An Interleukin 4 (II,-4) Mutant Protein Inhibits both IL-4 or II.-13-induced Human Immunoglobulin G4 (IgG4) and IgE Synthesis and B Cell Proliferation: Support for a Common Component Shared by II,-4 and IL-13 Receptors

L-4 directs mouse and human B cells to produce, respectively, IgG1 and IgE or IgG4 and IgE (1-6) . Recently, we (7) and others (8) cloned and expressed another T cellderived cytokine (IL-13) . As with IL-4, IL-13 induces human B cells to switch to IgG4 and IgE production in an IL-4independent fashion (7-9, 10) . IL-13 shares many other properties with IL-4 . Like IL-4, it has growth-promoting effects on preactivated B cells (7, 9) and it suppresses the production of the proinflammatory rytokines (IL-la, (3, IL-6, IL-8, and TNF-ca) and other monokines (GM-CSF, M-CSF, GCSF, IL-10, and IL-12) by activated monocytes, whereas, it enhances the production of the IL-1R antagonist (10a) . In addition, IL-13 modulates the expression of various surface molecules