Molecular biology of astroviruses: selected highlights

Human astrovirus, the prototype of the Astroviridae family, is a non-enveloped positive-strand RNA virus with distinctive morphology. Initially named for a characteristic 5-6 point star evident on the surface of faecally shed viral particles by direct electron microscopy, a recent study using cryoelectron microscopy and image reconstruction indicates that viral particles consist of a smoothly rippled, solid capsid decorated with short spikes. Mechanisms underlying the assembly of these viral particles have not been fully elucidated. However, studies of two full-length cDNA clones of human astrovirus serotype 1 suggest that capsid residue Thr227 plays a critical role in the assembly of infectious viral progeny. The development of a full-length clone (pAVIC) from which infectious RNA can be transcribed has also facilitated studies of the viral 3C-like serine protease, encoded in ORF1a. These studies demonstrate that the full-length ORF1a product (101 kDa) is processed in vitro to an N-terminal 64 kDa fragment and a C-terminal 38 kDa fragment. Mutation of the predicted catalytic triad inhibits proteolysis. In other studies based on modifications of pAVIC, preliminary evidence supports the feasibility of developing a reporter cell line to facilitate astrovirus detection.

Detection rate of Actinobacillus actinomycetemcomitans on the permanent 1st molars of primary school children in Taiwan by polymerase chain reaction

BACKGROUND, AIMS

Actinobacillus actinomycetemcomitans (Aa) has been implicated as the putative micro-organism for localized juvenile periodontitis (LJP). The most distinct clinical features of LJP include severe angular bony defects of the mesial sides of permanent first molars and the onset of disease during puberty. Currently, no large-scale studies have been performed which address the change in detection rates of Aa on the mesial sides of permanent 1st molars following eruption and up to puberty.

METHOD

In this study, subgingival plaque samples were taken from the mesial pockets of 2 randomly selected permanent 1st molars from 328 primary school children and 50 adult staff, and analyzed by polymerase chain reaction (PCR) to detect Aa.

RESULTS

The results showed a 5.5% prevalence rate of Aa which increased after the eruption of 1st molars and peaked near puberty. There were no significant differences in the detection rates of Aa among different groups in terms of gender, plaque index (PII), and gingival index (GI); however, the higher detection rates of Aa were significantly associated with increased probing depths at p<0.05.

CONCLUSION

PCR analysis of the subgingival plaques demonstrated a prevalence of Aa which peaked near puberty, suggesting that Aa may be important for LJP in Taiwan.

An outbreak of enterovirus 71 infection in Taiwan, 1998. II. Laboratory diagnosis and genetic analysis

BACKGROUND

An epidemic of enterovirus 71 (EV71) occurred in Taiwan from April to December of 1998, with two peaks, one in June and the other in October. Many enteroviruses were isolated in our laboratory from 258 cases during this outbreak. Approximately half of the enteroviruses isolated were EV71 and one fifth were coxsackievirus A16.

OBJECTIVES

To analyze laboratory findings in the EV71 epidemic of 1998 in Taiwan, various EV71 specimens in different cell lines were examined. In addition, genetic analysis of 5' non-coding region (NCR) was performed to analyze the strain variation in this outbreak.

RESULTS

The cytopathic effect induced by EV71 was observed 2-13 (mean of 4.5) days post-inoculation in Vero cells and 4-15 (mean of 6.6) days in green monkey kidney (GMK) cells inoculated with throat swabs. Of the total positive EV71 cases, virus was most frequently obtained from throat swabs (91.7%), less from stools (64.8%), and none from cerebral spinal fluid (CSF). Molecular analyses of EV71 by sequencing the 5' NCR of 34 strains obtained from different clinical categories and various geographic areas showed that their sequences differed (0-13 bp in 681 bp sequenced) by approximately 0-2%. The sequences of these isolates differed from EV71 prototype BrCr or MS strain by 17.5-19%, with the exception of two samples which exhibited nucleotide variation by only 8.9 and 8.2%, when compared to the MS strain.

CONCLUSION

EV71 was most frequently isolated from throat swab specimens in Vero cells. The molecular analyses of the 5' NCR of EV71 revealed that most isolates from this epidemic belonged to a group of closely related clones and only two were in a different group which was clustered with the EV71 MS strain.

Use of Truquant BR radioimmunoassay for early detection of breast cancer recurrence in patients with stage II and stage III disease

PURPOSE

The Truquant BR radioimmunoassay (RIA) (Biomira Diagnostics Inc, Rexdale, Canada) uses the monoclonal antibody B27.29 to quantitate the MUC-1 gene product (CA 27.29 antigen) in serum. We evaluated CA 27.29 antigen in a controlled, prospective clinical trial for its ability to predict relapse in stage II and stage III breast cancer patients.

PATIENTS AND METHODS

Over a 2-year period, 166 patients who had completed therapy for stage II (80.1%) or III (19.9%) breast cancer and were clinically free of disease were serially tested for CA 27.29 antigen levels. The study was double-masked and cancer recurrence was documented based on clinical findings. Patients with two consecutive CA 27.29 antigen test results above the upper limit of normal were considered positive.

RESULTS

The Truquant BR RIA had a sensitivity of 57.7%, specificity of 97.9%, positive predictive value of 83.3%, and negative predictive value of 92.6%. The recurrence rate was 15.7%. A Cox regression analysis showed that the only variable to correlate with recurrent disease was the CA 27.29 antigen test result. Patients with a positive test result had increased odds of having a recurrence (odds ratio, 6.8; P < .00001). The test was effective in predicting recurrence in patients with both distant and locoregional disease. In a subgroup of patients with bone pain, CA 27.29 antigen level was found to identify reliably patients who would subsequently develop recurrent disease.

CONCLUSION

These data demonstrate that the Truquant BR RIA can be used as an aid to predict recurrent breast cancer in patients with stage II and III disease.

Cloning the gene encoding Schistosoma mansoni p50, an immunophilin

A 2.2-kb fragment of genomic DNA encoding Schistosoma mansoni immunophilin p50 (Smp50) was identified on a 14-kb genomic clone. The sequence of Smp50 reveals seven exons interrupted by six small introns ranging from 28-35 bp in size. The transcription start point, defined by primer extension analysis of schistosome RNA, begins at 30 bp upstream from the start AUG codon. Smp50 lacks a TATA box and appears to be a single-copy gene.

Identification and characterization of Schistosoma mansoni p17.7, a cyclophilin

Antibodies affinity purified against tegumental components of schistosomula were used to screen a Schistosoma mansoni lambda gt11 adult worm cDNA expression library. One of the reactive clones was determined by sequence analysis to encode a protein homologous to cyclophilins of other species, in particular cyclophilin A. The 0.8-kb cDNA clone contained an open reading frame of 483 nucleotides which corresponds to a translation product of 161 amino acids with a deduced molecular size of 17.7 kDa. We have chosen to designate this clone as S. mansoni p17.7 (Smp17.7). The overexpressed and purified recombinant Smp17.7 (rSmp17.7) was demonstrated to possess peptidylprolyl cis-trans isomerase (PPIase) or rotamase activity typical of cyclophilins. Western blot analysis of Nonidet P-40 and a total soluble extract of adult schistosomes probed with affinity-purified antisera to rSmp17.7, demonstrated the presence of this protein in the parasite. Immunofluorescence studies using the purified antisera indicates a localization in various tissues including the tegument and the gut. As cyclophilin is able to interact with cyclosporin A (CsA), which has been shown to be antischistosomal in mice infected with S. mansoni, the characterization of this S. mansoni cyclophilin homologue may allow a better understanding of the schistosomicidal nature of cyclosporin A and lead to a novel strategy of therapy for schistosomiasis.

Schistosoma mansoni: characterization of p50, an immunophilin

A 1.4-kb cDNA clone encoding a 50-kDa homologue of p59, a heat shock binding immunophilin, has been isolated from a Schistosoma mansoni cercariae cDNA library. We have designated this clone S. mansoni p50 (Smp50). From the sequence comparison, we speculate that Smp50 is similar in structural organization to other p59 proteins. As with other p59s, Smp50 also shows homology to various FK binding proteins (FKBPs). The amino acids in human FKBP12 which are proposed to be important for FK506 interaction are conserved in the schistosome protein. We have expressed and purified the recombinant protein (rSmp50) from Escherichia coli. rSmp50 demonstrated peptidyl-prolyl cis-transisomerase (PPIase) activity, typical of immunophilins. Western blot analysis of extracts from S. mansoni adult worms probed with rabbit polyclonal antisera, generated against the recombinant polypeptide, has indicated the presence of Smp50 in the parasite. The antisera did not cross-react with proteins from E. coli or HeLa cell extracts. All of the p59s characterized to date have been from vertebrate species. Therefore, our finding represents the first identification of the protein in an invertebrate system.