It is well-known that an unbalanced T-cell immune response can be harmful due to an excessive reaction of CD8+ T-cells, which leads to lung tissue damage [12,50], or a Th2-biased CD4+ T-cell response resulting in excessive mucus production and airway hyperresponsiveness [27,28,29,50,51,52]. The gene discussed is CD4; the disease is airway hyperresponsiveness.