Virus respiratoire syncytial et allergie : cause ou conséquence ?

Abstract

The relationship of cause and effect between infection due to the Respiratory Syncytial Virus and allergy is a topic for discussion. Animal models favour a strong relationship between RSV and allergy, by demonstrating that there exists a TH2 predominant lymphocytic profile which is accommpanied by the recruitment of eosinophils in the respiratory tract and the production of IgE specific anti-RSV. However, in infants the evidence is more complex. There are arguments for a reduction of interferon gamma secretion by monocytes which correlates with the severity of respiratory symptoms. This decrease has been demonstrated in the bronchial secretions of those infants at high risk of developing atopic disease. Studies on TH2 cytokines are more contradictory. An elevation of IL-10 bas been reported in infants who remain symptommatic after an episode of acute bronchiolitis. However, no significant variaton of IL-4 of IL-13 bas been demonstrated. The majority of clinical medium-tem studies do not show any correlation between atopy and early RSV respiratory infection. The presence of eosinophils in the blood or respiratory tract is infrequently associated with RSV-bronchiolitis and recently the evidence for IgE anti-RSV has been questioned. In depth analysis tends to support the hypothesis that the Th2 immunological profile (the physiological profile in newborns) could play a role in enhancing the severity of RSV infection either because there, is an excess of TH2 activity (a marker for atopic predisposition) or a deficit of Th1 activity combined with a subsequent reduction of the protective properties of interferon gamma.