Persistent rubella virus infection of human synovial cells cultured in vitro

Sphingomyelin synthase 1 supports two steps of rubella virus life cycle

Our knowledge of the regulatory mechanisms that govern the replication of the rubella virus (RV) in human cells is limited. To gain insight into the host-pathogen interaction, we conducted a loss-of-function screening using the CRISPR-Cas9 system in the human placenta-derived JAR cells. We identified sphingomyelin synthase 1 (SGMS1 or SMS1) as a susceptibility factor for RV infection. Genetic knockout of SGMS1 rendered JAR cells resistant to infection by RV. The re-introduction of SGMS1 restored cellular susceptibility to RV infection. The restricted step of RV infection was post-endocytosis processes associated with the endosomal acidification. In the late phase of the RV replication cycle, the maintenance of viral persistence was disrupted, partly due to the attenuated viral gene expression. Our results shed light on the unique regulation of RV replication by a host factor during the early and late phases of viral life cycle.

Rubella virus-associated chronic inflammation in primary immunodeficiency diseases

PURPOSE OF THE REVIEW

The aim of this article is to summarize recent data on rubella virus (RuV) vaccine in chronic inflammation focusing on granulomas in individuals with primary immunodeficiencies (PIDs).

RECENT FINDINGS

The live attenuated RuV vaccine has been recently associated with cutaneous and visceral granulomas in children with various PIDs. RuV vaccine strain can persist for decades subclinically in currently unknown body site(s) before emerging in granulomas. Histologically, RuV is predominately localized in M2 macrophages in the granuloma centers. Multiple mutations accumulate during persistence resulting in emergence of immunodeficiency-related vaccine-derived rubella viruses (iVDRVs) with altered immunological, replication, and persistence properties. Viral RNA was detected in granuloma biopsies and nasopharyngeal secretions and infectious virus were isolated from the granuloma lesions. The risk of iVDRV transmissibility to contacts needs to be evaluated. Several broad-spectrum antiviral drugs have been tested recently but did not provide significant clinical improvement. Hematopoietic stem cell transplantation remains the only reliable option for curing chronic RuV-associated granulomas in PIDs.

SUMMARY

Persistence of vaccine-derived RuVs appears to be a crucial factor in a significant proportion of granulomatous disease in PIDs. RuV testing of granulomas in PID individuals might help with case management.

The Efficacy of the Interferon Alpha/Beta Response versus Arboviruses Is Temperature Dependent

Interferon alpha/beta (IFN-α/β) is a critical mediator of protection against most viruses, with host survival frequently impossible in its absence. Many studies have investigated the pathways involved in the induction of IFN-α/β after virus infection and the resultant upregulation of antiviral IFN-stimulated genes (ISGs) through IFN-α/β receptor complex signaling. However, other than examining the effects of genetic deletion of induction or effector pathway components, little is known regarding the functionality of these responses in intact hosts and whether host genetic or environmental factors might influence their potency. Here, we demonstrate that the IFN-α/β response against multiple arthropod-vectored viruses, which replicate over a wide temperature range, is extremely sensitive to fluctuations in temperature, exhibiting reduced antiviral efficacy at subnormal cellular temperatures and increased efficacy at supranormal temperatures. The effect involves both IFN-α/β and ISG upregulation pathways with a major aspect of altered potency reflecting highly temperature-dependent transcription of IFN response genes that leads to altered IFN-α/β and ISG protein levels. Discordantly, signaling steps prior to transcription that were examined showed the opposite effect from gene transcription, with potentiation at low temperature and inhibition at high temperature. Finally, we demonstrate that by lowering the temperature of mice, chikungunya arbovirus replication and disease are exacerbated in an IFN-α/β-dependent manner. This finding raises the potential for use of hyperthermia as a therapeutic modality for viral infections and in other contexts such as antitumor therapy. The increased IFN-α/β efficacy at high temperatures may also reflect an innate immune-relevant aspect of the febrile response.

The interferon alpha/beta (IFN-α/β) response is a first-line innate defense against arthropod-borne viruses (arboviruses). Arboviruses, such as chikungunya virus (CHIKV), can infect cells and replicate across a wide temperature range due to their replication in both mammalian/avian and arthropod hosts. Accordingly, these viruses can cause human disease in tissues regularly exposed to temperatures below the normal mammalian core temperature, 37°C. We questioned whether temperature variation could affect the efficacy of IFN-α/β responses against these viruses and help to explain some aspects of human disease manifestations. We observed that IFN-α/β efficacy was dramatically lower at subnormal temperatures and modestly enhanced at febrile temperatures, with the effects involving altered IFN-α/β response gene transcription but not IFN-α/β pathway signaling. These results provide insight into the functioning of the IFN-α/β response in vivo and suggest that temperature elevation may represent an immune-enhancing therapeutic modality for a wide variety of IFN-α/β-sensitive infections and pathologies.

Persistent infection of human fetal endothelial cells with rubella virus

Cardiovascular abnormalities are the leading cause of neonatal death among patients with congenital rubella syndrome (CRS). Although persistence of rubella virus (RV) in fetal endothelium has been repeatedly suggested as a possible cause of cardiovascular birth defects, evidence of the permissiveness of fetal endothelial cells to RV is lacking. In this study we evaluated the ability of RV to infect and persist in primary fetal endothelial cells derived from human umbilical vein (HUVEC). We found that wild type (wt) low passage clinical RV productively infected HUVEC cultures without producing cytopathology or ultrastructural changes. RV did not inhibit host cell protein synthesis, cell proliferation, or interfere with the cell cycle. Persistently infected cultures were easily established at low and high multiplicities of infection (MOI) with both laboratory and wt clinical RV strains. However, synchronous infections of entire HUVEC monolayers were only observed with clinical RV strains. The release of infectious virions into media remained at consistently high levels for several subcultures of infected HUVEC. The results indicate that macrovascular fetal endothelial cells are highly permissive to RV and allow slow persistent RV replication. The findings provide more evidence for the suggestion that vascular pathologies in CRS are triggered by persistent rubella virus infection of the endothelium.

The immunobiology of viral arthritides

A large range of human viruses are associated with the development of arthritis or arthralgia. Although there are many parallels with autoimmune arthritides, there is little evidence that viral arthritides lead to autoimmune disease. In humans viral arthritides usually last from weeks to months, can be debilitating, and are usually treated with non-steroidal anti-inflammatory drugs, but with variable success. Viral arthritides likely arise from immunopathological inflammatory responses directed at viruses and/or their products residing and/or replicating within joint tissues. Macrophages recruited by monocyte chemoattractant protein-1 (MCP-1/CCL2) and activated by interferon, and proinflammatory mediators like tumour necrosis factor alpha, interferon gamma, interleukin-6 and interleukin-1beta appear to be common elements in this group of diseases. The challenge for new treatments is to target excessive inflammation without compromising anti-viral immunity. Recent evidence from mouse models suggests targeting MCP-1 or complement may emerge as viable new treatment options for viral arthritides.

Infection and musculoskeletal conditions: Viral causes of arthritis

Several viruses cause postinfectious arthritis. The disease is a typical manifestation of arthritogenic alphaviruses, rubella virus and human parvovirus B19. In addition, arthritis is not uncommon after infection by HIV, cytomegalovirus, hepatitis B virus, hepatitis C virus, or Epstein-Barr virus (EBV). Also prolonged arthritis may result from viral infections, particularly with alphaviruses and human parvovirus B19. Viruses such as EBV and B19 may have significant roles in initiating chronic arthropathies, which in some cases may be indistinguishable from rheumatoid arthritis.

RC-IAL cell line: sensitivity of rubella virus grow

OBJECTIVE

The rapid growth of the rubella virus in RC-IAL2 with development of cytopathic effect, in response to rubella virus infection, is described. For purposes of comparison, the rubella virus RA-27/3 strain was titered simultaneously in the RC-IAL, Vero, SIRC and RK13 cell lines.

METHODS

Rubella virus RA-27/3 strain are inoculated in the RC-IAL cell line (rabbit Kidney, Institute Adolfo Lutz). Plates containing 1.5x10(5) cells/ml of RC-IAL line were inoculated with 0.1ml s RA-27/3 strain virus containing 1x 10(4)TCID50/0.1ml. A 25% cytopathic effect was observed after 48 hours and 100% after 96 hours. The results obtained were compared to those observed with the SIRC, Vero and RK13 cell lines. Rubella virus was detected by immunohistochemistry.

RESULTS

With the results, it was possible to conclude that the RC-IAL cell line is a very good substrate for culturing rubella virus. The cells inoculated with rubella virus were examined by phase contrast microscopy and showed the characteristic rounded, bipolar and multipolar cells. The CPE in RC-IAL was observed in the first 48 hours and the curve of the increased infectivity was practically the same as observed in other cell lines.

CONCLUSIONS

These findings are important since this is one the few cell lines described in the literature with a cytopathic effect. So it can be used for antigen preparation and serological testing for the diagnosis of specific rubella antibodies.

Rubella virus and chronic joint disease: is there an association?

Synovial fluid samples and/or biopsies from 79 patients with various chronic inflammatory joint diseases or traumatic joint injury were tested for rubella virus (RV) in order to confirm or refute results from other studies that suggested RV as a cause of chronic inflammatory joint disease. Sixty-eight of the 72 patients tested had RV antibodies. RV RNA was detected by reverse transcription-PCR in the synovial fluid cells from two patients. RV was also isolated by cell culture from the synovial fluid of one of these two patients. This patient was a 42-year-old female with common variable immune deficiency and Mycoplasma hominis arthritis, while the other was a 68-year-old female with rheumatoid arthritis. While these results fail to confirm that RV is associated with chronic inflammatory joint disease, they suggest that RV may persist within a joint and be reactivated when cell-mediated immunity is suppressed.

Cellular and humoral immune responses to rubella virus structural proteins E1, E2, and C

Better understanding of cell-mediated immune responses to rubella virus would provide the basis for the development of safe and effective vaccines against rubella and would aid in analysis of the pathophysiology of congenital rubella syndrome. We have expressed individual rubella virus structural proteins, E1, E2 and C, via vaccinia virus recombinants. Using the expressed recombinant proteins as antigens, we were able to demonstrate antigen-specific lymphocyte proliferative responses in control individuals and individuals with congenital rubella syndrome. Among the two human groups studied, E1 glycoprotein proved to be a better immunogen than E2 or C. For the control individuals, significant differences in proliferative responses to the structural proteins E1, E2, and C were observed. These differences were not significant in individuals with congenital rubella syndrome. In parallel to the lymphoproliferative responses, immunoglobulin G responses were also found directed mainly to the E1 glycoprotein. These results suggest that E1 may be the most important rubella virus antigen to study in determining the domains required for constructing subunit vaccines against rubella.

Rubella vaccines: past, present and future

The association between rubella in pregnancy and congenital anomalies was first reported 50 years ago, by N. McAlister Gregg, an Australian ophthalmologist [1]. During the next 20 years his findings were confirmed by others (reviewed in [2]). However, the first reports of the isolation of rubella virus in cell cultures and development of tests for neutralizing antibodies were not published until 1962 [3, 4]. Subsequent studies conducted in the UK and North America during a pandemic of rubella in 1963–4, were therefore able to make a more accurate estimate of the risks of maternal rubella at different stages of pregnancy. It was estimated that about 30000 rubella-damaged babies were born in the USA alone in 1963–4 [5]. This emphasized the importance of developing a vaccine to prevent infection in pregnancy and thereby, the birth of babies with rubella-induced congenital defects.

Processing and intracellular transport of rubella virus structural proteins in COS cells

Plasmids encoding rubella virus (RV) structural proteins C-E2-E1, E2-E1, E2, and E1 have been constructed in the eukaryotic expression vector pCMV5. The processing and intracellular transport of these proteins have been examined by transient expression of the cDNAs in COS cells. Compared to alphaviruses, processing of RV glycoprotein moieties occurred relatively slowly and the transport of glycoproteins E2 and E1 to the plasma membrane was inefficient. Indirect immunofluorescence revealed that the majority of RV antigen in transfected and infected COS cells was localized to the Golgi region, including the capsid protein. Accumulation of capsid protein in the juxtanuclear region was determined to be RV glycoprotein dependent. Unlike alphaviruses, RV E1 did not require E2 for targeting to the Golgi where it was retained. E2 was however necessary for cell surface expression of E1. This study revealed that the processing and transport of RV structural proteins is quite different from alphaviruses and that the accumulation of antigens in the Golgi region may be significant in light of previous reports which suggest that RV buds from the internal membranes in some cell types.

Generation of defective-interfering particles by rubella virus in Vero cells

The generation of defective-interfering (DI) particles by rubella virus during serial undiluted passage and persistent infection in Vero cells was studied. A series of 24 serial undiluted passages was initiated with plaque-purified virus. The virus titer remained relatively constant through the first nine passages, after which it declined, reaching a low level of 20-fold less than the originating stock by passage 15. In subsequent passages, the titer cycled. Intracellular DI RNAs were first detectable at passage 4, at which time DI RNAs of 7500 and 1400 nucleotides in length were observable. Thus, the rate of which DI RNAs were generated by rubella virus during serial undiluted passage was similar to the rate of DI generation by other enveloped RNA viruses during serial undiluted passage. The longer rubella DI RNA was present in all passages subsequent to passage 4, while the 1400-nucleotide DI RNA was replaced by a DI RNA of 800 nucleotides in length by passage 15. Subsequent to passage 7, the relative amount of genomic RNA declined dramatically and the DI RNAs became the predominant intracellular virus-specific RNA species. Negative-polarity RNA species corresponding to the 7500- and 800-nucleotide DI RNA species were identified. The 7500- and 1400-nucleotide DI RNA species were encapsidated into virus particles while the presence of the 800-nucleotide DI RNA species in virus particles could not be detected. Interestingly, the rubella virus subgenomic RNA was present in virus particles in preparations containing DI RNAs. A persistent infection was initiated by subculturing the surviving cells from a high multiplicity of infection with plaque-purified virus. Intracellular DI RNAs were first detectable at Day 19 after initiation of persistence and became significant by Day 26. The amount of genomic RNA began to decrease at Day 47 and was undetectable after Day 68. Through Day 54, there were several DI RNA species present, but at later times, one of these species became predominant. Thus, DI particles were generated during persistent infection, but their presence was not necessary for initiation of persistence.