Immunomodulation with soluble IFN-gamma receptor: preliminary study

A bivalent immunoadhesin of the human interferon-gamma receptor is an effective inhibitor of IFN-gamma activity

We describe here the bioengineering of a bivalent IFN-gamma-RFc immunoadhesin consisting of the extracellular domain of the human IFN-gamma receptor alpha chain (IFN-gamma-R) fused to a human IgG1 Fc region (encoding hinge, CH2 and CH3 domain) that was efficiently expressed as a covalently linked homodimer in insect cells and purified in a one-step purification procedure. The IFN-gamma-RFc fusion protein exerted a 3-fold higher ligand binding affinity in binding competition studies in vitro compared with the monovalent extracellular IFN-gamma-R domain. In addition, the in vitro antagonistic activity of IFN-gamma-RFc, as determined by inhibition of IFN-gamma-induced virus protection and HLA-DR expression, was more than 30-fold higher in comparison with the monovalent soluble receptor. The described IFN-gamma-R immunoadhesin is a potential therapeutic reagent to interfere with the disease-promoting activities of IFN-gamma in several autoimmune diseases.

The sigma ligand SR 31747 prevents the development of acute graft-versus-host disease in mice by blocking IFN-gamma and GM-CSF mRNA expression

SR 31747 is a sigma ligand which prevents the development of acute graft-versus-host reaction (GvHR) in hybrid B6D2F1 mice injected with C57BL/6 parental spleen cells. In the present study, we showed that this drug dramatically impaired the GvHR-associated increase in the numbers of both B-lymphocytes and polymorphonuclear cells (PMNs) in the spleen. Because SR 31747 blocked the GvHR-induced expression of both interleukin-2 and transferrin receptors on T-lymphocytes, it is very likely that this molecule prevented the disease through an inhibition of T-lymphocyte activation. Cytokine messenger RNA analyses on spleen cells revealed that SR 31747 blocked IFN-gamma and GM-CSF but not IL-4 transcription. These effects, which are different from those observed with either cyclosporin-A or dexamethasone, strongly suggest that SR 31747 preferentially inhibits the Th1 lymphocyte subset.

The myxoma virus-soluble interferon-gamma receptor homolog, M-T7, inhibits interferon-gamma in a species-specific manner

The myxoma virus M-T7 protein contains significant sequence similarity to the ligand binding domain of the mammalian interferon-gamma receptors, and functions as a soluble homolog which can bind and inhibit the biological activities of rabbit interferon-gamma (Upton, C., Mossman, K., and McFadden, G. (1992) Science 258:1369-1372). M-T7, the most abundantly secreted protein from myxoma virus-infected cells, was shown to be expressed in significant biological amounts as a typical poxvirus early gene product, efficiently secreted at early times of infection to levels that exceed 5 x 10(7) molecules/cell, and function as a stable inhibitory protein in infected cell supernatants until late times of infection. M-T7 was specific in binding and inhibiting rabbit interferon-gamma, and did not bind either human or murine interferon-gamma. Scatchard analysis of rabbit interferon-gamma binding curves yielded a single high affinity binding site on M-T7, with a Kd of 1.2 x 10(-9) M, which is comparable to the affinity between soluble forms of cellular interferon-gamma receptors and their cognate ligands. In comparison, rabbit interferon-gamma was shown to bind its cellular receptor with a Kd of 5.9 x 10(-10) M, again comparable to the affinity of membrane bound forms of other mammalian interferon-gamma receptors for interferon-gamma. Thus, the myxoma virus M-T7 protein is a functional soluble interferon-gamma receptor homolog which binds and inhibits interferon-gamma with high affinity in a species-specific manner.