Is the interpretation of rapid antigen testing for respiratory syncytial virus as simple as positive or negative?

OBJECTIVE: To measure the performance characteristics of an immunochromatographic rapid antigen test for respiratory syncytial virus (RSV) and determine how its interpretation should be contextualised in patients presenting to the emergency department (ED) with bronchiolitis. DESIGN: Diagnostic accuracy study of a rapid RSV test. SETTING: County hospital ED. INTERVENTION: We took paired nasal samples from consecutively enrolled infants with bronchiolitis and tested them with a rapid immunochromatographic antigen test and reverse transcriptase PCR gold standard. OUTCOME MEASURES: Sensitivity, specificity, the effect of point prevalence, clinical findings and overall context on predictive values. We used these to construct a graphical contextual model to show how the results of RSV antigen tests from infants presenting within 24 h should influence interpretation of subsequent antigen tests. RESULTS: We analysed 607 patients. The sensitivity and specificity for immunochromatographic testing was 79.4% (95% CI 73.9% to 84.2%) and 67.1% (95% CI 61.9% to 72%) respectively. We found little evidence of spectrum bias. In our contextual model the best predictor of a positive RT-PCR test was a positive antigen test OR 5.47 (95% CI 3.65 to 8.18) and the number of other infants having positive tests within 24 h OR 1.48 (95% CI 1.26 to 1.72) per infant. Increasing numbers presenting to the ED with bronchiolitis in a given day increases the probability of RSV infection. CONCLUSIONS: The RSV antigen test we examined had modest performance characteristics. The results of the antigen test should be interpreted in the context of the results of previous tests.

Comparison of respiratory virus detection rates for infants and toddlers by use of flocked swabs, saline aspirates, and saline aspirates mixed in universal transport medium for room temperature storage and shipping.

A nylon flocked swab/universal transport medium collection method developed for bacterial sexually transmitted infections was adapted to detect respiratory viruses in infants and toddlers. This method significantly outperformed the traditional use of nasal aspirates in terms of PCR-based virus detection (P = 0.016), and the samples were easier for clinicians to evaluate, store, and transport.

Demyelinating and nondemyelinating strains of mouse hepatitis virus differ in their neural cell tropism.

Some strains of mouse hepatitis virus (MHV) can induce chronic inflammatory demyelination in mice that mimics certain pathological features of multiple sclerosis. We have examined neural cell tropism of demyelinating and nondemyelinating strains of MHV in order to determine whether central nervous system (CNS) cell tropism plays a role in demyelination. Previous studies demonstrated that recombinant MHV strains, isogenic other than for the spike gene, differ in the extent of neurovirulence and the ability to induce demyelination. Here we demonstrate that these strains also differ in their abilities to infect a particular cell type(s) in the brain. Furthermore, there is a correlation between the differential localization of viral antigen in spinal cord gray matter and that in white matter during acute infection and the ability to induce demyelination later on. Viral antigen from demyelinating strains is detected initially in both gray and white matter, with subsequent localization to white matter of the spinal cord, whereas viral antigen localization of nondemyelinating strains is restricted mainly to gray matter. This observation suggests that the localization of viral antigen to white matter during the acute stage of infection is essential for the induction of chronic demyelination. Overall, these observations suggest that isogenic demyelinating and nondemyelinating strains of MHV, differing in the spike protein expressed, infect neurons and glial cells in different proportions and that differential tropism to a particular CNS cell type may play a significant role in mediating the onset and mechanisms of demyelination.

CD147 immunoglobulin superfamily receptor function and role in pathology.

The immunoglobulin superfamily member CD147 plays an important role in fetal, neuronal, lymphocyte and extracellular matrix development. Here we review the current understanding of CD147 expression and protein interactions with regard to CD147 function and its role in pathologic conditions including heart disease, Alzheimer's disease, stroke and cancer. A model linking hypoxic conditions found within the tumor microenvironment to upregulation of CD147 expression and tumor progression is introduced.

FOXP3 is a homo-oligomer and a component of a supramolecular regulatory complex disabled in the human XLAAD/IPEX autoimmune disease.

We have found that FOXP3 is an oligomeric component of a large supramolecular complex. Certain FOXP3 mutants with single amino acid deletions in the leucine zipper domain of FOXP3 are associated with the X-linked autoimmunity-allergic dysregulation (XLAAD) and immunodysregulation, polyendocrinopathy and enteropathy, X-linked (IPEX) syndrome in humans. We report that the single amino acid deletion found in human XLAAD/IPEX patients within the leucine zipper domain of FOXP3 does not disrupt its ability to join the larger protein complex, but eliminates FOXP3 homo-oligomerization as well as heteromerization with FOXP1. We found that the zinc finger-leucine zipper domain region of FOXP3 is sufficient to mediate both homodimerization and homotetramerization. However, the same domain region from XLAAD/IPEX FOXP3 containing an E251 deletion prevents oligomerizaton and the protein remains monomeric. We also found that wild-type FOXP3 directly binds to the human IL-2 promoter, but the E251 deletion in FOXP3 in XLAAD/IPEX patient's T cells disrupts its association with the IL-2 promoter in vivo and in vitro, and limits repression of IL-2 transcription after T-cell activation. Our results suggest that compromising FOXP3 homo-oligomerization and hetero-oligomerization with the FOXP1 protein impairs DNA-binding properties leading to distinct biochemical phenotypes in humans with the XLAAD/IPEX autoimmune syndrome. This study explains some features of the pathogenesis of a disease syndrome that arises as a consequence of specific assembly failure of a transcriptional repressor due to certain mutations within the FOXP3 leucine zipper.

FOXP3 interactions with histone acetyltransferase and class II histone deacetylases are required for repression.

The forkhead family protein FOXP3 acts as a repressor of transcription and is both an essential and sufficient regulator of the development and function of regulatory T cells. The molecular mechanism by which FOXP3-mediated transcriptional repression occurs remains unclear. Here, we report that transcriptional repression by FOXP3 involves a histone acetyltransferase-deacetylase complex that includes histone acetyltransferase TIP60 (Tat-interactive protein, 60 kDa) and class II histone deacetylases HDAC7 and HDAC9. The N-terminal 106-190 aa of FOXP3 are required for TIP60-FOXP3, HDAC7-FOXP3 association, as well as for the transcriptional repression of FOXP3 via its forkhead domain. FOXP3 can be acetylated in primary human regulatory T cells, and TIP60 promotes FOXP3 acetylation in vivo. Overexpression of TIP60 but not its histone acetyltransferase-deficient mutant promotes, whereas knockdown of endogenous TIP60 relieved, FOXP3-mediated transcriptional repression. A minimum FOXP3 ensemble containing native TIP60 and HDAC7 is necessary for IL-2 production regulation in T cells. Moreover, FOXP3 association with HDAC9 is antagonized by T cell stimulation and can be restored by the protein deacetylation inhibitor trichostatin A, indicating a complex dynamic aspect of T suppressor cell regulation. These findings identify a previously uncharacterized complex-based mechanism by which FOXP3 actively mediates transcriptional repression.

FOXP3 ensembles in T-cell regulation.

Our recent studies have identified dynamic protein ensembles containing forkhead box protein 3 (FOXP3) that provide insight into the molecular complexity of suppressor T-cell activities, and it is our goal to determine how these ensembles regulate FOXP3's transcriptional activity in vivo. In this review, we summarize our current understanding of how FOXP3 expression is induced and how FOXP3 functions in vivo as a transcriptional regulator by assembling a multisubunit complex involved in histone modification as well as chromatin remodeling.

Both spike and background genes contribute to murine coronavirus neurovirulence.

Various strains of mouse hepatitis virus (MHV) exhibit different pathogenic phenotypes. Infection with the A59 strain of MHV induces both encephalitis and hepatitis, while the highly neurovirulent JHM strain induces a fatal encephalitis with little, if any, hepatitis. The pathogenic phenotype for each strain is determined by the genetic composition of the viral genome, as well as the host immune response. Using isogenic recombinant viruses with A59 background genes differing only in the spike gene, we have previously shown that high neurovirulence is associated with the JHM spike protein, the protein responsible for attachment to the host cell receptor (J. J. Phillips, M. M. Chua, G. F. Rall, and S. R. Weiss, Virology 301:109-120, 2002). Using another set of isogenic recombinant viruses with JHM background genes expressing either the JHM or A59 spike, we have further investigated the roles of viral genes in pathogenesis. Here, we demonstrate that the high neurovirulence of JHM is associated with accelerated spread through the brain and a heightened innate immune response that is characterized by high numbers of infiltrating neutrophils and macrophages, suggesting an immunopathogenic component to neurovirulence. While expression of the JHM spike is sufficient to confer a neurovirulent phenotype, as well as increased macrophage infiltration, background genes contribute to virulence as well, at least in part, by dictating the extent of the T-cell immune response.

Amino acid substitutions within the heptad repeat domain 1 of murine coronavirus spike protein restrict viral antigen spread in the central nervous system.

Targeted recombination was carried out to select mouse hepatitis viruses (MHVs) in a defined genetic background, containing an MHV-JHM spike gene encoding either three heptad repeat 1 (HR1) substitutions (Q1067H, Q1094H, and L1114R) or L1114R alone. The recombinant virus, which expresses spike with the three substitutions, was nonfusogenic at neutral pH. Its replication was significantly inhibited by lysosomotropic agents, and it was highly neuroattenuated in vivo. In contrast, the recombinant expressing spike with L1114R alone mediated cell-to-cell fusion at neutral pH and replicated efficiently despite the presence of lysosomotropic agents; however, it still caused only subclinical morbidity and no mortality in animals. Thus, both recombinant viruses were highly attenuated and expressed viral antigen which was restricted to the olfactory bulbs and was markedly absent from other regions of the brains at 5 days postinfection. These data demonstrate that amino acid substitutions, in particular L1114R, within HR1 of the JHM spike reduced the ability of MHV to spread in the central nervous system. Furthermore, the requirements for low pH for fusion and viral entry are not prerequisites for the highly attenuated phenotype.