Expression of leukemogenic recombinant viruses associated with a recessive gene in HRS/J mice

Genetic alterations of RNA leukemia viruses associated with the development of spontaneous thymic leukemia in AKR/J mice

T1-oligonucleotide fingerprinting and mapping were used to study the expression of RNA leukemia viruses in leukemic and preleukemic AKR/J mice, with techniques designed to minimize the loss or inadvertent selection of viruses in vitro before biochemical analysis. In leukemic animals, complex mixtures of ecotropic and mink-tropic viruses were expressed. Unique but similar polytropic virus-like genomes were present in each tumor isolate. In preleukemic mice, viral isolates from the thymus that were grown on NIH3T3 fibroblasts contained genomes with non-Akv polytropic virus-related oligonucleotides. This phenomenon was not evident in fingerprints of viruses from the spleen and bone marrow of the same animals. Remarkably, the non-Akv oligonucleotides located in the 3' portion of the P15E gene, the U3 noncoding region, and the 5' part of the gp70 gene were often expressed independently. Our results suggest the following. (i) Recombinant viruses can be detected in the thymuses of young preleukemic AKR mice and increase in relative abundance with age. (ii) During in vivo generation of the recombinant leukemogenic viruses, the selection of polytropic virus-related sequences in the 3' part of p15E and the U3 region and the 5' portion of gp70 occurs independently. (iii) Independent biological properties encoded in the gp70 and p15E regions of env of the recombinant viruses may mediate viral selection or leukemogenicity. (iv) The leukemogenic polytropic viruses of AKR/J mice arise via genetic recombination involving at least three endogenous viral sequences.

Leukemogenesis by Gross passage A murine leukemia virus: expression of viruses with recombinant env genes in transformed cells

Gross passage A murine leukemia virus (MuLV) derived from extracts of C3Hf/Bi mouse leukemias has been shown to be a virus complex consisting of ecotropic, xenotropic, and recombinant, dualtropic MuLV components. The three virus components were distinguished biochemically by differences in the molecular weights and peptide maps of their primary env gene products synthesized in infected cells in vivo and in vitro. Virus expression was studied in primary leukemias induced in C3Hf/Bi mice by Gross passage A virus extracts and by the individual ecotropic and recombinant MuLV components that were isolated in vitro. Our findings suggest that expression of the recombinant MuLV component of the Gross passage A virus complex is necessary and sufficient for the induction of leukemias in C3Hf/Bi mice. In contrast, induction of leukemias by the ecotropic virus component appears to involve generation of a second virus with characteristics of recombinant, dualtropic MuLV.

Expression of Ia antigen on epidermal keratinocytes is a consequence of cellular immunity

Ia antigen is seen in the normal epidermis only in Langerhans cells. However, when there is damage to the epidermis induced by cellular immunity Ia is expressed in the keratinocytes. This phenomenon is not seen in trauma or chemical inflammation. It is suggested that the expression of Ia in keratinocytes is due to cellular immunity possibly due to a lymphokine.

Immunodeficiency and reticulum cell sarcoma in mice segregating for HRS/J and SJL/J genes

Hairless (hr/hr) mice segregating for SJL/J and HRS/J genes (SJL-HRS) were compared to their haired counterparts with respect to immune responsiveness, tumour development and ecotropic murine leukemia virus (MuLV) expression. Homozygosity at the hairless locus did not affect expression of MuLV. There was however, a significant depression of the cellular immune response of these mice as characterized by depressed reactions in phytohemagglutinin, concanavalin A and mixed leukocyte assays. Haired and hairless mice did not differ significantly in response to B-cell mitogens or in production of cytotoxic antibody. The depressed cellular immune response in hr/hr mice is associated with a distinctive histologic type of spontaneous reticulum cell sarcomas. The importance of these results in relation to previous studies of HRS/J hairless mice is discussed.

Sequence-specific antibodies show that maturation of Moloney leukemia virus envelope polyprotein involves removal of a COOH-terminal peptide

We followed maturation of the glycosylated envelope polyprotein Pr80env of a murine retrovirus by using antisera specific to subregions of the protein, including an antiserum directed against a synthetic peptide corresponding to the COOH-terminus of Pr80env. Shortly after synthesis and glycosylation, Pr80env is cleaved into two species, gp70 and Pr15E, that are found associated, perhaps through disulfide bonds, in infected cells. Pr15E is further cleaved at the time of virus maturation to form virus protein p15E. NH2-Terminal protein sequence analysis showed that Pr15E had an NH2 terminus in common with p15E. Pr15E, but not p15E, is precipitated by antibody against the COOH-terminal peptide; hence, p15E is missing a peptide at the COOH-terminus. Our data indicate that Pr15E is the predominant species in cells and p15E is the major species in virus.

Genetics of susceptibility for radiation-induced leukemia. Mapping of genes involved to chromosomes 1, 2, and 4, and implications for a viral etiology in the disease

Susceptibility to radiation-induced leukemia in (A/J x B10)F2 mice is encoded for by genes in chromosomes 1, 2, and 4. The loci involved in chromosomes 1 and 4 are close to or similar to xenotropic virus inducibility locus on chromosome 1 and a locus-affecting expression of xenotropic MuLV envelope-related cell surface antigens. Radiation-induced leukemia-1 (Ril-1) on chromosome 2 plays an overriding influence in susceptibility to the disease. This locus might encode ecotropic viral-associated genetic information or might contain cellular sequences with oncogenic potential. These findings are of interest in view of the importance of recombinant viruses to leukemogenesis. Furthermore, it is intriguing that Ril-1 is located in a chromosomal site rich in thymus differentiation-specific loci. An explanation for tissue-specific activation of endogenous viruses is that activation of the virus in question is dependent on differentiation-specific steps.

Genomes of murine leukemia viruses isolated from wild mice

The genomes of murine leukemia viruses (MuLV) isolated from wild mice have been studied. Detailed restriction endonuclease maps of the 8.8-kilobase (kb) unintegrated linear viral DNAs were derived for five ecotropic and five amphotropic MuLV's from California field mice, for Friend MuLV, and for one ecotropic and one xenotropic MuLV from Mus musculus castaneus. In general, the California MuLV's were similar in their leftward 6 kb (corresponding to the leftward long terminal repeat [LTR], gag, and pol) and rightward 1 kb (7.8 to 8.8 kb, corresponding to p15E and the rightward LTR). For the region spanning 6.0 to 7.7 kb (which includes the sequences that encode gp70) the amphotropic MuLV's shared few enzyme sites with the ecotropic MuLV's, although the California ecotropic MuLV's were highly related to each other in this region, as were the amphotropic MuLV's. Cross-hybridization studies between amphotropic and California ecotropic MuLV DNAs indicated that they were not homologous in the region 6.3 to 7.6 kb; the California ecotropic viral DNAs cross-hybridized in this region to AKR ecotropic MuLV. When the California viral DNAs were compared with AKR ecotropic viral DNA, many differences in enzyme sites were noted throughout the genome. The U3 regions of the wild mouse LTRs showed partial homology to this region in AKR MuLV. The LTR of Moloney MuLV was highly related to that of the California MuLV's, whereas the LTR of Friend MuLV appeared to be a recombinant between the two types of LTRs. The M. musculus castaneus isolates were most closely related to ecotropic and xenotropic MuLV's isolated from inbred mice. One amphotropic MuLV DNA was cloned from supercoiled viral DNA at its unique EcoRI site in pBR322. Viral DNAs with one and two LTRs were isolated. After digestion with EcoRI, DNAs of both types were infectious. It is concluded that ecotropic and amphotropic MuLV's differ primarily in the region which encodes gp70.

A single dominant gene determines susceptibility to a leukaemogenic recombinant retrovirus

The production of recombinant retroviruses is an important episode in the natural history of thymic leukaemia in AKR and HRS/J (hr/hr) mices. These viruses apparently originate from ecotropic and xenotropic precursors in the late preleukaemic stage of the disease. Analyses of their structural proteins and genomic oligonucleotides indicate that they arise by recombination of env genes of the precursor viruses. This event leads to a viral envelope glycoprotein (gp70) with some peptides that have features of the gp70 glycoproteins of ecotropic and xenotropic viruses, and others that are unique for each recombinant virus. The former property explains the broad host range of recombinant viruses, and hence their designation as dual tropic or polytropic viruses. It has been postulated that the unique aspect of each recombinant's gp70 determines the phenotypes of leukaemic cells. Polytropic viruses may be highly thymotropic. Their systemic administration results in an infection that confines itself virtually to the thymus. Moreover, these viruses are leukaemogenic whereas their precursors are not, or only weakly so. The leukaemogenicity of polytropic viruses is, however, restricted to certain inbred strains of mice. The HRS/J isolate PTV-1 is leukaemogenic in HRS/J and CBA/J mice, but not in SWR/J or NIH/Swiss mice. The experiments described here demonstrate that a single dominant gene permits infection by thymocytes by a leukaemogenic polytrophic virus. CBA/J mice, which develop thymic leukaemia after infection by this virus, posesses this gene, whereas leukaemia-resistant NFS mice lack it.

Relation between HLA-DR-like antigens and secretory component (SC) in jejunal epithelium of patients with coeliac disease or dermatitis herpetiformis

HLA-DR-like antigens and secretory component (SC) were localized immunohistochemically in adjacent tissue sections of ethanol-fixed paraffin-embedded jejunal mucosa from control subjects and patients with coeliac disease (CD) or dermatitis herpetiformis (DH). HLA-DR-like antigens were found in a patchy distribution apically in the columnar epithelial cells facing the gut lumen and in the upper part of the crypt epithelium. The staining pattern was similar in controls and patients with CD or DH. SC was normally most abundant in the crypt epithelium but the concentration of SC in the surface epithelium increased with increasing villous atrophy both in CD and DH patients. Despite this sign of immaturity, the surface cells retained their capacity to express HLA-DR-like antigens in the pathological mucosa.

Immunoregulation

The immune system of higher vertebrates is a complex network of separate, interacting cell populations, each ontogenetically endowed with specific regulatory (inductive or suppressive) or effector functions. The products of at least two major gene clusters-the immunoglobulin structural genes and the genes of the major histocompatibility complex-are expressed as active and passive recognition structures on cells of the immune system and at least some of their secreted products. Macrophages play a critical role in the initiation of immune responses. Regulatory subsets of thymus-derived lymphocytes interact with macrophages and with each other in the control of immune effector cells. At every level of the immune response, cell interactions require that these regulatory cells recognize gene products of the major histocompatibility complex. Due to recent technical advances, rapid progress is being made in identifying subsets of human immunoregulatory cells; those identified to date show strong functional homology to previously well characterized murine cell subsets.

Surface phenotypes in T-cell leukaemia are determined by oncogenic retroviruses

Spontaneous thymic leukaemia in experimental mice is the result of a complex series of genetically controlled events. An important step in this process involves the production by thymocytes of recombinant polytropic retroviruses (MCF viruses). These leukaemogenic agents arise by recombination of genes from the env regions of endogenous precursor viruses. Sequences in these regions encode the envelope glycoprotein gp70 (ref. 6). Thus far, each cloned isolate of recombinant virus from AKR and HRS/J mice has been found to possess unique oligonucleotide sequences in its env region, as well as clone-specific peptides in its gp70 (refs 7,8). Therefore, the polytropic viruses of these leukaemia-susceptible mice are extremely diverse. These findings suggest that random recombination of env genes gives rise to leukaemogenic polytropic viruses. McGrath and Weissman have proposed that thymocytes with cell surface receptors for the gp70 of a particular leukaemogenic virus are the target cells for malignant transformation by that specific virus. In view of the diversity of polytropic viral gp70, their hypothesis would predict extensive phenotypic diversity among spontaneous thymic leukaemias. In contrast, leukaemias induced by a particular leukaemogenic recombinant virus would always have the same phenotype. Here we verify these predictions experimentally.