Human cells treated with interferon synthesize two proteins that exhibit high homology to murine Mxl protein, which has previously been identffied as the mediator of interferon-induced cellular resistance of mouse cells against influenza viruses. Using murine Mxl cDNA as a hybridization probe, we have isolated cDNA clones originating from two distinct human Mx genes, designated MxA and MxB. In human fibroblasts, expression of MxA and MxB is strongly induced by alpha interferon (IFN-a) Influenza viruses are important human pathogens (35), and one might therefore expect that humans possess a very efficient influenza virus defense system. During the course of viral infections, including influenza virus infections, interferons (IFNs) are synthesized which, in turn, induce an antiviral state in cells surrounding the initial site of virus replication. It is believed that IFNs thus help to limit virus spread and permit the immune system to destroy the invading virus without causing severe tissue damage. The beneficial role of IFNs in host defense against many viruses has been documented in animal model systems (see reference 7 for a review), suggesting that IFN may play a similar role in humans. From an experimental mouse model of influenza virus resistance, we have concluded that IFN exerts its protective effect through the activation of a cellular resistance gene, designated Mx (see reference 30 for a review). Exposure of mouse cells to IFN induces the synthesis of the 72-kilodalton (kDa) Mxl protein, which, in turn, is capable of selectively blocking the multiplication of influenza viruses (1, 21, 31). The molecular mechanism principally responsible for the IFN-mediated inhibition of influenza virus multiplication is not yet resolved (16,20,25).Evidence in favor of a similar influenza virus defense system in humans includes the observations that IFN can block influenza virus multiplication very efficiently in cultured human fibroblasts (10) and that IFN treatment causes the accumulation of an Mx-related protein in these cells (11,29). This Mx-related human protein has an apparent molecular mass of about 78 kDa, and, unlike murine Mxl protein, it accumulates in the cell cytoplasm rather than the nucleus. Although available data are compatible with the view that the Mx-related human protein plays a role in defense against * Corresponding author. influenza virus, no direct experimental evidence supporting this notion has yet been presented.One approach to the elucidation of the physiological role of Mx-like proteins of humans is to molecularly clone the human Mx cDNAs and then to express them in transfected cells and to test such cells for newly acquired functions, in particular influenza virus resistance. In this paper we report the first step toward this goal, the isolation and characterization of two Mx-related human cDNAs. We show that the corresponding mRNAs originate from two distinct human Mx genes; the expression of both genes is stimulated by IFN-a, IFN-P, Newcastle disease virus (NDV), and, to a lesser extent...

Mouse Mx protein, an interferon (IFN)-induced nuclear protein, confers selective resistance to influenza virus. We show here that, as with influenza virus-resistant Mx+ mouse embryo cells, influenza virus mRNA accumulation and protein synthesis are strongly inhibited in rat embryo cells treated with IFN-0d$. IFN-x$/ induced in rat cells the synthesis of Mx-related mRNAs migrating on Northern (RNA) gels as two bands of about 3.5 and 2.5 kilobases which directed the synthesis of three electrophoretically distinct proteins called rat Mx proteins 1, 2, and 3. The three rat proteins were antigenically related to the mouse Mx protein but differed in molecular weight and intracellular location. Rat Mx protein 1 was found predominantly in the nucleus and, on the basis of several criteria, resembled the nuclear mouse Mx protein. It was induced by IFN-aI/, in all 28

Accumulation of Mx gene products in cells of patients and experimental animals has been recognized as a useful marker for detecting minute quantities of biologically active interferon (IFN). Goetschy et al. (J. Goetschy, H. Zeller, J. Content, and M. A. Horisberger, J. Virol. 63:2616-2622, 1989) reported that not only IFNs but also interleukin-1 (IL-1) and tumor necrosis factor (TNF) were potent inducers of the human Mx genes. However, we observed no Mx induction in cultured human fibroblasts or in human peripheral blood mononuclear cells treated with various concentrations of IL-1 alpha or TNF-alpha. Mx induction was found in the spleens of mice treated with TNF-alpha or IL-1 alpha, but this effect could be neutralized with antibodies to murine IFN-alpha/beta. Of the other cytokines that we tested (IL-2, IL-6, and granulocyte-macrophage colony-stimulating factor), only IL-2 induced the Mx genes in peripheral blood mononuclear cells, but antibodies to human IFN-beta efficiently neutralized this effect. Our results thus indicate that IFNs are the only cytokines with intrinsic Mx-inducing activity.

The human MxA protein can be detected in the cytoplasm of IFN-alpha/beta-treated cells, whereas other cytokines, including IFN-gamma, are poor inducers. Because IFN-alpha/beta is predominantly synthesized in response to viral infections, MxA protein should be detectable in virally infected tissue. Biopsy specimens (n = 64) of 12 different dermatoses were therefore screened with an MxA-specific monoclonal antibody on formalin-fixed, paraffin-embedded and microwave-treated tissue sections. As expected, high amounts of MxA protein were found in acute viral skin lesions (chickenpox, Herpes zoster, and Herpes labialis). In addition, MxA protein was also detected in some inflammatory skin lesions of unknown etiology (lupus erythematosus, lichen planus, Schoenlein-Hennoch's anaphylactoid purpura and psoriasis). MxA protein was not found in non-viral infections (bacterial, mycotic, and parasitic) and was also not detectable in various other dermatoses (eczema, scleroderma, urticaria, granulomatous and bullous disorders). MxA staining proved a reliable, sensitive histochemical viral marker for infectious dermatoses. The positive results in non-infectious inflammatory dermatoses might implicate viral involvement or activation of the IFN system by thus far unknown mechanisms.

The present study deals with the detailed investigation of the IgE antibody response of a gum arabic-allergic patient. The patient showed multiple serologic and skin test sensitizations to a range of pollen, other inhalants and foods, and bee venom, and to the recombinant allergens Bet v 1 and Bet v 2. Moreover, the patient's serum reacted strongly to gum-arabic extract. The NaIO4-treated and thus deglycosylated extract showed no binding to IgE. In contrast, removal of the protein backbone by basic hydrolysis did not deplete the IgE reactivity. Therefore, it is concluded that the gum arabic-specific IgE antibodies of this patient were mainly directed against the carbohydrate fraction of this material. In IgE-inhibition assays, cross-reactions occurred in the range of 60% between gum arabic and known immunogenic N-glycans containing alpha1-3-linked fucose. Since the inhibition graphs were not parallel and the inhibition was not complete with heterologue antigens, the cross-reacting epitopes of gum arabic appeared to be different from the latter well-known cross-reactive carbohydrate determinants (CCD). Inhibition may have been caused by a partial immunologic identity of the investigated carbohydrate moieties. A strong IgE response to the fucose-containing glycan from bromelain was measured in a glycan ELISA that utilizes purified glycopeptides at the solid phase. This response, which may explain the multiple sensitizations without clinical significance diagnosed in the patient, could originate from inhalation of pollen, which is known to contain similar glycans, or from occupational sensitization during work as a baker and confectioner. Since the gum-arabic protein showed only very weak participation in the IgE reactivity, the clinical symptoms of the patient caused by gum arabic may be attributed to carbohydrate epitopes. Due to the repetitive polysaccharide sequence of gum arabic, several epitopes for the cross-linking of IgE should exist.