relationship. This review will explore the historical development of these stocks and describe some of the major advances in several areas of medical malacology that hawe been made possible be their use.

An introduction to arrays

DNA microarrays are a new technology that allows the analysis of large numbers of genes at a high resolution by the hybridization of labelled DNA, which may be reverse-transcribed from mRNA, to a substrate containing thousands of spotted cDNAs or oligonucleotides. The amount of hybridized target is analysed, giving information on gene expression, polymorphisms or mutations present and allowing the gene profiling of different subtypes of disease. This technique has massive implications for the further understanding of the complicated genetic alterations involved in tumourigenesis and other disease processes and also for the generation of accurate prognostic information and optimization of treatment in these situations.

Differential gene expression in haemocytes of the snail Biomphalaria glabrata: effects of Schistosoma mansoni infection

Parasite encapsulation and destruction in Biomphalaria glabrata has been shown to involve the cellular component of the snail's internal defence system, the haemocytes. To identify genes involved in the immunobiology of these cells, we used the method of differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) to investigate differential gene regulation in haemocytes isolated from Schistosoma mansoni exposed and unexposed snails. RNA isolated from circulating haemocytes from resistant snails (BS-90 stock), previously exposed to S. mansoni, was analysed using 12 different arbitrary primers in conjunction with an anchored Oligo d(T(11)CG) primer. Transcription profiles between haemocytes of parasite exposed and unexposed snails were compared and a total of 87 differentially regulated bands were identified and isolated. Of these, 65 bands were cloned and used as probes in Southern blots to show the presence of corresponding sequences in the snail genome. RT-PCR was performed to verify the regulation of these transcripts. DNA sequence analysis showed that the majority of the cloned sequences were novel, although a few showed a high degree of sequence similarity to other sequences in the DNA and protein databases. One of these included a differentially expressed transcript that showed a significant degree of sequence identity to E. coli transposase Tn5, an enzyme whose activity is normally associated with generating mobility and instability in the genome.

Molecular studies of Biomphalaria glabrata, an intermediate host of Schistosoma mansoni

The freshwater gastropod Biomphalaria glabrata is one of the most important invertebrate hosts of the helminth parasite Schistosoma mansoni. Investigators are using different strategies to determine the molecular basis of this snail-parasite relationship. Of particular interest are the identification of parasite resistance genes in the snail, and the application of molecular probes to better understand the epidemiology of schistosomiasis. This review will focus on recent advances that have been made on genome analysis of B. glabrata. Much of this work has centred on the use of random amplification of polymorphic DNA-PCR-based technology, with restriction fragment length polymorphism analysis and the generation of expressed sequence tags from the snail. A brief discussion of how parasite products may complicate this analysis is also given, along with an indication of the scope of the problems that lie ahead.

The identification of markers segregating with resistance to Schistosoma mansoni infection in the snail Biomphalaria glabrata

Both snail and parasite genes determine the susceptibility of the snail Biomphalaria glabrata to infection with the trematode Schistosoma mansoni. To identify molecular markers associated with resistance to the parasite in the snail host, we performed genetic crosses between parasite-resistant and -susceptible isogenic snails. Because resistance to infection in adult snails is controlled by a single locus, DNA samples from individual F2 and F1 backcross progeny, segregating for either the resistant or susceptible phenotypes, were pooled (bulked segregant). Genotypes for both parents were determined with 205 arbitrary decamer primers by random amplified polymorphic DNA-PCR. Of the 205 primers, 144 were informative, and the relative allele frequencies between the pools for these primers were determined. Two primers, OPM-04 and OPZ-11, produced fragments in the resistant parent of one cross that were inherited in a dominant fashion in the resistant F2 and backcross-bulked segregant progeny. Subsequent typing of DNA samples of individual progeny snails showed that the 1.2-kb marker amplified by primer OPM-04 and the 1.0-kb marker produced by primer OPZ-11 segregated in the same dominant fashion with the resistant phenotype. Sequence analysis of the 1.2-kb marker showed that it corresponds to a repetitive sequence in the snail genome with no homology to existing DNA sequences in the public databases. Analysis of the 1. 0-kb marker showed that it also corresponds to a repetitive sequence in the B. glabrata genome that contains an imperfect ORF, with homology to retrovirus-related group-specific antigens (gag) polyprotein.

Tandemly repeated genomic sequence demonstrates inter- and intra-strain genetic variation in Schistosoma japonicum

Genetic variability within and among four geographical strains of Schistosoma japonicum was examined using a novel repetitive element. The element, termed Sirh1.0, was isolated from genomic DNA of a Philippine strain of S. japonicum using a combination of restriction fragment PCR and band-stab PCR. Sjrh1.0 is a tandemly repeated element, the sequence of which appears to be species-specific, in that it hybridized to DNA from S. japonicum but not to DNA from S. mansoni. Its sequence does not match previously deposited sequences in GenBank. When employed as a probe in Southern hybridization analysis, radiolabelled Sjrh1.0 revealed sex-specific and strain-specific differences in genomic DNA of individual worms. We also found individual genetic variation within geographical isolates of the Asian schistosome.

CD4+ T cell-mediated granulomatous pathology in schistosomiasis is downregulated by a B cell-dependent mechanism requiring Fc receptor signaling

The effector functions of CD4+ T lymphocytes are generally thought to be controlled by distinct populations of regulatory T cells and their soluble products. The role of B cells in the regulation of CD4-dependent host responses is less well understood. Hepatic egg granuloma formation and fibrosis in murine schistosomiasis are dependent on CD4+ lymphocytes, and previous studies have implicated CD8+ T cells or cross-regulatory cytokines produced by T helper (Th) lymphocytes as controlling elements of this pathologic process. In this report, we demonstrate that B cell-deficient (muMT) mice exposed to Schistosoma mansoni develop augmented tissue pathology and, more importantly, fail to undergo the spontaneous downmodulation in disease normally observed during late stages of infection. Unexpectedly, B cell deficiency did not significantly alter T cell proliferative response or cause a shift in the Th1/Th2 balance. Since schistosome-infected Fc receptor-deficient (FcR gamma chain knockout) mice display the same exacerbated egg pathology as that observed in infected muMT mice, the B cell- dependent regulatory mechanism revealed by these experiments appears to require receptor-mediated cell triggering. Together, the data demonstrate that humoral immune response/FcR interactions can play a major role in negatively controlling inflammatory disease induced by CD4+ T cells.

A laboratory-based approach to biological control of snails

Development of Schistosoma mansoni in the intermediate host Biomphalaria glabrata is influenced by a number of parasite and snail genes. Understanding the genetics involved in this complex host/ parasite relationship may lead to an often discussed approach of introducing resistant B. glabrata into the field as a means of biological control for the parasite. For the snail, juvenile susceptibility to the parasite is controlled by at least four genes, whereas one gene seems to be responsible for adult nonsusceptibility. Obtaining DNA from F2 progeny snails from crosses between parasite-resistant and -susceptible snails, we have searched for molecular markers that show linkage to either the resistant or susceptible phenotype. Both restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) approaches have been used. To date, using a variety of snail and heterologous species probes, no RFLP marker has been found that segregates with either the resistant or susceptible phenotype in F2 progeny snails. More promising results however have been found with the RAPD approach, where a 1.3 kb marker appears in nearly all resistant progeny, and a 1.1 kb marker appears in all susceptible progeny.

Familial transmission of the FMR1 CGG repeat

To better define the nature of FMR1 CGG-repeat expansions, changes in allele sizes for 191 families with fragile X and for 33 families with gray-zone repeats (40-60) were analyzed. Expansion of the fragile X chromosome to the full mutation was seen in 13.4% of offspring from premutation mothers with 56-59 repeats, 20.6% of those with 60-69 repeats, 57.8% of those with 70-79 repeats, 72.9% of those with 80-89 repeats, and 97.3% of those with 90-199 repeats. For premutation fathers, the majority (62%) of their daughters had a larger repeat number, while a few had either a smaller (22%) or the same (16%) repeat number, compared with their fathers' sizes. However, daughters with a smaller repeat number were observed only if their fathers had > or = 80 repeats. Fifteen (39.5%) of 38 such daughters carried a smaller repeat than did their fathers. We observed that a similar repeat number was inherited more often than expected by chance, among the members of a sibship segregating fragile X. This familial clustering, observed in the offspring of both males and females with a premutation, implies there may be an additional factor, independent of parental repeat size, that influences CGG-repeat instability. Instability in gray-zone allele transmissions was observed in 25% of alleles with 50-60 CGGs but in <8% of those with 40-49 CGGs. Examination of gray-zone allele organization revealed that long tracts of pure CGGs (>34) are not always unstably transmitted. These results raise new questions regarding the familial factors that may determine transmission expansions.

Schistosoma mansoni: unisexual infections sensitized mice for granuloma formation around intravenously injected eggs

Mice carrying unisexual infection with male or female Schistosoma mansoni for 9 weeks developed accelerated and augmented reactions to S. mansoni eggs injected intravenously. The size of circumoval granulomas observed in the lungs of unisexually infected mice did not differ significantly from the reactions seen in bisexually infected mice. Tissue eosinophilia in the granulomas was also augmented similarly over that in naive mice by unisexual or bisexual infection. The cross-reactivity between worm and egg antigens is relevant to the development of acute toxemic schistosomiasis mansoni and, perhaps, to the consideration of antigens to be used for vaccination against S. mansoni infection.

Male reproductive success of Schistosoma mansoni-infected Biomphalaria glabrata snails

Infection of Biomphalaria glabrata by Schistosoma mansoni results in a dramatic reduction in the snail's ability to produce eggs. We studied the ability of such parasitically castrated snails to fertilize the eggs of uninfected snails. Pigmented B. glabrata snails (13141 stock) were infected with S. mansoni miracidia and reared individually until they ceased laying eggs. These infected snails were then given the opportunity to mate with uninfected albino (NMRI) snails. Each of the infected snails was paired with a different albino partner each subsequent week. Sperm transfer by the infected snails was evident from the production of pigmented progeny by the uninfected albino snails. Infected snails successfully acted as males for up to 6 wk after parasitic castration had occurred. The duration of allosperm use by uninfected recipients was lengthy, regardless of the infection status of the pigmented sperm donor.

Use of RAPD-PCR to differentiate genetically defined lines of an intermediate host of Schistosoma mansoni, Biomphalaria glabrata

The genetic differentiation among several laboratory-maintained pedigree snail lines of Biomphalaria glabrata (with different susceptibility phenotypes to Schistosoma mansoni infection) was assessed with the random amplified polymorphic DNA method. Out of the 20 primers tested, 2 (OPA-01 and OPA-06) gave reproducible markers with either individual or bulked DNA samples from resistant (BS-90, 10-R2, LAC-line) and susceptible (M-line) snails. Arbitrary primer, OPA-01, amplification of BS-90 DNA identified a 180-bp strain-specific fragment and a 400-bp marker in the susceptible M-line stock. In the 10-R2 and LAC snail lines, OPA-01 specific markers of 200 bp and 550 bp were identified. Amplification with primer OPA-06 identified several major strain-specific markers in the BS-90 (150 bp, 400 bp, 800 bp) and M-line (1,100 bp) snails. The heritability of the RAPD markers was evaluated in progeny snails derived from a cross between the BS-90 and M-line stocks. Results showed that markers were inherited in a dominant or codominant fashion. The 1,100-bp M-line marker was inherited in all susceptible progeny snails analyzed.

Detection of common viruses using the polymerase chain reaction to assess levels of viral presence in type 1 (insulin-dependent) diabetic patients

The polymerase chain reaction was used to detect a range of common viruses in the peripheral blood of Type 1 diabetic and non-diabetic control patients in order to identify any abnormal viral presence, with possible roles in the pathogenesis of Type 1 diabetes. Peripheral blood from 17 newly diagnosed Type 1 diabetic patients, 38 Type 1 diabetic patients with disease of longer duration, and 43 age and sex matched non-diabetic controls was obtained. Samples were screened for cytomegalovirus, Epstein-Barr virus, enterovirus (including coxsackie), and mumps virus. Cytomegalovirus was detected in control patients only (5%), Epstein-Barr virus was detected equally in newly diagnosed and control patients (12%), and enterovirus was detected slightly more frequently in diabetic than non-diabetic patients (41% and 31%, respectively). Mumps virus was not detected in any of the samples. It is concluded that Type 1 diabetic individuals are neither more prone to persistence of common viruses nor to more frequent acute infections with the viruses tested for than non-diabetic individuals. If common viruses are involved in the pathogenesis of Type 1 diabetes then they act either as non-specific agents to which the host has abnormal immune responses, or, the diabetogenic viruses are eliminated from the body by the time of disease diagnosis.

An IL-12-based vaccination method for preventing fibrosis induced by schistosome infection

The harmful fibrosis which often occurs in the context of infectious disease involves the excessive deposition of connective tissue matrix, particularly collagen, and is mostly resistant to pharmacological and immunological intervention. In schistosomiasis, fibrosis is associated with the granulomatous response to parasite eggs trapped in the liver. We have previously shown that interleukin (IL)-12 administered peritoneally with eggs prevents subsequent pulmonary granuloma formation on intravenous challenge with eggs. Here we show that sensitization with eggs plus IL-12 partly inhibits granuloma formation and dramatically reduces the tissue fibrosis induced by natural infection with Schistosoma mansoni worms. These results are an example of a vaccine against parasites which acts by preventing pathology rather than infection. IL-12 is known to favour the priming of TH1 rather than Th2 cells, and the effects on fibrosis are accompanied by replacement of the Th2-dominated pattern of cytokine expression characteristic of S. mansoni infection with one dominated by Th1 cytokines. Elevated Th2 cytokine expression and fibrosis are common manifestations of a wide variety of infectious diseases and atopic disorders which might be ameliorated by vaccination with antigen and IL-12.

Microsatellite instability in colorectal cancer: improved assessment using fluorescent polymerase chain reaction

BACKGROUND & AIMS

Microsatellite instability was first described in hereditary nonpolyposis colorectal cancers and sporadic colorectal cancers, in which it was associated with a good prognosis. The aim of this study was to assess the advantages of a novel fluorescent assay for detecting microsatellite instability.

METHODS

Eleven fluorescently tagged microsatellites and an automated DNA sequencer were used to investigate 54 sporadic colorectal adenocarcinomas.

RESULTS

This fluorescent assay combined accurate allele sizing with cross-sectional data display and allowed improved assessment of microsatellite instability. Twenty-two percent of cancers (12 of 54) showed microsatellite instability with at least one marker. For tumors showing microsatellite instability, results were obtained for a minimum of eight markers. Six tumors showed microsatellite instability at high frequency (at least 63% of markers affected), and 42% of the patients who had a tumor showing microsatellite instability had a synchronous and/or metachronous colorectal tumor (vs. 7% of patients whose tumor did not show microsatellite instability). Patients with a microsatellite instability-positive tumor had an improved prognosis (P = 0.03).

CONCLUSIONS

The use of this fluorescent assay improved the assessment of microsatellite instability with the automated analysis and cross-sectional data display. The assay identified a subgroup of patients who showed microsatellite instability and who also showed clinical features that differed from the microsatellite instability-negative cases.

p53 allelic imbalance in astrocytoma detected using fluorescent PCR of microsatellite repeat polymorphisms

Previous reports have shown that p53 gene alteration plays an important role in tumourigenesis. Allelic loss of 17p in astrocytomas was detected in previous studies by restriction fragment length polymorphisms (RFLP). In this study we have analysed 47 cases of astrocytic tumours (26 glioblastomas [grade IV], 11 anaplastic astrocytomas [grade III], seven fibrillary astrocytomas [grade II] and three pilocytic astrocytomas [grade I]) for the presence of allelic imbalance at the p53 gene locus using intragenic markers. We used an informative method based on microsatellite polymorphisms at the p53 gene locus and fluorescent PCR. The fluorescently-labelled PCR products were then detected and analysed using an automated DNA sequencer with appropriate software. Seven of 47 (14.9%) cases were homozygous (uninformative). Five of the remaining 40 cases (12.5%) showed allelic imbalance at the p53 locus (three anaplastic astrocytomas [grade III] and two glioblastomas [grade IV]). None of the fibrillary astrocytomas (grade II) or pilocytic astrocytomas (grade I) showed allelic imbalance at the p53 locus. These results suggest that allelic imbalance at the p53 locus is not frequent and when it does occur is in high grade tumours.

Suppressive effect of interleukin-4 neutralization differs for granulomas around Schistosoma mansoni eggs injected into mice compared with those around eggs laid in infected mice

The principal pathological manifestation of murine Schistosoma mansoni infection is the egg-induced granuloma. Synchronous pulmonary granulomas forming around intravenously injected schistosome eggs are widely used to study the immunopathology of schistosomiasis. A number of anticytokine antibody treatments have a remarkable effect in modulating granulomas in this model but little effect on the size of hepatic granulomas around laid eggs during experimental infection. To examine this discrepancy, we examined the effects of anticytokine antibodies on liver and lung granulomas around injected eggs and around eggs laid during infection in both locations. Anti-interleukin-4 (IL-4) treatment greatly reduced the volume of granulomas around eggs injected into the liver via the portal vein and around eggs injected into the lung via the tail vein. On the contrary, granulomas around eggs laid by worms in either the liver or the lung during the course of infection were not significantly decreased in size by anti-IL-4 treatment. Thus, site is not important for the disparate effects of anti-IL-4 in granuloma formation around injected versus laid eggs. This effect is seen in naive and sensitized animals and is most probably due to differences in the quality of injected eggs versus those laid in situ by the worms.

Comparison of two strains of Schistosoma mansoni with respect to the sites and kinetics of immune elimination in irradiated cercaria-immunized mice

A comparison was made of the sites of elimination of NMRI and Mill Hill strains of Schistosoma mansoni in C57BL/6J mice previously immunized with 50 krad gamma-irradiated cercariae of the homologous strain. In the first experiment, the fate of percutaneous challenge infections with 75Se-labeled cercariae was evaluated by autoradiography of tissue squashes and hepatic portal perfusion. For both strains of parasite, migration from skin to lungs was delayed but not reduced in immunized mice relative to controls, with immune elimination taking place at some point after migration to the lungs. In a second experiment, resistance to the Mill Hill strain of S. mansoni was compared in mice challenged by percutaneous infection with cercariae and by intravenous injection with lung schistosomula. Both types of challenge were shown to be vulnerable to immune elimination. We conclude that under the conditions employed in this study, there is no significant difference between the NMRI and Mill Hill strains of S. mansoni in the patterns of migration and elimination, with most or all elimination in both control and immunized mice taking place after migration from the skin.

UVB-induced immune suppression and infection with Schistosoma mansoni

Irradiation with ultraviolet B (UVB, 290-320 nm) causes a systemic immunosuppression of cell-mediated immunity. The question of whether UV immunosuppression modulates the course of infectious diseases is important because UVB levels in sunlight are sufficient to predict significant UV-induced immunosuppression at most latitudes. We have investigated the effect of immunosuppressive doses of UVB on the disease caused by the helminth parasite Schistosoma mansoni. C57BL/6 mice were irradiated once or three times weekly over 60-80 days with UV from a bank of FS40 sunlamps. Each UV treatment consisted of an immunosuppressive UV dose, as determined by suppression of contact hypersensitivity to trinitrochlorobenzene, corresponding to about 15-30 min of noonday tropical sunlight exposure under ideal clear sky conditions. Cumulative UV doses were between 80 and 170 kJ/m2. Worm and egg burdens, liver granuloma diameters and liver fibrosis showed minimal changes (< 20%) compared with parameters in unirradiated animals. Ultraviolet irradiation (a total of 55 kJ/m2 administered in six treatments) did not impair the resistance to rechallenge conferred by vaccination with 60Co-irradiated cercariae. We have thus observed a dichotomy between UV immunosuppression and both disease and vaccination in this helminth infection, in contrast to the effects of UVB shown in other infectious diseases.

Elevated expression of Th1 cytokines and nitric oxide synthase in the lungs of vaccinated mice after challenge infection with Schistosoma mansoni

C57BL/6 mice were vaccinated with irradiated cercariae of Schistosoma mansoni, and, at various times after challenge infection, total lung mRNA was isolated to assess the induction of several cytokines that previously had been shown in in vitro studies to be involved in the activation of macrophages and/or endothelial cells for nitric oxide (NO) production and killing of schistosomula. Vaccinated mice demonstrated a highly significant increase in IFN-gamma mRNA upon subsequent infection when compared with infected nonvaccinated controls. A similar, although less dramatic, increase in two other macrophage-activating cytokines, TNF-alpha and IL-2, also was observed. In contrast, although the Th2 cytokines IL-4, IL-5, IL-10, and IL-13 were elevated in challenged vaccinated animals, only IL-10 and IL-13 showed increases that were significant with respect to the mRNA levels observed in challenged controls. Neutralization of IFN-gamma reduced immunity in vaccinated animals and resulted in decreased IFN-gamma, IL-2, IL-10, TNF-alpha, and IL-12 p40 but markedly increased IL-4, IL-5, and IL-13 mRNA expression and serum IgE levels. Pulmonary NO synthase expression was elevated in immunized mice at a time at which immune elimination of schistosomula is believed to occur. Moreover, suppression of NO synthase activity with the inhibitor aminoguanidine reduced immunity, as measured by a 32 to 33% increase in worm burden. Together, these data support previous in vitro studies that suggest a role for NO in schistosomulum killing. Furthermore, the observation that the down-regulatory cytokines IL-4, IL-10, and IL-13 are induced together with IFN-gamma may provide an explanation for the failure of this vaccine to provide complete protection.

Genetic diversity of Schistosoma mansoni: quantifying strain heterogeneity using a polymorphic DNA element

Intraspecific genetic variation among 14 geographic isolates of Schistosoma mansoni was quantified using a molecular marker to examine individual genotypes. Genetic crosses demonstrated maternal inheritance of S. mansoni DNA element pSM750. This element revealed diagnostic banding profiles, which allowed accurate strain identification. Most strains had similarity indices greater than 0.75 indicating that within-strain variation in these laboratory parasite populations was low. However, individual parasites from the NMRI strain were quite diverse (S = 0.40). Genetic heterogeneity among strains was quantified using a phenogram of mean genetic distance. Strain diversity between two geographic regions was quantified using a similarity index and was estimated to be substantial among isolates collected from a single local site.

Elevated expression of Th1 cytokines and nitric oxide synthase in the lungs of vaccinated mice after challenge infection with Schistosoma mansoni

C57BL/6 mice were vaccinated with irradiated cercariae of Schistosoma mansoni, and, at various times after challenge infection, total lung mRNA was isolated to assess the induction of several cytokines that previously had been shown in in vitro studies to be involved in the activation of macrophages and/or endothelial cells for nitric oxide (NO) production and killing of schistosomula. Vaccinated mice demonstrated a highly significant increase in IFN-gamma mRNA upon subsequent infection when compared with infected nonvaccinated controls. A similar, although less dramatic, increase in two other macrophage-activating cytokines, TNF-alpha and IL-2, also was observed. In contrast, although the Th2 cytokines IL-4, IL-5, IL-10, and IL-13 were elevated in challenged vaccinated animals, only IL-10 and IL-13 showed increases that were significant with respect to the mRNA levels observed in challenged controls. Neutralization of IFN-gamma reduced immunity in vaccinated animals and resulted in decreased IFN-gamma, IL-2, IL-10, TNF-alpha, and IL-12 p40 but markedly increased IL-4, IL-5, and IL-13 mRNA expression and serum IgE levels. Pulmonary NO synthase expression was elevated in immunized mice at a time at which immune elimination of schistosomula is believed to occur. Moreover, suppression of NO synthase activity with the inhibitor aminoguanidine reduced immunity, as measured by a 32 to 33% increase in worm burden. Together, these data support previous in vitro studies that suggest a role for NO in schistosomulum killing. Furthermore, the observation that the down-regulatory cytokines IL-4, IL-10, and IL-13 are induced together with IFN-gamma may provide an explanation for the failure of this vaccine to provide complete protection.

Frequency of allele loss of DCC, p53, RBI, WT1, NF1, NM23 and APC/MCC in colorectal cancer assayed by fluorescent multiplex polymerase chain reaction

We report here the use of multiplex fluorescent polymerase chain reaction (PCR) for quantitative allele loss detection using microsatellites with 2-5 base pair repeat motifs. Allele loss of APC, DCC, p53 and RB1 in colorectal tumours has been reported previously using a variety of methods. However, not all workers used intragenic markers. We have used microsatellite polymorphisms which map within, or are closely linked to, these tumour-suppressor gene loci in order to determine whether these loci are indeed the targets for alteration in colorectal cancer. In addition, we have assayed two other tumour-suppressor genes, WT1 and NF1, to see whether they play a role in colorectal carcinogenesis. The putative metastasis-suppressor gene, NM23, was also investigated since there have been conflicting reports about its involvement in colorectal carcinogenesis. Allele loss was detected at the DCC (29%), p53 (66%), RB1 (50%) and NF1 (14%) loci and in the APC/MCC region (50%), but not at the WT1 or NM23 loci. These rapid, and mostly gene-specific, fluorescent multiplex PCR assays for allele loss detection could be modified to devise a single molecular diagnostic test for the important lesions in colorectal cancer.

PCR in situ hybridisation detection of HPV 16 in fixed CaSki and fixed SiHa cell lines

AIMS

To investigate the feasibility of using fixed cells with the polymerase chain reaction (PCR) in situ hybridisation and to investigate possible reasons for reaction failure.

METHODS

Fixed SiHa and CaSki cells were used in an experimental model of PCR in situ hybridisation for the detection of low and intermediate copy number viral infection in fixed cells.

RESULTS

PCR in situ hybridisation was able to detect one to two copies of human papillomavirus (HPV) 16 in SiHa cells, using small fragment amplicons (120 base pairs), confirming the high detection sensitivity and flexibility of the technique. Problems were encountered with localisation of PCR amplified product in CaSki cells (200-300 copies of HPV 16 per cell) owing to diffusion of product post amplification. Overall, 40% of reactions were successful, which confirms the current unreliability of the technique. Within cell preparations, about 50% of cells contained amplified product.

CONCLUSION

PCR in situ hybridisation represents the marriage of two revolutionary molecular pathological techniques. However, it is currently unreliable, with reaction failure common. Standardised, dedicated equipment is urgently required if the technique is to achieve universal acceptance. In the future, the technique may be used to detect chromosomal translocations in human tumours and to study cellular gene expression.

In situ hybridisation for the identification of Helicobacter pylori in paraffin wax embedded tissue

A method for identifying Helicobacter pylori using a non-isotopic in situ hybridisation technique is described. A probe generated by polymerase chain reaction (PCR) with primers directed against parts of the Helicobacter pylori 16SrRNA sequence was used. Paraffin wax embedded gastric biopsy specimens from patients with and without gastritis were hybridised with the probe, and the method was shown to be sensitive and specific for H pylori.

Schistosoma mansoni: relationship between low fecundity and reduced susceptibility to parasite infection in the snail Biomphalaria glabrata

Biomphalaria glabrata snails which were not susceptible as juveniles to infection by Schistosoma mansoni were selectively bred (by self-fertilization) from the highly susceptible NMRI laboratory snail stock. The susceptibility rate among juvenile snails derived from interbreeding NMRI parents was initially 85-95%, but after several generations of selection, less than 5% of exposed snails became infected by the parasite. Selection for low susceptibility also resulted in a large proportion of snails that displayed low fecundity and produced abnormal egg masses. Individual adult snails which were isolated from an interbreeding population of nonselected NMRI snails usually produced well-developed egg masses each containing 15-30 embryos. However, when juvenile snails from this same population were reared in isolation and not allowed to cross-fertilize, many displayed a pattern of low fecundity and abnormal egg production similar to that observed in the selected low susceptible line. Furthermore, it was found that many of the isolated snails which exhibited low egg production were also not susceptible to parasitic infection.

A search for candidate viruses in type 1 diabetic pancreas using the polymerase chain reaction

In order to investigate a possible viral aetiology for Type 1 diabetes the polymerase chain reaction (PCR) technique was used. Pancreatic tissue from Type 1 diabetic subjects was examined for the presence of a panel of common viruses. Primers specific for mumps, measles, cytomegalovirus, and Epstein Barr virus, as well as primers located in a highly conserved region of the enterovirus genome which are capable of detecting all of the following family members: Coxsackie B, echovirus, polio, mengovirus, and encephalomyocarditis virus were used to screen 18 Type 1 diabetic subjects of whom 3 had proven insulitis, 12 Type 2 diabetic subjects and 18 non-diabetic controls. Epstein Barr virus was detected in two Type 1 (13%), two Type 2 (22%), and three of the normal nondiabetic pancreases (20%), and the DNA sequences confirmed by direct sequencing. Cytomegalovirus was detected in one of the normal pancreases only and no evidence of any of the other viruses was found. It is concluded that the Type 1 diabetic pancreatic samples studied did not show persistence of infection with any of the above viruses. Non-persistent acute infection of the pancreas by the above viruses cannot be excluded in the aetiology of Type 1 diabetes from this study.

Human papilloma viruses: a study of their prevalence in the normal larynx

The association of human papilloma viruses (HPV) with laryngopharyngeal squamous cell carcinoma is under investigation. The suitability of control tissue in the reported series, invariably obtained from histologically normal tissue adjacent to a squamous cell carcinoma or from patients with benign laryngopharyngeal disease, is questionable. The present study determined the prevalence of HPV in a series of normal larynges. Twelve autopsy larynges were collected. DNA was obtained by SDS proteinase K digestion. Evidence of HPV infection was documented by the polymerase chain reaction using oligonucleotide primers complementary to sequences in the E6 region of HPV types 11, 16 and 18. Four female and eight male larynges, mean age 65 years (SD = 16 years) were collected 72 hours postmortem (median value). HPV type 11 was isolated from three specimens. A 25 per cent prevalence rate for HPV 11 was found. No other HPV types were isolated.

The importance of fixation procedures on DNA template and its suitability for solution-phase polymerase chain reaction and PCR in situ hybridization

Conventional solution-phase polymerase chain reaction (PCR) and in situ PCR/PCR in situ hybridization are powerful tools for retrospective analysis of fixed paraffin wax-embedded material. Amplification failure using these techniques is now encountered in some centres using archival fixed tissues. Such 'failures' may not only be due to absent target DNA sequences in the tissues, but may be a direct effect of the type of fixative, fixation time and/or fixation temperature used. The type of nucleic acid extraction procedure applied will also influence amplification results. This is particularly true with in situ PCR/PCR in situ hybridization. To examine these effects in solution-phase PCR, beta-globin gene was amplified in 100 mg pieces of tonsillar tissue fixed in Formal saline, 10% formalin, neutral buffered formaldehyde, Carnoy's Bouin's, buffered formaldehyde sublimate, Zenker's, Helly's and glutaraldehyde at 0 to 4 degrees C, room temperature and 37 degrees C fixation temperatures and for fixation periods of 6, 24, 48 and 72 hours and 1 week. DNA extraction procedures used were simple boiling and 5 days' proteinase K digestion at 37 degrees C. Amplified product was visible primarily yet variably from tissue fixed in neutral buffered formaldehyde and Carnoy's, whereas fixation in mercuric chloride-based fixatives produced consistently negative results. Room temperature and 37 degrees C fixation temperature appeared most conducive to yielding amplifiable DNA template. Fixation times of 24 and 48 hours in neutral buffered formaldehyde and Carnoy's again favoured amplification.(ABSTRACT TRUNCATED AT 250 WORDS)

Schistosoma mansoni: analysis of an unusual infection phenotype in the intermediate host snail Biomphalaria glabrata

Snails from a B. glabrata stock, selected for nonsusceptibility to the NMRI strain of S. mansoni, exhibited unusual schistosome infections, with multiple sporocysts prominent in the head-foot (foot-sporocysts). When F1 progeny from numerous crosses between well-defined susceptible (S) and resistant (R) parental snails were exposed, 60% of the infected snails also exhibited this unusual phenotype. F1 progeny from S x S snail crosses developed normal infections. Foot-sporocysts usually developed much later than secondary sporocysts of normal infections and before 12 weeks postexposure the tissue reaction surrounding foot-sporocysts was less intense than reactions to sporocysts in other tissues of the body. Cercariae were seen emerging directly from foot-sporocysts. Infection of S x R hybrid progeny by three other strains of S. mansoni also resulted in the production of foot-sporocysts. Development of the foot-sporocyst infection phenotype in progeny from many snail crosses suggests that this phenotype is more common than previously recognized. Over 50% of the F1 progeny from S x R parental crosses developed patent infections, a fact relevant to the possible biological control of schistosomiasis by the introduction of refractory snails into endemic areas.

Epstein-Barr virus in normal, pre-malignant, and malignant lesions of the uterine cervix

AIM--To detect the presence or absence of Epstein-Barr virus (EBV) in cervical lesions ranging from normality to invasive malignancy. METHODS--Eighteen randomly selected cases of invasive squamous cell carcinomas of the uterine cervix were examined as well as 25 cases each of normal cervices and those showing cervical intra-epithelial neoplasia (CIN) I, II, and III. DNA-DNA in situ hybridisation, using a biotinylated probe to the Bam H1 "W" fragment of EBV, was carried out in addition to the polymerase chain reaction using specific primer sequences that flank a 153 base pair segment of the Bam H1 "W" region of the EBV genome and which do not cross-amplify other DNA herpes viruses. Positive control material included paraffin wax embedded P3 HR1 lymphoblastoid cells (containing high copy numbers of EBV) and two nasopharyngeal carcinomas positive for EBV. RESULTS--Neither normal nor CIN I tissue was positive. Eight per cent of CIN II tissue was positive; 8% of CIN III, and 43% of carcinomas were positive for EBV. CONCLUSION--The study shows that the virus is present in some cases of cervical carcinoma and to a lesser degree in some premalignant lesions of the cervix, but the exact association between it and cervical oncogenesis, be it causative or incidental, remains to be determined.

Analysis of cytokine mRNA expression during primary granuloma formation induced by eggs of Schistosoma mansoni

Granulomas induced by parasite eggs are the primary lesions in mice infected with Schistosoma mansoni. Temporal analysis of cytokine mRNA expression in lung tissue containing synchronized granulomas demonstrated a Th0-like pattern of lymphokine expression. IFN-gamma, IL-1 beta, and IL-6 were the primary cytokines induced by day 1 in developing lung granulomas initiated by i.v. egg injection. These changes were followed by increases in expression of IL-2, IL-4, and IL-10 mRNA on day 3 and TNF-alpha and IL-5 mRNA on day 6. Nearly all cytokine mRNA reached maximal levels by day 6, which preceded the peak in granuloma size seen on day 14. In vivo treatment of egg-injected mice with either anti-IL-2 or anti-IL-4 antibodies significantly diminished the size of circumoval granulomas in the lungs. Both groups of antibody-treated animals displayed a marked reduction in IL-4 as well as IL-5 mRNA expression, although IFN-gamma and IL-2 mRNA levels were unchanged or slightly increased. These findings confirm previous observations suggesting a role for IL-2 in egg-induced pathology via the generation of Th2-associated responses, and also indicate a primary function for IL-4 in granuloma formation. Analysis of responses after injection of eggs into nude mice demonstrated that only the Th2 cytokines IL-4 and IL-5 are exclusively dependent on T cells for their induction. Taken together, these data suggest that Th2 cells producing IL-4 play a major role in egg granuloma formation, and that the induction and ultimate down-modulation of Th2-like responses may be influenced by non-T-cell-derived cytokines.