A murine interferon y (IFN-y) receptor cDNA was isolated by screening a murine T-cell hybridoma library prepared in AgtlO with probes prepared from a human IFN-y receptor cDNA. The 2.1-kilobase (kb) cDNA encoded a serine-rich polypeptide of 477 amino acids that was 52% identical to the human protein. Interferon y (IFN-y) is a potent immunomodulatory cytokine produced by activated T cells and natural killer cells (1). IFN-y is perhaps best recognized for its ability to enhance natural, cell-mediated, and humoral immunity by regulating the differentiation, activation and/or function of a wide variety of immune cell types, such as macrophages (2-4) and B cells (5, 6). However, it also induces a number of other biologic responses on cells, such as fibroblasts (7, 8) (19), and although the murine transfectants displayed the capacity to bind human IFN-y, they failed to respond to it. Thus, it remains uncertain whether unresponsiveness was due merely to limited expression of the human IFN-y receptor at the cell surface or to a deficiency of an additional human component needed to form a functionally active receptor. To further investigate this issue, we examined the biologic responsiveness of human cells that expressed murine IFN-y receptors. In the current communication, we report the cloning and sequencing of a murine IFN-y receptor cDNAAfWe also demonstrate that, unlike its human counterpart, the murine IFN-y receptor cDNA can be stably expressed at high levels in human cells. However, despite expression of 530,000 murine IFN-y receptors per cell, the human cells respond only to the homologous human ligand and not to the murine ligand. These results thus support the concept that additional species-specific components are necessary to form a functionally active IFN-y receptor. MATERIALS AND METHODSReagents. The murine and human IFN-y preparations used in these studies were supplied as highly purified recombinant proteins derived from Escherichia coli and expressed specific antiviral activities of 1 and 3 x 107 units/mg, respectively. The proteins were radioiodinated with Bolton-Hunter reagent (ICN), as described (16). Polyvalent rabbit antirecombinant murine IFN-y (21) was affinity-purified by chromatography on murine IFN-y-Sepharose columns. Purified GR20, a rat monoclonal antibody (mAb) specific for the murine IFN-y receptor (17) was provided

Human adenovirus type 5 (Ad5) is a DNA virus which replicates as efficiently in human A549 cells treated with human interferon-U2 (IFN) as in untreated cells. Vesicular stomatitis virus (VSV), on the other hand, is a negative-strand RNA virus which is very sensitive to the effects of IFN treatment in A549 cells. The IFN-mediated inhibition of VSV replication was not observed in cells coinfected with AdS. Abrogation of IFN-mediated antiviral activity was maximal when Ad5 infection preceded VSV infection by at least 36 h, but did not require adenovirus DNA synthesis for manifestation. Coinfection experiments with VSV and deletion variants of adenovirus demonstrated that neither virus-associated RNA synthesis nor expression of adenovirus early regions E1B, E2A, E3, or E4 are required for abrogation of IFN-mediated inhibition of VSV replication. However, expression of early region ElA was essential, suggesting that EIA products can modulate, either directly or indirectly, IFN activity in adenovirus-infected cells.

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We have characterized sequences expressed in Chinese hamster ovary (CHO) cells which are related to the intracisternal A-particle (IAP) genes of mice and Syrian hamsters. Several cDNA clones homologous to Syrian hamster IAP probes have been isolated and used to evaluate the abundance and expression of these retroviruslike sequences. DNA blot analysis with homologous Chinese hamster IAP probes revealed that IAP-related sequences are present in CHO cell DNA at moderately repetitive levels (approximately 300 copies per haploid genome). Sequence analysis has revealed the existence of at least two distinct families of IAP-related sequences in CHO cell DNA. Family I sequences exhibit identical 4.5-kilobase-pair internal deletions relative to complete IAP genomes of mice or Syrian hamsters, but family II sequences showed no major sequence discontinuities relative to the IAP genes of other species. Both families are expressed as abundant cytoplasmic RNA in CHO cells, but only family II sequences produce abundant transcripts of a size consistent with that of a full-length IAP RNA. Intact gag, pol, or env open reading frames were not present in sequences of either family, although incomplete open reading frames spanning putative p27 and protease regions of IAP genes were observed.

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