Evaluates whether interleukin-4 (IL-4) is required for mounting murine T-helper Th2 responses. Conclusion that IL-4 is required for the generation of the Th2-derived cytokines and that immune responses dependent on these cytokines are impaired; Disruption of the IL-4 gene; Cytokine secretion after polyclonal T-cell stimulation; Details of the study.