CD4 and airway hyperresponsiveness: Data from Il4-disrupted (knockout) (IL-4KO) mice and CD4-depleted mice revealed the attenuated hallmark signs of asthma, including the accumulation of eosinophils in BAL fluid and airway hyperresponsiveness, indicating that IL-4 production from CD4+ T cells is a key factor in the development of asthma [12–14].