Identity of murine lymphocyte alloantigens DAG, ALA-1, Ly-8, and Ly-6?

The major locus for mouse adenovirus susceptibility maps to genes of the hematopoietic cell surface-expressed LY6 family

Susceptibility to mouse adenovirus type 1 is associated with the major quantitative trait locus Msq1. Msq1 was originally mapped to a 13-Mb region of mouse chromosome (Chr) 15 in crosses between SJL/J and BALB/cJ inbred mice. We have now narrowed Msq1 to a 0.75-Mb interval from 74.68 to 75.43 Mb, defined by two anonymous markers, rs8259436 and D15Spn14, using data from 1396 backcross mice. The critical interval includes 14 Ly6 or Ly6-related genes, including Ly6a (encoding Sca-1/TAP), Ly6e (Sca-2/Tsa1), Ly6g (Gr-1), and gpihbp1 (GPI-anchored high-density lipoprotein-binding protein 1), as well as the gene encoding an aldosterone synthase (Cyp11b2). The Ly6 family members are attractive candidates for virus susceptibility genes because their products are GPI-anchored membrane proteins expressed on lymphoid and myeloid cells, with proposed functions in cell adhesion and cell signaling. To determine interstrain variation in susceptibility and produce additional resources for cloning Msq1, we assayed the susceptibility phenotype of four previously untested inbred mouse strains. Susceptibility of strain 129S6/SvEvTac was subsequently localized to the Ly6 complex region, using polymorphic genetic markers on Chr 15 in a population of 271 (129S6/SvEvTac x BALB/cJ)F(1) x BALB/cJ backcross mice. We identified a major 129S6/SvEvTac susceptibility allele, Msq1(129S6), on Chr 15 in the same region as Msq1(SJL). The results indicate that a major host factor in mouse adenovirus type 1 susceptibility is likely to be a member of the Ly6 gene family.

Genes on chromosomes 1 and 4 in the mouse are associated with repair of radiation-induced chromatin damage

Early-passage skin fibroblasts from different inbred and congenic strains of mice were X-irradiated (1 Gy), and the number of chromatid breaks was determined at 2.0 h after irradiation. The cells from DBA/2N, C3H/HeN, STS/A, C57BL/6N, BALB/cJ, and AKR/N had 25 to 42 chromatid breaks per 100 metaphase cells (efficient repair phenotype). NZB/NJ had greater than 78 and BALB/cAn had 87 to 110 chromatid breaks per 100 cells (inefficient repair phenotype). Differences between BALB/cAn and BALB/c. DBA/2 congenic strains which carry less than 1% of the DBA/2 genome indicate that two genes, one on chromosome 1 linked to bcl-2-Pep-3 and the other on chromosome 4 closely linked to Fv-1, affect the efficiency with which the cells repair radiation-induced chromatin damage.

Ly-6A.2 and Ly-6E.1 molecules are antithetical and identical to MALA-1

Rat monoclonal antibodies YE3/19.1, defining the murine-activated lymphocyte antigen MALA-1, and D7, detecting an Ly-6 locus-controlled antigen, bound highly purified Ly-6E.1. On western blots of lymphocyte surface proteins which had been solubilized and electrophoretically separated in octylglucoside, they detected bands which comigrated with Ly-6A.2 or Ly-6E.1 antigens. On cells or in an immunoassay they blocked alloantibodies against Ly-6A.2 or Ly-6E.1. The tissue distribution of MALA-1 also correlated with Ly-6A.2 or Ly-6E.1. Upon octylglucoside or sodium dodecyl sulfate-polyacrylamide gel electrophoresis, these antigens displayed similar sizes. Thus, Ly-6A.2 and Ly-6E.1 are most likely products of alternate alleles. Electrophoretic analysis showed a similar size and charge for Ly-6A.2, Ly-6B.2, Ly-6D.2, and Ly-27.2. Ly-6C.2 and Ly-28.2 appeared to be identical, and were similar in size to Ly-6A.2, but they differed in charge and in intrachain disulfide constraints. Since Ly-6D.2 and Ly-27.2 may represent the same or different epitopes on the Ly-6A.2 molecule, the previously postulated five Ly-6-like antigens that were thought to be separable on the basis of tissue distribution, may represent no more than three separate proteins which can be assigned to one of two distinct categories by electrophoretic mobility in gels containing octylglucoside.

Studies of murine lymphocytes and alloantigens. I. Ly-6 mitogen and MLR responses

Antisera to the mouse lymphocyte surface alloantigens Ly-6.1 and Ly-6.2 were used to further study the functional distribution of these antigens. After selective depletion with antiserum + rabbit complement (RC), lymph node or spleen cells from Ly-6 congenic (C3H and C3H.B6-Ly-6b) and noncongenic strains of mice were tested for: (a) their proliferative responses to T- and B-cell mitogens; and (b) their proliferative responses to alloantigens, or ability to stimulate in the MLR. Lymphoid cells required in the proliferative responses to the mitogens leucoagglutinin, concanavalin A (Con A), lipopolysaccharide (LPS), and pokeweed mitogen (PWM) were Ly-6+. Lymph node responder cells in the mixed lymphocyte reaction (MLR) were also Ly-6+, whereas spleen stimulator cells were Ly-6-. Treatment of lymph node cells with anti-Ly-6 sera in the absence of RC had no specific blocking effect on the response to any of these mitogens. The studies indicate that the Ly-6 antigen is a potentially valuable marker for distinguishing between functionally distinct Ly-1+ T-cell subsets.

Studies of the mouse Ly-6 alloantigen system. II. Complexities of the Ly-6 region

The discovery of several monoclonal antibodies provided the impetus to revisit the Ly-6 group of antigens. Our serological data point to the existence of at least five separate Ly-6 antigens. They are distinguished by the patterns of their tissue expression as (1) the classical Ly-6 alloantigen of peripheral lymphocytes (Ly-m6.2A), (2) a bone marrow cell-restricted antigen (Ly-m6.2B), (3) an antigen shared by bone marrow cells and peripheral lymphocytes (Ly-m6.2C, possibly identical with H9/25), (4) an antigen expressed on bone marrow cells, thymocytes, and peripheral lymphocytes (Ly-m6.2D), and (5) an antigen occurring exclusively on lymphoblasts (Ly-m6.1E, similar to Ala-1). ThB is a sixth distinct antigen of the group. The assumption that separate antigens exist is supported by distinctive distribution patterns in normal and neoplastic tissues. The genes controlling Ly-6 antigens are closely linked, as they are transmitted as two haplotypes only. One incidence of a crossover within the Ly-6 region was observed: the Ly-6B.2 alloantigen was expressed in NZB mice, which type Ly-6.1 for other Ly-6 specificities.

Genetic basis for Ly-6- defect: complementation between Ly-6- and Thy-1- mutant cell lines

Selection of antigen loss variants from the BW5147 cell line after chemical mutagenesis, using antibodies to Thy-1.1, Ly-6.2 and H9/25 allospecificities, produced cell lines with a pleiotropic defect in cell surface antigen expression; selection against any antigen led to the loss of all three determinants. The genetic basis for the mutant phenotype has been analyzed by gene complementation by somatic cell hybridization between Ly-6- or H9/25- and Thy-1- mutants, which comprise different Thy-1 gene complementation classes. The Ly-6- and H9/25- mutants can be classified as belonging to either the A or E Thy-1- mutant class.

Further analysis of the Ly-6 genetic region: isolation and characterization of cell lines with altered expression of Ly-6 antigens

The identity, or close linkage, or a series of murine alloantigens encoded by the Ly-6 genetic region has been well documented. We have investigated the relationship between two component antigens, Ly-6.2 and H9/25, by generating and characterizing a number of variant cell lines which have altered antigen expression, isolated by chemical mutagenesis and immunoselection of BW5147 lymphoid cells. Cloned cell lines, selected by either antiserum, show loss of both antigens and also fail to express Thy-1, a further genetically linked, but unrelated determinant. The relevance of these findings to furthering understanding of the structure of the Ly-6 region and regulation of antigen expression is discussed.

Biochemical characterization of H9/25, an allospecificity encoded by the Ly-6 region

H9/25, an allospecificity encoded by the Ly-6 region, was biochemically characterized. It was sensitive to pepsin and heat treatment, but was resistant to periodate oxidation. Its apparent molecular weight was approximately 12000 daltons by gel filtration. The antigenic molecule was partially purified by gel filtration and antibody affinity chromatography. The partially purified antigen molecule was radioiodinated, immunoprecipitated with monoclonal antibody H9/25, and analyzed by SDS-polyacrylamide gel electrophoresis. The autoradiograph showed the molecular weight of H9/25 to be approximately 15000 daltons under reducing conditions. These results indicate that H9/25 is a protein with a single polypeptide chain of 12000-15000 daltons molecular weight, and the antigenic specificity is carried by a peptide but not a carbohydrate moiety.

Evidence for expression of Ly-6.2 on non-bone marrow-derived cells in kidney, skin and connective tissues

Mouse alloantigen Ly-6.2 is detectable in various non-lymphoid tissues such as kidney, but it is not clear whether or not this expression is due to bone-marrow derived passenger leukocytes. To determine whether non-marrow derived cells express Ly-6.2, we examined the expression of this antigen in kidney and on isolated connective tissue and epidermal cells. Studies in radiation chimeras demonstrated that the kidney did not become Ly-6.2 positive when negative animals were reconstituted with positive marrow. Thus, passenger leukocytes cannot account for the renal expression of Ly-6.2, indicating that most of this antigen is on non-marrow-derived (parenchymal) cells in kidney. Various isolated cell types--fibroblasts, osteocytes, chondrocytes and skin epidermal cells--were found to be Ly-6.2 positive. Indeed, absorption and cytotoxicity results suggested that the amount of Ly-6.2 on fibroblasts exceeded the amount of an H-2 antigen on these cells. Comparison of fibroblasts to lymphocytes indicated that fibroblasts had 13--60 times more Ly-6.2 than spleen cells and three times more than PHA blasts. The results indicate that the Ly-6.2 detected in non-lymphoid tissues is predominantly on the parenchymal or connective tissue elements of those tissues.

Immunoselection in vitro of a non-metastatic variant from a highly metastatic tumor

Immunoselection of a non-metastatic variant of the highly metastatic MDAY-D2 tumor of DBA/2 mice was achieved by means of an antiserum directed to the LY6.2 surface marker of MDAY-D2. While the new tumor (MDAY-D2.L61) expresses no detectable LY6.2, other measurable surface markers including H2d, FcR and TAA remain unchanged. The phenotypic behavior of MDAY-D2.L61 is that of a non-metastatic tumor and has remained stable after 1 year of maintenance in vivo and in vitro. Immunoselection can now be used to derive variants with stable phenotypic behavior from heterogeneous parent tumor cell populations.

Ly-6 region regulates expression of multiple allospecificities

The relationship between two alloantigens on mouse lymphocytes, that is Ly-6.2 and H9/25, which have previously been shown to have identical strain distribution patterns, was further investigated. Analysis of 39 (AKR x CBA) x CBA backcross progeny showed no segregation between these two antigens, indicating a close genetic linkage between them. Serological analysis showed that Ly-6.2 and H9/25 are differentially expressed on T-cell hybrid lines. Furthermore, cross-absorption of anti-Ly-6.2 serum with two cell lines revealed a heterogeneity among Ly-6 specificities. Semipurified H9/25 antigen failed to block anti-Ly-6.2 serum while anti-Ly-6.2 serum did not significantly block monoclonal antibody H9/25. These results suggest the presence of multiple allospecificities encoded for by the Ly-6 region.

Studies of the mouse Ly-6 alloantigen system. I. Serological characterization of mouse Ly-6 alloantigen by monoclonal antibodies

Three monoclonal antibodies were produced by fusing mouse myeloma cell line NS-1 with spleen cells from C3H/An mice hyperimmunized with B6-H-2k spleen cells. These antibodies recognized an alloantigen displaying a similar strain distribution pattern to the Ly-6.2 and Ala-1.2 alloantigens. Analysis of CxB and BxH recombinant inbred mice revealed close linkage of genes controlling Ly-m6 and Ly-6. The monoclonal antibodies lysed 70 percent of cells in lymph nodes and 60 percent in spleen in direct cytotoxicity assays, but did not lyse significant numbers of cells of thymus and bone marrow. Separated T and B cells were reactive with the antibodies, but T cells were more sensitive to the antibody and complement than B cells. Virtually all cells in cultures of cells activated in the mixed lymphocyte reaction or by Concanavalin A were reactive with the monoclonal antibodies. Direct plaque-forming cells were completely eliminated by the monoclonal antibody and complement. By absorption tests, cells from all organs tested so far (thymus, lymph node, spleen, bone marrow, brain, kidney and liver) were shown to express the Ly-m6 determinant. Tumor cell lines with T, B or stem cell characteristics were reactive with the monoclonal antibody by direct cytotoxicity and absorption assays.

Monoclonal antibodies to ThB detect close linkage of Ly-6 and a gene regulating ThB expression

We have generated three hybridomas producing rat monoclonal antibodies to a surface antigen, ThB, that is shared by murine B lymphocytes and approximately 50 percent of murine thymocytes. These antibodies, produced by immunizations with MOPC-104E cells, appear to recognize the same antigen that was previously detected by rabbit and goat antisera to MOPC-104E cells (Yutoku et al. 1974, Yutoku et al. 1976). Using these antibodies, we have studied a genetic polymorphism that is associated with the level of ThB expression on B lymphocytes but not with the antigen's expression on thymocytes. We present evidence that this trait is controlled by one gene, Thb, which we find to be very closely linked to the gene or genes controlling the Ly-6, Ly-8, DAG, and Ala 1 antigen(s). While the latter four antigens were described as markers on mature T (or activated T and B) lymphocytes, ThB is restricted to immature thymocytes and all B cells. ThB is not expressed on kidney, although some investigators (McKenzie et al. 1977 a, Halloran et al. 1978) report Ly-6 expression on that tissue. SJL/J, C57BL/10JHz, DBA/2J, and AKR/J are among the mouse strains carrying the Thbh allele, while BALB/cN, CBA/J, C3H.SW/SnHz, and A/J carry the Thb1 allele. The ThB antigen has not yet been identified as a glycoprotein after cell-surface iodination, NP-40 solubilization, and immunoprecipitation.