Experimental rhinovirus 16 infection increases intercellular adhesion molecule-1 expression in bronchial epithelium of asthmatics regardless of inhaled steroid treatment.

BACKGROUND: Rhinovirus infections in airway epithelial cells in vitro have been shown to upregulate intercellular adhesion molecule-1 (ICAM-1) expression. Epithelial ICAM-1, in its dual role as the major rhinovirus receptor and as adhesion molecule for inflammatory cells may be involved in the pathogenesis of rhinovirus-induced exacerbations of asthma. OBJECTIVE: We aimed to investigate the effect of experimental rhinovirus 16 (RV16) infection on ICAM-1 expression in bronchial mucosal biopsies in asthma. In addition, the effect of 2 weeks pretreatment with inhaled budesonide (800 microg b.d.) on RV16-associated changes in ICAM-1 expression was studied. METHODS: The study had a parallel, placebo-controlled design in 25 steroid-naive nonsmoking atopic asthmatic subjects. After 2 weeks budesonide (BUD) or placebo (PLAC) pretreatment bronchoscopy was performed 2 days before (day -2) and 6 days after (day 6) RV16 inoculation (on days 0 and 1). Immunohistochemical staining for ICAM-1 was performed on snap-frozen bronchial biopsies. ICAM-1 staining intensity on the basal epithelial cells was scored semiquantitatively from 1 (weak) to 3 (intense). Similarly, epithelial intactness was noted (1 = basal cells only, 2 = basal and parabasal cells, 3 = intact epithelium). RESULTS: ICAM-1 scores were not significantly different between the groups at day -2 (P > or = 0.08). Subsequent RV16 infection was associated with a trend towards an increase in ICAM-1 expression in the BUD-group (P = 0.07), whereas the increase was significant in the PLAC-group (P = 0.03). However, the increase was not significantly different between the groups (P = 0.74). Epithelial intactness score was not different between the groups before RV16 infection (P > or = 0.07), and no significant changes were observed in either group (P > or = 0.59). Moreover, ICAM-1 score did not correlate significantly with epithelium score in either group, at any time-point (P > or = 0.27). CONCLUSION: We conclude that an RV16 common cold in atopic asthmatic subjects is associated with increased ICAM-1 expression in the bronchial epithelium, which is not related to epithelial intactness. Glucocorticoid treatment does not appear to prevent the RV16-associated increased ICAM-1 expression. This suggests that other treatment modalities are required to protect against the spreading of infection during rhinovirus-induced exacerbations in asthma.

Experimental rhinovirus 16 infection causes variable airway obstruction in subjects with atopic asthma.

Exacerbations of asthma are often associated with rhinovirus infections. However, it has not been investigated whether rhinovirus infection can induce variable airway obstruction in asthma. We examined the effect of experimental rhinovirus 16 (RV16) infection on daily home recordings of FEV(1) in 27 subjects (nonsmoking, atopic, mildly asthmatic) who participated in a parallel placebo-controlled study. The subjects used a microspirometer to record FEV(1) three times daily from 4 d before until 10 d after RV16 (n = 19) or placebo (n = 8) inoculation. In addition, symptoms of asthma and symptoms of common cold were scored. Airway hyperresponsiveness to histamine was measured 3 d before and on Days 4 and 11 after RV16/placebo administration. Home recordings of FEV(1) decreased significantly after RV16 infection, reaching a minimum 2 d after inoculation (ANOVA, p

Relationship between exhaled nitric oxide and airway hyperresponsiveness following experimental rhinovirus infection in asthmatic subjects.

Exhaled nitric oxide (NO) is elevated in asthmatics, and varies with disease severity. We postulated that a respiratory virus infection increases exhaled NO levels in asthma, and examined the relationship between the virus-induced changes in exhaled NO and in airway hyperresponsiveness to histamine. In a parallel study, seven patients underwent experimental rhinovirus 16 (RV16) inoculation at days 0 and 1, whilst seven patients received placebo. Exhaled NO was measured at baseline (day 0) and at days 1, 2 and 3 after inoculation. Histamine challenges were performed prior to (day -7) and after inoculation (day 3), and were expressed as provocative concentration causing a 20% fall in forced expiratory volume in one second (FEV1) (PC20). Following RV16 infection there was a significant increase in NO at days 2 and 3 as compared to baseline (median change (range): 4.2 (7.5) parts per billion (ppb), p=0.03, and 3.0 (10.1) ppb, p=0.02, respectively). Furthermore, PC20 decreased significantly following RV16 infection (mean+/-SD change in doubling dose: -0.65+/-0.54, p=0.02), whereas PC20 did not change in the placebo group (p=0.1). There was a significant correlation between the RV16-induced changes in exhaled NO levels at day 2 and the accompanying changes in PC20 at day 3 (rank correlation coefficient (rs): 0.86, p=0.01). Hence, the greater the increase in exhaled NO, the smaller the decrease in PC20. We conclude that rhinovirus infection increases exhaled nitric oxide levels in asthmatics, and that this increase is inversely associated with worsening of airway hyperresponsiveness to histamine. These results suggest that viral induction of nitric oxide synthase within the airways may play a protective role in exacerbations of asthma.

Experimental rhinovirus 16 infection. Effects on cell differentials and soluble markers in sputum in asthmatic subjects.

Asthma exacerbations are often associated with respiratory virus infections, particularly with rhinovirus. In the present study we investigated the effect of experimental rhinovirus 16 (RV16) infection on airway inflammation as assessed by analysis of hypertonic saline-induced sputum. Twenty-seven nonsmoking atopic, mildly asthmatic subjects participated in a placebo-controlled parallel study. RV16 (n = 19) or its diluent (n = 8) was nasally administered. Sputum inductions were performed at entry and on Days 2 and 9 after inoculation, and airway responsiveness to histamine (PC20) was measured on Days 4 and 11. Cell differentials and levels of albumin, eosinophil cationic protein (ECP), IL-8, and IL-6 were determined. The cellular origin of IL-8 was investigated by intracellular staining. RV infection was confirmed by culture and/or by antibody titer rise in each of the RV16-treated subjects. There were no significant changes in the sputum differentials of nonsquamous cells (MANOVA, p > or = 0.40). In the RV16 group, there was a significant increase in the levels of ECP, IL-8, and IL-6 at Day 2 after infection (p < 0.05), whereas the albumin levels did not change (p = 0.82). The levels of IL-8 and IL-6 remained elevated for as long as 9 d after infection (p < 0.05). The increase in the percentage of IL-8 positive cells at Day 2 after infection could be attributed to the increase in IL-8 positive neutrophils (p < 0.02). There was a significant decrease in PC20 at Day 4 (p = 0.02), which was no longer significant at Day 11 (p = 0.19). The decrease in PC20 correlated significantly with the increase in ECP in the first week (r = -0.60) and with the change in the percentage eosinophils in the second week after inoculation (r = -0.58). We conclude that experimental RV16 infection in atopic asthmatic subjects increases airway hyperresponsiveness in conjunction with augmented airway inflammation, as reflected by an increase in ECP, IL-8, and IL-6 in sputum. Our results suggest that the RV16-enhanced airway hyperresponsiveness is associated with eosinophilic inflammation.

Effect of a rhinovirus-caused upper respiratory illness on pulmonary function test and exercise responses.

Upper respiratory illness (URI) may cause more frequent acute disability among athletes than all other diseases combined. The purposes of this study were to determine the impact of a rhinovirus-caused URI on resting pulmonary function submaximal exercise responses and on maximal exercise functional capacity. Twenty-four men and 21 women (18-29 yr) of varying fitness levels were assigned to the experimental group (URI), and 10 additional individuals served as a control group (CRL). An initial serological screening was performed on all URI group subjects to exclude those with the rhinovirus 16 (HRV16) antibody. All subjects completed both a baseline pulmonary function test and a graded exercise test to volitional fatigue. URI subjects were inoculated with HRV 16 on two consecutive days within 10 d of completing these tests. The day following the second inoculation (peak of illness), post-inoculation pulmonary function and graded exercise tests were performed. A noninfected control group completed these same pulmonary and exercise tests 1 wk apart. ANOVA identified no significant differences (P < 0.05) at minutes 2, 5, and 8 for the physiological responses measured between the pre- and post-exercise tests for both the URI and CRL, groups. Furthermore, there were no significant differences between maximal exercise performance between running trials for either group. There was also no significant interaction between treatment (pre/post URI) and group for any of the pulmonary function measures obtained. In conclusion, physiological responses to pulmonary function testing and submaximal and maximal exercise do not appear to be altered by an URI.

Rhinovirus-specific T cells recognize both shared and serotype-restricted viral epitopes.

To characterize rhinovirus (RV)-specific T cells, RV16- and RV49-specific CD4 T cells were cloned from peripheral blood, and cytokine secretion and serotype specificity were defined. Each RV-specific clone secreted high levels of interferon-gamma, and several also produced interleukin-4 and -5. To test serotype specificity, each clone was incubated separately with five different RV serotypes. Although 2 of 31 clones proliferated only in response to the virus used in cloning, the rest had significant proliferation in response to 2-5 different serotypes. Thus, RV-specific T cells can be activated by either serotype-specific or shared viral epitopes, raising the possibility that repeated activation of T cells by shared viral determinants in vivo could induce potent recall T cell responses. It is likely that enhanced T cell responses to shared viral epitopes contribute to antiviral activity, airway inflammation, or both.

Detection of rhinovirus RNA in lower airway cells during experimentally induced infection.

Rhinovirus (RV) infections are presumed to be localized to the upper airway, yet can cause severe lower airway symptoms in children and adults with asthma. To test the hypothesis that rhinovirus infection of the upper airway may be associated with the presence of virus in lower airway cells, we used the techniques of reverse transcription-polymerase chain reaction (RT-PCR) and Southern blotting to detect RV RNA in lower airway cells from eight allergic volunteers experimentally infected with RV16. Bronchoscopy with bronchoalveolar lavage (BAL) was done 1 mo before, and 2 and 4 d after an experimental infection with RV16. All subjects developed cold symptoms, and infection was confirmed by culturing RV16 from nasal secretions. Rhinovirus RNA was detected in both nasal lavage and lower airway cells from all eight subjects 2 to 4 d after an experimental inoculation, but not in any of the precold specimens from either the nose or the lower airway. These findings suggest that RV can infect cells of the lower airway, and raise the possibility that such an effect can promote asthma exacerbations in the susceptible host through direct enhancement of local inflammation.

Effects of experimental rhinovirus 16 infection on airway hyperresponsiveness to bradykinin in asthmatic subjects in vivo.

Disturbance of the balance between excitatory and inhibitory activity of the airway sensory nerves has been implicated in asthma pathogenesis, particularly during exacerbations of the disease. The objective of this study was to examine the effect of experimental rhinovirus 16 (RV16) infection on airway responsiveness to bradykinin, a potent sensory nerve stimulus, in asthma. Thirteen atopic, mildly asthmatic subjects participated in a parallel, placebo-controlled study. A total dose of 2.6 to 5.6 x 10(4) TCID50 RV16 (n = 7) or its diluent (n = 6) was inoculated on 2 consecutive days (Days 0 and 1). Histamine and bradykinin challenges were performed before (Days-7 and-6) and after (Days 3 and 4) inoculation. The response was measured by FEV1 and partial flow-volume curves, and it was expressed as PC20FEV1 and PC40V40p, respectively (changes expressed in doubling dose: DD). Before inoculation, PC20FEV1 and PC40V40p to histamine were not significantly different between the groups (p > or = 0.22), whereas PC20FEV1 and PC40V40p to bradykinin tended to be higher in the RV16 group (p = 0.11 and p = 0.06, respectively). PC20FEV1 and PC40V40p to histamine decreased significantly in the RV16 group (mean change +/- SEM: -0.65 +/- 0.20 DD, p = 0.02 and -0.98 +/- 0.28 DD, p = 0.01, respectively), but not in the placebo group (p > or = 0.26). PC40V40p to bradykinin increased significantly in the placebo group (+2.46 +/- 0.92 DD, p = 0.04), with a similar trend for PC20FEV1 (+1.50 +/- 0.62 DD, p = 0.06), whereas there were no significant changes in the RV16 group (p > or = 0.77). These changes in PC40V40p to histamine and bradykinin were significantly different between the groups (p = 0.02). We conclude that repeated bradykinin challenge over a 10-d interval induces tachyphylaxis in asthmatic subjects in vivo and that experimental RV16 infection abolishes such tachyphylaxis to bradykinin while it enhances airway responsiveness to histamine. These results do not favor a predominant role of airway sensory nerves in rhinovirus-induced exacerbations of asthma.

Effect of experimental rhinovirus 16 colds on airway hyperresponsiveness to histamine and interleukin-8 in nasal lavage in asthmatic subjects in vivo.

BACKGROUND: Asthma exacerbations are closely associated with respiratory virus infections. However, the pathophysiological consequences of such infections in asthma are largely unclear. OBJECTIVE: To examine the effect of rhinovirus 16 (RV16) infection on airway hypersensitivity to histamine, and on interleukin-8 (IL-8) in nasal lavage. METHODS: Twenty-seven non-smoking atopic, mildly asthmatic subjects participated in a placebo-controlled, parallel study. A dose of 0.5-2.9 x 10(4) TCID50 RV16 or placebo was nasally administered. Cold symptoms were recorded by questionnaire throughout the study. Histamine challenges were performed at entry, and on days 4 and 11 after inoculation. Nasal lavages were obtained at entry, and on days 2 and 9. The response to histamine was measured by PC20 (changes expressed as doubling doses: DD) IL-8 levels were obtained by ELISA, and were expressed in ng/ml. RESULTS: RV infection was confirmed by culture of nasal lavage and/or by antibody titre rise in each of the RV16-treated subjects. Among the 19 RV 16-treated subjects, eight developed severe cold symptoms. Baseline FEV1, did not change significantly during the study in either treatment group (P = 0.99). However, in the RV16-treated subjects there was a decrease in PC20 at day 4, which was most pronounced in those with a severe cold (mean change +/- SEM: -1.14 +/- 0.28 DD, P = 0.01). In addition, IL-8 levels increased in the RV16 group at days 2 and 9 (P < 0.001). The increase in nasal IL-8 at day 2 correlated significantly with the change in PC20 at day 4 (r = -0.48, P = 0.04). CONCLUSION: We conclude that the severity of cold, as induced by experimental RV16 infection, is a determinant of the increase in airway hypersensitivity to histamine in patients with asthma. Our results suggest that this may be mediated by an inflammatory mechanism, involving the release of chemokines such as IL-8.

The role of respiratory viruses in asthma.

Respiratory infections are common causes of increased asthma for patients of all ages. Current evidence indicates that viral, and not bacterial, infections are the most important respiratory illnesses which increase the severity of asthma. Of the respiratory viral infections associated with increased asthma, rhinoviruses, i.e. the cause of common colds, have proven to be the virus most often found in association with increased asthma severity. Although the association between rhinovirus infections and asthma is most dramatically illustrated in children, asthma patients of all ages can be affected and the attacks of asthma can be severe. Studies to establish the mechanisms by which rhinoviruses enhance asthma severity have begun to focus on how this virus promotes allergic inflammation. We have found that experimental rhinovirus infections enhance airway responsiveness and, perhaps most importantly, the likelihood that a late allergic reaction will occur to an antigen challenge. Furthermore, using bronchoscopy and segmental antigen challenge, we have found that rhinovirus infections promote mast cell release of histamine and the recruitment of eosinophils to the airways. These data support the concept that rhinovirus infections act to promote allergic inflammation and by this mechanism increase both the likelihood of asthma occurring and the severity of wheezing.

Rhinovirus inhibits antigen-specific T cell proliferation through an intercellular adhesion molecule-1-dependent mechanism.

To determine whether binding of human rhinovirus (HRV) to intracellular adhesion molecule-1 might disrupt airway immune processes, effects of a major HRV group, HRV-16, on T cell proliferation and cytotoxicity were defined. HRV (1-10 TCID50/cell) significantly inhibited T cell proliferation induced by antigen but not proliferation secondary to mitogens, interleukin-2, or an irradiated allogeneic T cell line. Noninfectious (UV-irradiated) HRV had similar effects. Inhibition of T cell proliferation was dependent on HRV binding to intercellular adhesion molecule-1 on monocytes, indicating that the virus interferes with lymphocyte activation indirectly through effects on antigen-presenting cells. In addition, HRV inhibited T cell cytotoxic responses but not NK cell activity. If these effects also occur in vivo, the resulting disturbance in local airway immunity could increase the chances of successful viral replication, and might also be a factor in the pathogenesis of secondary viral or bacterial respiratory tract infections.

Rhinovirus produces nonspecific activation of lymphocytes through a monocyte-dependent mechanism.

There is evidence that rhinovirus (RV) infections are frequent causes of increased asthmatic symptoms and can specifically enhance allergic inflammation in the airway. To further define effects of RV infection on cellular immunity, we have begun to develop in vitro models for study. When human PBMC were incubated with 35S-labeled RV16, specific binding via ICAM-1 on monocytes was observed. Incubation of PBMC with RV also led to a dose-related increase in the expression of the early activation marker CD69 on 30 to 70% of T cells. The RV16-induced increases in CD69 were blocked by anti-ICAM-1 mAb, and were not elicited by UV-inactivated (noninfectious) virus. The degree of CD69 enhancement correlated with the number of monocytes in mixtures of PBMC, did not occur in monocyte-depleted cultures, and was mediated by one or more soluble factor(s). RV also induced secretion of IFN-gamma from both peripheral blood T cells and NK cells, and IFN-gamma mRNA was greatest in T cells that were CD69+. Finally, supernatant from RV-activated CD3+CD69+ cells had biologic activity that promoted eosinophil survival in vitro; this RV16-associated activity was blocked when co-incubations were performed with IFN-gamma mAbs. These observations suggest that RV nonspecifically activates a large proportion of T cells through a monocyte-dependent mechanism. Such changes in vivo could enhance airway inflammation, and this may include effects on inflammatory cells in the airways of allergic individuals.

Rhinovirus enters but does not replicate inside monocytes and airway macrophages.

Potential interactions between rhinovirus (RV) and both the airway macrophage and its precursor cell, the blood monocyte, were investigated in terms of direct binding, intracellular replication, cell survival, and cytokine production. When HeLa cell suspensions are inoculated with RV as a positive control, virus titer increases by 100-fold in the first 24 h, confirming intracellular replication. In contrast, RV titer in monocyte and macrophage suspensions steadily decreased. Despite a lack of productive RV replication, cell-associated RV RNA was detectable using a biotin-labeled cDNA probe as early as 6 h after inoculation. Direct binding of RV16 to macrophages was confirmed using radiolabeled virus, although preincubation with anti-ICAM-1 mAb did not block this interaction. Synthesis of RV RNA, as indicated by [3H]uridine incorporation in actinomycin D-treated cells, was detected in HeLa cells but not macrophages, suggesting that the viral RNA detected inside macrophages was from input virus and was not newly synthesized. RV inoculation did not adversely affect monocyte or macrophage viability. Finally, RV caused macrophage activation, as indicated by the induction of TNF-alpha secretion. These in vitro findings suggest that macrophages interact with major group RV in vivo, and raise the possibility that there is a second cellular receptor for these viruses. Furthermore, macrophages do not serve as permissive host cells during in vivo RV infection, but instead may be active participants in anti-RV immunity and RV-induced airway inflammation.

Rhinovirus inhalation causes long-lasting excessive airway narrowing in response to methacholine in asthmatic subjects in vivo.

Exacerbations of asthma are often associated with respiratory infections, and particularly those caused by rhinovirus. The causative role of rhinovirus in these acute episodes is still unclear, since it has not been determined whether or not infection with the virus promotes excessive airway narrowing in asthma. We tested the hypothesis that experimental infection with inhaled wild-type rhinovirus 16 (RV16) increases the maximal degree of airway narrowing in response to bronchoconstrictor stimuli in patients with mild to moderate asthma. Fourteen nonsmoking subjects with atopic asthma and normal FEV1 values participated in a double-blind, placebo-controlled, parallel study. A total dose of 3 x 10(4) of the 50% tissue-culture-infective dose (TCID50) of RV16 or a placebo was administered by pipette, atomizer, and nebulizer in equal doses into both nostrils on two consecutive days. Dose-response curves for inhaled methacholine were recorded 1 d before and 2, 7, and 15 d after RV16 infection or placebo. The response to methacholine was measured by the percent decrease in FEV1, and the maximal degree of airway narrowing was expressed by the average response on the plateau of the dose-response curve. In the seven subjects receiving the virus, RV16 infection was confirmed in nasal washings and/or by an increase in antibody titer, whereas these tests were negative in the placebo group. There was no significant change in baseline FEV1 during the study in either group (p = 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)

A common cold virus, rhinovirus 16, potentiates airway inflammation after segmental antigen bronchoprovocation in allergic subjects.

Many patients with asthma have increased wheezing with colds. We hypothesized that rhinovirus colds might increase asthma by augmenting airway allergic responses (histamine release and eosinophil influx) after antigen challenge. Seven allergic rhinitis patients and five normal volunteers were infected with rhinovirus type 16 (RV16) and evaluated by segmental bronchoprovocation and bronchoalveolar lavage. Segmental challenge with saline and antigen was performed 1 mo before infection, during the acute infection, and 1 mo after infection. Lavage was performed immediately and 48 h after antigen challenge. Data were analyzed by two-way analysis of variance, and a P value of < or = 0.05 was considered to be significant. All volunteers inoculated with RV16 developed an acute respiratory infection. BAL fluid obtained from allergic rhinitis subjects during the acute viral infection, and 1 mo after infection, showed the following significant RV16-associated changes after antigen challenge: (a) an enhanced release of histamine immediately after local antigen challenge; (b) persistent histamine leak 48 h afterwards; and (c) a greater recruitment of eosinophils to the airway 48 h after challenge. These changes were not seen in non-allergic volunteers infected with RV16 and challenged with antigen, nor in allergic volunteers repetitively challenged with antigen but not infected with RV16, nor in RV16 infected allergic volunteers sham challenged with saline. We conclude that rhinovirus upper respiratory infection significantly augments immediate and late allergic responses in the airways of allergic individuals after local antigen challenge. These data suggest that one mechanism of increased asthma during a cold is an accentuation of allergic responses in the airway which may then contribute to bronchial inflammation.

The effect of T-cell depletion on enhanced basophil histamine release after in vitro incubation with live influenza A virus.

A number of mechanisms participate in virus-induced asthma. Previously, we described enhanced basophil histamine release (HR) during an experimentally induced rhinovirus infection and after in vitro incubation of peripheral blood mononuclear cells (PBMC) with influenza virus. This study extends our previous observations and examines the effect of influenza A virus on basophil leukotriene C4 (LTC4) release as well as the effect of T-cell depletion on virus-enhanced basophil HR. PBMC were isolated from ragweed-allergic subjects and incubated with live influenza A virus or control medium (allantoic fluid). After incubation with influenza A, ragweed antigen (AgE) stimulated LTC4 and HR were enhanced (P less than 0.05). To further define the role of T cells in virus-enhanced basophil secretion, PBMC were isolated and divided into two aliquots. In one aliquot, T cells were removed by magnetic bead separation of mouse monoclonal anti-CD3-coated lymphocytes. T-cell-depleted and nontreated PBMC suspensions were incubated with influenza A or control medium, collected, and challenged with AgE to release histamine. Basophil HR was enhanced in the virus-treated group of PBMC that had not undergone T-cell depletion. In contrast, virus incubation did not enhance HR in the T-cell-depleted fraction. Finally, preliminary analysis of the supernate from virus-treated leukocytes indicates the presence of interferon-gamma. These findings suggest that T cells, and their cytokine products, play an integral role in the process by which viruses enhance basophil HR.

Experimental rhinovirus 16 infection potentiates histamine release after antigen bronchoprovocation in allergic subjects.

Viral respiratory infections exacerbate asthma in many patients. We hypothesized that one mechanism by which this effect occurs may include potentiated or altered mediator release by mast cells and/or basophils to favor the development of late-phase asthmatic reaction (LAR). Therefore, we studied eight subjects with allergic rhinitis before and during an experimentally induced rhinovirus 16 (RV16) infection. We determined levels of plasma histamine and tryptase, and we observed the associated patterns of airway obstruction that developed following inhaled antigen challenge. Bronchial responsiveness to histamine, methacholine, and antigen were all significantly increased during the RV16 illness. Further, the incidence of LAR was significantly higher (five of eight) during the infection than before (one of eight; p = 0.014). In addition, in those patients whose pattern of response following antigen challenge converted from an immediate response only before infection to a dual response (immediate + late phase) during infection, plasma histamine concentrations after challenge were significantly greater than in those whose pattern of response did not change. We conclude that one mechanism by which RV16 infection increases the likelihood of LAR could include enhanced mediator release from pulmonary mast cells or from circulating or recruited basophils.

In vitro incubation with influenza virus primes human polymorphonuclear leukocyte generation of superoxide.

Viral respiratory illnesses exacerbate asthma, increase airway responsiveness, and enhance the frequency of late asthmatic reactions. A number of mechanisms have been identified to explain how respiratory viral illnesses provoke wheezing, including enhanced inflammatory activity of leukocytes. To further understand how respiratory virus-caused illnesses promote leukocyte-dependent airway injury, the following study evaluated the effect of an in vitro incubation of influenza A virus on human polymorphonuclear leukocyte (PMN) generation of superoxide (O2-). PMNs were isolated from anticoagulated human blood following density gradient centrifugation; purified PMNs were then incubated (37 degrees C x 30 min) with influenza virus (PMN:virus ratio of 5:1 [egg-infective dose 50%] and 10:1) in the presence of 10% autologous serum. After incubation, the viable PMNs (greater than 95% exclusion of trypan blue) were activated, by the chemotactic peptide formyl-methionine-leucine-phenylalanine (fMLP), calcium ionophore A23187, or phorbol myristate acetate (PMA), and O2- generation was then measured. Generation of O2- to fMLP and A23187 was significantly enhanced from PMNs that had been incubated with influenza virus. Although influenza virus itself did not generate O2-, it caused a transient increase in intracellular calcium ([Ca2+]i), when measured with Indo-1-loaded cells. These results suggest that influenza virus primes PMNs to generate increased amounts of O2- and that the priming effect is associated with a transient increase in [Ca2+]. Consequently, we postulate that influenza virus priming produces PMNs of enhanced inflammatory potential to cause greater airway injury, obstruction, and responsiveness during a viral respiratory infection.

Adenovirus 21 infection in an isolated antarctic station: transmission of the virus and susceptibility of the population.

Natural dissemination of viral respiratory illness to susceptible men may occur with surprising difficulty. This was especially evident during a 1977 outbreak of adenovirus type 21 (Ad-21) at McMurdo Station, a US research base in Antarctica. The unique circumstances at McMurdo allowed 125 men from the US to join and intermingle with 75 men who had wintered for 6 months in complete isolation. For an additional 5-week (September 2 to October 4, 1977) isolation period, respiratory illness etiology and transmission were monitored in the combined population. A total of 89% of the population was susceptible (neutralizing antibody titer, less than 1:3) to Ad-21 but only 15.0% were infected. Illness spread very slowly (1.5 cases/100 persons/week) with no epidemic peak and was much less severe than Ad-21 outbreaks in other settings. The incidence of infection (17.3%) and illness (9.6%) was low even in men who had wintered over, with values very similar to those of the newcomers (13.9% and 8.9%, respectively). Thus, despite a harsh environment and frequent prolonged gatherings of susceptible personnel, even a respiratory virus type with known epidemic potential was surprisingly difficult to transmit.