CD40-mediated tumor necrosis factor receptor-associated factor 3 signaling upregulates IL-4-induced germline Cepsilon transcription in a human B cell line

Induction of germline C epsilon transcription in B cells by IL-4, which is a critical initiating step for IgE class switching, is enhanced by CD40 engagement. Although signaling by CD40 is initiated by the binding of tumor necrosis factor receptor-associated factor (TRAF) family members to its cytoplasmic domain, whether those TRAF family proteins mediate enhancement of germline Cepsilon transcription is not evident. We report here that CD40-induced TRAF3-dependent activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase 1 (MEK1) is involved in the upregulation of IL-4-driven germline C epsilon transcription in a human Burkitt's lymphoma B cell line, DG75. Among the six known TRAF proteins, TRAF2, 3, 5, and 6 associated with CD40 in an unstimulated state, and the levels of these four proteins were unaffected by anti-CD40 stimulation. Antisense oligodeoxynucleotide (ODN) for TRAF3 inhibited CD40-induced activation of MEK1-ERK pathway by decreasing expression of TRAF3 protein, but antisense ODNs for TRAF2, 5, and 6 were ineffective. Furthermore, CD40-mediated enhancement of IL-4-driven germline C epsilon transcription was inhibited by antisense ODN for TRAF3 and by a MEK1 inhibitor, PD98059. These results suggest that in DG75 cells, TRAF3-induced MEK1 activation may be involved in CD40-mediated upregulation of IL-4-driven germline C epsilon transcription.

Expression of epsilon germ-line gene transcripts and mRNA for the epsilon heavy chain of IgE in nasal B cells and the effects of topical corticosteroid

We have studied the expression of the gene encoding the epsilon heavy chain of IgE in nasal B cells of hayfever patients. We developed probes to detect transcripts of the epsilon germ-line gene and the rearranged gene by in situ hybridization of biopsy sections from the nasal mucosa. We compared tissue from hayfever patients out of season with that of normal controls, and also of hayfever patients treated with topical corticosteroid (fluticasone propionate) or placebo for 6 weeks and then challenged with antigen. epsilon chain mRNA was expressed in an unexpectedly high proportion of nasal B cells of both hayfever patients and normal subjects. However, although similar numbers of B cells were found in both groups, the proportion of cells that express epsilon chain mRNA was several times higher in the hayfever patients. No transcripts of the epsilon germ-line gene were detected in either group before allergen challenge. When hayfever patients were administered antigen locally, early (10-30 min) and late (1-24 h) symptoms ensued. After 24 h, coincident with an increase in the number of cells expressing mRNA for IL-4 in the tissue, epsilon germ-line gene transcripts appeared in the nasal B cells. The induction by allergen of IL-4 mRNA and epsilon germ-line gene transcripts was suppressed by fluticasone propionate treatment. Our results suggest that local IgE synthesis and cytokine regulation of heavy chain switching to IgE occur in the nasal mucosa.

The organic component of diesel exhaust particles and phenanthrene, a major polyaromatic hydrocarbon constituent, enhances IgE production by IgE-secreting EBV-transformed human B cells in vitro

Suspended airborne particulate matter such as diesel exhaust particles (DEP) have been implicated in the increased incidence of respiratory allergic diseases that has occurred over the past century. Studies in vitro and in vivo have shown that DEP may enhance allergic antibody (IgE) expression. DEP contain a wide spectrum of polycyclic aromatic hydrocarbons (PAH) that have been reported to have direct effects on the immune system, including the modulation of IgE production using various human and murine cell populations. We investigated the effects of the organic extract of DEP (PAH-DEP) and particularly, phenanthrene, a major component of DEP, in vitro on IgE production by 2C4/F3, a human Epstein-Barr virus transformed isotype switched, IgE producing B cell line. Phenanthrene consistently enhanced 2C4/F3 IgE production two- to threefold. This in vitro enhancement was associated with an increased expression of total IgE mRNA. Furthermore, the pattern of mRNA's coding for distinct isoforms of the epsilon chain was altered by both DEP-PAH and phenanthrene. While phenanthrene increased the level of productive epsilon transcripts, it did not increase epsilon germ line transcription. These effects were not due to an alteration of the cell cycle. Unstimulated 2C4/F3 cells contained detectable mRNA for IL6, IL10, TNF-alpha, and interestingly IL4; however, addition of PAH-DEP or phenanthrene did not significantly alter the level of these cytokines and thus did not appear to account for our findings. Thus, we have used our in vitro model to dissect the mechanism of DEP-PAH on IgE production in postswitch IgE producing cells and shown that phenanthrene, an important component in DEP and other pollutants, can act in a similar manner.