Chronic graft-versus-host in Ig knockin transgenic mice abrogates B cell tolerance in anti-double-stranded DNA B cells

Anti-dsDNA Abs are specific diagnostic markers of systemic lupus erythematosus, and are also implicated in kidney pathology. Anti-dsDNA B cells have been shown to be tolerized in nonautoimmune mice. The immunodysregulation that causes these cells to break tolerance is presumably part of the fundamental defects in systemic lupus erythematosus. To explore these mechanisms, we used the chronic graft-versus-host model mediated by MHC class II differences. Induction of chronic graft-vs-host in anti-DNA H chain knockin (3H9.KI) transgenic mice on a nonautoimmune background resulted in specific activation of anti-dsDNA B cells, as evidenced by high titers of soluble Ab in sera and a high frequency (70%) of anti-dsDNA B cell clones recovered as hybridomas. In addition, the lambda(+)-anti-dsDNA B cells developed increased expression of cell surface activation markers, and concentrated in the T cell area of the follicle with an Ab-forming cell-compatible phenotype. Genetic analysis of the hybridoma clones showed strong evidence of secondary rearrangements of the L chain associated with anti-dsDNA reactivity. Thus, our study indicates that alloreactive T cell help can break tolerance in a complex manner, involving several events.

Selective enhancement of Leu-CAM expression by interleukin 6 during differentiation of human promonocytic U937 cells

Interleukin 6 (IL-6) is a cytokine with multiple biological activities on various tissues and cells. We have investigated the effect of recombinant human IL-6 (rhIL-6) on growth and differentiation of U937. Recombinant human IL-6 induced a dose-dependent growth inhibition, apparent around day 4, of up to 50% by day 8 of culture. Concomitant with this, changes in cytochemical activities were observed, indicative of differentiation. A panel of U937 antigens was analysed after culture with rhIL-6. Expression of the majority of these membrane antigens was unaffected, with the exception of two classes. First, rhIL-6 had a profound effect on members of the leucocytic cell adhesion molecules (Leu-CAM) family. Expression of the alpha-chain of CR3 (complement receptor 3; CD11b) was enhanced in a dose-dependent fashion, with maximal expression around day 7. Parallel to this a simultaneous increase in beta-chain (CD18) expression was found. Furthermore, enhanced expression of CR3 was, accompanied by increased rosetting with sheep erythrocytes sensitized with C3bi. A much lower, but significant, enhancement was observed for the alpha-chain of the p150,95 antigen (CD11c). Expression of leucocyte function-associated antigen-1, (LFA-1), (CD11a/CD18) remained unchanged. Remarkably, however, expression of a ligand of LFA-1, intercellular adhesion molecule-1 (ICAM-1; CD54), was enhanced with similar kinetics as CR3 and p150,95. A specific anti-rhIL-6 antiserum completely inhibited the IL-6 effect. These observations provide further support for an important role of IL-6 in the regulation of myeloid cell development in man.