Effect of virus infection on levels of transcripts for cellular genes

Malignant rabbit fibroma virus (MV) induces tumors composed of proliferating cells, principally fibroblasts, and vasculature. These tumors are associated with large amounts of collagen and other connective tissue proteins. We studied the effect of MV infection on levels of mRNA for alpha 1 chains of collagens type I, III and V in RK-13 fibroblasts and alpha 2 chain of collagen type I. MV infection induces expression of specific collagen genes at particular time points after infection in vitro. Expression of these collagen genes is clearly different in MV-infected cells compared to uninfected cells. Transcript levels for a cellular transcription factor that regulates expression of alpha 1 chain type I collagen, cbf-a, were increased in MV-infected cells prior to the increase in type I collagen mRNA. The virus infection also specifically induced increased levels of mRNA for the cellular transcription factors c-fos and SP1. MV infection is therefore associated with increased levels of specific cellular mRNAs, and is correspondingly associated with increased mRNA for transcription factors that may regulate transcription of these genes. The ability of malignant fibroma virus to influence expression of cellular genes may be exerted through the cells' own transcription regulatory apparatus.

Epidermal growth factor-like growth factors. I. Breast malignancies and other epithelial proliferations in transgenic mice

BACKGROUND

Growth factors recognized by the epidermal growth factor receptor are important in tumor production in some organs. The family of epidermal growth factor-like growth factors includes a group of poxviral growth factors: Shope growth factor (SGF), myxoma growth factor MGF), and vaccinia growth factor. These viral growth factors are glycoproteins, whereas all other members of the epidermal growth factor family are proteins.

EXPERIMENTAL DESIGN

To understand the potential significance of poxviral growth factors, we made transgenic mice using three different constructs: SGF and MGF cloned downstream from the metallothionein (MT) promoter (MTSGF), and SGF downstream from Rous sarcoma virus long terminal repeat.

RESULTS

Founder transgenic mice for each construct were identified, and lines established. Expression of transgenes in MT-SGF mice and MT-MGF mice was induced by feeding animals Zn at 2 months of age. Two months later, both MT-SGF and MT-MGF mice showed proliferation and arborization of breast ducts and ductules, with slight intraductal proliferation in virgin mice. They also showed gastric epithelial hyperplasia, particularly in MT-MGF mice. Stromal and epithelial hyperplasia were found in several organs. The transgenes were expressed in epithelia and stroma of breast, lungs, liver and stomach. Rous sarcoma virus long terminal repeat-SGF transgenic mice developed atypical preneoplastic mammary ductal proliferations in both virgin and nonvirgin females by 6 months of age. In 1/3 of 8-month-old females, invasive secretory adenocarcinoma developed. These mice also developed severe epithelial atypia in the stomach, and papillary gastric tumors.

CONCLUSIONS

Poxviral growth factors may thus be helpful in the study of mammary and gastric oncogenesis and provide insight into growth factor-induced tumor development.

Surfactant protein A-binding proteins. Characterization and structures

An alveolar cell membrane protein acts as a surfactant protein A (SP-A) receptor; it binds SP-A and regulates surfactant secretion. We identified such alveolar cell membrane SP-A-binding proteins using anti-idiotype antibodies directed against the surfactant protein binding region of anti-surfactant antibodies. These monoclonal anti-idiotype antibodies, A2C and A2R, also recognize an alveolar cell membrane protein of approximately 30 kDa. A pulmonary protein of approximately 30 kDa binds SP-A. Unique cDNAs encoding this protein were identified in human (4.1-kilobase) and porcine (1.8-kilobase) lung expression libraries. Coding regions of these cDNAs cross-hybridize with each other under stringent conditions. Both cDNAs encode similar approximately 32-kDa proteins that bind SP-A. The human and porcine SP-A recognition (SPAR) proteins resemble each other, as well as other cell membrane receptors. Their projected structures are consistent with cell membrane receptors. Recombinant human and porcine SPAR proteins bind SP-A as well as the two anti-idiotype antibodies just as do native lung proteins of approximately 30 kDa. SPAR transcripts are expressed primarily in lung. The cellular distribution of these transcripts, as determined by in situ hybridization, is similar to that of SPAR protein, as determined by immunohistochemistry; both are found in cells consistent with type II pneumocytes. SPAR-producing cells resemble the alveolar cells expressing SP-B and SP-C transcripts in appearance, location, and distribution. Therefore, cDNAs for pulmonary SP-A-binding proteins from two disparate species have been isolated and sequenced, and the recombinant proteins they encode bind the same ligand. Further structural, functional, and genetic studies of these proteins may help explain how pulmonary surfactant secretion is regulated.

A 34-kd protein with strong homology to ras-like proteins inhibits epidermal growth factor activity

Epidermal growth factor (EGF) and its analog, transforming growth factor-alpha, are felt to be important in oncogenesis. When malignant rabbit fibroma virus infects RK-13 rabbit kidney cells, a 34-kd protein that inhibits the effects of EGF on certain target cell lines is produced. We have purified this protein using high-pressure liquid chromatography and gel electrophoresis. This purified protein abolishes EGF-induced cellular proliferation. It also causes the EGF receptor-bearing A431 carcinoma cell line to stop proliferating in vitro. This purified 34-kd EGF inhibitor (EGFI) redirects cellular protein phosphorylation in the presence or absence of EGF. Whereas EGF increases phosphorylation of cellular proteins in normal rat kidney cells, clone 49F, and A431 EGFI generally decreases it. Both EGF and EGFI cause increased protein production in A431 and normal rat kidney cells. The major species of protein synthesized by cells seem invariant to EGFI, with or without EGF. The partial protein sequence of two fragments of EGFI shows striking similarity to two ras like proteins. Possible means by which such a ras-like protein might inhibit EGF-induced cellular proliferation are discussed. Therefore, a purified 34-kd ras-like protein inhibits EGF-induced cellular proliferation and changes the targets for cellular protein phosphorylation. Studies are in progress to characterize this protein further, both structurally and functionally.

Sequence and analysis of the BamHI "D" fragment of Shope fibroma virus: comparison with similar regions of related poxviruses

Differences observed in the virulence of two related leporipoxviruses are closely tied to a particular region of their genomes. For the virulent poxvirus of this pair, malignant rabbit fibroma virus (MV), this region is the BamHI "C" fragment, which is 10.7 kb. For the avirulent poxvirus, Shope fibroma virus, SFV, this region is the corresponding BamHI "D" fragment, which is 13.1 kb. As part of our attempt to understand the virulence of these two viruses, we sequenced these two DNA fragments. The sequence for the BamHI "C" fragment of MV is reported elsewhere (Strayer et al., 1991). We report here the sequence for SFV's BamHI "D" fragment and resultant open reading frames, and compare both DNA and open reading frame structures to those of MV and other known poxviruses. The BamHI "D" fragment of SFV contains 12 open reading frames of 100 amino acids or more, arranged similarly to orf's in MV and vaccinia. Striking similarities between SFV and MV are seen in certain parts of this restriction fragment, including substantial stretches of DNA in which the two viruses are identical. Clear homologies exist between these leporipox virus genomes and those of other related poxviruses. To understand the pathogenesis of virus infection, one must appreciate the structure of those viral genes that play important roles in infection.

Applications of anti-curosurf antibodies to understanding the biology of alveolar surfactant

The structure of surfactant-binding proteins from alveolar cell membranes was investigated using monoclonal anti-idiotypic antibodies directed against surfactant-binding regions of anti-surfactant monoclonal antibodies. Two different series of monoclonal anti-surfactant antibodies were used. One series included antibodies against rabbit surfactant, and the other antibodies against porcine surfactant. In addition, two monoclonal anti-idiotype antibodies were made. These anti-idiotype antibodies, called A2R and A2C, bind both anti-Curosurf and anti-rabbit surfactant antibodies comparably. They recognize a 30-kDa cell membrane protein on alveolar and bronchial epithelial cells. In addition, A2C and A2R block the binding of radiolabeled surfactant to these cells. Using a combination of A2C and A2R cDNA expression libraries from both human and porcine lungs were screened. One independent clone was identified in each library that produced protein that bound these monoclonal antibodies. The protein encoded by the cDNA in each clone bound radiolabeled recombinant surfactant protein-A. It is concluded that human and porcine alveolar cell SP-A binding proteins have been identified and its cDNA cloned. The potential implications of this finding for the understanding and treatment of surfactant deficiency states are considerable.

Sequence and analysis of a portion of the genomes of Shope fibroma virus and malignant rabbit fibroma virus that is important for viral replication in lymphocytes

The 10.7-kb BamHI "C" restriction fragment of malignant rabbit fibroma virus (MV) contains genes that are important for its immunosuppressive activity. When this fragment is transferred to a related avirulent leporipoxvirus, Shope fibroma virus (SFV), recombinant viruses show clinical features characteristic of MV: they replicate in lymphocytes and alter immune function in vitro, induce disseminated tumors in recipient rabbits, and are immunosuppressive in vivo. The 10.7-kb BamHI "C" restriction fragment of MV was sequenced in its entirety. Its DNA sequence and the 14 ORF's derived from analyzing this sequence are discussed. Analysis of known open reading frames to which the ORF's from MV's Bam "C" fragment show homology permits us to identify some MV ORF's showing high degrees of similarity to known and postulated proteins produced by vaccinia virus. Functions for some of these vaccinia proteins are known, while functions for others are hypothetical or unknown. Further analysis of genetic determinants of MV's virulence has indicated that two overlapping restriction subfragments of the BamHI "C" fragment can transfer MV's virulent behavior to SFV. The 0.7-kb region in which these two subfragments overlap includes the C-terminus of MV orf C-7 and the N terminus of MV orf C-8. These correspond to the C- and N-termini, respectively, of SFV orf's D-9 and D-10 and to vaccinia orf's D-6 (early transcription factor) and D-7 (subunit of RNA polymerase). We sequenced the region of SFV's BamHI "D" fragment in this area and illustrate here the comparative sequences of this portion of SFV's genome and orf's. On the basis of comparisons between MV, SFV, and vaccinia in this area we discuss the potential significance of these observations.

In vivo and in vitro inactivation of bovine surfactant by an anti-surfactant monoclonal antibody

In this study the importance of a low-weight surfactant protein (11 kDa) is demonstrated by selectively blocking this protein with a monoclonal antibody. In adult rats respiratory failure was induced by repeated bronchoalveolar lavage to remove all pulmonary surfactant. It was shown that surfactant mixed with the antibody was not capable of restoring lung function when compared with surfactant alone or surfactant mixed with control serum. Using the pulsating bubble surfactometer, it could be demonstrated that surfactant mixed with this antibody had a significant higher minimum surface tension when compared with surfactant alone, or surfactant mixed with an unrelated mouse immunoglobulin G (IgG). The inhibition of surfactant function by the monoclonal antibody suggests the importance of the 11 kDa protein for normal surfactant function.

In vivo and in vitro inactivation of bovine surfactant by an anti-surfactant monoclonal antibody

In this study the importance of a low-weight surfactant protein (11 kDa) is demonstrated by selectively blocking this protein with a monoclonal antibody. In adult rats respiratory failure was induced by repeated bronchoalveolar lavage to remove all pulmonary surfactant. It was shown that surfactant mixed with the antibody was not capable of restoring lung function when compared with surfactant alone or surfactant mixed with control serum. Using the pulsating bubble surfactometer, it could be demonstrated that surfactant mixed with this antibody had a significant higher minimum surface tension when compared with surfactant alone, or surfactant mixed with an unrelated mouse immunoglobulin G (IgG). The inhibition of surfactant function by the monoclonal antibody suggests the importance of the 11 kDa protein for normal surfactant function.

Identification of a cell membrane protein that binds alveolar surfactant

Alveolar surfactants are complex mixtures of proteins and phospholipids produced by type II alveolar cells and responsible for lowering pulmonary surface tension. The process by which surfactant is produced and exported and by which its production by pulmonary cells is regulated are not well understood. This study was designed to identify a cellular receptor for surfactant constituents. To do so, monoclonal anti-idiotypic antibodies directed against antibodies to porcine and rabbit surfactant proteins were prepared. These monoclonal anti-idiotypic antibodies bind both alveolar lining and bronchial epithelial cells in rabbit, porcine, and human lungs. Macrophages and other nonepithelial cells do not react with these antibodies. Western blot analysis indicates that both A2R and A2C recognize the same proteins in both pig and rabbit lungs: a 30-kd protein and additional proteins at 52 and 60 kd. Preincubating lung wash cells with A2C or A2R prevents binding of porcine or rabbit surfactant preparations, respectively, by these cells. Preincubating frozen sections of lung tissue with surfactant inhibits binding of A2R and A2C to the lung. Antibody directed to a cell membrane protein that recognizes alveolar surfactant may be useful in elucidating the structure and function of this receptor and in understanding the cellular physiology and pathophysiology of the surfactant system.

Effects of antisurfactant antibodies on the course of mild respiratory distress syndrome

The role of surfactant-associated proteins in surfactant function was studied by selectively blocking these proteins with monoclonal antibodies. Four monoclonal antibodies, M1, M2, M3, and M4 were identified and their reactivities examined by Western blot analysis. M1, M2, and M4 bind, respectively, 8-, 10- and both 10- and 34-kD proteins. M3 antibody did not recognize a protein as assayed by this technique. These antibodies were then administered intratracheally to adult rats that had been partially depleted of lung surfactant by broncholavage. None of these antibodies had any deleterious effect on pulmonary function. On the other hand, M4 antibody significantly improved gas exchange. Possible mechanisms by which antibody may effect such improvement are discussed.

Immunogenicity of surfactant. II. Porcine and bovine surfactants

Protein-containing surfactants of human and animal origin are being used increasingly to treat neonatal and adult respiratory distress syndromes. This trend led us to examine the antigenicity of two important preparations of animal surfactant, cow lung surfactant extract (CLSE) and a porcine surfactant preparation, Curosurf. We describe here 15 monoclonal antibodies against Curosurf and four against CLSE. Antibodies were studied by Western blot analysis to determine their ability to recognize protein components of their respective surfactant preparations. They were also tested for their ability to inactivate surfactant in vitro, assayed using the pulsating bubble surfactometer. Several antibodies directed against CLSE or Curosurf functionally inactivate the surfactant to which they were raised. We determined the degree of immunologic cross-reactivity between antibodies directed to CLSE and Curosurf against the other surfactant and also against human surfactant, both by Western blot and by examining functional inactivation in vitro. Antibodies to these animal surfactants that are commonly used therapeutically may inactivate the specific animal surfactant to which they were raised, as well as human and other surfactants. Generally, when antibodies inactivate surfactant from more than one animal species, they inactivate heterologous surfactants comparably to the extent to which they inactivate the surfactant to which they are directed. Immune complexes between anti-surfactant antibodies and surfactant have been described in the course of neonatal respiratory distress syndrome. The potential pathophysiological importance of anti-surfactant antibodies may therefore lie in their ability to inactivate administered surfactant, other similar surfactants and endogenous surfactant. In so doing, these antibodies may potentiate surfactant deficiency or pulmonary injury initiated by other stimuli.

Immunogenicity of surfactant. I. Human alveolar surfactant

The immunogenicity of lung surfactant derived from amniotic fluid has been well established. We have set out to examine the antigenic similarity of human surfactant to non-human alveolar surfactants currently being used therapeutically in clinical trials with neonatal respiratory distress syndrome. To this end, we raised a series of eight monoclonal antibodies in rats directed to human surfactant (H1 to H8). All antibodies bound human surfactant as measured by ELISA. Four of these monoclonal antibodies bound surfactant components by Western blot analysis: all bound a 9-10-kD species. In addition, one antibody (H2) bound a protein of 16 kD, one (H8) a 6-kD protein, and one (H6) a 30-kD protein. When mixed with surfactant, three antibodies, H4, H7 and H8, profoundly altered surfactant activity in vitro in the pulsating bubble surfactometer. Three other antibodies, H1, H2, and H5 moderately inhibited surfactant's surface activity. We also examined the cross-reactivity of these monoclonal antibodies with bovine (CLSE) and porcine (Curosurf) surfactants. By Western blot analysis, only H6 bound these heterologous surfactants. Other antibodies did so by ELISA. However, functional assays indicated that antibodies H7, H8 and H4 all greatly inhibited CLSE surface activity in vitro. Five antibodies (H1-H4 and H8) inhibited Curosurf function. Thus, human surfactant species, especially low molecular weight species, are highly antigenic. Antibodies to alveolar surfactants may inhibit surfactant function in vitro. As indicated by Western blot and cross-inhibition data, human lower molecular weight surfactants share epitopes with proteins from therapeutically important porcine and bovine surfactants. The potential importance of these findings to treatment of neonatal respiratory distress syndrome with heterologous surfactants is discussed.

Determinants of the ability of malignant fibroma virus to induce immune dysfunction and tumor dissemination in vivo

The relationship of virus-induced immunological dysfunction and tumor dissemination was studied using two related tumor-causing leporipoxviruses: malignant fibroma virus (MV) and Shope fibroma virus (SFV). Recombinant viruses, produced by transferring MV's 10.7 kb BamHI C fragment to SFV, replicate in lymphocytes and suppress lymphocyte function in vitro. Those recombinants that replicate in lymphocytes and suppress lymphocyte function in vitro share about 3.5 kb from MV's C fragment. Some recombinants mimic MV in producing immune suppression and disseminated virus infection in vivo. Other recombinants, even some that are highly immunosuppressive in vitro (e.g. R71), only variably induce immune suppression in vivo, and do not cause disseminated disease. A segment of DNA from MV that transfers to Shope fibroma virus almost all of MV's virulence in vivo was identified.

Natural cell-mediated immunity in the rabbit

Susceptibility and resistance to tumors represent the interplay of many factors. One factor felt to govern the development of tumors is natural killer and natural cytotoxic cellular activity. The constitutional resistance of rabbits to spontaneous tumor development raises questions regarding the activity of natural cell-mediated immunity in this species. We therefore examined the ability of rabbit spleen, lymph node, and peripheral blood lymphocytes to mediate natural killer cell (NK) and natural cytotoxic cell (NC) activity in vitro. Using classical approaches to the study of NK and NC activity, we found no evidence of these activities in leporine spleen, lymph node, and peripheral blood lymphocytes. Preincubation of these cells with IL-2 did not induce such activity. Antibody-dependent cell-mediated cytotoxic reactivity (ADCC), which is believed to be mediated by NK cells, was also undetectable in rabbit lymphocytes. As controls, lymphocytes from other species were capable of mediating NK, NC, and ADCC functions normally in these experiments. Finally, we were unable to identify a population of large granular lymphocytes, the cells believed to mediate NK activity in other animals. Therefore, we could not demonstrate in the rabbit either natural cell-mediated immunity or the population of cells usually associated with natural cell-mediated immunity. If such activity exists in rabbits, it is different from that seen in other animals. More likely, the basis for the natural resistance of rabbits to tumor development must be sought elsewhere.

Molecular analysis of immunosuppression induced by virus replication in lymphocytes

The relationship between immunosuppression and oncogenesis can be determined by studying the molecular interactions between tumor-inducing viruses and lymphocytes. We approached this study by using a unique system of two genetically related Leporipoxviruses, malignant fibroma virus (MV), and Shope fibroma virus (SFV). MV induces a syndrome of a highly lethal, disseminated myxosarcoma, severe immune suppression, and replicates in lymphocytes both in vivo and in vitro. In contrast, SFV causes a benign fibromyxosarcoma without immune dysfunction and cannot replicate in lymphocytes. Earlier studies demonstrated that transfer of a 10.8-kb Bam HI piece of MV (fragment "C") to SFV resulted in the ability of SFV to replicate in lymphocytes and suppress immune function. These results suggested that lymphocytotropic replication and immune suppression was located on the left side of fragment C. We extended these studies by generating families of recombinants between MV and SFV by using subfragments of fragment C. The resulting recombinant viruses were analyzed for their ability to replicate in lymphocytes, suppress immune function, and produce tumors. Those recombinants expressing MV-like characteristics were mapped by endonuclease digestion. This study demonstrates that recombinants containing a 3.6-kb Nde I subfragment, as well as those containing an overlapping 1.9-kb Hinc II subfragment, were capable of replicating in lymphocytes, suppressing immune functions, and inducing disseminated tumors in rabbits. Our study has therefore identified a portion of MV DNA sufficient to transfer the unique pathogenicity of MV to SFV, and suggests that control of immune suppression and tumor dissemination may not necessarily be mediated by the same viral genes.

Molecular analysis of immunosuppression induced by virus replication in lymphocytes

The relationship between immunosuppression and oncogenesis can be determined by studying the molecular interactions between tumor-inducing viruses and lymphocytes. We approached this study by using a unique system of two genetically related Leporipoxviruses, malignant fibroma virus (MV), and Shope fibroma virus (SFV). MV induces a syndrome of a highly lethal, disseminated myxosarcoma, severe immune suppression, and replicates in lymphocytes both in vivo and in vitro. In contrast, SFV causes a benign fibromyxosarcoma without immune dysfunction and cannot replicate in lymphocytes. Earlier studies demonstrated that transfer of a 10.8-kb Bam HI piece of MV (fragment "C") to SFV resulted in the ability of SFV to replicate in lymphocytes and suppress immune function. These results suggested that lymphocytotropic replication and immune suppression was located on the left side of fragment C. We extended these studies by generating families of recombinants between MV and SFV by using subfragments of fragment C. The resulting recombinant viruses were analyzed for their ability to replicate in lymphocytes, suppress immune function, and produce tumors. Those recombinants expressing MV-like characteristics were mapped by endonuclease digestion. This study demonstrates that recombinants containing a 3.6-kb Nde I subfragment, as well as those containing an overlapping 1.9-kb Hinc II subfragment, were capable of replicating in lymphocytes, suppressing immune functions, and inducing disseminated tumors in rabbits. Our study has therefore identified a portion of MV DNA sufficient to transfer the unique pathogenicity of MV to SFV, and suggests that control of immune suppression and tumor dissemination may not necessarily be mediated by the same viral genes.

Antigenicity of low molecular weight surfactant species

The authors tested the antigenicity of human lung surfactant isolated from amniotic fluid. Mice and rabbits were immunized. Rabbit polyclonal antisera to these surfactant preparations were absorbed with normal human plasma proteins. Polyclonal antisera reacted with both high molecular weight (35 kd) surfactant apoprotein and to lower molecular weight species, both 18 kd and 9 kd. Mice were used to generate monoclonal antibodies to surfactant. Enzyme-linked immunosorbant assay was used to identify five monoclonal antibodies that reacted with surfactant. By Western blot analysis, all of these recognized a low molecular weight surfactant species (9 kd) that could be either SP-B or SP-C. One reacted with a 37 kd protein in the surfactant preparation, consistent with SP-A. One monoclonal antibody also recognized a higher molecular weight species (44 kd) of unknown origin. The ability of antisera and monoclonal antibodies to inhibit the functional activity of surfactant was assayed using a pulsating bubble surfactometer. Rabbit polyclonal antisera inhibited initial surface adsorption to equilibrium surface tension and increased the minimum surface tension after 1 and 5 minutes of initiation of pulsations. This inhibitory activity of the antisera was noted in divalent F(ab')2 fragments. Monovalent F(ab) fragments and control normal rabbit sera did not inhibit surfactant function in this assay. Of the anti-surfactant monoclonal antibodies that reacted with surfactant by ELISA and Western blot, three inhibited its capacity to lower surface tension on the pulsating bubble apparatus. The other two monoclonal antibodies showed no functional inhibitory activity. It is concluded that both the 35 kd SP-A and the 9 kd proteins of human surfactant are highly immunogenic and partially crossreactive. Resulting antibodies could alter the ability of surfactant to perform its physiologic function, ie, to lower surface tension.

Surfactant replacement: immunological considerations

We sought to analyse the potential immunogenicity of human alveolar surfactant as it is currently used in the treatment of neonatal respiratory distress syndrome (RDS). An enzyme linked immunosorbant assay capable of detecting specific immune complexes between surfactant and antibodies directed to surfactant was developed. Premature infants with RDS were divided into groups: one group received surfactant replacement and one received conventional therapy. Plasma samples obtained from these infants at birth and thereafter were examined for specific circulating immune complexes between surfactant and anti-surfactant antibodies. All babies were also examined for clinical and serological evidence of immune complex-mediated tissue damage. We found that almost all infants with RDS, regardless of their therapy, showed evidence of circulating surfactant-anti-surfactant immune complexes. Plasma samples from infants without RDS showed no such complexes. Immune complexes appeared early in postnatal life, usually within the first week, and diminished thereafter. We detected no evidence of altered plasma complement levels or end organ damage attributable to these immune complexes. Thus, circulating immune complexes between surfactant and antibodies to surfactant are common in neonatal respiratory distress syndrome, though they do not appear to cause injury. Since not only human but heterologous surfactants are now used in treating RDS, we feel that cautious evaluation of potential immune reactions to the administered materials should be undertaken.

Arsenic-induced skin toxicity

We reviewed available literature on the effects of inorganic arsenic on the skin to determine the potential hazards and to collate information regarding dosage and exposure to the incidence of skin cancer. Arsenic intake may result from occupational or medicinal exposure, or from drinking well water in areas with high arsenic levels in the soil. Arsenic causes a variety of benign skin lesions including hyperpigmentation and hyperkeratosis. Some hyperkeratotic lesions and squamous cell carcinomas in situ may progress to invasive carcinoma; other invasive squamous cell carcinomas will develop de novo. These cutaneous squamous cancers may metastasize; mortality is low, but has been reported. Locally invasive but non-metastasizing basal cell carcinomas may arise as well. These lesions occur in a characteristic pattern of distribution and are usually multiple. Observers reporting medicinally administered arsenic have described dose-response relationships between the amount of arsenic ingested and the frequency of various skin lesions. For arsenic found in drinking water, however, there is more controversy regarding the doses and exposure times necessary for cutaneous toxicity.

Immunosuppression during viral oncogenesis. V. Resistance to virus-induced immunosuppressive factor

Rabbits given malignant rabbit fibroma virus (MV) develop severe immunologic dysfunction during the course of infection. Splenic T lymphocytes from these rabbits elaborate a soluble non-specific immunosuppressive factor (virus-induced suppressor factor (VISF]. As malignant rabbit fibroma virus infection progresses, normal immunologic responsiveness returns. This recovery is multi-factorial and involves production by T lymphocytes of a soluble factor capable of antagonizing the activity of VISF. This soluble anti-suppressor factor (ASF) is not a generalized immunologic potentiator. Its sole apparent effect on immune function appears to be to antagonize the activity of VISF. The protective effects of ASF are evident only when suppressor factors and ASF are simultaneously present in culture. Pre-treatment of target cells with ASF-containing culture supernatants does not render them insensitive to the immunosuppressive effects of subsequent treatment with VISF. In addition, ASF appears to be directly responsible for antagonizing VISF activity. That is, ASF does not appear to initiate an anti-suppressive cascade by activating a population of cells that in turn generate secondary protective factors. ASF-producing cells do not bind Vicia villosa lectin, as do contra-suppressor cells described by others. In almost all of these features, the system we describe herein differs from systems in which other investigators have described factors that antagonize the effects of suppressor factors.

Immunosuppression during viral oncogenesis. V. Resistance to virus-induced immunosuppressive factor

Rabbits given malignant rabbit fibroma virus (MV) develop severe immunologic dysfunction during the course of infection. Splenic T lymphocytes from these rabbits elaborate a soluble non-specific immunosuppressive factor (virus-induced suppressor factor (VISF]. As malignant rabbit fibroma virus infection progresses, normal immunologic responsiveness returns. This recovery is multi-factorial and involves production by T lymphocytes of a soluble factor capable of antagonizing the activity of VISF. This soluble anti-suppressor factor (ASF) is not a generalized immunologic potentiator. Its sole apparent effect on immune function appears to be to antagonize the activity of VISF. The protective effects of ASF are evident only when suppressor factors and ASF are simultaneously present in culture. Pre-treatment of target cells with ASF-containing culture supernatants does not render them insensitive to the immunosuppressive effects of subsequent treatment with VISF. In addition, ASF appears to be directly responsible for antagonizing VISF activity. That is, ASF does not appear to initiate an anti-suppressive cascade by activating a population of cells that in turn generate secondary protective factors. ASF-producing cells do not bind Vicia villosa lectin, as do contra-suppressor cells described by others. In almost all of these features, the system we describe herein differs from systems in which other investigators have described factors that antagonize the effects of suppressor factors.

Immunologic consequences of exogenous surfactant administration

In conclusion, we have shown that human surfactant is immunogenic and that circulating surfactant-antisurfactant immune complexes are detectable in the plasma from infants and in adults with RDS. We found these immune complexes regardless of whether exogenous surfactant was used in the individual treatment regimen. These immune complexes do not yet seem to cause disease in the short term. Long-term effects, if any, are unknown. Indications for surfactant replacement therapy in neonatal RDS are clear. Trials of exogenous surfactant are just beginning in adult RDS, and potential immunogenicity will be of even greater concern in these patients. In all such situations, potential for side effects must be balanced against therapeutic efficacy and the gravity of the disease. Our data indicate that surfactants, particularly heterologous surfactants, are potent immunogens. One cannot assume that using homologous or heterologous surfactants in patients with RDS will always be immunologically innocuous. Nonetheless, based on present data, moderately long-term follow-up (2 to 4 years), we are encouraged by our observation that no selective adverse effects attributable to human surfactant have been recognized, yet mortality from RDS in infants less than 30 weeks has been nearly cut in half.

Immunosuppression during viral oncogenesis. IV. Generation of soluble virus-induced immunologic suppressor molecules

We describe herein functional attributes and generation of immunologic suppressor activity elaborated in response to oncogenic virus infection. Malignant rabbit fibroma virus-induced immunologic suppressor factor (VISF) is a T cell product produced in peak quantities by spleen cells taken from infected rabbits 7 days after infection in vivo. Its production does not appear to require macrophage participation. VISF is highly labile, 3.5 to 12 kDa, and capable of suppressing both B and T lymphocytic responses. Indomethacin and the cyclic nucleotides cAMP and cGMP inhibit its generation. VISF activity is neither antigen nor species specific. It suppresses murine and leporine immune responses to antigens unrelated to the inducing virus. Comparable suppressor activity may be induced by infecting an apparently non-functional rabbit T lymphoma line, RL-5, with malignant rabbit fibroma virus. VISF is principally a suppressor-inducer factor: in vitro, lymphocytes exposed to VISF do not show decreased immunologic responsiveness until 4 days of culture. VISF induces T suppressor cell activity when normal spleen cells are exposed briefly to VISF. Thus, immunosuppressive consequences of malignant fibroma virus infection are partially mediated by a small, non-specific T cell-derived suppressor lymphokine with unique functional characteristics. Non-specific immunologic dysfunction that often attends virus infections may reflect the activity of such factors in humans as well.

Lymphocyte-virus interactions. Identification of a restriction fragment permitting virus replication in lymphocytes

We are interested in understanding the effects of virus infection on lymphocyte function. To approach this question, we used a unique system of two genetically related leporipoxviruses to generate recombinants. One of these viruses, malignant fibroma virus (MV), replicates in many different cell types, including lymphocytes. The other, Shope fibroma virus (SFV), replicates principally in fibroblasts, but cannot replicate in lymphocytes. Fibroblasts infected with SFV received restriction fragments from MV by transfection. Recombinant viruses were selected in vitro for their ability to replicate in lymphocytes. By these means we have identified one restriction fragment, the 10.8-kb BamHI "C" fragment, capable of transferring from MV to SFV the ability to replicate in lymphocytes. A family of recombinants bearing different sized inserts of this restriction fragment has been isolated and is being characterized. Lymphocytotropic recombinants bearing portions of this restriction fragment produce colony morphology in vitro intermediate between MV's plaques and SFV's foci. On the basis of their ability to grow in and suppress mitogen responsiveness of lymphocytes, these recombinants may be classified into four different groups. Group 1 viruses are the most immunosuppressive, whereas those of group 4 are least. These traits correlate with ability to replicate in lymphocytes. Genetic analysis of recombinants indicates that the most immunosuppressive recombinants do not necessarily contain the most fragment C DNA. Therefore, we have identified a restriction fragment, one or more of the genes of which are sufficient to allow an otherwise nonlymphocytotropic virus to replicate in lymphocytes. Additional genetic and immunologic analysis should permit us to determine the structure and function of the protein responsible for this effect.

Immunosuppression during viral oncogenesis. IV. Generation of soluble virus-induced immunologic suppressor molecules

We describe herein functional attributes and generation of immunologic suppressor activity elaborated in response to oncogenic virus infection. Malignant rabbit fibroma virus-induced immunologic suppressor factor (VISF) is a T cell product produced in peak quantities by spleen cells taken from infected rabbits 7 days after infection in vivo. Its production does not appear to require macrophage participation. VISF is highly labile, 3.5 to 12 kDa, and capable of suppressing both B and T lymphocytic responses. Indomethacin and the cyclic nucleotides cAMP and cGMP inhibit its generation. VISF activity is neither antigen nor species specific. It suppresses murine and leporine immune responses to antigens unrelated to the inducing virus. Comparable suppressor activity may be induced by infecting an apparently non-functional rabbit T lymphoma line, RL-5, with malignant rabbit fibroma virus. VISF is principally a suppressor-inducer factor: in vitro, lymphocytes exposed to VISF do not show decreased immunologic responsiveness until 4 days of culture. VISF induces T suppressor cell activity when normal spleen cells are exposed briefly to VISF. Thus, immunosuppressive consequences of malignant fibroma virus infection are partially mediated by a small, non-specific T cell-derived suppressor lymphokine with unique functional characteristics. Non-specific immunologic dysfunction that often attends virus infections may reflect the activity of such factors in humans as well.

Lymphocyte-virus interactions. Identification of a restriction fragment permitting virus replication in lymphocytes

We are interested in understanding the effects of virus infection on lymphocyte function. To approach this question, we used a unique system of two genetically related leporipoxviruses to generate recombinants. One of these viruses, malignant fibroma virus (MV), replicates in many different cell types, including lymphocytes. The other, Shope fibroma virus (SFV), replicates principally in fibroblasts, but cannot replicate in lymphocytes. Fibroblasts infected with SFV received restriction fragments from MV by transfection. Recombinant viruses were selected in vitro for their ability to replicate in lymphocytes. By these means we have identified one restriction fragment, the 10.8-kb BamHI "C" fragment, capable of transferring from MV to SFV the ability to replicate in lymphocytes. A family of recombinants bearing different sized inserts of this restriction fragment has been isolated and is being characterized. Lymphocytotropic recombinants bearing portions of this restriction fragment produce colony morphology in vitro intermediate between MV's plaques and SFV's foci. On the basis of their ability to grow in and suppress mitogen responsiveness of lymphocytes, these recombinants may be classified into four different groups. Group 1 viruses are the most immunosuppressive, whereas those of group 4 are least. These traits correlate with ability to replicate in lymphocytes. Genetic analysis of recombinants indicates that the most immunosuppressive recombinants do not necessarily contain the most fragment C DNA. Therefore, we have identified a restriction fragment, one or more of the genes of which are sufficient to allow an otherwise nonlymphocytotropic virus to replicate in lymphocytes. Additional genetic and immunologic analysis should permit us to determine the structure and function of the protein responsible for this effect.

Inhibition of epidermal growth factor-induced cellular proliferation

The authors tested whether two oncogenic poxviruses, Shope fibroma virus (SFV) and malignant rabbit fibroma virus (MV), coded for an epidermal growth factor (EGF)-like protein. Virus-free lysates of SFV or MV-infected rabbit kidney cells do not appreciably affect proliferation of EGF-unresponsive RK-13 cells. Comparable lysates inhibit the background proliferation of two EGF-responsive cell lines, human foreskin fibroblasts and normal rat kidney cells. Inhibition of EGF-stimulated proliferation is also observed in a dose-dependent fashion. This inhibition is greatest when the virus lysate preparations are added either simultaneously with or before EGF. When EGF is added to cultures 24 hours before the SFV or MV preparations, the latter then have little or no effect on EGF-induced target cell proliferation. The inhibitory factor competed with radiolabeled EGF for its receptor site. Electroblotting shows a protein of 35 kd molecular weight in the lysates of virus-infected RK-13 cells which reacts with anti-EGF antibody. These findings interpreted to indicate that SFV and MV code for an inhibitor of EGF activity, and that this inhibition occurs at least in part by competitive inhibition of EGF-EGF receptor interactions.

Growth of malignant rabbit fibroma virus in lymphoid cells

To understand better the immunosuppressive capacity of malignant rabbit fibroma virus (MV), we characterized MV growth in lymphoid cells. Replication of MV occurs in unstimulated normal spleen cells in vitro and is enhanced by adding T- or B-lymphocyte mitogens. In splenic T-lymphocyte preparations, comparable results are found: virus growth in the absence of mitogen, augmented by adding Con A. Unlike mature T cells, thymic lymphocytes support MV replication only when mitogen is added. When spleen cells from rabbits infected with MV in vivo are removed and cultured without mitogen, MV growth is again observed, with virus titer increasing about 10-fold per day of culture. In spleen cell populations from MV tumor-bearing rabbits, MV grows best in T lymphocytes, moderately in B lymphocytes, and least efficiently in adherent cells. When spleen cells are examined immediately following sacrifice, MV antigens are expressed solely on T lymphocytes from rabbits infected in vivo with MV 7 days previously. However, following overnight incubation in vitro a population of non-T lymphocytes displays cell membrane virus antigens. MV adapts itself somewhat to growth in lymphocytes, showing significantly greater growth in lymphocytes following passage in lymphocytes than is observed for non-lymphocyte-propagated virus. MV-infected lymphocytes also elaborate a factor that enhances MV growth in lymphocytes. Thus, MV replicates preferentially in mature T lymphocytes but will grow well in B cells as well. In vivo infection produces relatively small amounts of recoverable virus. However, when these lymphocytes are cultured in vitro virus replicates very well without added mitogens. These growth patterns may help to understand MV-induced immunologic dysfunction.

Virus-lymphocyte interactions during the course of immunosuppressive virus infection

Malignant rabbit fibroma virus (MV) is a lymphocytotropic leporipoxvirus which produces profound immunological dysfunction and lethal fibromyxosarcoma. We examined virus recovery from splenic lymphocytes as a function of time after inoculation in vivo, and correlated this with both immunological function and expression of virus-induced host suppressor activity. MV was most abundant in lymphocytes obtained 4 days following inoculation. At that time, immune function was relatively normal and host suppressor activity was not observed. By 7 days after infection, when active host immunosuppressor functions were observed, virus recovery was decreased. Eleven days post-inoculation host immune function began to recover despite increasing virus-induced tumours and developing opportunistic infection. Simultaneously, MV was no longer recoverable from spleen cells. Spleen cells from day 11 tumour-bearing rabbits did not support MV replication as efficiently as did normal or day 4 or 7 splenic lymphocytes, but they did not alter the ability of MV to grow in the latter cells. By fluorescence examination and cytofluorography, splenic lymphocytes bearing MV antigens were abundant 7 days after infection but disappeared by 11 days. This was temporally related to production of neutralizing antibody to MV, and development of virus-specific lymphocyte proliferative activity. The composition of splenic lymphocytes changed as well: the normal ratio of about 1:1 for B and T cells changed to 1:2 by day 7, and then inverted to almost 2:1 by day 11. Rabbits infected with MV thus appear to recover their immune function, concurrently eliminate virus-infected lymphocytes, and elaborate high titres of neutralizing serum antibodies despite progressive infections and tumour development.

Immunosuppression in viral oncogenesis. III. Effects of virus infection on interleukin 1 and interleukin 2 generation and responsiveness

Malignant rabbit fibroma virus (MV) is an oncogenic immunosuppressive leporipoxvirus. We studied the effects of MV infection and MV-associated tumor-induced suppressor factor (TISF) on the production of and responsiveness to interleukins 1 and 2. Adherent cells from MV tumor-bearing rabbits elaborate adequate amounts of IL 1 in response to E. coli endotoxin. Neither live virus nor TISF alters the production or the responsiveness to IL 1. However, when we examined spleen cells from rabbits 7 days after MV inoculation, we noted that their ability to produce and respond to IL 2 is deficient. Despite their relatively poor capacity to produce IL 2, these spleen cells express receptor for IL 2 in normal amounts, as measured by the monoclonal antibody 7D4. TISF derived from T lymphocytes from MV tumor-bearing rabbits is by itself capable of inhibiting partially normal secretion of IL 2 and also the response of the cloned murine T cell line HT-2 to added IL 2. Full expression of the immunosuppressive capacity of spleen cells from MV tumor-bearing rabbits requires cell-cell contact, however, and cannot be replaced by either live virus or spleen cell supernatants. Such spleen cells inhibit normal mitogen responsiveness, a defect not remedied by adding exogenous IL 2. Immunologic dysfunction induced by MV infection is transient, and by 11 days after virus inoculation, actively mediated recovery from immunosuppression is observed. We found that spleen cells from rabbits studied 11 days postinoculation secreted IL 2 normally. Thus, immunologic dysfunction secondary to infection with malignant rabbit fibroma virus reflects deficiencies in both elaboration of and response to IL 2, and return of immune function later in the course of the infection is associated with return of the ability of lymphocytes to secrete IL 2.

Immunosuppression in viral oncogenesis. III. Effects of virus infection on interleukin 1 and interleukin 2 generation and responsiveness

Malignant rabbit fibroma virus (MV) is an oncogenic immunosuppressive leporipoxvirus. We studied the effects of MV infection and MV-associated tumor-induced suppressor factor (TISF) on the production of and responsiveness to interleukins 1 and 2. Adherent cells from MV tumor-bearing rabbits elaborate adequate amounts of IL 1 in response to E. coli endotoxin. Neither live virus nor TISF alters the production or the responsiveness to IL 1. However, when we examined spleen cells from rabbits 7 days after MV inoculation, we noted that their ability to produce and respond to IL 2 is deficient. Despite their relatively poor capacity to produce IL 2, these spleen cells express receptor for IL 2 in normal amounts, as measured by the monoclonal antibody 7D4. TISF derived from T lymphocytes from MV tumor-bearing rabbits is by itself capable of inhibiting partially normal secretion of IL 2 and also the response of the cloned murine T cell line HT-2 to added IL 2. Full expression of the immunosuppressive capacity of spleen cells from MV tumor-bearing rabbits requires cell-cell contact, however, and cannot be replaced by either live virus or spleen cell supernatants. Such spleen cells inhibit normal mitogen responsiveness, a defect not remedied by adding exogenous IL 2. Immunologic dysfunction induced by MV infection is transient, and by 11 days after virus inoculation, actively mediated recovery from immunosuppression is observed. We found that spleen cells from rabbits studied 11 days postinoculation secreted IL 2 normally. Thus, immunologic dysfunction secondary to infection with malignant rabbit fibroma virus reflects deficiencies in both elaboration of and response to IL 2, and return of immune function later in the course of the infection is associated with return of the ability of lymphocytes to secrete IL 2.

Inhibition of virus replication does not alter malignant rabbit fibroma virus-induced immunosuppression

Malignant rabbit fibroma virus (MV) directly suppresses generation of antibody responses and mitogen induced T and B lymphocyte proliferation. We investigated whether this phenomenon required expression of the complete viral genome. Phosphonoacetic acid (PAA) inhibits poxvirus specific DNA polymerases. Adding PAA to cultures reduces both MV replication and mitogen-driven rabbit lymphocyte proliferation in a dose-dependent fashion. A dose of PAA adequate to inhibit MV replication by about 97%, but insufficient to reduce lymphocyte proliferation appreciably, does not affect the ability of MV to suppress lymphocyte proliferation or initiation of antibody production. Spleen cells from MV tumour-bearing rabbits contain very little virus, but inhibit the proliferative and antibody forming responses of normal spleen cells. This activity is shown here to reflect the production by T lymphocytes of a soluble mediator of greater than 25 kD molecular weight. Adding PAA to these mixed spleen cell cultures does not alter the ability of MV to induce T suppressor activity in host lymphocytes. Thus, these immunosuppressive capabilities of MV appear to reflect early MV gene functions.

Transcriptional mapping of early RNA from regions of the Shope fibroma and malignant rabbit fibroma virus genomes

Malignant rabbit fibroma virus (MV) is a recombinant poxvirus derived from Shope fibroma virus (SFV) and rabbit myxoma virus (D. S. Strayer, E. Skaletsky, G. F. Cabirac, P. A. Sharp, L. B. Corbeil, S. Sell, and J. L. Leibowitz, 1983a, J. Immunol. 130, 399-404; W. Block, C. Upton, and G. McFadden, 1984, Virology 140, 113-124). We report here the transcriptional mapping of early RNAs transcribed from the SFV sequences within MV and from the corresponding regions in SFV. Hybridization analysis and S1 nuclease mapping of RNA using viral DNA probes were used to define 5' and 3' ends of the various transcripts. The RNAs described here are transcribed in one direction in a densely arranged head to tail fashion similar to that described for some vaccinia virus early transcriptional units. At late times of infection the early SFV RNAs are not detected whereas the early MV RNAs are present in minor amounts. The early SFV and MV transcripts range in size from 3170 to 425 nucleotides (nt) long. All of the longer transcripts are produced as a result of read through transcription. Three MV transcripts contain fused SFV and rabbit myxoma virus sequences due to transcription through the recombination junction region in the MV genome. Two other MV transcripts are transcribed from a unique initiation site near another recombination junction region resulting in RNAs that are composed of SFV sequences having unique 5' ends.

Reversal of virus-induced immune suppression

We studied the immunosuppressive capacity of splenic lymphocytes from rabbits at different stages of progressive myxosarcoma induced by malignant rabbit fibroma virus (MV). Spleen cells taken from rabbits 7 days after virus inoculation proliferate poorly in response to Con A, and suppress normal responses to the mitogen. Those from animals 11 days after virus injection have recovered partially from MV-induced suppression. Further, their Con A responses are no longer suppressed by day 7 spleen cells. Supernatants from cultures of spleen cells from rabbits given MV 7 days previously suppress both antibody-producing and proliferative responses to unrelated antigens. Comparable supernatants from rabbits receiving MV 11 days before sacrifice neither suppress nor augment such responses. Mixing cells from 7 or 11 day MV rabbits with normal spleen cells gives similar results. When supernatants from spleen cell of rabbits with tumors induced 7 and 11 days previously are mixed, the supernatants from rabbits with 11-day-old tumors inhibit the suppressive capacity of those from animals with 7-day-old tumors. Similarly, mixing spleen cells from rabbits given MV 7 and 11 days previously results in culture supernatants that do not suppress normal antibody and proliferative responses. The ability of cells from rabbits given MV 11 days before to inhibit the effects of cells from rabbits given MV 7 days previously does not involve the production of interferon. Thus, despite progressive tumor burden, immunologic recovery is observed in rabbits 11 days after tumor virus inoculation. One factor in this recovery may be the generation of active inhibitors of virus-induced immunosuppression. Similar mechanisms may apply to recovery of immunologic function in other virus infections as well.

Reversal of virus-induced immune suppression

We studied the immunosuppressive capacity of splenic lymphocytes from rabbits at different stages of progressive myxosarcoma induced by malignant rabbit fibroma virus (MV). Spleen cells taken from rabbits 7 days after virus inoculation proliferate poorly in response to Con A, and suppress normal responses to the mitogen. Those from animals 11 days after virus injection have recovered partially from MV-induced suppression. Further, their Con A responses are no longer suppressed by day 7 spleen cells. Supernatants from cultures of spleen cells from rabbits given MV 7 days previously suppress both antibody-producing and proliferative responses to unrelated antigens. Comparable supernatants from rabbits receiving MV 11 days before sacrifice neither suppress nor augment such responses. Mixing cells from 7 or 11 day MV rabbits with normal spleen cells gives similar results. When supernatants from spleen cell of rabbits with tumors induced 7 and 11 days previously are mixed, the supernatants from rabbits with 11-day-old tumors inhibit the suppressive capacity of those from animals with 7-day-old tumors. Similarly, mixing spleen cells from rabbits given MV 7 and 11 days previously results in culture supernatants that do not suppress normal antibody and proliferative responses. The ability of cells from rabbits given MV 11 days before to inhibit the effects of cells from rabbits given MV 7 days previously does not involve the production of interferon. Thus, despite progressive tumor burden, immunologic recovery is observed in rabbits 11 days after tumor virus inoculation. One factor in this recovery may be the generation of active inhibitors of virus-induced immunosuppression. Similar mechanisms may apply to recovery of immunologic function in other virus infections as well.

Surfactant-anti-surfactant immune complexes in infants with respiratory distress syndrome

The authors sought to determine whether treatment of respiratory distress syndrome (RDS) with human surfactant resulted in the formation of detectable circulating immune complexes. Preterm infants with severe RDS were divided into two groups: one group received human surfactant by intratracheal instillation and the other group did not. Both groups received ventilatory management involving intermittent mandatory ventilation. Plasma samples were drawn from these babies prior to treatment and at intervals thereafter. The authors developed an ELISA assay specific for surfactant-anti-surfactant immune complexes and analyzed the plasma samples for such immune complexes. Complement levels were also measured. They found that with time plasma from RDS infants in both groups showed evidence of surfactant-anti-surfactant immune complex formation. The concentrations of immune complexes generally peaked within the first week of life and then appeared to diminish over 1-4 weeks after birth in RDS infants. There was no evidence at any time in either group of immune-complex-mediated injury or of decreased serum complement levels. It is concluded that circulating immune complexes between surfactant and antibodies to surfactant are probably found in most neonates with respiratory distress syndrome, that they do not produce pulmonary damage detectable by clinical and serologic means, and that treatment of neonatal RDS with human surfactant similarly does not produce lung injury as determined with these techniques.

In vitro growth of two related leporipoxviruses in lymphoid cells

We examined the in vitro growth patterns of two leporipoxviruses, malignant rabbit fibroma virus (MV) and Shope fibroma virus (SFV), in lymphoid cells. MV replicates well in normal spleen cells in vitro. At low m.o.i. (0.001), dramatic virus growth occurs in unstimulated cell cultures. This growth is enhanced by addition of the T lymphocyte mitogen, concanavilin A, or the B lymphocyte mitogen, Escherichia coli lipopolysaccharide. Shope fibroma virus does not grow in lymphocytes in culture, with or without mitogen stimulation. MV itself profoundly inhibits lymphocyte mitogenesis, while SFV does not. MV and SFV added to normal lymphocytes do not appear to alter their viability in culture. Thus, MV appears to be novel in its ability to replicate to high titer in resting lymphocytes. This growth pattern may be useful in understanding MV-induced immunologic dysfunction.

Characterization, molecular cloning, and physical mapping of the Shope fibroma virus genome

Five strains of Shope fibroma virus (SFV), a strain of rabbit myxoma virus, and a strain of vaccinia virus were compared by restriction endonuclease digestion of their viral DNAs. Restriction digest patterns revealed that SFV and rabbit myxoma, both members of the Leporipoxvirus genus, were distinct from vaccinia, an Orthopoxvirus. All strains of SFV examined had a high degree of nucleotide sequence homology as shown by conservation of restriction sites within their genomes. However, restriction patterns of SFV and myxoma were quite different from one another suggesting that the genomes from these two viruses of the Leporipoxvirus genus do not share a large, highly conserved region of homology as do the viruses belonging to the Orthopoxvirus genus. Restriction mapping identified inverted terminal repeats of approximately 12 kb in length. Restriction fragments representing all but 400 bp of the termini were cloned in plasmid vectors.

Strain differences in Shope fibroma virus. An immunopathologic study

The pathogenic effects of plaque-purified Boerlage and Patuxent strains of Shope fibroma virus (SFV) in neonatal rabbits are compared with results of previous reports which used nonpurified SFV. Clinically, the Boerlage strain produced large tumors; whereas the same dose of Patuxent strain SFV induced much smaller tumors locally. Neither virus caused metastatic or extensively invasive local spread in our study. Some Patuxent recipients died of respiratory infections prior to sacrifice. However, both groups of rabbits handled the tumor well; the tumor began regressing 15-20 days after inoculation. Histologically, the tumors produced by those viruses were identical. Patuxent strain recipients were otherwise normal. Boerlage strain recipients showed increased persistence of extramedullary hematopoiesis and scattered foci of parenchymal necrosis in their livers. They also showed considerable cell death in thymic lobules. In rabbits given Patuxent strain SFV, virus antigens were detected only in the tumor by immunohistologic examination. Boerlage viral antigens were found in the tumor and overlying skin. We also detected virus systemically in Boerlage recipients: it was present in fixed tissue phagocytes in the spleen and liver and also in parenchymal cells of the lungs, liver, and kidney. Boerlage strain SFV recipients also showed detectable virus in their thymus, both at the periphery of the thymic lobules and in the connective tissue separating thymic lobules from each other. Despite the disseminated nature of the infection, rabbits that received the latter strain fared as well as those receiving Patuxent strain SFV.

Immunologic dysfunction during viral oncogenesis. II. Inhibition of cellular immunity to viral antigens by malignant rabbit fibroma virus

The ability of two related viruses--Shope fibroma virus (SFV) and malignant rabbit fibroma virus (MV)--to induce virus-specific immune responses in lymphocytes of recipient animals was studied. SFV produces a benign local tumor which regresses in 12-14 days. Using an assay for virus-induced lymphocyte blastogenesis lymphocytes reactive to SFV were detected, both in rabbits bearing SFV-induced tumors and in rabbits whose SFV-induced tumor had regressed. These virus-reactive cells were detected in peripheral blood and spleen, and in lymph nodes draining the primary tumor. In contrast, MV produces a disseminated tumor and eventual death. MV does not induce detectable blastogenic responses in lymphocyte populations. SFV and MV are antigenically cross reactive: rabbits immune to SFV do not develop MV-induced tumors, and antisera to each virus neutralize both equally. Lymphocytes from SFV-infected rabbits proliferate in vitro in response to MV that has been inactivated by ultraviolet light (uv/MV) but not to infectious MV. In contrast, lymphocytes from rabbits infected with MV do not respond to uv-inactivated MV or to SFV. Thus, infectious MV inhibits the development of normal blastogenic responses in vivo and prevents the expression of those responses in lymphocytes from MV-resistant, SFV-immune rabbits in vitro. The relevance of this impairment to the differences in the clinical courses of SFV- and MV-induced tumors is discussed.

Streptozotocin prevents development of nitrosamine-induced pancreatic cancer in the Syrian hamster

Administration of the nitrosamine carcinogen N-nitroso-bis (2-oxopropyl) amine (BOP) by subcutaneous injection (5 mg/kg/week) led to the development of invasive pancreatic ductular adenocarcinoma in 100% of normal Syrian hamsters by 24 weeks. Pretreatment of a second group of hamsters with the beta-cell toxin streptozotocin in a diabetogenic dose (50 mg/kg i.p. X 3) completely prevented the development of pancreatic cancer when BOP was subsequently administered. The mechanism of blockade by streptozotocin is unknown. This study suggests the potential importance of the endocrine pancreas in exocrine pancreatic carcinogenesis.

Immunologic dysfunction during viral oncogenesis. I. Nonspecific immunosuppression caused by malignant rabbit fibroma virus

Malignant rabbit fibroma virus (MV) is a potent oncogenic poxvirus that produces a rapidly progressive syndrome of disseminated myxosarcoma, immunosuppression, and fatal gram-negative infection. MV is probably a recombinant between Shope fibroma virus (SFV) and rabbit myxoma virus, and is capable of preventing or aborting the in vitro proliferative responses of rabbit lymphocytes to B and T lymphocyte mitogens. Proliferative responses to sheep erythrocytes (SRBC) are similarly affected, although MV does not alter ongoing antibody responses to SRBC. Splenic lymphocytes from MV tumor-bearing rabbits suppress antibody and proliferative responses to SRBC when added to lymphocytes from SRBC-primed rabbits. Finally, lysates of cultured splenic lymphocytes from rabbits given MV suppress both proliferative and antibody-forming responses to SRBC. When MV is removed from these lysates by UV inactivation or by centrifugation, the suppressive activity remains. We therefore conclude that MV induces immunologic unresponsiveness in rabbits by at least two mechanisms. First, a direct suppressive effect of added virus on in vitro lymphocyte proliferation is seen. There is no effect in this situation if an antibody response is already in progress. Second, spleen cells exposed to MV in vivo produce one or more soluble factors capable of suppressing both proliferative and antibody responses of normal lymphocytes.

Immunologic dysfunction during viral oncogenesis. I. Nonspecific immunosuppression caused by malignant rabbit fibroma virus

Malignant rabbit fibroma virus (MV) is a potent oncogenic poxvirus that produces a rapidly progressive syndrome of disseminated myxosarcoma, immunosuppression, and fatal gram-negative infection. MV is probably a recombinant between Shope fibroma virus (SFV) and rabbit myxoma virus, and is capable of preventing or aborting the in vitro proliferative responses of rabbit lymphocytes to B and T lymphocyte mitogens. Proliferative responses to sheep erythrocytes (SRBC) are similarly affected, although MV does not alter ongoing antibody responses to SRBC. Splenic lymphocytes from MV tumor-bearing rabbits suppress antibody and proliferative responses to SRBC when added to lymphocytes from SRBC-primed rabbits. Finally, lysates of cultured splenic lymphocytes from rabbits given MV suppress both proliferative and antibody-forming responses to SRBC. When MV is removed from these lysates by UV inactivation or by centrifugation, the suppressive activity remains. We therefore conclude that MV induces immunologic unresponsiveness in rabbits by at least two mechanisms. First, a direct suppressive effect of added virus on in vitro lymphocyte proliferation is seen. There is no effect in this situation if an antibody response is already in progress. Second, spleen cells exposed to MV in vivo produce one or more soluble factors capable of suppressing both proliferative and antibody responses of normal lymphocytes.

Malignant rabbit fibroma virus: observations on the culture and histopathologic characteristics of a new virus-induced rabbit tumor

The clinical, histopathologic, and cultural characteristics of a newly isolated poxvirus, malignant rabbit fibroma virus (MV), were investigated. MV was isolated from tumors induced by an uncloned stock of Shope fibroma virus (SFV). MV, SFV, and rabbit myxoma virus were compared. Similarly to myxoma virus, MV grew to higher titer in vitro than did SFV and produced plaques rather than foci on rabbit kidney cell monolayers. Unlike the local, self-limited fibroblastic proliferations observed in SFV recipients, MV and myxoma caused a fulminant clinical syndrome characterized by malignant histology, metastases, and supervening fatal gram-negative infection with Pasteurella multocida. MV induced a large, protuberant local tumor and discrete metastases histologically resembling myxosarcomas. Draining lymph nodes contained metastases and showed diffuse cortical hyperplasia. Kupffer's cells were prominent in the liver, and macrophages were abundant in the splenic sinusoids. The lungs and trachea were spared, but the conjunctiva and nasal mucosa showed squamous metaplasia and atypia, with overlying Pasteurella infection and underlying tumor. Myxoma virus infection produced similar mucosal changes, but both of these as well as the epidermis overlying the myxomas showed cytoplasmic virus inclusions. Neither the skin nor the epithelial surfaces overlying MV-induced tumors nor the tumors themselves contained virus inclusions. Thus the tumor syndrome caused by MV differed from other known rabbit tumors. Endonuclease restriction digests showed that the MV genome resembled, but was distinct from, rabbit myxoma virus. Opportunistic infection associated with MV-induced disseminated tumor may be an experimental model for the infectious complications that often supervene in host-tumor relationships.

Immunohistology of malignant rabbit fibroma virus--a comparative study with rabbit myxoma virus

Malignant rabbit fibroma virus (MV) causes a syndrome that consists of disseminated malignant tumors and immunosuppression complicated by severe Pasteurella multocida infection and death. Tissues from rabbits given MV and rabbit myxoma virus were examined by direct immunofluorescence with the use of antibody against virus antigens. Primary and metastatic tumors caused by MV and rabbit myxoma virus were composed of soft tissue cells containing virus antigens. Skin appendages and epidermis overlying the respective tumors showed scant MV but abundant myxoma virus antigen. Both viruses were present systemically in the reticuloendothelial system. Epithelial cells from the liver, kidney, and lung of myxoma virus-infected rabbits contained virus, whereas in MV tumor-bearing rabbits, these cells were uninvolved. However, nasal mucosal and conjunctival epithelia, the locations of Pasteurella infection, showed squamous metaplasia and contained large amounts of MV and myxoma antigens. By analogy to other respiratory tract pathogens, these epithelial changes were probably etiologically significant for development of pasteurellosis in rabbits bearing virus-induced tumors. Thus by immunopathologic as well as clinical examination, MV produces a syndrome distinct from that seen with rabbit myxoma virus. MV induced severe immunosuppression despite T-lymphocyte hyperplasia in the lymphoid tissues observed. The combination of a systemic virus infection, epithelial alterations that impaired clearance mechanisms, and immunologic dysfunction is likely to contribute to the inability of rabbits given MV to survive their gram-negative infection.

Immunity to pasteurellosis in compromised rabbits

Pasteurellosis in the rabbit inoculated with a malignant variant of Shope fibroma virus (SFV-MV) is presented as a model for the study of immunosuppression and immunoprophylaxis in pasteurellosis. The rabbits, before the inoculation, were healthy carriers of Pasteurella multocida. They were intradermally inoculated with SFV-MV, and 3 to 6 days later, a primary tumor appeared at the site of inoculation. By postinoculation day (PID) 7 or 8, the rabbits had snuffles, conjunctivitis, and tumor metastases; death occurred on PID 10 to 14. Rabbits given the nonmalignant Patuxent strain of SFV developed local primary tumors, but not pasteurellosis nor metastases. In SFV-MV-inoculated rabbits, there was decreased responsiveness of spleen lymphocytes to B and T cell mitogens by day 6, and of spleen and peripheral blood lymphocytes by day 10. In addition, SFV-MV antigen was detected (by immunofluorescence) in mononuclear phagocytes in all major organs and in epithelial cells of the conjunctiva and nasal mucosa. Both nasal and conjunctival epithelia showed squamous metaplasia as well. These changes did not appear in SFV-infected rabbits. With SFV-MV-inoculated rabbits, we obtained partial protection against pasteurellosis by immunization with heat-killed P multocida or a cross-protective core lipopolysaccharide mutant of Escherichia coli (J5). Rabbits were immunized before the inoculation with SFV-MV which precipitated "spontaneous" pasteurellosis due to impaired defenses. Rabbits immunized with J5 or P multocida had less severe conjunctivitis and snuffles than nonimmunized controls, indicating that immunization with the J5 mutant may be useful as prophylaxis against pasteurellosis in compromised hosts.

Malignant rabbit fibroma virus causes secondary immunosuppression in rabbits

Shope fibroma virus (SFV) causes a localized, self-limited, fibroblastic proliferation in adult rabbits. Extracts of Shope fibroma tumors were found to contain a second virus that induces a rapidly progressive disseminated tumor. Dissemination of this malignant fibroma is associated with activation of commensal mucosal infection with Pasteurella multocida, causing purulent conjunctivitis and rhinitis and resulting in death from nasal obstruction. We have isolated this new agent by two cycles of plaque purification. It is a poxvirus that is antigenically virtually identical to SFV as measured by a plaque reduction assay, but behaves differently both in vivo and in vitro. We have called this virus malignant rabbit fibroma virus (MV). Electrophoresis of restriction digests made with HIND III indicates that despite the antigenic similarity of SFV and MV, the locations of HIND III sites in the two viral genomes are quite different. These experiments have enabled us to determine that MV was present in small quantities in our initial uncloned stock of Patuxent strain SFV. Lymphocytes from rabbits bearing MV-induced tumors responded poorly to both B and T lymphocyte mitogens. This nonspecific immunologic dysfunction is evident at or before the time when metastases and Gram-negative infection develop, and it becomes more profound as the disease progresses. MV-induced tumors may provide a model for Gram-negative infection and decreased immunologic responsiveness associated with malignancies.