Evaluation of RIDA®GENE norovirus GI/GII real time RT-PCR using stool specimens collected from children and adults with acute gastroenteritis

BACKGROUND

Norovirus is the leading cause of epidemic and sporadic acute gastroenteritis (AGE) in the United States. Widespread prevalence necessitates implementation of accurate norovirus detection assays in clinical diagnostic laboratories.

OBJECTIVE

To evaluate RIDA^®GENE norovirus GI/GII real-time RT-PCR assay (RGN RT-PCR) using stool samples from patients with sporadic AGE.

STUDY DESIGN

Patients between 14 days to 101 years of age with symptoms of AGE were enrolled prospectively at four sites across the United States during 2014-2015. Stool specimens were screened for the presence of norovirus RNA by the RGN RT-PCR assay. Results were compared with a reference method that included conventional RT-PCR and sequencing of a partial region of the 5'end of the norovirus ORF2 gene.

RESULTS

A total of 259 (36.0%) of 719 specimens tested positive for norovirus by the reference method. The RGN RT-PCR assay detected norovirus in 244 (94%) of these 259 norovirus positive specimens. The sensitivity and specificity (95% confidence interval) of the RGN RT-PCR assay for detecting norovirus genogroup (G) I was 82.8% (63.5-93.5) and 99.1% (98.0-99.6) and for GII was 94.8% (90.8-97.2) and 98.6% (96.9-99.4), respectively. Seven specimens tested positive by the RGN-RT PCR that were negative by the reference method. The fifteen false negative samples were typed as GII.4 Sydney, GII.13, GI.3, GI.5, GI.2, GII.1, and GII.3 in the reference method.

CONCLUSIONS

The RGN RT-PCR assay had a high sensitivity and specificity for the detection of norovirus in stool specimens from patients with sporadic AGE.

Association of mouse mammary tumor virus superantigen with MHC class II during biosynthesis

Mouse mammary tumor viruses encode superantigens that interact with MHC class II proteins and stimulate T cells. We show here that presentation of mouse mammary tumor virus superantigen does not require DM. Furthermore, we have identified a strong class II peptide binding motif in the Mtv-7 superantigen, and we show that this motif is necessary for association with class II molecules in in vitro translation and in vivo functional assays. Our results suggest that endogenously synthesized viral superantigen can bind to MHC class II heterodimers during biosynthesis in the endoplasmic reticulum in a manner analogous to that used by the class II-associated invariant chain.

Individual hydrogen bonds play a critical role in MHC class II: peptide interactions: implications for the dynamic aspects of class II trafficking and DM-mediated peptide exchange

Determination of the crystal structure of class II: peptide complexes has shown that in addition to pocket interactions involving the side chains of the peptide, peptide binding to MHC class II molecules is characterized by a series of hydrogen bonds which are contributed by genetically conserved amino acid residues in the class II molecule to the main chain of the peptide. Our experiments have revealed an unexpectedly large contribution of hydrogen bonds at the periphery of the MHC peptide binding pocket to MHC class II function. Kinetic studies have shown that peptide dissociation rates are profoundly accelerated by loss of a single hydrogen bonding residue. The magnitude of the effects seen with the loss in potential for a single hydrogen bond support a co-operative model in which individual bonds between class II and peptide are dependent on the integrity of neighboring interactions. Collectively our studies have revealed that MHC class II structure, peptide binding and intracellular trafficking events are critically dependent on the integrity of the hydrogen bonding network between class II molecules and its bound peptide.

Deviant trafficking of I-Ad mutant molecules is reflected in their peptide binding properties

I-Ad molecules harboring single amino acid changes in the conserved 80-82 region of the beta-chain show altered trafficking in invariant chain (Ii)-negative cell lines. Since residues beta81 and beta82 form hydrogen bonds with the backbone of bound peptide, alterations in this region may result in distinct MHC class II conformers that are targeted aberrantly. We examined the assembly and peptide binding properties of the mutant I-Ad molecules generated by in vitro translation. Indeed, loss of a single hydrogen bond at beta81, or of two hydrogen bonds at beta82, is sufficient to render I-Ad incapable of stable interaction with CLIP and other antigenic peptides, despite normal assembly with intact invariant chain. These results suggest that stable interaction of MHC class II molecules with peptide requires the integrity of the H-bond network between residues in the MHC class II alpha-helices and bound peptide, and that conformational features revealed by stable peptide binding are critical for MHC class II intracellular transport.