REGULATION OF CYTOKINE EXPRESSION BY AN AUTOREACTIVE B-CELL CLONE DERIVED FROM MRL MP-LPR/LPR MICE/

The B cell line, MRL159.5, was established by somatic hybridization be tween splenic MRL/MP-1pr/1pr (1pr) mice B cells and 2.52M, a hypoxanth ine-aminopterine-thymidine (HAT) medium-sensitive B cell line mutant. It possessed a receptor molecule for mouse erythrocytes treated with b romelain (Br-MRBC) on its surface, likely to be an autoreactive B cell clone specific for Br-MRBC as detected by rosette-forming assay with Br-MRBC. MRL159.5 spontaneously produced IL-6 and secreted IgM, and wa s induced to augment IgM secretion when treated with Br-MRBC or IL-6. Triggering of CD40 led to an augmentation of IgM secretion as well as IL-6 expression. Blocking the binding of IL-6 to its cellular receptor through the use of inhibitory antibodies inhibited CD40-induced IgM s ecretion, suggesting a possible autocrine role of IL-6 for CD40-induce d differentiation of this B cell hybridoma. Addition of IL-4 or Br-MRB C augmented IL-6 expression as well as IgM secretion by CD40-activated MRL159.5 cells. CD40 also augmented tumour necrosis factor-alpha (TNF -alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF) expression but resulted in decreased IL-10 expression. Furthermore, un der conditions where IL-6 expression was augmented, IL-6R alpha (gp80) expression was downregulated, suggesting a negative feedback mechanis m of an IL-6 autocrine loop in this hybridoma. These results demonstra te a role by which T cell-dependent activation through CD40 regulates an IL-6 autocrine loop, controlling differentiation of autoreactive B cells in autoimmune disease.