Abstract
Viral bronchiolitis is the most common cause of hospitalization in infants under 6 months of age, and 70% of all cases of bronchiolitis are caused by respiratory syncytial virus (RSV). Early RSV infection is associated with respiratory problems such as asthma and wheezing later in life. RSV infection is usually spread by contaminated secretions and infects the upper then lower respiratory tracts. Infected cells release proinflammatory cytokines and chemokines, including IL-1, tumor necrosis factor-α, IL-6, and IL-8. These activate other cells and recruit inflammatory cells, including macrophages, neutrophils, eosinophils, and T lymphocytes, into the airway wall and surrounding tissues. The pattern of cytokine production by T lymphocytes can be biased toward 'T-helper-1' or 'T-helper-2' cytokines, depending on the local immunologic environment, infection history, and host genetics. T-helper-1 responses are generally efficient in antiviral defense, but young infants have an inherent bias toward T-helper-2 responses. The ideal intervention for RSV infection would be preventive, but the options are currently limited. Vaccines based on protein subunits, live attenuated strains of RSV, DNA vaccines, and synthetic peptides are being developed; passive antibody therapy is at present impractical in otherwise healthy children. Effective vaccines for use in neonates continue to be elusive but simply delaying infection beyond the first 6 months of life might reduce the delayed morbidity associated with infantile disease.
Highlights
The World Health Organization estimates that approximately 14 million people die each year from infections that are transmitted via the respiratory tract, most of which occur in childhood
Viral infections of the respiratory tract are serious during infancy, and viral bronchiolitis is the most common cause of infantile hospitalization in the developed world [1]
A recent study found that T-cell activation was elevated for 5 months after infantile bronchiolitis, regardless of severity [28]; this is in marked contrast to the rapid normalization of soluble IL-2 receptor levels in other acute viral infections
Summary
The World Health Organization estimates that approximately 14 million people die each year from infections that are transmitted via the respiratory tract, most of which occur in childhood. A recent study found that T-cell activation (as measured by plasma levels of soluble serum IL-2 receptor, sCD25) was elevated for 5 months after infantile bronchiolitis, regardless of severity [28]; this is in marked contrast to the rapid normalization of soluble IL-2 receptor levels in other acute viral infections Such studies suggest that effects from RSV infections may be responsible for respiratory problems later in life. From data obtained in mouse experiments, it was hypothesized that initial RSV infection increased Th2 sensitization to subsequent respiratory infections and to inhaled antigen To test this hypothesis, IL-4 and IFN-γ production, and proliferative responses to RSV antigens and nonviral allergens was measured in peripheral blood cells of 7- and 8-year-old children [5]. Both of these factors may contribute to delayed respiratory problems in some individuals, and are not mutually exclusive
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