A biological model to explain the association between human rhinovirus respiratory infections and bronchial asthma

Human rhinoviruses (HRVs) are a frequent cause or upper respiratory tract infections in children and adults, and can exacerbate existing pulmonary disease. The major group of HRV attach to the receptor intercellular adhesion molecule (ICAM)-1, which is expressed on many cell types including epithelial cells. To study the influence of biological mediators on ICAM-1 expression, and consequently HRV attachment and infection, we have established an in vitro model system to evaluate the effects or pre-exposure to different cytokines on surface expression of ICAM-1 of uninfected and HRV-14-infected epithelial cells. The results of our studies show that the cytokines interleukin (IL)-1 beta, IL-8 and tumour necrosing factor (TNF)alpha increased ICAM-1 expression on epithelial cells. Epithelial cells infected with live HRV-14 displayed a significant upregulation of ICAM-1 compared to baseline. In contrast, interferon (IFN)gamma, whilst increasing the level of ICAM-1 expression on uninfected cells, induced a marked persistent downregulation of ICAM-1 expression on HRV-infected epithelial cells. In addition, IFN gamma appeared to completely override the ICAM-1 upregulation induced by IL-1 beta, IL-8 and TNF alpha, during HRV infection. We have further demonstrated that type 2 T-helper cell (Th2)-associated cytokines, predominantly IL-13, induce a marked upregulation or epithelial cell surface ICAM-1, thus increasing cellular binding sites for HRV attachment. As the airway mucosa or asthmatic subjects is predominantly infiltrated by activated type 2 T-helper cells with a simultaneous decrease of type 1 T-helper cells, our observations could explain the increased susceptibility to human rhinovirus infection observed in asthma.