Cross-linking of both Fc gamma RI and Fc gamma RII induces secretion of tumor necrosis factor by human monocytes, requiring high affinity Fc-Fc gamma R interactions. Functional activation of Fc gamma RII by treatment with proteases or neuraminidase.

Cross-linking of Fc gamma R on human monocytes with human IgG has been shown to induce secretion of the inflammatory and immunoregulatory cytokine TNF. In the present study we examined the role of both constitutively expressed monocyte Fc gamma R, the 72-kDa high affinity Fc gamma R (Fc gamma RI), and the 40-kDa low affinity receptor (Fc gamma RII), in the induction of TNF secretion. On the basis of preferential binding of the Fc moiety of murine mAb of different isotype, Fc gamma RI and Fc gamma RII were selectively cross-linked by using either solid-phase murine (m)IgG2a, or solid-phase mIgG1, respectively. On freshly isolated, untreated monocytes only cross-linking of Fc gamma RI with solid-phase mIgG2a induced TNF secretion. The interaction between Fc gamma RII and mIgG1 could be enhanced by treatment of monocytes with proteases or with the desialylating enzyme neuraminidase. After treatment of monocytes with these enzymes, TNF secretion was effectively induced by solid-phase mIgG1, apparently through cross-linking of Fc gamma RII. However, mIgG1-induced TNF secretion differed between protease-treated monocytes from high responder individuals and monocytes from low responder individuals, TNF secretion being considerably less in the latter population. Protease-treated monocytes and mononuclear cells from individuals with an inherited defect in cell membrane expression of Fc gamma RI were induced to secrete TNF by solid-phase human IgG, confirming the capacity of Fc gamma RII to induce TNF secretion. It was not possible to induce TNF secretion by cross-linking Fc gamma RI or Fc gamma RII with anti-Fc gamma R mAb and soluble or solid-phase anti-mIgG, indicating that high affinity Fc-Fc gamma R interactions are necessary to induce release of this cytokine.

Fc-receptor cross-linking induces rapid secretion of tumor necrosis factor (cachectin) by human peripheral blood monocytes.

In this study it was demonstrated that cross-linking of FcR on human monocytes induces the secretion of the cytotoxic and immunoregulatory cytokine TNF. Both soluble and insoluble immune complexes, solid-phase antibody and antibody-coated phagocytizable particles were used to cross-link FcR on monocytes. It was observed that monocytes secreted large amounts of TNF in each of these instances. Kinetic studies performed with soluble immune complexes showed that TNF was secreted very rapidly, e.g., within 2 h after addition of immune complexes to monocytes. These findings are relevant for the understanding of FcR-mediated immune responses by monocytes and macrophages, for example antibody-dependent cellular cytotoxicity and phagocytosis, and for disease states associated with circulating or tissue-fixed immune complexes.