Generation and analysis of interleukin-4 deficient mice.

Interleukin-4 (IL-4) promotes the growth and differentiation of many hematopoietic cells in vitro; in particular, it directs the immunoglobulin (Ig) class switch to IgG1 and IgE. Mice homozygous for a mutation that inactivates the IL-4 gene were generated to test the requirement for IL-4 in vivo. In the mutant mice T and B cell development was normal, but the serum levels of IgG1 and IgE were strongly reduced. The IgG1 dominance in a T cell-dependent immune response was lost, and IgE was not detectable upon nematode infection. Thus, some but not all of the in vitro properties of IL-4 are critical for the physiology of the immune system in vivo.