Suppression of B-cell proliferation to lipopolysaccharide is mediated through induction of the nitric oxide pathway by tumor necrosis factor-α in mice with acute graft-versus-host disease

Abstract

Graft-versus-host disease (GVHD) is associated with impaired B-cell responses. We investigated the mechanism of impaired proliferation of B cells in response to the mitogen lipopolysaccharide (LPS) by analyzing the production of tumor necrosis factor-α (TNF-α) and nitric oxide (NO), both of which have independently been described as important effector mechanisms in the pathogenesis of acute GVHD. A threefold decrease of mature surface Ig- positive (sIg+) B cells was observed in GVHD spleens isolated 2 weeks after transplant. However, proliferation of these cells in response to LPS was suppressed by more than 35-fold. Activated GVHD splenocytes secreted large amounts of TNF-α and NO in culture. Neutralization of TNF-α with anti-TNF- α antibody (Ab) both abrogated NO production and restored LPS-induced proliferation of B cells to levels found in non-GVHD control mice. The specific inhibition of NO synthesis with L(G)-monomethyl-arginine (NMMA) restored splenocyte responses but did not significantly reduce TNF-α levels, showing that TNF-α per se did not cause immunosuppression. These data show that, during GVHD, induction of the NO pathway is an important mechanism that mediates B-cell hyporesponsiveness to LPS and that this pathway is induced by TNF-α.