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Background: The role of CD8 + T cells in IgE synthesis remains unclear. Objective: The aim of this study was to investigate IL-4 production and CD40 ligand expression by human CD8 + T cells. Methods: We conducted functional and phenotypic analyses of human T cells in peritoneal washings from severe combined immunodeficiency mice reconstituted with PBMCs from normal and atopic human donors. We also examined the expression of IL-4 and CD40 ligand by CD8 + T cells from a patient with adenosine deaminase deficiency who received autologous T cell–directed gene therapy. Results: Transfer of atopic cells into the mice caused production of IgE and IgG with increased expression of IL-4 and CD40 ligand mRNA. In addition, both intracellular IL-4 and cell surface CD40 ligand were detected in CD8 + and in CD4 + T cells. CD8 + T-cell lines generated from the patient's T cells carrying the adenosine deaminase gene expressed not only IL-4 mRNA and protein but also CD40 ligand mRNA and protein after being stimulated with an anti-CD3 mAb. After anti-CD3 stimulation and paraformaldehyde fixation, CD8 + T cells induced IgE synthesis by normal human B cells in the presence of recombinant IL-4. Conclusion: Taken together, these results demonstrate that IL-4–producing and CD40 ligand–expressing CD8 + cells are detectable among human T cells and suggest that such cells may promote IgE production by B cells under some conditions. (J Allergy Clin Immunol 1999;103:S405-11.)

Nuclear factor-kappa B (NF-kappa B) is a transcription factor that binds to the consensus DNA sequence in the cis-acting elements of various genes. Although NF-kappa B activates the expression of many genes involved in immune and inflammatory responses, little is known about the role of NF-kappa B activation in the induction of IgE synthesis in human B cells. Therefore we first examined the participation of NF-kappa B in germline C epsilon transcription in a human Burkitt lymphoma B cell line, DND39. Stimulation of DND39 cells with IL-4 or anti-CD40 monoclonal antibody (mAb) activated phosphatidylinositol 3-kinase and subsequently induced nuclear expression of NF-kappa B, which was identified by electrophoretic mobility shift assays. n-Acetyl-L-cysteine (NAC), a potent antioxidant, blocked NF-kappa B activation caused by IL-4 and by anti-CD40 mAb. Although inhibition of IL-4-driven germline C epsilon transcription by NAC was not sufficient, the agent remarkably diminished anti-CD40 mAb-mediated up-regulation of germline C epsilon transcription. Second, we studied the effect of NAC on IgE synthesis in human normal B cells costimulated with IL-4 and anti-CD40 mAb. NAC was effective in inhibiting mature C epsilon transcription and IgE synthesis in the T cell-independent culture system. However, NAC did not significantly affect the spontaneous production of IgE by atopic B cells. These results indicate that NF-kappa B activity is commonly inducible in DND39 cells by IL-4 and anti-CD40 mAb and suggest that NF-kappa B sensitive to NAC may play a role in regulating IgE synthesis in B cells.

IL-4 with the IgE-inducing activity is shown to upregulate the expression of IL-4 receptor (IL-4R) on lymphocytes. Antisense strategy was used that aimed at investigating the significance of IL-4-induced upregulation of IL-4R on B cells in human IgE production. When an antisense phosphorothioate oligodeoxynucleotide to IL-4R (S-oligo 1) was added to B cells together with IL-4, the agent selectively abrogated the upregulation of IL-4R without affecting its constitutive level expression. Moreover, S-oligo 1 had a suppressive effect on the T-cell-independent synthesis of IgE by B cells costimulated with IL-4 and anti-CD40 antibody. This suppression was accompanied by inhibition of mature but not germline C epsilon transcription. These findings indicate that constitutively expressed IL-4R provides a signal or signals responsible for the induction of germline C epsilon transcription and suggest that IL-4R upregulation may be required for the subsequent class switch recombination that leads to mature C epsilon transcription and IgE synthesis. The IL-4R signal transduction mechanism underlying germline C epsilon transcription was also analyzed in a human Burkitt lymphoma B-cell line, DND39. Induction of germline C epsilon transcripts in DND39 cells by IL-4 required at least two distinct signaling cascades. One was mediated by enhancement of tyrosine phosphorylation of a 57 kd protein associated with phospholipase C-gamma 1 (PLC-gamma 1) that resulted in PLC-gamma 1 activation, inositol lipid hydrolysis, and protein kinase C delta translocation. The other was dependent on phosphatidylinositol 3-kinase, whose activation induced protein kinase C zeta translocation. In fact, kinase inhibitors such as herbimycin A, K-252a, and wortmannin were effective in inhibiting IL-4-induced germline C epsilon transcription. Therefore, in addition to activation of protein tyrosine kinases, coordinated actions of PLC-gamma 1 and phosphatidylinositol 3-kinase may be involved in IL-4-driven germline C epsilon transcription in DND39 cells.