Rhinovirus-induced lower respiratory illness is increased in asthma and related to virus load and Th1/2 cytokine and IL-10 production

Abstract

Acute exacerbations are the major cause of asthma morbidity, mortality, and health-care costs and are difficult to treat and prevent. The majority of asthma exacerbations are associated with rhinovirus (RV) infection, but evidence supporting a causal relationship is weak and mechanisms are poorly understood. We hypothesized that in asthmatic, but not normal, subjects RV infection would induce clinical, physiologic, and pathologic lower airway responses typical of an asthma exacerbation and that these changes would be related to virus replication and impaired T helper 1 (Th1)/IL-10 or augmented Th2 immune responses. We investigated physiologic, virologic, and immunopathologic responses to experimental RV infection in blood, induced sputum, and bronchial lavage in 10 asthmatic and 15 normal volunteers. RV infection induced significantly greater lower respiratory symptoms and lung function impairment and increases in bronchial hyperreactivity and eosinophilic lower airway inflammation in asthmatic compared with normal subjects. In asthmatic, but not normal, subjects virus load was significantly related to lower respiratory symptoms, bronchial hyperreactivity, and reductions in blood total and CD8(+) lymphocytes; lung function impairment was significantly related to neutrophilic and eosinophilic lower airway inflammation. The same virologic and clinical outcomes were strongly related to deficient IFN-gamma and IL-10 responses and to augmented IL-4, IL-5, and IL-13 responses. This study demonstrates increased RV-induced clinical illness severity in asthmatic compared with normal subjects, provides evidence of strong relationships between virus load, lower airway virus-induced inflammation and asthma exacerbation severity, and indicates augmented Th2 or impaired Th1 or IL-10 immunity are likely important mechanisms.

Fig. 1.

Lower respiratory symptom scores and lung function (PEF) during RV16 infection. Lower respiratory (chest) symptom scores were determined after RV16 inoculation in the asthmatic and normal subject groups. Chest scores are displayed in a–d and PEF are shown in e and f. Chest symptoms were more severe in the asthmatic group. Daily chest scores were significantly increased above baseline for the asthmatics on days 1 and 3–7 (a) and for the normals only on day 6 (b). *, P < 0.05 and **, P < 0.01 compared with the corresponding baseline day. The peak chest score (c; P = 0.05) and the 2-week total chest score (d ; P = 0.017) were both significantly greater in the asthmatic group compared with those recorded in the normal group. Daily PEF is expressed as the percentage change in morning PEF from baseline. In e, individual 3-day rolling mean data are plotted for days −4 to 14 (asthmatics, ●; normals, ○) as is the group median percentage change (asthmatics, solid line; normals, dotted line). In the normal group no significant change in PEF was seen on any of the days after inoculation. In contrast in the asthmatic group there were significant falls in PEF on days 1–8 and 12–14 (**, P < 0.01; *, P < 0.05 compared with baseline). In addition, the maximum percentage fall in PEF (f) was greater in the asthmatics (P = 0.003).

Fig. 2.

Differences in BAL leukocyte concentrations during RV infection and relationships between virus load and airway inflammation and clinical illness severity are shown. (a) At day 4 BAL leukocyte concentrations were greater in the asthmatic than in the normal group. This difference was significant for eosinophils (Middle) and approached statistical significance for lymphocytes (Left) and neutrophils (Right). (b–e) The relationships between RV virus load and BAL inflammatory cells numbers and clinical illness severity were investigated in the two subject groups. In the asthmatic group (●) there was a significant correlation between peak virus load after inoculation and total chest symptom score (b) and the fall in histamine PC₂₀ at day 6 (d) and between the maximum fall in PEF and the day 4 BAL neutrophil concentration (c) and the BAL day 4 eosinophil concentration (e). There were no significant correlations in the normal group (○).

Fig. 3.

Relationships between blood CD4⁺ IFN-γ and IL-10 production and nasal lavage virus load and between BAL CD4⁺ IFN-γ and IL-4, IL-5, and IL-13 production and reductions in lung function and lower respiratory symptoms in asthmatic subjects. (a and b) Peripheral blood CD4⁺ IFN-γ and IL-10 production were assessed at baseline before experimental RV infection by intracellular cytokine staining. In the asthmatic group there was a significant inverse correlation between peak virus load and both CD4⁺ IFN-γ (a) and IL-10 (b) production and between total cold symptom score and IL-10 production (data not shown; P < 0.001). (c–f) BAL CD4⁺ IFN-γ and IL-4, IL-5, and IL-13 production were assessed at baseline before experimental RV infection by intracellular cytokine staining. In the asthmatic group there was a significant inverse correlation between the maximum fall in PEF and CD4⁺ IFN-γ production (c) and significant positive correlations between CD4⁺ IL-4 (d), IL-5 (e), and IL-13 (f) production and total chest symptom score.

Fig. 4.

Deficient induction of Th1 cytokines and IL-10 and augmented induction of Th2 cytokines from BAL cells from asthmatic compared with normal subjects. BAL cells from the baseline bronchoscopy before experimental RV infection were incubated for 48 h with medium alone (open symbols) or RV-16, LPS, or PHA (closed symbols). Cytokine release into supernatants of cells from normal (squares) or asthmatic subjects (circles) was assessed by ELISA. (a–c) Significant induction of the Th1 cytokines IFN-γ (a), IL-10 (b), and IL-12 (c) was restricted to normal subjects. (d–f) Levels of the Th2 cytokine IL-4 were significantly greater in the stimulated asthmatic cells than in stimulated normal cells (d), and significant induction of the Th2 cytokines IL-5 (e) and IL-13 (f) was restricted to cells from asthmatic subjects. (g and h) In contrast, the T cell cytokine IL-2 (g) and the Th17 cytokine IL-17 (h) were induced normally in both subject groups.