Immunostimulatory CpG-oligodeoxynucleotides induce a factor that inhibits macrophage adhesion

Abstract

Selected phosphorothioate oligodeoxynucleotides containing CpG (CpG-ODN) activate immune responses, including immunoglobulin synthesis, B cell proliferation, and cytokine production by monocytes. We examined the effect of a CpG-ODN(1760) on the adhesion of macrophages derived from human blood monocytes in vitro. CpG-ODN (6 μg/mL) completely inhibited the adherence of macrophages to plastic or glass during 7 or more days of culture. A non-CpG control ODN (1814) was without effect. Two other CpG-ODNs (1826 and 1842) also completely inhibited macrophage adherence. The specific inhibitor of CpG-ODN, quinacrine (0.1 μmol/L), blocked this action. CpG-ODN reduced the rate of senescence and cell death of monocytes in culture but did not influence their phagocytosis, procoagulant activity, or support of the mixed lymphocyte-response. Four days of exposure of monocytes to CpG-ODN up-regulated the expression of the endotoxin receptor CD14 and down-regulated the mannose (scavenger) receptor, a result that is consistent with blocking the maturation of monocytes to macrophages. Incubation of peripheral blood monocytes (PBMCs) with CpG-ODN resulted in the generation of a heat labile factor that inhibited macrophage differentiation and accounts for the efficacy of the CpG-ODN. T cells selected from PBMCs by magnetic beads generated the majority of this factor. Cytokines (interleukin-3 (IL-3], IL-4, IL-6, IL-10, interferon-γ, tumor necrosis factor-α transforming growth factor-β, granulocyte-macrophage colony-stimulating factor, monocyte chemotactic protein-1) did not inhibit macrophage adherence like CpG-ODN did. Antibodies to IL-6 or IL-10 did not block the activity of CpG-ODN. Dexamethasone inhibited macrophage adherence, and lipopolysaccharide had a minor effect. We conclude that immunostimulatory CpG-ODNs inhibit macrophage adherence by provoking the production of an unidentified heat-labile factor.