Interleukin-4 signaling in B lymphocytes from patients with X-linked severe combined immunodeficiency

Interleukin-4 (IL-4) is an important cytokine for B and T lymphocyte function and mediates its effects via a receptor that contains gamma(c), B cells derived from patients with X-linked severe combined immunodeficiency (X-SCID) are deficient in gamma(c) and provide a useful model in which to dissect the role of this subunit in IL-4-mediated signaling. me found that although IL-4 stimulation of X-SCID B cells did not result in Janus tyrosine kinase-3 (JAK3) phosphorylation, other IL-4 substrates including JAK1 and IRS-1 were phosphorylated, Additionally, we detected signal transducers and activators of transcription 6 (STAT6) tyrosine phosphorylation and DNA binding activity in X-SCID B cells with a wide range of gamma(c) mutations. However, reconstitution of these X-SCID B cells with gamma(c) enhanced IL-4-mediated responses including STAT6 phosphorylation and DNA binding activity and resulted in increased CD23 expression. Thus, gamma(c) is not necessary to trigger IL-4-mediated responses in B cells, but its presence is important for optimal IL-4-signaling, These results suggest that two distinct IL-4 signaling pathways exist.