The 11B11 monoclonal antibody reacts with mouse IL-4 (interleukin-4) a multifunctional 14 kDa cytokine. IL-4 is expressed primarily by activated Th2 cells and NK cells, and at lower levels by mast cells, and basophils. IL-4 signals through the IL-4Rα. Upon receptor binding IL-4 stimulates activated B and T lymphocyte proliferation, and the differentiation of B cells into plasma cells. It also induces B cell class switching to IgE, and up-regulates MHC class II production while decreasing the production of Th1 cells, macrophages, IFNγ, and dendritic cell IL-12. Like other Th2 associated cytokines, IL-4 is involved in the airway inflammation observed in the lungs of patients with allergic asthma. The 11B11 monoclonal antibody has been shown to neutralize the bioactivity of natural or recombinant IL-4.