Mouse cells carrying the dominant resistance gene Mx develop a more efficient antiviral state toward influenza viruses in response to interferon than do Mx-negative cells. We have identified an Mx gene-associated product by labeling cultured peritoneal macrophages and embryonic cells with [3S]methionine in the presence or absence of interferon. The radioactive proteins from unfractionated cytoplasmic extracts were separated electrophoretically in two dimensions and were revealed by fluorography. A protein with a Mr of 72,500 and an isoelectric point of 6.3 was induced by mouse interferon type I (a mixture of a and (3 interferons) in cells carrying the gene Mx but not in cells lacking Mx. The induction of this protein could be blocked by actinomycin D. The maximal rate of synthesis was reached in embryonic cells 4-5 hr after treatment with 103 reference units of interferon per ml. When the allele Mx (present in the inbred mouse strain A2G)was repeatedly backcrossed on different genetic backgrounds (BALB/c, C57BL/6, A/J), a clear correlation between the inducibility by interferon of this protein and the presence of the allele Mx was observed. The results suggest that this protein induced by the interaction of interferon with Mx plays a role in the selective antiviral state against influenza viruses that is observed in interferon-treated Mx-bearing cells.

MxA gene expression is known to be regulated tightly and exclusively by type I interferons (IFNs). The kinetics of MxA gene expression was analyzed in peripheral blood mononuclear cells from 11 healthy volunteers vaccinated with the 17-D strain of yellow fever virus. A reliable induction of MxA RNA and MxA protein was found in the absence of easily detectable serum IFN activity. Thus, steady-state MxA RNA levels were elevated 8-to 30-fold above prevaccination levels on day 5 after vaccination. The average increase of MxA protein was --50-fold. In contrast, no induction of MxA RNA or MxA protein was detectable in 3 similarly vaccinated controls who were immune because of previous vaccinations. The IFN marker 2'-5'-oligoadenylate (2-5A) synthetase known to react to both type I and type II IFNs showed a similar response but did not differentiate equally well between nonimmune and immune vaccinees. P2-microglobulin and neopterin reacted poorly, remaining at low levels within the normal range. These results demonstrate that MxA gene expression is a good marker for detecting minute quantities of biologically active type I IFN during viral infections.Interferons (IFNs) are produced in response to viral infection and contribute to host defense by establishing an antiviral state in target cells [I]. Viruses induce predominantly two classes of IFNs, namely IFN-a and IFN-{1, collectively called type I IFNs [2]. It is not always possible, however, to detect circulating type I IFNs in the serum of patients most likely because type I IFNs are produced early in infection and may no longer be present in later serum samples or may not be formed in detectable quantities. For example, serum IFN is not usually found in patients with acute viral hepatitis [3,4], although IFN-induced changes occur in the liver and are suggestive oflocal IFN production and action [5]. Therefore, more reliable alternatives to direct serum IFN measurements are needed.Several assays have been developed that are based on the capacity of IFNs to induce expression of IFN-responsive genes in peripheral blood mononuclear cells (PBMC). Increased levels of an IFN-induced gene product indicate that the cells have been exposed to IFN in vivo and are respond-

Human chromosome 21 has been analyzed by pulsed‐field gel electrophoresis using somatic cell hybrids containing limited regions of the chromosome and greater than 60 unique sequence probes. Thirty‐three independent NotI fragments have been identified, totalling 43 million bp. This must account for essentially the entire long arm, and therefore gaps remaining in the map must be small. The extent of the pulsed‐field map has allowed the direct correlation of the physical map with the cytogenetic map: translocation breakpoints can be unambiguously positioned along the long arm and the distances between them measured in base pairs. Three breakpoints have been identified, providing physical confirmation of cytogenetic landmarks. Information on sequence organization has been obtained: (i) 60% of the unique sequence probes are located within 11 physical linkage groups which can be contained in only 20% of the long arm; (ii) 9/21 genes are clustered within 4%; (iii) translocation breakpoints appear to occur within CpG island regions, making their identification difficult by pulsed‐field techniques. This analysis contributes to the human genome mapping effort, and provides information to guide the rapid investigation of the biology of chromosome 21.

SUMMARYA recombinant interferon (IFN) hybrid has been found to have a broad host-range of activity in an antiviral assay (plaque reduction of vesicular stomatitis virus) and also high efficacy as an antiviral agent in at least 12 different animal cell species. The IFN hybrid consists of amino acids 1 to 60 from HulFN-c~B and amino acids 61 to 166 from HuIFN-c~D. The profile of cross-species activity of the IFN-,B/D hybrid has been compared with that of HulFN-c~F, and of the parents HulFN-c~B and -c~D. When both IFN-c~B and -aD were active in a cell species, the hybrid IFN had comparable or better activity than the more active parental IFN. The hybrid shared a broad cross-species activity with IFN-c~D. However, the IFN-c~B/D hybrid was 10-fold more active on human cells, 30-fold more active on rabbit cells, and 50-fold more active on mouse cells than IFN-~D.Numerous studies using crude or partially purified mixtures of interferon (IFN) have shown that these preparations usually exert antiviral activity in a defined variety of cell species (for review, see Stewart, 1981). These studies were refined when recombinant IFN became available, when it was observed that the profile of host-range specificity could vary widely between individual species of IFN (Streuli et al., 1981;Yelverton et al., 1981;. Cross-species efficacy has proved to be a useful biological parameter to discriminate between IFN-c~ hybrids constructed by combining gene fragments of individual species of HulFN-c~. In particular, the spectrum of activity of some IFN-~A/D hybrids is different from that of either parent (Streuli et al., 1981;Rehberg et al., 1982; Weck et al., 1981b). The construction of human hybrid molecules with high specific activity on unrelated animal species might provide a useful tool for studying the biology of the IFN system in various animal species.The purpose of this report is to describe the antiviral properties of a recombinant human IFN hybrid which has not only a very broad host-range of activity but also a high efficacy. The hybrid comprises amino acids 1 to 60 from IFN-c~B and amino acids 61 to 166 from IFN-c~D as previously described (Meister et al., 1986).The types of recombinant IFN (> 90~ pure) used in this study were produced in yeast, and their final purification involved affinity immunochromatography using monoclonal antibodies. IFN titres calibrated against HulFN-c~ (NIH standard G 023-901-527) on human diploid cells were: IFN-c~B/D hybrid (0.5 x 108 IU/mg), IFN-c~B (2.5 x 108 IU/mg), IFN-c~D (4 x 10 ° IU/mg) and IFN-c~F (0.5 x 108 IU/mg). Whenever possible, the target cells were diploid cells with a finite life span in tissue culture. They were obtained by digestion of tissues with a neutral protease (Dispase, Boehringer-Mannheim) at pH 6.7 in phosphate-buffered saline. All cells were propagated in Eagle's MEM supplemented with 10~o foetal bovine serum and antibiotics. Primary cells and established cell lines were subcultured using a solution of trypsin (1:250) in EDTA (Gibco).The cross-species activity of IFN ...

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