CD4 and airway hyperresponsiveness: Previous studies have reported that vaccinating BALB/c mice with RSV G protein can elicit a Th2-type biased CD4+ T cell response upon RSV challenge, and that this skewed Th2-type response is associated with aspects of disease pathogenesis that include airway hyperresponsiveness, mucus over-production, and pulmonary eosinophilia [57–59].