A soluble form of IL-13 receptor alpha 1 promotes IgG2a and IgG2b production by murine germinal center B cells

A functional IL-13R involves at least two cell surface proteins, the IL-13R alpha 1 and IL-4R alpha. Using a soluble form of the murine IL-13R alpha 1 (sIL-13R), we reveal several novel features of this system. The sIL-13R pr omotes proliferation and augmentation of Ag-specific IgM, IgG2a, and IgG2b production by murine germinal center (GC)B cells in vitro. These effects we re enhanced by CD40 signaling and were not inhibited by an anti-IL4R alpha mAb, a result suggesting other ligands. In GC cell cultures, sIL-13R also p romoted IL-6 production, and interestingly, sIL-13R-induced IgG2a and IgG2b augmentation was absent in GC cells isolated from nd-deficient mice. Furth ermore, the effects of the sIL-13R molecule were inhibited in the presence of an anti-IL-13 mAb, and preincubation of GC cells with IL-13 enhanced the sIL-13R-mediated effects. When sIL-13R was injected into mice, it served a s an adjuvant-promoting production to varying degrees of IgM and IgG isotop es. We thus propose that IL-13R alpha 1 is a molecule involved in B cell di fferentiation, using a mechanism that may involve regulation of IL-6-respon sive elements. Taken together, our data reveal previously unknown activitie s as well as suggest that the ligand for the sIL-13R might be a component o f the IL-13R complex or a counterstructure yet to be defined.