Leukotriene D4 enhances immunoglobulin production in CD40-activated human B lymphocytes

Background: Cysteinyl-leukotrienes (cysLTs) are lipid mediators recognized for their role in asthma and allergic inflammation. CysLT(1), one of the receptors for cysLTs, is expressed, among others, in bronchial smooth muscle cells, phagocytes, and B lymphocytes. The potential role of CysLT(1) in B lymphocytes remains unexplored. Objective: We examined the modulation of expression and function of CysLT(1) in human B lymphocytes. Methods: Human B lymphocytes were purified from peripheral blood and analyzed by means of RT-PCR and flow cytometry, after culture with IL-4 and anti-CD40 antibody or CD154-transfected fibroblasts. Functional responses to leukotriene (LT) D-4 in terms of cytosolic calcium flux, proliferation, and immunoglobulin production were also examined. Results: B lymphocytes expressed CysLT1 at both the mRNA and protein levels. Two-fold to 3-fold enhancement of CysLT(1) expression was observed after B-cell exposure to a combination of activating anti-CD40 antibody and IL-4. The expression of CysLT1 was also enhanced when B lymphocytes were cocultured with CD154-transfected fibroblasts in the presence of IL-4. Moreover, IL-4 and CD40-activated B lymphocytes showed an increased responsiveness to LTD4 in terms of cytosolic calcium flux, which was totally prevented by the selective CysLT(1) antagonist montelukast. Stimulation of IL-4 and CD40-activated B lymphocytes with picomolar concentrations of LTD4 induced mature epsilon transcripts and upregulated IgE and IgG production 2-fold to 3-fold. Conclusion: We have demonstrated that expression of CysLT(1), can be upregulated in B lymphocytes after stimulation with CD154, with consequent increased responsiveness of the cells to LTD4 in terms of immunoglobulin production. Clinical implications: This study provides evidence that cysLTs generated during allergic reactions can affect B-cell function and enhance IgE and IgG production, which may further contribute to the allergic process.