G(RADA1): a new cell surface antigen of mouse leukemia defined by naturally occurring antibody and its relationship to murine leukemia virus

Resistance to Moloney Murine Sarcoma Virus (M-MuSV) Tumor Induction is Associated with Natural Antibody Production to «Endogenous» Moloney Leukemia Virus (M-MuLV) in Balb/Mo Mice

BALB/Mo mice are characterized by early expression of « endogenized » M-MuLV and are resistant to M-MuSV tumor induction. Furthermore, compared to normal BALB/c mice, sera from BALB/Mo mice exhibit a significant reactivity which is specific for M-MuLV when tested in a 125I-labelled Staphylococcus protein A binding assay. The possible significance of this reactivity in conferring tumor resistance is explored.

Natural Antilymphoma Antibodies in C3Hf Mice Serum: Lack of Identity with Autoimmune and anti Murine Leukemia Virus Antibodies

Absorption experiments on C3Hf normal mouse sera followed by cytotoxic tests on EL4 lymphoma cells were done to investigate a possible identity between natural antilymphoma antibodies (NAA) and various types of autoantibodies known to be present in normal mouse sera. Single C3Hf normal sera were also tested both by cytotoxicity on EL4 cells and by radioimmune precipitation assay (RIP) on 125I-labelled AKR ecotropic virus to ascertain whether or not viral antigen are the target structures of the NAA activity. The study provides evidence that NAA coexist with autoanticorpal and antiviral activities although they are distinct entities.

Correlation between the Presence of Natural Antitumor Antibodies and Activation of Mulv Endogenous Virus in Balb/C Mice

Individual 3-month-old or 12-month-old BALB/c mice, as well as 5-month-old nu/nu or nu/ + BALB/c mice, showed a direct correlation between the serum level of natural antitumor cytotoxic antibodies and the capacity of spleen cells to infect SC-1 cells permissive for murine ecotropic viruses. Pooled or individual sera from 3-month-old BALB/c mice, negative for the presence of natural antitumor cytotoxic antibodies and whose spleen cells were unable to infect the SC-1 cells, were negative both for SC-1 cells and SC-1 cells infected by MuLV. On the contrary, pooled or individual sera from 15-month-old BALB/c mice, positive for the presence of natural antitumor antibodies and with infecting spleen cells, were cytotoxic for infected SC-1 cells but not for the uninfected ones. The infection of SC-1 cells by MuLV could be inhibited by 3-month-old spleen cells, and this effect was suppressed by depriving the inhibiting spleen cells of T cells by means of an anti-Thy-1 antibody plus complement. The cells with infectious capacity did not belong to the T-cell compartment, as demonstrated by the lack of infection after passing the infecting spleen cells through an anti-Ig column, whereas T-deprivation did not modify the infectious capacity. A natural anti-gp70 monoclonal antibody, which exerted a complement-dependent cytotoxic effect on tumor cells, stronghly inhibited the infection of the permissive SC-1 cells by MuLV.

Concordant lung xenograft rejection in a hamster-to-rat model

This study was conducted to investigate the functional and morphological aspects of orthotopic lung xenograft rejection in a concordant hamster-to-rat donor-recipient species combination. By postoperative day (POD) 3, allotransplanted grafts demonstrated good aeration, but infiltrates were seen in all the xenotransplanted lungs. Antihamster lymphocytotoxic antibody titers increased to 5.2 +/- 1.1 by POD 3 (P < 0.05 vs POD 1) and reached 7.0 +/- 0.8 by POD 5 (P < 0.05 vs PODs 1 and 3). The CD4+/CD8+ ratio in peripheral blood lymphocytes increased significantly on POD 3 (P < 0.05 vs untransplanted), but decreased by POD 5 (P < 0.05). Histologically, on POD 3 the xenotransplanted grafts were characterized by perivascular cellular infiltrates and edema. Cytologically, the cells consisted of small round lymphocytes, monocytes, and occasional neutrophils. Immunohistochemical analysis showed heavy IgM and C3 deposits in the vascular endothelium, without any IgG deposits. Allotransplanted grafts showed moderate W 3/25 + (28.3 +/- 17.3%) and MRC OX8 + (38.7 +/- 0.7%) cellular infiltrations on POD 3, but ED1 + (8.0 +/- 3.7%) cells were rare. Conversely, in the xenotransplanted grafts, ED1 + (34.2 +/- 16.4%) cells were more prevalent than MRC OX8 + (18.1 +/- 16.5%) cells on POD 3, at P < 0.01 and P < 0.05 vs allograft, respectively. These results indicate that both antidonor antibodies and macrophages/monocytes play an important role in the concordant lung xenograft rejection.

Prolongation of lung xenograft survival in rats with a short course of deoxyspergualin and cyclosporin A

The efficacy of 15-deoxyspergualin (DSG), cyclosporin A (CyA), and splenectomy--alone or in combination--in prolonging the survival of concordant lung xenotransplants was studied in the hamster-to-rat model. In the untreated group, rejection occurred within 3 days, with an elevation of lymphocytotoxic antibody titers. The rejected lung revealed that ED1 + cells were more prevalent than MRC OX8 + cells in the perivascular infiltrates. In the DSG group, the antibody response was suppressed and median survival increased to 7.5 days. The rejected lungs demonstrated a highly significant depression in ED1 + cellular infiltration and a moderate MRC OX8 + cellular infiltration. When maintenance CyA was combined with a short course of DSG, survival dramatically increased to beyond 100 days. There were no deposits of IgM, IgG, or C3 or of any cell infiltrate in the grafts of two animals sacrificed 107 and 119 days post-transplantation. We conclude that initial treatment with DSG combined with continuous CyA can suppress acute rejection in the hamster-to-rat lung xenograft model, resulting in long-term graft survival.

Cell surface antigens of radiation leukemia virus-induced BALB/c leukemias defined by syngeneic cytotoxic T lymphocytes

Two cell surface antigens of mouse leukemias were defined by BALB/c cytotoxic T lymphocytes (CTL) generated against syngeneic radiation leukemia virus (RadLV)-induced leukemia, BALBRV1 or BALBRVD. Hyperimmunization of BALB/c mice with irradiated leukemias followed by in vitro sensitization of primed spleen cells resulted in the generation of CTL with high killing activity. The specificity of CTL was examined by direct cytotoxicity assays and competitive inhibition assays. A shared cell surface antigen, designated as BALBRV1 antigen, was detected by BALB/c anti-BALBRV1 CTL. BALBRV1 antigen was expressed not only on RadLV-induced BALB/c leukemias except for BALBRVD, but also on spontaneous or X-ray-induced BALB/c leukemias, chemically-induced leukemias with the H-2d haplotype and some chemically-induced BALB/c sarcomas. In contrast, a unique cell surface antigen, designated as BALBRVD antigen, was detected by BALB/c anti-BALBRVD CTL. BALBRVD antigen was expressed only on BALBRVD, but not on thirty-nine normal lymphoid or tumor cells. These two antigens could be distinguished from those previously defined on Friend, Moloney, Rauscher or Gross murine leukemia virus (MuLV) leukemias, or MuLV-related antigens. Both cytotoxic responses were blocked by antisera against H-2Kd, but not H-2Dd. The relationship of BALBRV1 antigen and BALBRVD antigen to endogenous MuLV is discussed with regard to the antigenic distribution on tumor cell lines.

Leukemia X fibroblast hybrid cells prolong the lives of leukemic mice

ASL-1 leukemia X LM(TK-) fibroblast hybrid cells prolong the livers of leukemic (A/JXC3H/HeJ)F1 mice. The hybrid cells, like the fibroblast cells used in forming the hybrid, have lost malignant growth properties in immunocompetent recipients and are rejected. Mice receiving hybrid cells along with ASL-1 cells exhibit immunity toward the leukemia cells; approximately 50% of the animals injected with 10(6) or more hybrid cells along with ASL-1 cells survive more than 60 days; animals in the control group injected with leukemia cells alone invariably die in shorter intervals. The immunity generated is persistent for at least 6 months. Some leukemic mice receiving doses of combination chemotherapy which are insufficient to cure them of the disease survive for prolonged and at times indefinite periods if they are injected with hybrid cells. The immunity generated in mice receiving hybrid cells is directed toward a leukemia-associated antigen of leukemia cells expressed by hybrid cells as well. In mixed lymphocyte culture a heightened stimulation of spleen cells from hybrid cell-injected mice toward ASL-1 cells is observed.

Cellular expression of murine leukemia virus gp70-related antigen on thymocytes of uninfected mice correlates with Fv-4 gene-controlled resistance to Friend leukemia virus infection

Alleles at the Fv-4 locus have been shown to determine susceptibility (Fv-4s) and resistance (Fv-4r) to infection with ecotropic murine leukemia viruses (MuLV). The resistance is dominant in heterozygous mice. BALB/c mice are Fv-4ss and a semicongenic line BALB/c-Fv-4wr, homozygous for Fv-4r allele and called C4W, is being developed. Extracts of 125I-labeled thymocytes from BALB/c and C4W mice were precipitated by a series of antisera against MuLV and the precipitates examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Thymocytes from C4W mice expressed 80K and 73K glycoproteins related to the gp70 of MuLV, while only the 73K glycoprotein was occasionally detectable on BALB/c thymocytes. Genetic studies showed that a locus controlling expression of the 80K protein was dominant and associated with the resistant allele at Fv-4. This membrane gp70 may be important in the Fv-4-mediated resistance to exogenous virus infection.

H-2 control of the cytotoxic antibody response against a newly defined MuLV-related cell-surface antigen: G(B10.A)

H-2-congeneic C57BL mice with milk transmission of B-tropic murine leukemia virus (V+ mice) have a much higher lymphoma incidence than the same strains without milk-transmitted virus (V- mice). Gene(s) within the major histocompatibility complex (H-2) influence virus titers, lymphoma incidence, lymphoma type and the anti-MuLV envelope antibody response. In this paper, we report that the prevalence of cytotoxic antibodies to virus-induced lymphomas is also regulated by the H-2 complex. Milk transmission of MuLV resulted in the formation of cytotoxic antibodies against primary virus-induced C57BL lymphomas. These antibodies detect an antigen that is also present on the RADAI tumor-cell line, and on normal spleen cells of young adult B10.A (H-2a) mice of both V+ and V- sublines, but not on spleen cells of young adult B10 (H-2a) mice of either subline. These cytotoxic antibodies were detected in the sera of B10V+ and B10.A(5R)V+ animals, but not in the sera of B10.AV+ mice. This indicates that the prevalence of these antibodies is controlled by a gene in the K- and/or I-A region of the H-2 complex. The presence of these cytotoxic antibodies in serum is recessively inherited. The specificity of the cytotoxic antibodies was investigated with a standard panel of transplantable tumor-cell lines. Of these, only the RADAI cells expressed the target antigen in direct cytotoxicity tests and by absorption. The ability of B10V+ sera to lyse the B10.AV+ and RADAI tumor cells is ascribed to antibody activity against a new MuLV-related cell-surface protein: G(B10.A). Immunochemical analysis and absorption experiments with different types of purified MuLV and MuLV-infected cell lines indicate that the cytotoxic antibodies belong to low-avidity IgM antibodies that are directed to MuLV.

A cell surface antigen of the mouse related to xenotropic MuLv defined by naturally occurring antibody and monoclonal antibody. Relation to Gix G(rada1), G(aksl2) systems of MuLV-related antigens

A new cell surface antigen of the mouse related to xenotropic murine leukemia virus (MuLV) is described. The antigen, designated G(erld), is defined by cytotoxic tests with the B6-x-ray-induced ERLD and naturally occurring antibody. G(erld) is distinct from all previously defined cell surface antigens. Monoclonal antibody with the same specificity has been developed. Inbred mouse strains are classified as G(erld)+ or G(erld)- according to the presence of absence of the antigen on lymphoid cells. G(erld)+ strains differ with regard to quantitative expression of G(erld) on normal thymocytes. The emergence of G(erld)+ tumors in G(erld)- strains indicates the presence of genes coding for the antigen even in strains not normally expressing the antigen. G(erld) has the characteristic of a differentiation antigen in normal mice. In G(erld)+ strains, high levels of the antigen are found on thymocytes with lower levels being detected on cells of spleen, lymph nodes and bone marrow. No G(erld) was detected in brain or kidney or on erythrocytes. The segregation ratios for G(erld) expression on thymocytes in backcross and F2 mice of crosses between G(erld)+ (B6, 129, and B6-Gix+) and G(erld)- (BALB/c) strains suggest that G(erld) expression is controlled by a single locus in B6, by two unlinked loci in 129, and by three unlinked loci in B6-Gix+ mice. Induction of the antigen by MuLV infection of permissive cells in vitro indicates that G(erld) is closely related to xenotropic and dualtropic MuLV; all xenotropic and dualtropic MuLV tested induced the antigen, whereas the majority of ecotropic and the two amphotropic MuLV failed to do so. As dualtropic MuLV are thought to be recombinants between ecotropic and xenotropic MuLV sequences, G(erld) coding by dualtropic MuLV may signify the contribution of the xenotropic part in the recombinational event. Serological and biochemical characterization indicates that G(erld) is related to the gp 70 component of the MuLV envelope. The relation of G(erld) to the previously defined gp 70-related cell surface antigens (Gix, G(rada), and G(aksl2) is discussed, particularly with regard to their characteristics as differentiation antigens, the genetic origin of dualtropic MuLV, and the leukemogenicity of MuLV.

Alloantigen-induced T-cell proliferation: Lyt phenotype of responding cells and blocking of proliferation by Lyt antisera

Cytotoxic T cells of the mouse express Lyt-1 as well as Lyt-2 and -3 on their surface, and T-cell cytotoxicity can be blocked by Lyt-2 and Lyt-3 (but not Lyt-1) antisera in the absence of added complement [Nakayama, E., Shiku, H., Stockert, E., Oettgen, H. F. & Old, L. J. (1979) Proc. Natl. Acad. Sci. USA 76, 1977-1981]. This analysis has now been extended to the study of the Lyt phenotype of T cells responding to alloantigens, concanavalin A (Con A), and phytohemagglutinin (PHA) and the effect of Lyt antibody on T-cell proliferation and the generation of H-2-specific killer T cells. H-2 (D/K and I), Con A, and PHA stimulation was abolished by pretreating responding cell populations with Lyt-1 antiserum and complement. Pretreatment with Lyt-2 or -3 antiserum and complement did not decrease alloantigen or Con A stimulation but did abolish PHA stimulation. Cytotoxic cells were not generated in H-2 alloantigen-primed cultures pretreated with Lyt-1, -2, or -3 antiserum and complement. When responding cells were cultured with Lyt antiserum in the absence of added complement, Lyt-2 or -3 antiserum (but not Lyt-1 antiserum) blocked alloantigen-induced proliferation and delayed generation of killer cells. Under similar conditions, Con A and PHA stimulation was not blocked by Lyt-1,-2, or -3 antiserum. Evidence from these Lyt elimination and blocking tests and from direct Lyt phenotyping of responding cells leads to the following conclusions. Two populations of Lyt(+) cells are involved: Lyt-1(+)2(-)3(-) and Lyt-1(+)2(+)3(+). Current evidence does not favor the existence of Lyt-1(-)2(+)3(+) cells but indicates that pre-killer and killer cells derive from the Lyt-1(+)2(+)3(+) population and have a Lyt-1(+)2(+)3(+) phenotype. H-2 (D/K and I) and PHA stimulation ordinarily activate the Lyt-1(+)2(+)3(+) population, whereas Con A and I region or Mls locus antigens activate the Lyt-1(+)2(-)3(-) population. However, when Lyt-1(+)2(+)3(+) cells are eliminated or blocked by Lyt-2 or -3 antiserum, H-2 alloantigen stimulation leads to proliferation of the Lyt-1(+)2(-)3(-) population. Blocking of H-2-induced proliferation by Lyt-2 or -3 antiserum adds further support to the possibility that molecules bearing Lyt-2 and -3 determinants are involved in T-cell recognition.

Binding of anti-tumor immunoglobulins and their daunomycin conjugates to the tumor and its metastase. In vitro and in vivo studies with Lewis lung carcinoma

The present study was undertaken in order to evaluate the possibility of using anti-tumor antibodies as specific carriers of chemotherapeutic drugs to tumor metastases. Xenogeneic and syngeneic antisera were prepared against a metastasizing C57BL tumor, the Lewis lung carcinoma (3LL). The binding of absorbed xenogeneic and syngeneic anti-3LL sera or their Ig fractions to 3LL tumor cells was assayed by direct and indirect methods. Antisera prepared against tumor cells from a local growth reacted to a similar extent with those obtained from the lung metastases. Radioiodinated immunoglobulins from syngeneic antisera injected into mice bearing metastases localized preferentially in metastasis-bearing lungs as compared to several other organs tested. No such preferential uptake was observed either in mice bearing metastases injected with iodinated normal Ig or in normal mice injected with iodinated anti-3LL Ig. This relative accumulation in the metastasis-bearing lungs was observed 3-4 days after the inoculation, when the whole Ig fraction was used, whereas a specific antibody-enriched preparation localized as early as 24 h after injection. Daunomycin--anti-3LL-Ig conjugates were effective inhibitors of tumor cells from both local and the metastatic growths. They were more active than either the free drug or drug conjugates of normal Ig, in in vitro assays.

Autoimmune and lymphoproliferative disease in (B6-GIX+ X 129)F1 mice: relation to naturally occurring antibodies against murine leukemia virus-related cell surface antigens

G(IX) congeneic mouse strains, C57BL/6-G(IX) (+)(B6-G(IX) (+)) and 129-G(IX) (-), have been derived from the prototype strains, B6(G(IX) (-)) and 129(G(IX) (+)). The hybrids, (B6-G(IX) (+) x 129)F(1) (G(IX) (+)F(1)) and (B6 x 129-G(IX) (-))F(1) (G(IX) (-)F(1)), differ only in regard to genetic loci controlling G(IX) antigen expression. G(IX) (+)F(1) mice spontaneously produce G(IX) antibody and often show signs of autoimmune disease and lymphoproliferative disease. G(IX) (-)F(1) mice and mice of the two parental strains (B6-G(IX) (+) and 129) of G(IX) (+)F(1) do not produce G(IX) antibody and seldom show signs of these diseases. G((ERLD)), and G((RADA1)), antibodies, natural thymocytotoxic autoantibody, and antinuclear antibodies were produced by G(IX) (+)F(1) mice. However, these four antibodies were also found in the other strains. G(IX) (+)F(1) mice develop pronounced diffuse glomerulonephritis similar to that found in systemic lupus erythematosus in man. Incidence studies in which mice were examined according to age rather than state of health showed that the lesions occurred in 38% of G(IX) (+)F(1) mice but not in G(IX) (-)F(1), B6-G(IX) (+), or 129 mice. Lymphoproliferative lesions were either reticulum cell sarcoma (RCS) type A or reactive lymphoid hyperplasia (RLH). RCS occurred more often in G(IX) (+)F(1) (38%) than in G(IX) (-)F(1) (12%) or B6-G(IX) (+) (8%). No RCS occurred in mice of the 129 strain. RLH occurred in G(IX) (+)F(1) mice (10%) but not in the other strains. From these results, the following conclusions are drawn: (i) Severe glomerulonephritis and the increased occurrence of lymphoproliferative lesions in these animals depend on the presence of G(IX) antigen; (ii) besides genes controlling G(IX) antigen expression, other genes from both parental strains are required to create the basis in the progeny F(1) mice for the development of these diseases; and (iii) the chronic production of G(IX) antibody may be necessary for the development of the severe glomerulonephritis and for the increased occurrence of lymphoproliferative diseases in G(IX) (+)F(1) mice.

Polymorphism of B-tropic leukemia viruses from BALB/c mice: association of a p30 antigen with N- versus B-tropism

Comparison of a number of murine leukemia virus clones by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed extensive protein polymorphism among B-tropic, but not N-tropic, isolates from BALB/c mice, particularly in migration of p30 proteins. A type-specific radioimmunoassay for p30 was developed which uniformly discriminated all B-tropic viruses from N-tropic viruses of BALB/c origin. N- and B-tropic viruses of C57BL/6 and AKR Fv-1b/b origin could also be distinguished by this assay.

Cell surface expression of the env gene polyprotein of dual-tropic mink cell focus-forming murine leukemia virus

Differences have been observed in the kinetics of processing of the env gene polyprotein of ecotropic, xenotropic, and dual-tropic mink cell focus-forming (MCF) murine leukemia virus. In pulse-chase experiments, the env gene polyprotein of the dural-tropic MCF virus exhibits a marked increase in stability relative to that of either ecotropic or xenotropic virus. A comparison of cell surface expression of env gene products of ecotropic, xenotropic, and dual-tropic MCF murine leukemia virus has been made. Only gp70 is accessible to lactoperoxidase-catalyzed radioiodination of fibroblasts infected by ecotropic or xenotropic virus, whereas both gp70 and the env gene polyprotein are expressed on the surface of dual-tropic MCF virus-infected cells.

Cell-surface antigens associated with recombinant mink cell focus-inducing murine leukemia viruses

Distinct type-specific antigens were detected on cells infected with cloned mink cell focus-inducing (MCF) murine leukemia viruses by means of cell surface immunofluorescence absorption assays with rabbit antisera raised against naturally-occurring AKR MCF viruses. The MCF type-specific antibodies were present in high titer and not absorbable by cells infected with ecotropic, xenotropic, or wild mouse amphotropic murine leukemia viruses, or combinations of ecotropic and xenotropic viruses. Three MCF subtype-specific reactions were identified. One subspecificity (operationally designated MCFA-1) defined antigenic determinant(s) distributed among MCF viruses in general. Another (MCFA-2) specified determinant(s) induced by all naturally occurring MCF isolates not of Friend or Moloney origin. A third subspecificity (MCFA-3) was induced by some MCF isolates, and not by others; the presence of this antigen did not correlate with the source of any presently known biological property of the viruses. In addition, type-specific antigenic determinants of ecotropic and xenotropic murine leukemia viruses were expressed on MCF virus-infected cells. The serological profile of MCF viruses thus supports the contention that they are env gene recombinants between ecotropic and xenotropic murine leukemia viruses. However, new, distinct MCF-specific determinants are also generated, and these could be useful markers in studying MCF viruses.

G(AKSL2): a new cell surface antigen of the mouse related to the dualtropic mink cell focus-inducing class of murine leukemia virus detected by naturally occurring antibody

Normal mouse sera were tested for cytotoxic antibody to surface antigens of cultured monolayer cells infected with AKR-derived ecotropic MuLV, xentropic MuLV, or dualtropic MCF 247 MuLV. Antibody to ecotropic MuLV-infected cells was found in a proportion of C57BL/6, C3Hf/Bi, AKR-Fv-1b, and (C3Hf/Bi X AKR)F1 mice, but not AKR or (AKR X C3Hf/Bi)F1 mice. Antibody to xenotropic MuLV-infected cells was virtually restricted to C57BL/6 mice. Antibody to MCF 247-infected cells was found in all strains tested, including AKR mice. Absorption analysis of (C3Hf/Bi x akr)f1 and AKR-Fv-1b sera with selective reactivity for MCF 247-infected cells showed that these sera recognize distinctive antigens on MCF 247-infected cells that are not present on ecotropic or xenotropic MuLV-infected cells. The transplantable AKR spontaneous leukemia AKSL2 was found to be uniquely sensitive to the cytotoxic action of naturally occurring antibody to MCF 247-related antigens and absorption tests with AKSL2 as the target cell and sera from a single AKR-Fv-1b mouse have permitted the definition of a new MuLV-related cell surface antigen, which has been designated G(AKSL2). Thymocytes from young mice of high leukemia-incidence strains (AKR, C58, and PL) express G(AKSL2), whereas thymocytes from 12 other strains do not. In AKR mice, the antigen is expressed in higher amounts on cells from thymus and bone marrow than on spleen cells. All AKR spontaneous leukemias tested express G(AKSL2), as did three MuLV-induced leukemias arising in G(AKSL2)- strains. Five X-ray-induced leukemias of G(AKSL2)- strains were G(AKSL2)-, as were MuLV+ and MuLV- chemically induced sarcomas. In the limited survey conducted to date, natural antibody to G(AKSL2) has been restricted to strains expressing G(AKSL2) in their normal tissues: AKR, AKR congenic mice AKR-Fv-1b and AKR hybrid mice (C3Hf/Bi x akr)f1 and (C57BL/6 X AKR)F1. In vitro G(AKSL2) induction tests involving MuLV infection of cultured monolayer cells showed that 8 of 12 newly isolated dualtropic MuLV shared the property of G(AKSL2) induction with the prototype MCF MuLV, MCF 247. Of the 12 ecotropic MuLV tested, only the N-tropic MuLV isolated from a leukemia originally induced by Passage A Gross virus induced G(AKSL2). The xenotropic and amphotropic MuLV isolates tested lacked G(AKSL2) inducing activity. Recognition of the g(aksl2) system provides a way to trace the origin and natural history of a class of dualtropic MCF MuLV in the mouse and to determine whether natural antibody to G(AKSL2) plays a role in AKR leukemogenesis.

Abelson antigen: a viral tumor antigen that is also a differentiation antigen of BALB/c mice

We report here the serologic detection of a cell surface antigen common to cells transformed by the Abelson murine leukemia virus (A-MuLV) and to normal hematopoietic cells from certain strains of mice. Serum from C57BL/6 mice hyperimmunized with syngeneic A-MuLV lymphoma cells was cytotoxic for the immunizing cells; this reaction was used as the serologic test system for recognition of A-MuLV antigens. Absorption analysis using 40 tumors and 21 cell lines revealed that two serologic specificities were detected by this test system: (i) FMR antigen(s) related to the Moloney MuLV helper (the virus from which A-MuLV was originally derived), and (ii) an antigen expressed on all cells transformed by A-MuLV. The A-MuLV-specific antigen was also present on uninfected cells from BALB/c bone marrow, spleen, and fetal liver but not from adult liver, thymus, lymph nodes, or peripheral blood. Abelson antigen was not expressed on bone marrow or spleen cells of 12 other mouse strains. In light of the original isolation of A-MuLV from a BALB/c mouse infected with Moloney virus, it is possible that Abelson antigen is a serologic marker for a gene of BALB/c mice, normally encoding a cell surface molecule, that was incorporated into the Moloney virus genome during the generation of A-MuLV.