T-Cell Responses in Adults During Natural Respiratory Syncytial Virus Infection.

Background: The pathogenesis of respiratory syncytial virus (RSV) in older adults may be due to age-related T-cell immunosenescence. Thus, we evaluated CD4 and CD8 T-cell responses during RSV infection in adults across the age spectrum. Methods: Peripheral blood mononuclear cells collected during RSV infection in adults, age 26-96 years, were stimulated with live RSV and peptide pools representing F, M, NP, and G proteins and analyzed by flow cytometry. Results: There were no significant age-related differences in frequency of CD4+ T cells synthesizing interferon (IFN)γ, interleukin (IL)2, IL4, IL10, or tumor necrosis factor (TNF)α or in CD8+IFNγ+ T cells. IL4+CD4+ T-cell numbers were low, as were IL13 and IL17 responses. However, in univariate analysis, CD4 T-cell IFNγ, IL2, IL4, IL10, and TNFα responses and CD8+IFNγ+ T cells were significantly increased with more severe illness requiring hospitalization. In multivariate analysis, viral load was also associated with increased T-cell responses. Conclusions: We found no evidence of diminished RSV-specific CD4 or CD8 T-cell responses in adults infected with RSV. However, adults with severe disease seemed to have more robust CD4 and CD8 T-cell responses during infection, suggesting that disease severity may have a greater association with T-cell responses than age.

Macrophages are required for influenza virus infection of human lymphocytes.

Monocyte and lymphocyte surface-expressed viral antigens have been demonstrated after exposure of unseparated human mononuclear leukocytes to influenza virus in vitro. The current studies, using [35S]methionine pulse-labeled purified preparations of virus-exposed macrophages, depleted of lymphocytes, demonstrate that the presence of these viral proteins does represent new synthesis. However, purified lymphocytes, depleted of monocytes-macrophages and exposed to influenza virus, showed no detectable viral protein synthesis. In further experiments, unseparated mononuclear leukocytes were exposed to virus and subsequently separated by countercurrent centrifugal elutriation. Both macrophages and lymphocytes were then shown to synthesize influenza proteins. Cell-free control or influenza virus-infected macrophage-derived supernatant fluids did not facilitate influenza virus infection of the lymphocytes. The data suggest that macrophages are required for influenza virus infection of human lymphocytes, and raise the possibility that macrophage facilitation of an abortive infection of lymphocytes plays a role in the generation of effective immunity to viral antigens.

Relation of serum antibody to glycoproteins of respiratory syncytial virus with immunity to infection in children.

Immunity in relation to passively transferred maternal and naturally-induced serum antibody to the viral proteins was determined in 34 children who were followed from birth through three years of age for respiratory syncytial virus infection (RSV). Sera were tested by immunoglobulin class-specific enzyme-linked immunosorbent assay using the attachment and fusion proteins of the Long strain. The basis for immunity for maternal antibody in primary infection was assessed by a comparison of the distribution of antibody titers in a) 7 children who had an upper respiratory illness to 12 whose illness was accompanied by lower respiratory disease and of b) 13 children with an RSV-associated illness in the first 6 months of life who were age-matched as to month and approximate day of birth with 11 not infected in the same period. Infection induced immunity was evaluated by a comparison of antibody titers in 19 children who were reinfected with RSV in the year following their primary infection to 15 in whom reinfection was not documented. A statistical analysis of titers revealed that antibody to the fusion protein is an important correlate of immunity. In all three comparisons, the children with less RSV disease had significantly higher IgG anti-F titers prior to infection. No differences were observed between IgA anti-F or IgG and IgA anti-G titers.

Viral respiratory infections in the institutionalized elderly: clinical and epidemiologic findings.

OBJECTIVE: To prospectively evaluate the incidence and impact of viral respiratory infection in the institutionalized elderly during a winter season. DESIGN: Prospective descriptive study, without intervention. METHOD: Patients with respiratory illnesses were evaluated by a directed history and physical examination. Nasopharyngeal secretions for viral culture were obtained, and acute and convalescent serum samples were obtained for analysis. Serologic evidence of infection with respiratory syncytial virus (RSV) and parainfluenza were determined by enzyme immunoassay (EIA), and influenza by hemagglutination-inhibition assay and EIA. SETTING: A 591-bed nursing home. PARTICIPANTS: Residents with signs or symptoms of acute respiratory illness (nasal congestion, pharyngitis, cough, wheezing, or respiratory difficulty) were eligible for study. RESULTS: A viral etiology was documented in 62 out of 149 illnesses (42%). RSV was the most common virus associated with illness; it was documented in 27% of respiratory illnesses, followed by rhinovirus (9%), parainfluenza (6%), and influenza (1%). RSV was associated with significantly more severe disease when compared with rhinovirus. Clustering of specific viral infections occurred, suggesting nosocomial transmission. CONCLUSIONS: Viruses are an important cause of acute respiratory infections in the institutionalized elderly during the winter months.

Intermittent compression pump for nonhealing wounds in patients with limb ischemia. The Mayo Clinic experience (1998-2000).

BACKGROUND: The aim of this retrospective observational study was to review the use of an intermittent pneumatic compression device on nonhealing wounds in patients with critical limb ischemia at Mayo Clinic Rochester. METHODS: The setting was a community and referral multidisciplinary wound care clinic. The authors analysed 107 patients, median age 73, with critical limb ischemia and active ulcers started using a compression device between 1998 and 2000; 101 patients had lower extremity ulcers, and 25% had a history of amputation, and 64% had diabetes. Of all the wounds, 64% were multifactorial in etiology, and 60% had associated transcutaneous oxygen tension levels below 20 mmHg. Patients were typically asked to use the device at home on the affected limb(s) for 6 hours daily. The main outcome criterion was complete wound healing with limb preservation. RESULTS: The median follow-up after initiation of treatment was 6 months. Complete wound healing with limb preservation was achieved by 40% of patients with TcPO(2) levels below 20 mmHg; by 48% with osteomyelitis or active wound infection; by 46% with diabetes treated with insulin; and by 28% with a previous amputation. Half of all amputations occurred in patients with prior amputations. Seven patients discontinued the device because of pain experienced with its use. CONCLUSIONS: Patients with critical limb ischemia and nonhealing wounds at high risk of amputation can achieve complete wound healing and limb preservation by using an intermittent pneumatic compression device.

Humoral, mucosal, and cellular immune response to topical immunization with a subunit respiratory syncytial virus vaccine.

The efficacy of topical immunization with the respiratory syncytial virus (RSV) fusion (F) protein was tested in mice using cholera toxin B chain (CTB) as an adjuvant. The dose of CTB required for the adjuvant effect (as measured by local and systemic antibody stimulation) and protection from viral challenge was > or = 5 micrograms. With this dose, mice immunized intranasally with CTB plus F protein were highly protected from viral replication in the upper and lower respiratory tract. This protection was associated with the induction of mucosal IgA and serum IgG and neutralizing antibody. Addition of parenteral immunization with F protein to the topical vaccination provided protection from viral challenge nearly equivalent to immunization with live RSV intranasally. Topical and parenteral immunization with F protein was not associated with induction of splenic cytotoxic T cells, in contrast to live virus given intranasally.

Mucosal immunization with a subunit respiratory syncytial virus vaccine in mice.

The protective efficacy of mucosal immunization with purified respiratory syncytial virus (RSV) fusion protein (F) using cholera toxin (CT) as an adjuvant was assessed in mice. Intranasal vaccination with F+CT induced F-specific serum IgG and nasal IgA and resulted in 75% protection from nasal virus replication compared with control mice. Intranasal CT+F with simultaneous parenteral F provided complete protection equivalent to intranasal live virus immunization.

Humoral immunity to respiratory syncytial virus infection in the elderly.

The relationship between serum immunoglobulins and the severity and risk of Respiratory Syncytial Virus (RSV) infection in the institutionalized elderly was prospectively assessed during the winter of 1989-1990 at a 591 bed nursing home. Forty RSV infections were identified out of 149 respiratory illnesses by isolation of the virus or by a greater than or equal to 4-fold rise in RSV-specific IgG by EIA. Acute serum RSV IgG levels were similar in those with RSV infection and those with non-RSV illness. Additionally, among the RSV-infected elderly there was no correlation between severity of clinical symptoms and level of acute IgG titers by EIA or virus neutralization. The results of this study suggest that humoral immunity does not play a major role in reducing the risk of infection nor modulating the clinical severity of illness in elderly persons with RSV infections.

Formalin-inactivated respiratory syncytial virus vaccine induces antibodies to the fusion glycoprotein that are deficient in fusion-inhibiting activity.

The fusion (F) glycoprotein of respiratory syncytial virus (RSV) induces neutralizing antibodies and antibodies that inhibit fusion of infected cells (FI antibody). It was previously shown that infants and children immunized with Formalin-inactivated RSV 20 years ago developed antibodies that bound to the F glycoprotein but were deficient in neutralizing activity. A reexamination of these sera indicated that they were also deficient in FI activity. Thus, Formalin-inactivated RSV vaccine stimulated an unbalanced immune response in which an unusually large proportion of the induced antibodies were directed against nonprotective epitopes rather than against the epitopes that induce functional antibodies, i.e., neutralizing and FI antibodies. This deficiency in stimulation of functional antibodies probably decreased the protective efficacy of the vaccine and could have contributed to potentiation of disease in the vaccines during subsequent RSV infection.

Safety and immunogenicity of a respiratory syncytial virus subunit vaccine (PFP-2) in ambulatory adults over age 60.

The safety and immunogenicity of purified fusion protein (PFP-2) respiratory syncytial virus (RSV) vaccine was evaluated in a randomized placebo-controlled, double-blind study of 64 healthy adults over age 60. Vaccination was well tolerated with no significant acute side-effects. Twenty-nine of 33 vaccinees (87%) showed a greater than or equal to fourfold rise in serum IgG to the F protein of RSV at 8 weeks post vaccination. Twenty of 33 vaccine recipients (61%) had a greater than or equal to fourfold rise in serum neutralizing titer to group A and/or group B RSV. Response to vaccination was inversely correlated with pre-immunization serum neutralizing titers. Active surveillance throughout the ensuring winter identified three RSV infections in the placebo group and none in the vaccine group. Thus, PFP-2 was found to be safe and immunogenic in healthy older adults.

Monoclonal antibodies to respiratory syncytial virus proteins: identification of the fusion protein.

Six monoclonal antibodies directed against respiratory syncytial virus proteins were produced. Each was characterized by immunoprecipitation and indirect immunofluorescence. One was directed against the nucleocapsid protein. NP 44, two were directed against a 37,000-dalton protein, two were directed against the major envelope glycoprotein, GP 90, and one was directed against the 70,000-dalton envelope protein, VP 70. Indirect immunofluorescence stain patterns of infected HEp-2 cells defined GP 90 and VP 70 as viral proteins expressed on the cell surface, whereas NP 44 and the 37,000-dalton protein were detected as intracytoplasmic inclusions. One of the anti-GP 90 antibodies neutralized virus only in the presence of complement but did not inhibit cell-cell fusion. The anti-VP 70 antibody neutralized virus without complement and inhibited cell-cell fusion of previously infected HEp-2 cells, thus identifying VP 70 as the fusion protein.

Safety and immunogenicity of a respiratory syncytial virus subunit vaccine (PFP-2) in the institutionalized elderly.

The safety and immunogenicity of purified fusion protein (PFP-2) respiratory syncytial virus (RSV) vaccine was evaluated in an open label study in 37 frail institutionalized persons over age 65. Vaccination was well tolerated without significant side-effects. Thirty-six of 37 volunteers completed the study. Nineteen of 36 (53%) vaccinees had a greater than or equal to fourfold increase in IgG to F protein at 4 weeks and 17 (47%) had a greater than or equal to fourfold rise in neutralizing titers to either group A or B virus. Although response rate to PFP-2 vaccine in the frail elderly was somewhat diminished compared to results in the healthy elderly, the vaccine was well tolerated and relatively immunogenic.

Respiratory syncytial virus infection in adults.

Respiratory syncytial virus (RSV) is now recognized as a significant problem in certain adult populations. These include the elderly, persons with cardiopulmonary diseases, and immunocompromised hosts. Epidemiological evidence indicates that the impact of RSV in older adults may be similar to that of nonpandemic influenza. In addition, RSV has been found to cause 2 to 5% of adult community-acquired pneumonias. Attack rates in nursing homes are approximately 5 to 10% per year, with significant rates of pneumonia (10 to 20%) and death (2 to 5%). Clinical features may be difficult to distinguish from those of influenza but include nasal congestion, cough, wheezing, and low-grade fever. Bone marrow transplant patients prior to marrow engraftment are at highest risk for pneumonia and death. Diagnosis of RSV infection in adults is difficult because viral culture and antigen detection are insensitive, presumably due to low viral titers in nasal secretions, but early bronchoscopy is valuable in immunosuppressed patients. Treatment of RSV in the elderly is largely supportive, whereas early therapy with ribavirin and intravenous gamma globulin is associated with improved survival in immunocompromised persons. An effective RSV vaccine has not yet been developed, and thus prevention of RSV infection is limited to standard infection control practices such as hand washing and the use of gowns and gloves.

Transmission of Chlamydia pneumoniae.

To investigate the transmission of Chlamydia pneumoniae via hands and environmental surfaces, its survival on various surfaces was studied. The organism remained viable on formica countertops for 30 h and in tissue paper for 12 h. Measurable quantities of chlamydiae were transferred from these environmental surfaces to hands. However, titers were low and survival time on hands was limited to 10-15 min. C. pneumoniae survived small particle aerosolization well and was infectious to mice by both direct inoculation and aerosolization. These observations suggest that several mechanisms of transmission of C. pneumoniae are possible, including the transfer of fomites from environmental surfaces with subsequent autoinoculation.

Relationship of serum antibody to risk of respiratory syncytial virus infection in elderly adults.

The relationship of serum antibody to respiratory syncytial virus (RSV) and risk of RSV infection was prospectively evaluated in frail elderly persons. Baseline blood samples from 22 subjects who developed symptomatic RSV infection during the 26-month study and from 22 control subjects who did not become infected with RSV were compared. The mean serum IgG titer to RSV fusion protein was significantly lower in the RSV-infected group than in the controls (15.4 +/- 1.6 vs. 16.4 +/- 1.8, P = .05), as were the neutralizing titers to group A RSV (12.4 +/- 2.2 vs. 14.2 +/- 2.2, P = .008) and group B virus (9.1 +/- 2.1, vs. 10.3 +/- 1.5, P = .01). These results suggest that older adults with low titers of serum neutralizing antibody may be at greater risk of developing symptomatic RSV infection than those who have high antibody titers.

Identification of the virus-specific proteins of respiratory syncytial virus temperature-sensitive mutants by immunoprecipitation.

The proteins of Long strain RSV and three temperature-sensitive (ts) mutants of the A2 strain were compared by pulse labeling virus-infected cells with [35S]methionine and [3H]glucosamine followed by analysis of the cell lysates by polyacrylamide gel electrophoresis. At the permissive temperature (30 degrees) proteins ranging in molecular weight from 24,000 to 50,000 (VP24, VP27, VP33, VP44) could be identified. Immunoprecipitation of viral lysates by immune rabbit serum demonstrated antigenic similarity with VP27, VP44, VP50, and VP67 in all ts mutants and Long strain RSV. [3H]Glucosamine labeling demonstrated glycoproteins of 90,000 (GP90) and 50,000 (GP50) in Long strain and GP90 in the ts mutants.

A simple and reproducible method for collecting nasal secretions in frail elderly adults, for measurement of virus-specific IgA.

The standard method for collection of respiratory secretions, by use of a nasal wash (NW) to measure virus-specific IgA, is problematic in frail elderly adults. Therefore, a simplified collection approach using a nasal swab (NS) is described. NW and NS samples were collected from healthy young and frail elderly adults, and IgA titers to respiratory syncytial virus (RSV) fusion and attachment glycoproteins were determined by enzyme immunoassay. Correlation between IgA titers in NW and NS was excellent for each of the antigens (correlation coefficients,.71-.93). In addition, NS results were reproducible when frail elderly subjects were sampled several weeks apart and were nearly equivalent to results from NW samples. The ability to sample nasal secretions by use of an NS when an NW is not technically feasible will facilitate the study of mucosal immunity to RSV as well as the study of mucosal response to candidate RSV vaccines in frail elderly populations.

Protection of mice against dengue 2 virus encephalitis by immunization with the dengue 2 virus non-structural glycoprotein NS1.

Immunization of mice with the dengue 2 virus (DEN 2)-specified non-structural protein NS1 provided significant protection against intracerebral challenge with the virus in the absence of detectable neutralizing or other anti-virion antibody. NS1, purified from lysates of infected Vero cells by immunoaffinity chromatography, expressed an antigenic site(s) common to each of the four DEN serotypes, and hyperimmunization of rabbits with NS1 stimulated production of complement-fixing (CF) antibody with broad DEN serotype specificity. However, cross-protection was not observed: mice immunized with DEN 2 NS1 developed little or no heterologous CF antibody and were not protected against challenge with neurovirulent DEN 1. Induction of a protective immune response by NS1 suggests that it be considered for incorporation into possible synthetic or recombinant DNA DEN vaccines.

Monoclonal antibody neutralization escape mutants of respiratory syncytial virus with unique alterations in the attachment (G) protein.

Five monoclonal antibody (MAb) neutralization escape mutants of respiratory syncytial virus (RSV) were produced by growing the Long strain RSV (group A virus) in the presence of a neutralizing, group cross-reactive MAb specific for the attachment protein (G). Four viruses (RSV-2, -6, -14 and -15) had amino acid replacements clustered within a highly conserved centrally located 13 amino acid region (position 164-176). Reactivity with group A-specific MAbs and with polyclonal anti-G serum was maintained and growth kinetics were unaffected. An additional virus (RSV-3) had four amino acid substitutions in the cytoplasmic tail and transmembrane region of G, and had restricted growth and formed small syncytia. Immunofluorescent and Western blot analysis indicated that G protein was not membrane associated and had reduced incorporation into the virion, thereby escaping neutralization by L9 and polyclonal anti-G serum. The predominant form of G produced by RSV-3 was found in infected cell supernatants, consistent with the size of secreted G.

Purification and characterization of GP90, one of the envelope glycoproteins of respiratory syncytial virus.

The large glycoprotein, GP90, of respiratory syncytial virus (RSV) was purified by affinity chromatography using a monoclonal antibody. Hyperimmune rabbit antiserum directed specifically to the purified GP90 neutralized RSV to high titre but did not inhibit fusion of previously infected cells. 125I-labelled GP90 bound rapidly to HEp-2 cells in an unsaturable manner; binding was inhibited by the hyperimmune rabbit antiserum.