Crystal Potter

Basophils Initiate IL-4 Production during a Memory T-dependent Response

Experiments were performed to characterize and identify the cellular sources of the secondary interleukin (IL)-4 response to a T cell–dependent antigen. Mice were primed by immunization with goat anti–mouse immunoglobulin (Ig)D antibody (GaMD), which stimulates naive CD4+ T cells to secrete IL-4 in 3–4 d. When challenged with goat serum 14 d after immunization, GaMD-primed mice generated an IL-4 response that exceeded the primary response by ∼100-fold, started in <2 h, and lasted for 4 d. Studies with 4get mice, in which cells with an accessible Il4 gene express a green fluorescent protein (GFP), revealed CD4+ memory T cells, natural killer T cells, basophils, mast cells, and eosinophils as possible rapid producers of IL-4. GFP+CD4+ T cells and basophils expanded more in the spleen than the other cell types during the primary response to GaMD. Quantitation of in vivo IL-4 production by the in vivo cytokine capture assay after individual cell types were selectively stimulated or deleted demonstrated that basophils and memory CD4+ T cells account for most of the secondary IL-4 response, with basophils initiating that response through IgE/FcɛRI-mediated signaling but secreting IL-4 for <4 h and memory T cells secreting IL-4 within 4 h and continuing to secrete this cytokine for 4 d.

Selective stimulation of IL-4 receptor on smooth muscle induces airway hyperresponsiveness in mice

IL-4Rα expression on airway smooth muscle cells is sufficient for the development of airway hyperresponsiveness.

Differences in expression, affinity, and function of soluble (s)IL-4Rα and sIL-13Rα2 suggest opposite effects on allergic responses.

IL-4 and IL-13 are each bound by soluble receptors (sRs) that block their activity. Both of these sRs (sIL-4Rα and sIL-13Rα2) are present in low nanogram per milliliter concentrations in the serum from unstimulated mice, but differences in affinity and half-life suggest differences in function. Serum IL-4/sIL-4Rα complexes rapidly dissociate, releasing active IL-4, whereas sIL-13Rα2 and IL-13 form a stable complex that has a considerably longer half-life than uncomplexed IL-13, sIL-13Rα2, IL-4, or sIL-4Rα. Approximately 25% of sIL-13Rα2 in serum is complexed to IL-13; this percentage and the absolute quantity of sIL-13Rα2 in serum increase considerably during a Th2 response. sIL-13Rα2 gene expression is up-regulated by both IL-4 and IL-13; the effect of IL-4 is totally IL-4Rα-dependent while the effect of IL-13 is partially IL-4Rα-independent. Inhalation of an IL-13/sIL-13Rα2 complex does not affect the expression of IL-13-inducible genes but increases the expression of two genes, Vnn1 and Pira-1, whose products activate APCs and promote neutrophilic inflammation. These observations suggest that sIL-4Rα predominantly sustains, increases, and diffuses the effects of IL-4, whereas sIL-13Rα2 limits the direct effects of IL-13 to the site of IL-13 production and forms a stable complex with IL-13 that may modify the quality and intensity of an allergic inflammatory response.