Interleukin-1-inhibitor activity induced by respiratory syncytial virus: abrogation of virus-specific and alternate human lymphocyte proliferative responses

The continuing need for therapeutic agents for respiratory syncytial virus infection

Respiratory syncytial virus infections recur throughout life despite induction of immunity by the first natural infection. An effective vaccine has long been sought but no vaccine is currently licensed, although promising candidates are currently being developed based on greater knowledge of the virus properties. However, there are significant populations that may not be protected adequately by a vaccine or are unable to be vaccinated. Thus, there is a continued need for effective therapeutic agents to treat the infection, especially in higher-risk individuals, a perspective presented in this article.

Diverse and Unexpected Roles of Human Monocytes/Macrophages in the Immune Response to Influenza Virus

Human monocytes/macrophages play a central role in the immune response and defense of the host from influenza virus infection. They classically act as antigen-presenting cells for lymphocytes in the context of an immune cell cluster. In that setting, however, monocytes/macrophages exhibit additional, unexpected, roles. They are required for influenza virus infection of the lymphocytes in the cluster, and they are responsible for lymphocyte apoptosis via their synthesis and expression of the viral neuraminidase. Surprisingly, human alveolar macrophages, expected to be among the first cells to encounter the virus, are not susceptible to direct infection by a human influenza virus but can be infected when the virus is complexed with an antibody. Such monocyte/macrophage responses to influenza virus challenge should be considered part of a very complex but quite effective defense, since the common outcome is recovery of the host with development of immunity to the challenging strain of virus.

Respiratory syncytial virus suppression of the antiviral immune response: Implications for evaluation of candidate vaccines

Respiratory syncytial virus infections recur throughout life despite induction of immunity by the first natural infection. Results of an extensive series of studies indicate that the virus adversely affects the human antiviral recall response to challenge, although subsequent infections are less severe than the initial illness. The observations suggest that candidate vaccines for respiratory syncytial virus should not be expected to prevent clinical illness upon subsequent exposure. Candidate vaccines may be considered effective if they render a subsequent natural infection less severe. This is what would be expected from an initial and commonly more severe natural infection and sensitization.

Influenza Virus Infection of Human Lymphocytes Occurs in the Immune Cell Cluster of the Developing Antiviral Response

Monocytes-macrophages and lymphocytes are recruited to the respiratory tract in response to influenza virus challenge and are exposed to the virus during the establishment of immune defenses. The susceptibility of human lymphocytes to infection was assessed. The presence of monocytes-macrophages was required to attain infection of both resting and proliferating lymphocytes. Lymphocyte infection occurred in the context of immune cell clusters and was blocked by the addition of anti-intercellular adhesion molecule-1 (ICAM-1) antibody to prevent cell clustering. Both peripheral blood-derived and bronchoalveolar lymphocytes were susceptible to infection. Both CD4⁺ and CD8⁺ T lymphocytes were susceptible to influenza virus infection, and the infected CD4⁺ and CD8⁺ lymphocytes served as infectious foci for other nonpermissive or even virus-permissive cells. These data show that monocytes-macrophages and both CD4⁺ and CD8⁺ lymphocytes can become infected during the course of an immune response to influenza virus challenge. The described leukocyte interactions during infection may play an important role in the development of effective anti-influenza responses.

Reduced activation and proliferation of human lymphocytes exposed to respiratory syncytial virus compared to cells exposed to influenza virus

Both respiratory syncytial virus (RSV) and influenza A virus (IAV) may infect human peripheral blood mononuclear leukocytes (PBMC) during the immune response to viral challenge as the cells are recruited to the respiratory tract. The current studies demonstrated differences in PBMC responses to the two viruses very early after exposure, including reduced fos protein and CD69 expression and IL-2 production by RSV-exposed T lymphocytes. Exposure to RSV resulted in reduced lymphocyte proliferation despite evidence of a virus-specific T lymphocyte frequency equivalent to that for influenza virus. Reduced RSV-induced proliferation was not due to apoptosis, which was itself reduced relative to that of influenza virus-exposed T lymphocytes. The data indicate that differential immune responses to RSV and influenza virus are determined early after exposure of human PBMC and support the concept that the anamnestic immune response that might prevent clinically evident reinfection is attenuated very soon after exposure to RSV. Thus, candidate RSV vaccines should be expected to reduce but not prevent clinical illness upon subsequent infection by RSV. Furthermore, effective therapeutic agents for RSV are likely to be needed, especially for high-risk populations, even after vaccine development.

Serum antibodies critically affect virus-specific CD4+/CD8+ T cell balance during respiratory syncytial virus infections

Following infection with respiratory syncytial virus (RSV), reinfection in healthy individuals is common and presumably due to ineffective memory T cell responses. In peripheral blood of healthy adults, a higher CD4(+)/CD8(+) memory T cell ratio was observed compared with the ratio of virus-specific effector CD4(+)/CD8(+) T cells that we had found in earlier work during primary RSV infections. In mice, we show that an enhanced ratio of RSV-specific neutralizing to nonneutralizing Abs profoundly enhanced the CD4(+) T cell response during RSV infection. Moreover, FcγRs and complement factor C1q contributed to this Ab-mediated enhancement. Therefore, the increase in CD4(+) memory T cell response likely occurs through enhanced endosomal Ag processing dependent on FcγRs. The resulting shift in memory T cell response was likely amplified by suppressed T cell proliferation caused by RSV infection of APCs, a route important for Ag presentation via MHC class I molecules leading to CD8(+) T cell activation. Decreasing memory CD8(+) T cell numbers could explain the inadequate immunity during repeated RSV infections. Understanding this interplay of Ab-mediated CD4(+) memory T cell response enhancement and infection mediated CD8(+) memory T cell suppression is likely critical for development of effective RSV vaccines.

Common causes of uncommon seizures

Afebrile seizures associated with rotavirus gastroenteritis, respiratory syncytial virus bronchiolitis, influenza infection, asthma, blood transfusions, and intake of a number of drugs (including theophylline, cephalosporins, metronidazole, and acyclovir) with therapeutic drug levels are uncommonly encountered in clinical practice. Reviewed here are the incidence, etiology, clinical presentation, types, diagnosis, associated electroencephalographic changes, and cranial magnetic resonance imaging findings in the literature, as well as management and prognosis of these seizures.

The host response and molecular pathogenesis associated with respiratory syncytial virus infection

Since the isolation of respiratory syncytial virus (RSV) in 1956, its significance as an important human pathogen in infants, the elderly and the immunocompromised has been established. Many important mechanisms contributing to RSV infection, replication and disease pathogenesis have been uncovered; however, there is still insufficient knowledge in these and related areas, which must be addressed to facilitate the development of safe and effective vaccines and therapeutic treatments. A better understanding of the molecular pathogenesis of RSV infection, particularly the host-cell response and transcription profiles to RSV infection, is required to advance disease intervention strategies. Substantial information is accumulating regarding how RSV proteins modulate molecular signaling and regulation of cytokine and chemokine responses to infection, molecular signals regulating programmed cell death, and innate and adaptive immune responses to infection. This review discusses RSV manipulation of the host response to infection and related disease pathogenesis.

Subversion of pulmonary dendritic cell function by paramyxovirus infections

Lower respiratory tract infections caused by the paramyxoviruses human metapneumovirus (hMPV) and respiratory syncytial virus (RSV) are characterized by short-lasting virus-specific immunity and often long-term airway morbidity, both of which may be the result of alterations in the Ag-presenting function of the lung which follow these infections. In this study, we investigated whether hMPV and RSV experimental infections alter the phenotype and function of dendritic cell (DC) subsets that are recruited to the lung. Characterization of lung DC trafficking demonstrated a differential recruitment of plasmacytoid DC (pDC), conventional DC (cDC), and IFN-producing killer DC to the lung and draining lymph nodes after hMPV and RSV infection. In vitro infection of lung DC indicated that in pDC, production of IFN-alpha, TNF-alpha, and CCL5 was induced only by hMPV, whereas CCL3 and CCL4 were induced by both viruses. In cDC, a similar repertoire of cytokines was induced by hMPV and RSV, except for IFN-beta, which was not induced by RSV. The function of lung pDC was altered following hMPV or RSV infection in vivo, as we demonstrated a reduced capacity of lung pDC to produce IFN-alpha as well as other cytokines including IL-6, TNF-alpha, CCL2, CCL3, and CCL4 in response to TLR9 stimulation. Moreover, we observed an impaired capacity of cDC from infected mice to present Ag to CD4(+) T cells, an effect that lasted beyond the acute phase of infection. Our findings suggest that acute paramyxovirus infections can alter the long-term immune function of pulmonary DC.

Serum mannose-binding lectin levels are linked with respiratory syncytial virus (RSV) disease

The innate immune response facilitates the quality of the adaptive immune response and is critical to an individual's susceptibility to infection and disease. Mannose-binding lectin (MBL) is a plasma protein with anti-microbial properties that binds a wide range of pathogens to flag them for immune destruction independent of antibodies. In this study, serum MBL levels were measured in 81 children <5 years old experiencing acute respiratory syncytial virus infection and in 40 control children to determine the association with disease severity. Almost 70% of all RSV-infected children had low to intermediate MBL levels (<500 ng/ml) compared to controls, and most of the <6 months old RSV interned patients had low to intermediate levels. No differences were detected in MBL levels between case and control children <1 month old. Analysis of the T-cell compartment in peripheral blood mononuclear cells (PBMC) from acute RSV-infected and control children showed that the percent CD4+ T cells was statistically lower in RSV-infected children > or =6 months old compared to controls, while the percent CD8+ T cells in RSV-infected and control PBMC was generally similar. These results suggest that low serum MBL levels may be a marker of RSV disease severity in children and that MBL may be important in limiting RSV disease pathogenesis.

Characterization of the CD8+ T cell responses directed against respiratory syncytial virus during primary and secondary infection in C57BL/6 mice

The BALB/c mouse model for human respiratory syncytial virus infection has contributed significantly to our understanding of the relative role for CD4+ and CD8+ T cells to immune protection and pathogenic immune responses. To enable comparison of RSV-specific T cell responses in different mouse strains and allow dissection of immune mechanisms by using transgenic and knockout mice that are mostly available on a C57BL/6 background, we characterized the specificity, level and functional capabilities of CD8+ T cells during primary and secondary responses in lung parenchyma, airways and spleens of C57BL/6 mice. During the primary response, epitopes were recognized originating from the matrix, fusion, nucleo- and attachment proteins, whereas the secondary response focused predominantly on the matrix epitope. C57BL/6 mice are less permissive for hRSV infection than BALB/c mice, yet we found CD8+ T cell responses in the lungs and bronchoalveolar lavage, comparable to the responses described for BALB/c mice.

Respiratory Syncytial Virus Infection of Monocyte-Derived Dendritic Cells Decreases Their Capacity to Activate CD4 T Cells

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infections in children, the elderly, and immune-compromised individuals. CD4 and CD8 T cells play a crucial role in the elimination of RSV from the infected lung, but T cell memory is not sufficient to completely prevent reinfections. The nature of the adaptive immune response depends on innate immune reactions initiated after interaction of invading pathogens with host APCs. For respiratory pathogens myeloid dendritic cell (DC) precursors that are located underneath the epithelial cell layer lining the airways may play a crucial role in primary activation of T cells and regulating their functional potential. In this study, we investigated the role of human monocyte-derived DC in RSV infection. We showed that monocyte-derived DC can be productively infected, which results in maturation of the DC judged by the up-regulation of CD80, CD83, CD86, and HLA class II molecules. However, RSV infection of DC caused impaired CD4 T cell activation characterized by a lower T cell proliferation and ablation of cytokine production in activated T cells. The suppressive effect was caused by an as yet unidentified soluble factor produced by RSV-infected DC.

Neurologic complications associated with respiratory syncytial virus

Encephalopathy has been demonstrated to be associated with respiratory syncytial virus bronchiolitis. In this study, the data on all patients less than 14 years of age hospitalized with respiratory syncytial virus bronchiolitis over the past 4 years was reviewed. Patients who had concomitant diagnoses consistent with neurologic disease underwent detailed chart review. There were 964 patients (age 0.1 to 13.6 years) with a diagnosis of respiratory syncytial virus bronchiolitis. Thirty-six of these patients had concurrent neurologic diagnoses. Twenty-four patients were excluded because of preexistent neurologic disorders, probable simple febrile seizures, or a history of epilepsy. Twelve respiratory syncytial virus-positive patients had definite neurologic complications without another recognized cause. Seven of these patients had seizures (predominantly generalized tonic-clonic and one with status epilepticus), three had generalized encephalopathy (marked hypotonia and decreased responsiveness) of whom two also developed esotropia. Two patients developed isolated esotropia. There was an incidence of neurologic complications of 1.2% (0.7% seizures) in a total of 964 patients with respiratory syncytial virus bronchiolitis. This percentage does not include presumed simple febrile seizures or exacerbations of preexisting seizure disorder (further 1.3%). Neurologic complications occur with respiratory syncytial virus bronchiolitis, and physicians and other caregivers should be aware of this entity as well as the favorable prognosis.

Human CD8(+) T cell responses against five newly identified respiratory syncytial virus-derived epitopes

CD8(+) T lymphocytes play a major role in the clearance of respiratory syncytial virus (RSV) infections. To be able to study the primary CTL response in RSV-infected children, epitopes presented by a set of commonly used HLA alleles (HLA-A1, -A3, -B44 and -B51) were searched for. Five epitopes were characterized derived from the matrix (M), non-structural (NS2) and second matrix (M2) proteins of RSV. All epitopes were shown to be processed and presented by RSV-infected antigen-presenting cells. HLA-A1 tetramers for one of these epitopes derived from the M protein were constructed and used to quantify and phenotype the memory CD8(+) T cell pool in a panel of healthy adult donors. In about 60 % of the donors, CD8(+) T cells specific for the M protein could be identified. These cells belonged to the memory T cell subset characterized by expression of CD27 and CD28, and down-regulation of CCR7 and CD45RA. The frequency of tetramer-positive cells varied between 0.4 and 3 per 10(4) CD8(+) T cells in PBMC of healthy asymptomatic adult donors.

Detection of human respiratory syncytial virus sequences in peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMC) obtained from patients with lower respiratory infections were examined for the detection of human respiratory syncytial virus (RSV) sequences in the N region using the reverse transcription polymerase chain reaction (RT-PCR). RSV infection was confirmed by at least one method, i.e., virus isolation, enzyme immunoassay for viral antigen, and RT-PCR of nasopharyngeal secretions (NPS) samples. The detection rate for RSV RNA in PBMC obtained from RSV-infected patients was 40% (38/94), compared to 5% (1/20) in controls (P = 0.002). Between the groups positive (38) and negative (56) for RSV RNA in PBMC, there was no significant difference in clinical parameters. Seven patients had eight episodes of reinfection and RSV RNA was detected in 50% (4/8) during consecutive infections. Sequences of their PBMC samples were distinct from those of prototype strains of subgroup A and B. However, they were not always consistent with those of paired NPS samples. The findings suggested that RSV RNA could be detected in PBMC even during reinfection and as might have the possibility of quasispecies dynamics, reflecting the nature of RNA viruses.

Respiratory syncytial virus fusion protein mediates inhibition of mitogen-induced T-cell proliferation by contact

Human respiratory syncytial virus (HRSV) and bovine respiratory syncytial virus (BRSV) are major pathogens in infants and calves, respectively. Experimental BRSV infection of calves and lambs is associated with lymphopenia and a reduction in responsiveness of peripheral blood lymphocytes (PBLs) to mitogens ex vivo. In this report, we show that in vitro mitogen-induced proliferation of PBLs is inhibited after contact with RSV-infected and UV-inactivated cells or with cells expressing RSV envelope proteins on the cell surface. The protein responsible was identified as the RSV fusion protein (F), as cells infected with a recombinant RSV expressing F as the single envelope protein or cells transfected with a plasmid encoding F were able to induce this effect. Thus, direct contact with RSV F is necessary and sufficient to inhibit proliferation of PBLs. Interestingly, F derived from HRSV was more efficient in inhibiting human PBL proliferation, while F from BRSV was more efficient in inhibiting bovine PBLs. Since various T-cell activation markers were upregulated after presenter cell contact, T lymphocytes are viable and may still be activated by mitogen. However, a significant fraction of PBLs were delayed or defective in G0/G1 to S-phase transit.

Encephalopathy associated with respiratory syncytial virus bronchiolitis

Respiratory syncytial virus is an extremely common cause of childhood respiratory infections resulting in significant morbidity and mortality. Although apnea is a well-known complication in young infants with respiratory syncytial virus bronchiolitis, the encephalopathy associated with this infection is not well recognized. Our study reveals an incidence of encephalopathy of 1.8% in a total of 487 patients with respiratory syncytial virus bronchiolitis studied over a period of almost 4 years. Seizures were the presenting complication. Based on our study of a cohort of children with respiratory syncytial virus bronchiolitis, we believe that neurologic complications, although relatively uncommon, represent a significant component of this common childhood illness. Furthermore, respiratory syncytial virus has been shown to release several mediators that could directly or indirectly be neurotoxic and induce an encephalopathy associated with the respiratory illness.

Surfactant protein-A enhances uptake of respiratory syncytial virus by monocytes and U937 macrophages

Surfactant protein (SP)-A is a known opsonin for a variety of pulmonary pathogens. SP-A enhances ingestion of these pathogens by interaction with an SP-A receptor (SP-AR) found on phagocytic cells such as peripheral blood monocytes (PBMC) and alveolar macrophages. Respiratory syncytial virus (RSV) is the most important respiratory pathogen in children. Recent studies have indicated that SP-A levels may be decreased in RSV bronchiolitis and pneumonia. In this study we examined the role of SP-A in uptake of RSV by both PBMC and U937 macrophages, a human macrophage cell line known to express SP-ARs. In addition, we studied the effect of SP-A- mediated uptake of RSV on production of tumor necrosis factor (TNF)-alpha and interleukin (IL)-10 by these cells because incomplete immunity to recurrent RSV infection has been partially attributed to abnormal cytokine responses by macrophages. SP-A enhanced binding and uptake of fluorescently labeled RSV (RSV-FITC) by PBMC in a dose-dependent manner, with a maximal effect seen with 10 to 15 microg/ml SP-A as measured by both percent fluorescent monocytes and linear mean fluorescence (lmf) of individual cells. SP-A also enhanced uptake of RSV-FITC by U937 macrophages, with a maximal effect seen with 20 microg/ml SP-A as measured by both percent fluorescent monocytes and lmf. With respect to TNF-alpha levels, RSV alone slightly enhanced TNF-alpha production by PBMC and decreased TNF-alpha production by U937 macrophages measured at 12 h after addition of RSV. SP-A-mediated uptake of RSV significantly enhanced TNF-alpha production by PBMC and reversed the RSV-induced depression of TNF-alpha by U937 macrophages. RSV significantly enhanced IL-10 production by both cell types, which was reversed by SP-A-mediated uptake. These findings suggest that SP-A is an important opsonin for RSV and that SP-A-mediated uptake of RSV may alter some of the unusual cytokine responses that are postulated to be involved in incomplete immunity to recurrent infection.

Different expression of ICAM-1 and LFA-1 alpha by peripheral leukocytes during respiratory syncytial virus and influenza virus infection in young children

We compared the expression of intercellular adhesion molecule (ICAM)-1 and lymphocyte function-associated antigen (LFA)-1 alpha (alpha) on the surfaces of peripheral immunocompetent cells of young children infected with respiratory syncytial virus (RSV) and influenza virus. Flow cytometric analysis revealed a significantly higher percentage of CD14 + monocytes/macrophages that were strongly ICAM-1-positive in the influenza group than in age-matched controls, whereas the ICAM-1 expression levels of the RSV and control groups did not differ significantly. Analysis of LFA-1alpha expression by CD3 + T lymphocytes showed a significantly higher percentage of strongly positive cells in the influenza group than in the age-matched controls. By contrast, the percentage of cells that were strongly LFA-1alpha-positive was significantly lower in the RSV group than in the age-matched controls. These results suggest that no increase of adhesion molecule expression occurs in vivo in patients with RSV infection, and also that there is little activation of peripheral blood monocytes/macrophages and T lymphocytes in young children with RSV infection.

Le virus respiratoire syncytial: importance en pathologie, méthodes diagnostiques, traitement et prévention

Les bronchiolites à VRS sont fréquentes, épidémiques et nécessitent parfois l'hospitalisation des nourrissons, voire une réanimation.Le déterminisme des lésions pulmonaires est complexe, lié au virus et à la réaction immunitaire. Le traitement est symptomatique, et l'utilisation de la ribavirine est limitée aux formes sévères. Le diagnostic virologique doit être rapide, et la recherche immunologique directe des protéines virales est la technique la plus utilisée.

Evaluation of the live attenuated cpts 248/404 RSV vaccine in combination with a subunit RSV vaccine (PFP-2) in healthy young and older adults

The safety and immunogenicity of the live attenuated cold-passaged, temperature-sensitive (cpts) 248/404 respiratory syncytial virus (RSV) A2 and the RSV A2 purified F glycoprotein (PFP-2) vaccine candidates were evaluated in a placebo-controlled trial in 60 healthy young adults and 60 healthy elderly subjects using simultaneous and sequential (cpts 248/404 followed by PFP-2) vaccination schedules. Both vaccines were well tolerated. The cpts 248/404 vaccine was moderately infectious in both young and old volunteers, but was highly restricted in replication in those who were infected. After both vaccines, RSV neutralizing antibody (neut Ab) titers increased fourfold in 22% of young subjects and in 16% of elderly subjects. Of those with low levels of RSV neut Ab (titer <9), 10/12 (83% of) young subjects and six/eight (75% of) elderly subjects had a >/=four fold rise in neut Ab titer. Young and elderly subjects immunized simultaneously had similar serum IgG and IgA postimmunization titers to RSV F (IgG, 16.4 vs 16.2, IgA 11.6 vs 12. 5, respectively) as did those who were immunized sequentially (IgG 17.4 vs 17.0, IgA 13.0 vs 13.5). In both age groups, sequential immunization elicited higher postimmunization RSV F IgG and IgA titers than simultaneous immunization. Further studies that combine the PFP-2 subunit vaccine with a less attenuated RSV vaccine should be performed.

Differential effects of respiratory syncytial virus and adenovirus on mononuclear cell cytokine responses

Respiratory syncytial virus (RSV) and adenovirus (Advs) serotype 3 (Adv3) and 7h (Adv7h) are associated with mild to severe respiratory infection and are indistinguishable during the acute phases of the illnesses. However, outcome and long-term prognosis are different with both infections. RSV infection is associated with later development of asthma, and Adv, mainly Adv7h, with severe lung damage, bronchiectasis, and hyperlucent lung. We hypothesized that this difference could be partly due to different immune responses induced by these viruses. To test this hypothesis we quantified TCD4+, TCD8+, and BCD19+ expressing the interleukin-2 receptor-alpha chain (CD25) and interferon-gamma (IFN-gamma), interleukin (IL)-10, and IL-4 in the supernatant of peripheral blood mononuclear cells (PBMC) from school children infected in vitro with and without RSV, Adv7h, and Adv3 and after phytohemagglutinin (PHA) stimulation in the presence or absence of these viruses at a multiplicity of infection (MOI) of 1. PBMC from every child produced more IL-10 (p </= 0.05) when infected with RSV than with Advs and noninfected control, and Adv induced more (p </= 0.05) IFN-gamma than did RSV and control. The IL-10/IFN-gamma ratio was significantly higher (p </= 0.05) in RSV-infected and significantly lower (p </= 0.05) in Adv-infected PBMC, than in noninfected cells. PHA-stimulated BCD19+ RSV- infected cells expressed more (p </= 0.05) IL-2R than did Adv-infected cells. These results suggest that Advs induce a Th-1-type immune response that is not seen with RSV. These patterns persist despite intersubject variation in the absolute quantity of cytokine produced.

Reflex apnoea response and inflammatory mediators in infants with respiratory tract infection

The reflex apnoea response to water stimulation was evaluated in infants with respiratory syncytial virus (RSV) infection and compared to the response in non-infected infants who had sustained an apparent life-threatening event (ALTE) or were siblings of infants who had died of sudden infant death syndrome (SIDS). RSV-infected infants had a significantly (p < 0.05) reinforced reflex apnoea response compared with non-infected infants. There was a significant negative correlation between the concentration of interleukin 1 beta (IL-I beta) in pharyngeal secretions and the duration of apnoea (p < 0.01). Increased clinical severity was, however, associated with high (> 5.000 pg ml-1) concentrations of IL-1 beta. There was no correlation between apnoea and interleukin 6. These findings may be relevant for the understanding of why apnoea may be the presenting symptom of RSV infection, and offer an explanation of why a proportion of SIDS cases has a history of mild respiratory tract symptoms prior to death.

Antigens of bovine respiratory syncytial virus in peripheral blood lymphocytes of experimentally infected lambs

Eight lambs were experimentally infected with bovine respiratory syncytial virus (RSV) and the distribution of viral antigen in lymphocyte subpopulations studied by flow cytometry. Experimental infection with bovine RSV was characterised by significant changes in lymphocyte subpopulations. Infection was followed by a significant (P <0.001) reduction in the number of cells expressing the OvCD5 epitope (T cells), due to a fall in the number of cells expressing the OvCD4 epitope (helper) and those expressing the OvWC1 epitope (gamma/delta) 3-7 days post-inoculation. There was a significant increase in the number of OvCD5+ cells expressing the OvCD8 epitope (cytotoxic/suppressor) later. Flow cytometric analysis with bovine RSV-specific monoclonal antibodies revealed that viral antigens were present in all lymphocyte subpopulations but the main targets were T cells in general and OvCD4+ cells in particular. Challenge of primed lambs with bovine RSV had similar effects over a shorter period, followed by significant rises in the number of OvCD45+ (B) cells and OvCD5+ (T cells). Viral antigens were also present in lymphocytes subsets following challenge.

An ultrastructural study of the interaction of human eosinophils with respiratory syncytial virus

It was shown previously that eosinophils are activated in vivo and in vitro by respiratory syncytial virus (RSV) (Garofalo et al., J Pediatr 1992: 120: 28-32; Kimpen et al., Pediatr Res 1992: 32: 160-4). For study of the interaction of eosinophils and RSV on the ultrastructural level, normodense eosinophils were purified from peripheral blood of healthy human volunteers. After incubation with RSV in the presence or absence of autologous serum, the eosinophils were examined with immunofluorescence microscopy employing an RSV-specific monoclonal antibody, and with transmission electron microscopy. After 2-h incubation in the presence of live RSV, 25.6 +/- 12.9% of the eosinophils demonstrated positive fluorescence. This increased to 62.8 +/- 8.9% when fresh autologous serum was added during incubation (P = 0.015). The effect was abolished when the serum was heat-treated, indicating Fc-receptor-independent enhancement of viral uptake by the cells. In transmission electron microscopy, virions were seen in phagocytic vacuoles at the periphery of the cells. Eosinophil activation characterized by piece-meal degranulation was evident. In conclusion, activation of eosinophils during RSV bronchiolitis probably occurs in part by direct interaction of the cells with the virus.

Respiratory syncytial virus induces interleukin-10 by human alveolar macrophages. Suppression of early cytokine production and implications for incomplete immunity

Respiratory syncytial virus (RSV) causes repeated infections thought to be due to an ineffective immune response. We examined the hypothesis that incomplete immunity may result, in part, from RSV-infected alveolar macrophage production of IL-10 which can interfere with the production of immunoregulatory cytokines. We also assessed whether RSV induced the expression of the 2',5' oligoadenylate (2-5A)-dependent RNase L, an endoribonuclease involved in the antiviral activities of interferons. Human alveolar macrophages were exposed to medium (uninfected control), RSV, LPS, and RSV + LPS then were assessed for expression of the cytokines TNF-alpha, IL-1 beta, IL-8, IL-10, as well as 2-5A-dependent RNase L. LPS up-regulated the expression of protein and mRNA for all cytokines. RSV stimulated the protein levels of TNF-alpha, did not alter IL-1 beta, and decreased IL-8. RSV markedly stimulated protein expression of IL-10 and 2-5A-dependent RNase L. RSV had minor effects on the steady state mRNA levels of TNF-alpha, IL-1 beta, and IL-8, yet potently induced IL-10. Cells costimulated with RSV + LPS demonstrated reduced protein and mRNA levels of TNF-alpha, IL-1 beta, IL-8 but synergistically increased IL-10 levels compared to RSV- or LPS-activated cells. Kinetic analysis indicated that RSV induced a delayed and sustained increase in IL-10 transcripts. Furthermore, RSV-infected alveolar macrophage supernatants suppressed IL-1 beta and IL-8 production by LPS-stimulated alveolar macrophages as did recombinant IL-10. Anti-IL-10 neutralized these effects. These studies indicate that RSV is capable of suppressing production of early immunoregulatory cytokines through induction of IL-10 perhaps mediated by 2-5A-dependent RNase L (or other endoribonucleases) accounting for the ineffective immune response to this virus.

Use of FITC-labeled influenza virus and flow cytometry to assess binding and internalization of virus by monocytes-macrophages and lymphocytes

The binding of influenza virus to the surface of cells and the internalization of virus particles by all or a subset of cells are key points in the pathogenesis of viral infection. The current studies established a method for discrimination of surface-bound from internalized influenza virus. Fluorescein isothiocyanate (FITC) was attached to the viral hemagglutinin and neuroaminidase proteins; the fluorescent virus retained infectivity. A flow cytometric technique was then adapted for study of virus-cell interactions, with addition of ethidium bromide to quench green fluorescence associated with FITC-labeled virus that was cell-bound but remained external. Ethidium bromide was excluded by intact cell membranes, and internalized virions retained green fluorescence. Cells could be examined by fluorescence microscopy or flow cytometry, with flow cytometry allowing rapid, kinetic assessment of large numbers of cells and subsets of virus-exposed cells. The data showed that, whereas a majority of both monocytes-macrophages and lymphocytes bound influenza virus, a large percentage of monocytes-macrophages but only a very small percentage of lymphocytes internalized the virus. This procedure provides a simple and effective method to distinguish surface-bound from internalized influenza virus, and allows precise kinetic analyses on large numbers of cells.

Interleukin-1 receptor antagonist

IL-1ra is the first described naturally occurring receptor antagonist of any cytokine or hormone-like molecule. IL-1ra is a member of the IL-1 family by three criteria: amino acid sequence homology of 26 to 30% to IL-1 beta and 19% to IL-1 alpha; similarities in gene structure; and common gene localization to human chromosome 2q14. Two structural variants of IL-1ra exist: sIL-1ra, a secretory molecule produced by monocytes, macrophages, neutrophils, fibroblasts, and other cells; and icIL-1ra, an intracellular molecule produced by keratinocytes and other epithelial cells, macrophages, and fibroblasts. IL-1ra production by monocytes, macrophages, and neutrophils may be regulated in a differential fashion with IL-1 beta. Human IL-1ra binds to both human IL-1RIs and IL-1RIIs on cell surfaces, although with 100-fold greater avidity to IL-1RIs. IL-1ra may bind preferentially to soluble IL-1RIs and not at all to soluble IL-1RIIs. IL-1ra competitively inhibits binding of both IL-1 alpha and IL-1 beta to cell surface receptors without inducing any discernible intracellular responses. All three forms of IL-1 may bind to IL-1 receptors in a similar fashion but IL-1ra may lack the secondary interactions necessary to trigger cell responses. A 100-fold or greater excess of IL-1ra over IL-1 may be necessary to inhibit biological responses to IL-1 both in vitro and in vivo. The roles of sIL-1ra and icIL-1ra in normal physiology or in host defense mechanisms remain unclear. The administration of IL-1ra blocks the effects of IL-1 in some animal models of septic shock, inflammatory arthritis, graft-versus-host disease, and inflammatory bowel disease. The preliminary results of clinical trials in humans indicate possible efficacy of IL-1ra in sepsis syndrome, rheumatoid arthritis, and GVHD.

Immunologic response of adenoidal lymphocytes to respiratory syncytial virus

Adenoidal lymphocytes obtained from 43 subjects with serum antibodies to respiratory syncytial virus (RSV) were established in culture in vitro and analyzed for immunoglobulin (Ig) and RSV-specific antibody synthesis. Spontaneous synthesis of Ig was consistently observed in culture supernatants. The ratios of IgA to IgG and IgM to IgG in adenoidal lymphocyte culture supernatant were higher than in serum. In cell cultures stimulated with RSV or pokeweed mitogen, RSV antibody activity was detected in 25 of 43 (58.1%) for IgG, 5 of 43 (11.6%) for IgA, and 4 of 43 (9.3%) for IgM. Also, RSV-specific IgG was detected in some supernatants from unstimulated cultures. In seven cases the cultures of autologous tonsillar lymphocytes were also investigated. Autologous organs exhibited similar polyclonal Ig production and RSV-specific antibody synthesis. These observations demonstrate that both adenoids and palatine tonsils are continuously engaged in synthesis of local antibodies to viral pathogens available to the nasopharynx and respiratory mucosa.

The limited role of the human interferon system response to respiratory syncytial virus challenge: analysis and comparison to influenza virus challenge

The respiratory syncytial virus (RSV)-induced production of interferon (IFN) by human macrophages and mononuclear leukocytes (MNL) and the sensitivities of RSV to subtypes of IFN-alpha were examined and compared to IFN production induced by influenza virus. Influenza virus induced high titers of total IFN bioactivity, transcription of the IFN-alpha 1 and IFN-beta gene products and production of IFN-gamma. In contrast, RSV induced minimal or no detectable total IFN activity, and the absence of IFN bioactivity could not be attributed to inhibitors of IFN activity. There was no detectable transcription of IFN-alpha or IFN-beta gene products by the cells exposed to RSV. RSV-exposed MNL did produce small amounts of IFN-gamma, consistent with prior sensitization of the cell donors to the virus, but titers were substantially lower than those induced by influenza virus. RSV showed minimal but equivalent susceptibility to several subtypes of IFN-alpha. The data raise the possibility that the IFN system has a limited direct role in early host defense against RSV infection, but results should not be extrapolated directly to in vivo events.

Recent observations regarding the pathogenesis of recurrent respiratory syncytial virus infections: implications for vaccine development

Respiratory syncytial virus (RSV) and influenza virus are common pathogens for all age groups. Currently licensed influenza virus vaccines generally provide protection from clinically detectable disease caused by antigenically matched challenging viruses. In contrast, vaccine development for RSV has been hampered by the inability of candidate vaccines to induce protective immunity to naturally occurring infection. The precise mechanism(s) responsible for the RSV vaccine failures have not been determined. We raise the possibility that infection by RSV is associated with attenuation of both proliferative and non-proliferative RSV-specific responses by human mononuclear leucocytes that results in the suppression or delay of host anamnestic defences, allowing development of recurrent clinical illness despite pre-existing immunity.

Suppressed expression of ICAM-1 and LFA-1 and abrogation of leukocyte collaboration after exposure of human mononuclear leukocytes to respiratory syncytial virus in vitro. Comparison with exposure to influenza virus

Human mononuclear leukocytes (MNL) exposed to respiratory syncytial virus (RSV) produce net IL-1 inhibitor bioactivity with the anticipated consequences of cell cycle arrest, suppressed virus-specific proliferation, and reduced expression of activation markers. These studies were undertaken to investigate effects of exposure and resultant net IL-1 inhibitor activity on the expression of the intercellular adhesion molecule-1 (ICAM-1), and its ligand the lymphocyte function-associated antigen (LFA-1). MNL collected at 1, 4, and 24 h after exposure to influenza virus (which induces net IL-1 bioactivity) showed enhanced expression of ICAM-1 and LFA-1 relative to sham-exposed MNL and exhibited cell clustering. In contrast, exposure to RSV was associated with suppressed expression of both ICAM-1 and LFA-1 and with minimal detectable cell clustering throughout the culture period. Influenza virus-exposed MNL produced significantly more IL-1 and IFN-gamma (which require cell-cell collaboration for optimal production) than did RSV-exposed MNL. These data raise the possibility that exposure of MNL to RSV fails to elicit or blocks the early events necessary for cellular collaboration, contributing to early suppression of the clonal expansion of RSV-specific lymphocytes.