Analysis of Ly-6.2-bearing murine lymphocyte subpopulations in relation to the T-lymphocyte markers,Thy-1, Lyt-1, and Lyt-2

Using immunofluorescence with a monoclonal anti-Ly-6.2 antibody and FACS analysis we have confirmed that the Ly-6.2 antigen is present on approximately 70% of mature T cells and B cells but on few immature lymphocytes. There is a wide range of antigen density among the Ly-6.2⁺ populations, with the mean density higher on T cells than B cells. Following Con A activation of splenocytes there was a sixfold increase in Ly-6.2 antigen density though approximately 20% of the activated lymphocytes were Ly-6.2^?. The increase in Ly-6.2 density was specific since similar density increases did not occur for the closely linked antigens ThB and H $\text{9}\text{25}$. By panning a predominantly T-cell population for Lyt-2-bearing cells, it was found that Lyt-2⁺ lymphocytes were either negative or dully staining for Ly-6.2. However, activated cells bearing the Lyt-2 antigen were all Ly-6.2 positive. Double-staining experiments showed that T cells which had high Ly-6.2 antigen densities also had high Thy-1 antigen densities. Corticosteroid-resistant thymocytes were highly enriched for Ly-6.2-bearing cells compared to untreated thymocytes and had staining profiles for Ly-6.2 which were similar to peripheral T cells, supporting the idea that steroid treatment selects for a phenotypically mature thymic population.     

Isolation and characterization of cDNA clones for the mouse thymocyte B cell antigen (ThB).

The Thb locus is responsible for the expression of 15-kDa phosphatidyl inositol anchored molecules (ThB) on murine thymocytes and B cells. Thb expression as detected with mAb is polymorphic on B cells with two alleles, Thbh and Thb1 responsible for the high and low expression of ThB on B cells. The regulatory locus for Thb expression had been mapped with the Ly-6 cluster of genes to Chr 15. In our study we used expression cloning in COS cells to isolate cDNA clones that code for ThB after transfection; the cDNA products react with anti- ThB antibodies, but not with Ly-6A.2, -6B.2, -6C.2, or -6D.2 antibodies. One of these clones, pThB-A contains insert of 702 bases which was sequenced. The translated amino acid sequence has 11 cysteine residues, and together with the absence of potential N-linked glycosylation sites is similar to the structure of the Ly-6 molecules. The nucleotide and amino acid sequences of ThB cDNA were compared to those of Ly-6 genes and the Ly-6 related human CD59 and show clear homology. Finally using interspecies crosses, the structural Thb gene has been mapped to Chr 15; thus both structural and regulatory genes map to a similar site. The genetic map location near Ly-6 and the sequence similarity suggest that Thb and Ly-6 may have been derived from the same progenitor by gene duplication.     

Studies of the mouse Ly-6 alloantigen system

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 (Lym6.2C, 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.IE, 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.     

Interrelationships of the “Ly-6 complex” antigens

Competitive binding studies and immunoprecipitation experiments define at least five distinct epitopes encoded by Ly-6-linked genes—Ly-6A.2, Ly-6B.2, Ly-6C.2, Ly-6D.2, and ThB. Ly-6A.2, a 33 kd protein, and Ly-6D.2 are closely overlapping epitopes that can be distinguished by their unique thymus reactions of 10–20% or >90%, respectively. Similarly, the Ly-6C.2 antigen present on a 14 kd moiety loosely overlaps the Ly-6B.2 antigen. Ly-6C.2 and Ly-6B,2 antigens are distinct from Ly-6A.2 and Ly-6B.2, however. ThB is a 16–18 kd antigen which is not associated on the cell surface with any other Ly-6 antigens. In addition, independently derived antibodies made to the Ly-6C.2 antigen detect an identical epitope, as do antibodies to Ly-6A.2 and Ly-6B.2. These results imply the existence of a single antigenic site on each of these molecules.     

Further definition of the Ly-5 system

Ly-5 is expressed by cells of the hematopoietic branch of development. Further serological analysis of the Ly-5 system, aided by Ly-5 monoclonal antibodies and by two Ly-5 congenic mouse strains, reveals two new Ly-5 alloantigens, Ly-5. 3 and Ly-5.4. The data define three thymocyte phenotypes, Ly-5.1,3, Ly-5.2,4, and Ly-5.2,3, and three corresponding genotypes, Ly-5 ^a, Ly-5 ^b, and Ly-5 ^c, respectively. Ly-5 ^ais by far the most common allele. The Ly-5 ^callele is found only in the ST/bJ strain, a finding that accords with the presently unique pattern of restriction fragments previously observed in Southern blotting of ST/bJ DNA with an Ly-5 cDNA probe. Present serological and biochemical data favor the interpretation that the compound Ly-5 phenotype of thymocytes is attributable to two separate Ly-5 molecular isoforms that exhibit a discrete difference in protein composition, bear different Ly-5 antigens, and are produced jointly by thymocytes, unlike other Ly-5 isoforms previously shown to distinguish different hematopoietic cell lineages.     

A new lymphocyte alloantigen (Ly-10) controlled by a gene linked to theLyt-1 locus

Spleen cells from a (BALB/cxC57BL/6)F₁ mouse immunized with CBA/J spleen cells were fused with the myeloma cell line NS-1. One of the six established hybrid cell lines continuously secreted antibody that recognized a new antigenic specificity, tentatively called Ly-10.1. This newly found antigen is expressed on thymocytes, on splenic T and B cells, on bone-marrow cells, and on the cells derived from brain, kidney and liver. It is also expressed on a continuous cell line, 416B, with stem-cell characteristics. The unique tissue distribution and, furthermore, a distinct strain distribution pattern distinguishes Ly-10.1 from any known murine lymphocyte alloantigen. On the basis of reactivity with cells of the C57BL/6-Lyt-1^a congenic strain, one gene governing Ly-10 expression is assigned to the Lyt-1 region of chromosome 19.We chose the notation Ly-10 rather than Ly-9 to allow for a future decision that Lgp 100 (Ledbetter et al. 1979) should be renamed Ly-9.     

Molecular weight determination of two genetically linked cell surface murine antigens: ThB and Ly-6

Various murine tumor lines were screened by FACS analysis for the surface antigens ThB and Ly-6.2. Positive cell lines were used for immunoprecipitation studies. A monoclonal ThB-specific antibody immunoprecipitated a unique acidic protein of approximately 16 000 daltons from several positive tumors and from concanavalin A (Con-A) and LPS activated splenic lymphocytes. Monoclonal Ly-6.2-specific antibody was used to immunoprecipitate a 33 500 dalton protein that was shown to exist in four similarly sized forms with different basic charges. In the course of these studies, the apparent molecular weight of the surface antigen T 30, immunoprecipitated with a monoclonal T 30-specific antibody from the cell line EL4, was found to be approximately 25 000 daltons.     

Definition of new alloantigens encoded by genes in the Ly-6 complex

Three alloantigens encoded by Ly-6-linked genes are defined by monoclonal antibodies. The Ly-27.2 antigen is defined by antibody 5075-19.1, Ly-28.2 by 5075-3.6, -12.1, -16.10 and by 5095-16.6. The strain distribution pattern of these antibodies is the same and identical with Ly-6.2. However the tissue distribution of these antigens is unique and distinguishes these antigens from the Ly-6.2 antigen or any known antigen encoded by Ly-6-linked genes. Ly-27.2 is present on all thymocytes, T cells, and B cells but is absent from bone marrow cells, whereas Ly-28.2 is absent from most thymocytes and is present on a subpopulation of T cells and B cells but is found on 60–70% of bone marrow cells. No recombination between the Ly-6/Ly-27/Ly-28 loci was found in linkage studies using 41 recombinant inbred strains and 57 backcross mice and indicates very close linkage of these genes. In addition, close linkage to 24 minor histocompatibility genes was excluded using the Bailey HW bilineal congenic mice. The data presented indicate that either the Ly-6 complex is composed of a family of tightly linked genes or the antigens are the products of a single gene that undergoes extensive modification during differentiation.     

Biochemical identification of rat ART-1 and Ly-1 alloantigens

The results of this study indicate that the ART-1 and Ly-1 rat alloantigens are synonymous with each other and also with the leukocyte-common (L-C) antigen which has been previously identified as a major glycoprotein of rat thymocytes and T and B lymphocytes. This conclusion is supported by the following observations: (i) when labeling of rat lymphoid cells was studied with a fluorescence-activated cell sorter, the profiles obtained were similar for labeling with ART-1 and Ly-1 alloantibodies and a monoclonal antibody to L-C antigen: (ii) this labeling was almost completely inhibited by purified L-C antigen: (iii) preincubation with L-C antigen completely inhibited binding of the alloantibodies in a cellular radioimmunoassay; (iv) the cytotoxic effect of the alloantibodies was completely abolished by preincubation with purified L-C antigen; (v) the strain distribution of the ART-1 and Ly-1 alloantigens was identical for 11 rat strains and in linkage analysis the ART-1 and Ly-1 alloantigens were found to cosegregate.Genetic linkage studies have shown that the L-C antigen locus is unlinked to the major histocompatibility antigen (RT1), the immunoglobulin light chain (1^k) and to the coat color gene (C) loci.Abbreviations used in this paper BSA Bovine serum albumin - DAB Dulbecco's salt solution - FCS Fetal calf serum - L-C antigen Leucocyte-common antigen - LN Lymph node - TDL Thoracic duct lymphocytes     

A monoclonal antibody detecting the Ly-9.2 (Lgp 100) cell-membrane alloantigen

A mouse monoclonal cell line (20-1.5) was produced by the cell fusion method and the antibody secreted by this line defined the Ly-9.2 specificity — the reciprocal specificity to that previously identified as the Lgp 100 or the T100 molecule. Although most concentrated on lymph-node cells, the antigen is also found on thymocytes, spleen and bone-marrow cells as well as liver and brain tissue. The monoclonal antibody precipitates a 100000 molecular weight moiety from thymocytes. The antigenic specificities appear to be highly immunogeneic and antibodies to these specificities contaminate many antisera. These sera are noncytotoxic as is the case with the monoclonal antibody even though it is of the IgG2a subclass. As with T100 or Lgp 100, theLy-9 locus appears to be linked to theH-25 locus.     

Identification of new murine lymphocyte alloantigens: Antisera prepared between C57L, 129 and related strains define new loci

Antisera prepared by immunizing between the strains 129 and C57L and other related strains identified new antigens expressed on lymphocytes and in particular on thymocytes. Absorption analysis demonstrated that the antisera were complex, and contained several new antibodies including some which were not cytotoxic, but could be detected by rosetting. The loci defined by these antibodies are referred to asLy-9, Ly-11, Ly-12, Ly-13, andLy-14, although several of the antigens were not confined to lymphocytes. In addition, the Ea-7 specificities, previously considered to be purely red-cell alloantigens, were also found on thymocytes.     

Idiotype-specific T lymphocytes. I. Regulation of antibody production by idiotype-specific H-2-restricted T lymphocytes

Cytotoxic T lymphocytes (CTL) specific for MOPC-104E myeloma cells of BALB/c origin could be induced in BALB/c, (BALB/c X BALB.B)F1, and (BALB/c X BALB.K)F1 mice. (BALB/c X BALB.B)F1 CTL activity specific for MOPC-104E was effectively inhibited by anti-H-2d but not by anti-H-2b alloantiserum. However, the activity was hardly blocked by specific anti-idiotypic antibodies to MOPC-104E. For further analysis of the recognition of idiotype on target cells by CTL, the effect of those lymphocytes on anti-dextran B1355S antibody-producing B lymphocytes, which have a cross-reactive idiotype to MOPC-104E, was investigated. Lymphocytes from the CTL population did inhibit antibody production by dextran-immune spleen cells, but those from the CTL population specific for irrelevant myeloma cells (MOPC-167) did not. The (BALB/c X BALB.K)F1 CTL population suppressed the antibody production of BALB/c but not of BALB.K. This indicates that F1 cells can preferentially see H-2 antigens of immunizing myeloma cells on target B lymphocytes. The inhibition of antibody production was antigen specific and was only restricted to the PFC that were inhibitable by anti-idiotypic antibodies. The surface phenotypes of the cells that inhibited the antibody production were Thy-1+, Lyt-1-, Lyt-2+, and I-J-. These results strongly suggest that CTL specific for MOPC-104E recognize self H-2 antigens simultaneously with idiotypic determinants on B lymphocytes. Possible immunoregulatory roles of idiotype-specific CTL on antibody production systems are also suggested.     

The expression ofI-region gene products on lymphocytes

Mixed lymphocyte reaction (MLR) stimulation by purified T and B lymphocytes and thymocytes was studied. The MLR gene products involved were localized to theH-2 complex by the use of congenic mice differing atH-2, and to loci within theH-2 complex through the use of congenic mice bearing recombinant chromosome 17. Stimulation by T cells was investigated in detail. The role of small amounts of contaminating B lymphocytes, and that of backstimulation, was found to be of minor importance. T cells and thymocytes stimulated as well as or better than B cells in combinations differing in theI, S, and possibly parts of theD end, thus suggesting that these genetic regions control cell-surface products expressed on both T and B lymphocyte populations.Abbreviations used in this paper are MLR mixed lymphocyte reaction - GVHR graft-versus-host reaction - CML cell-mediated lympholysis - Thy-1 the gene for the T-cell antigens, synonymous with - Thy-1.1 synonym for ^AKR - Thy-1.2 synonym for ^C3H - MHC major histocompatibility complex - Ir genes immune response genes linked to the MHC - LPS E. coli 055.35 lipopolysaccharide For the genetic nomenclature of theH-2 complex (H-2K, H-2D, I, S, D regions,Ia, etc.) see Kleinet al. 1974, and Shreffleret al. 1974.     

Effect of thymocyte-stimulating factor-containing supernatants on the surface antigens of murine thymocytes.

Incubation of murine thymocytes in thymocyte-stimulating factor (TSF)-containing supernatants causes a four- to fivefold increase in the expression of the H-2^k and H-2^d antigens and a similar decrease in the expression of the TL antigen (in TL⁺ strains) on the surface of these cells. Experiments with antisera directed toward the private H-2K and H-2D antigens showed that TSF-containing supernatants cause approximately the same increase in the expression of the H-2K and H-2D antigens of thymocytes of the d and b haplotypes. With thymocytes of the k haplotype, only an increase in the expression of the H-2D antigens takes place, while no significant increase was found for the H-2K antigens. TSF-containing supernatants cause no significant change in the expression of the following antigens on the surface of thymocytes: Thy-1.1, Thy-1.2, Ly-1.2, Ly-2.2, Ly-6.2, Th-B, Ia-1,2,3,7, and G_IX. A factor similar to murine TSF, produced by human peripheral blood leukocytes, does not affect appreciably the expression of the H-2 antigens on the surface of murine thymocytes. The factor(s) causing the increased expression of the H-2 antigens on the surface of murine thymocytes appears to be produced by T lymphocytes. The factor(s) is eluted from a Sephadex G-100 column in at least two broad peaks with molecular weights of 300,000 and 90,000-25,000. Most of the activity enhancing the expression of the H-2 antigens is lost at pH 2, while most of it is maintained at pH 11.5 and at 56 °C. On the basis of these properties, it is concluded that the factor under study is probably different from the factor enhancing the phytohemagglutinin responsiveness of thymocytes.     

The human E48 antigen, highly homologous to the murine Ly-6 antigen ThB, is a GPI-anchored molecule apparently involved in keratinocyte cell-cell adhesion

The E48 antigen, a putative human homologue of the 20-kD protein present in desmosomal preparations of bovine muzzle, and formerly called desmoglein III (dg4), is a promising target antigen for antibody- based therapy of squamous cell carcinoma in man. To anticipate the effect of high antibody dose treatment, and to evaluate the possible biological involvement of the antigen in carcinogenesis, we set out to molecularly characterize the antigen. A cDNA clone encoding the E48 antigen was isolated by expression cloning in COS cells. Sequence analysis revealed that the clone contained an open reading frame of 128 amino acids, encoding a core protein of 13,286 kD. Database searching showed that the E48 antigen has a high level of sequence similarity with the mouse ThB antigen, a member of the Ly-6 antigen family. Phosphatidylinositol-specific (PI-specific) phospholipase-C treatment indicated that the E48 antigen is glycosylphosphatidylinositol-anchored (GPI-anchored) to the plasma membrane. The gene encoding the E48 antigen is a single copy gene, located on human chromosome 8 in the 8q24-qter region. The expression of the gene is confined to keratinocytes and squamous tumor cells. The putative mouse homologue, the ThB antigen, originally identified as an antigen on cells of the lymphocyte lineage, was shown to be highly expressed in squamous mouse epithelia. Moreover, the ThB expression level is in keratinocytes, in contrast to that in lymphocytes, not mouse strain related. Transfection of mouse SV40-polyoma transformed mouse NIH/3T3 cells with the E48 cDNA confirmed that the antigen is likely to be involved in cell-cell adhesion.     

Ly-4.2: Doubts concerning its validity as a B-cell marker

The serum used to define Ly-4.2, (BALB/c × SWR/J)F₁ anti-B10D2/n, was found to react equally with both donor B and T cells, contrary to the findings of McKenzie and Snell (1975) that the serum reacted mainly with B cells. The reaction with both B and T cells was demonstrated by a 90 to 100 percent killing of spleen, lymph node, and separated populations of B and T cells from both organs. Although the antiserum only lysed 10 to 20 percent of thymocytes, these cells could be used to remove all reactivity against lymph node and spleen cells. Depletion of the T cells in a lymph node suspension by Thy-1.2 treatment did not affect the percentage of lysis of residual cells. Attempts to remove possible contaminating antibodies by absorption with either donor thymus or EL4 cells were unsuccessful because these tissues removed all antibody activity. Neither did partial absorption with separated B and T cells affect the relative activity against these cells. The strain distribution of Ly-4.2 was similar to that reported in the literature, and backcross tests indicated that there was probably no linkage with theH-2 locus.     

Mouse serum amyloid P-component (SAP) levels controlled by a locus on chromosome 1

Recombinant inbred strains were used to demonstrate the existence of a major locus on chromosome 1, designated Sap, which controls the endogenous concentration of the mouse acute phase reactant, serum amyloid P-component (SAP). Levels of SAP were associated with alleles at the Ly-9 locus in two sets of RI strains: BXD (C57BL/6J × DBA/2) and BXH (C57BL/6J × C3H/HeJ). Low endogenous levels of SAP were present in the C57BL/6J progenitor strain and in most of the RI strains which inherited the Ly-9 ^ballele. High levels of SAP were present in the DBA/2J and C3H/HeJ progenitors and in most of the RI strains which inherited the Ly-9 ^aallele. In the BXD strains 91% of the genetic variation of SAP levels was accounted for by segregation at the Ly-9 locus while an additional 9% was attributed to genetic factors unlinked to Ly-9. In the BXH strains the percentage of genetic variation accounted for by Ly-9 segregation was reduced to 46%, while 54% was accounted for by other genetic factors. Because of background genetic variation it was not possible to detect any crossovers between Sap and Ly-9. However, in the BXD strains the linkage between Sap and Ly-9 appears to be quite close. The B6.C-H-25 ^ccongenic strain, which carries a segment of BALB/c chromosome 1 including the minor histocompatibility locus H-25 on a C57BL/6By background, had the same endogenous SAP level as the BALB/c donor strain.     

Mouse Ly-31.1 is an alloantigenic determinant of alkaline phosphatase predominantly expressed in the kidney and bone

The mouse lymphocyte surface alloantigen, Ly-31, defined by monoclonal antibody N1.10 (IgG2b, k) and controlled by a gene locus closely linked to theAkp-2 locus on chromosome 4, was biochemically investigated. By employing a quantitative immunoassay system, it was found that the Ly-31.1-specific antibody detected an allotypic determinant of mouse alkaline phosphatase. Ly-31.1, i. e., mouse alkaline phosphatase, was expressed predominantly in kidney and bone and was also detected in placenta, lung, and testis. Concerning tumor cell lines, they varied in the amount of antigen present, with both T and B lymphoid lineages selectively possessing the antigen. In normal lymphoid tissues, lesser amounts of antigen were detected. The binding of mouse alkaline phosphatase to Ly-31.1-specific monoclonal antibodies was specific in nature. The Ly-31.1 antigen was immunoprecipitated from the lysates of surface-radiolabeled YAC-1 moloney leukemia cells, and appeared as a single band of about 78 000 under both reduced and nonreduced conditions on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Furthermore, treatment of tumor cell lines with phosphatidylinositol-specific-phospholipase C resulted in the removal of Ly-31 antigen from the cell surface. These results suggest that a gene cluster containing theLy-31 andAkp-2 loci which control the alkaline phosphatase is formed on mouse chromosome 4. The Ly-31 antigen is the first enzyme demonstrated to be a lymphocyte surface alloantigen.