In vitro production of interleukin-1 receptor antagonist in IgG-mediated red cell incompatibility

Recently, proinflammatory cytokines including interleukin 1 (IL-1) have been implicated in the pathophysiology of immune-mediated hemolysis. Little is known, however, about the mechanisms by which inflammatory events in these reactions may be downregulated. IL-1 receptor antagonist (IL-1ra) inhibits the actions of IL-1 by competition for cellular receptors, and thus it may regulate the biologic actions of IL-1 during immune-mediated hemolysis. The production of IL-1ra by peripheral blood mononuclear cells (PBMNCs) in response to IgG-coated red cells in vitro was investigated.

Fresh PBMNCs were obtained by density gradient separation of heparinized whole blood. PBMNCs were cultured in the presence of anti-D-coated, Rh-positive red cells or uncoated Rh-negative red cells under nonadherent conditions. IL-1ra concentrations in the culture media were measured by enzyme-linked immunosorbent assay. IL-1ra and IL-1 beta gene expression was assessed by Northern blot analysis of PBMNC mRNA.

IL-1ra production was evident 4 hours after stimulation with IgG-coated red cells and increased progressively over 24 hours. Gene expression of IL-1ra was first detected at 2 hours, lagging behind that of IL-1 beta. IL-1ra gene expression was not inhibited by neutralizing polyclonal antibodies to IL-1. Immunocytochemical staining to determine the cellular source localized IL-1ra production to monocytes engaged in erythrophagocytosis. IL-1ra production was inhibited by dexamethasone (10(-7) M).

These results suggest that IL-1ra production may partly account for the variable pathophysiologic events seen in IgG-mediated autoimmune hemolysis and hemolytic transfusion reactions. Steroid treatment may also downregulate anti-inflammatory cytokine production in immune hemolysis.