H 9/25 monoclonal antibody recognizes a new allospecificity of mouse lymphocyte subpopulations: strain and tissue distribution

An antigen expressed by murine CD8+ T cells and activated B cells

A monoclonal antibody, H1F5, is described that reacts with a subset of Lyt-2 (CD8) mouse T cells and LPS-activated B cells. In both lymph nodes and spleen of BALB/c mice, the H1F5 antigen is coexpressed approximately on 20%-30% of the CD8+ T cells and approximately on 91% of LPS-activated B cells. In the thymus, few cells (less than 1%) are positive for the marker, but no correlation could be demonstrated with markers for mature T cells such as MEL-14 and PNA expression. Elimination of H1F5+ cells by complement lysis led to a 30%-50% reduction of specific lysis as measured in a primary allo CTL, indicating that the cytotoxic effector cells are injured. The relationship of this marker and other antigenic determinants on lymphocytes is discussed.

Ly-6: a multigene family in search of a function

Differentiation antigens can be simply defined as cell surface antigens that distinguish one cell type from another. The Ly-6 family of cell surface antigens might easily be regarded as a prototype for the analysis of the function of differentiation antigens on immunocompetent cells. Although a number of studies with antisera, in the late 1970s, established that the Ly-6 antigens exhibit an unusual pattern of expression on T and B lymphocytes, functional studies failed to demonstrate that the expression of Ly-6 defines a unique subpopulation of immunocompetent cells. Paradoxically, the development of anti-Ly-6 monoclonal antibodies led to a further decline in interest in this group of antigens, as the complexity of the results relegated Ly-6 to the realm of the die-hard immunogeneticist. Over the past five years, interest in Ly-6 has been rekindled and in this review Ethan Shevach and Patricia Korty summarize recent studies on the serology, biochemical and molecular structure, and the function of the products of this multigene family.

Ly-6 A/E antigen of murine T cells is associated with a distinct pathway of activation. Requirements for interferon and exogenous interleukin 2

The Ly-6 pathway of T cell activation was analyzed to identify its essential requirements. Using a monospecific chicken antiserum to Ly-6E, fully cross-reactive to its allelic counterpart, Ly-6A, but unreactive with other members of the Ly-6 family, we have found that interferon (IFN)-alpha/beta or gamma, Ly-6 antibody and interleukin 2 (IL 2) act synergistically in inducing T cell proliferation. The action of IFN can be attributed to induction of Ly-6A/E antigen on T cells, as described previously, and this induction is transcriptionally controlled. Exposure of T cells with elevated Ly-6 concentrations to chicken anti-Ly-6 antibody leads to expression of IL 2 receptors. Consequently, the addition of IL 2 drives T cell proliferation. Thus, in BALB/c mice the minimum requirements for activation by the Ly-6 pathway are IFN (as a means of inducing Ly-6). Ly-6 antibody (as inducer of IL 2 receptors) and IL 2. In mice of the Ly-6.2 haplotype, IFN is not an absolute requirement. This may be related to the fact that these animals, in contrast to those of Ly-6.1 haplotype, express Ly-6 constitutively on a substantial proportion of resting T cells. Thus, T cells of C57BL/6 or DBA/2 mice can be induced to proliferate with Ly-6 antibody and IL 2 alone, although IFN pretreatment enhances this response. In BALB/c mice the IL 2-driven proliferative response induced through the Ly-6 pathway occurs selectively in the L3T4- population.

Cloning and expression of a cDNA for the T-cell-activating protein TAP

The T-cell-activating protein TAP is a murine phosphatidylinositol-anchored glycoprotein whose expression is controlled by the Ly-6 locus. Previous studies have suggested an important role for this protein in physiological T-cell activation. Using oligonucleotide probes, we have now isolated a cDNA clone whose predicted sequence would encode a protein with an NH2-terminal sequence identical to that of the TAP molecule. Further analysis of the predicted protein sequence revealed a cysteine-rich protein with a hydrophobic domain at the COOH terminus and without N-linked glycosylation sites--all features consistent with our previous analysis of the TAP protein. In Southern blot analysis, the Ly-6.2 cDNA clone detects a multigene family and a restriction fragment length polymorphism that maps precisely to the Ly-6 locus. Expression of the cDNA clone in COS cells demonstrates that it codes for TAP and clarifies the relationship between the epitopes recognized by various alpha Ly-6 monoclonal antibodies. Finally, we have studied the expression of Ly-6 mRNA in a variety of cell lineages. Ly-6 transcripts were detected in all organs examined, including spleen, kidney, lung, brain, and heart. This demonstrates that the Ly-6 locus is transcriptionally active in a wide range of organs and suggests that the role of TAP or TAP-like proteins might extend to other tissues.

Selective up-regulation by interferon-gamma of surface molecules of the Ly-6 complex in resting T cells: the Ly-6A/E and TAP antigens are preferentially enhanced

Surface molecules encoded by the murine Ly-6 locus can transduce triggering signals in T cells and thus may play important roles in T cell function. Previously, we found that Ly-6 molecules are up-regulated by interferon (IFN)-alpha/beta in resting T cells. Here, we examined the possible influence of IFN-gamma on these molecules. Purified T cells from C57BL/6 (Ly-6.2) and BALB/c (Ly-6.1) mice were incubated in vitro with recombinant murine IFN-gamma and the expression of Ly-6 antigens was measured by flow cytofluorometry. It was found that both Ly-6A/E and T cell-activating protein (TAP) molecules are markedly enhanced while Ly-6C is less affected. Under the same conditions, other T cell surface molecules showed no or marginal changes. The effect of IFN-gamma on Ly-6A/E and TAP expression reached a maximum with as little as 10 U/ml and required only 18-24 h of incubation. Moreover, the enhancement of Ly-6A expression induced by IFN-gamma was stable for at least 5 days. Analysis of T cell subsets further revealed that IFN-gamma-induced augmentation of Ly-6A (C57BL/6 mice) involves both Lyt-2+ and L3T4+ cells while the increase of Ly-6E (BALB/c mice) is more pronounced in Lyt-2+ cells. The functional consequence of these phenotypic alterations was evaluated by studying the mitogenic responses of T cells to antibody-mediated Ly-6 cross-linking in the presence of phorbol myristate acetate. Pretreatment of resting T cells with IFN-gamma dramatically increased the responses to anti-Ly-6A and anti-Ly-6E monoclonal antibodies. IFN-gamma treatment also boosted the stimulation induced by anti-TAP monoclonal antibody when this stimulation was performed under suboptimal conditions. Therefore, IFN-gamma selectively up-regulates the Ly-6A/E and TAP activation pathways in resting T cells. We speculate that this effect may contribute to the immunoregulatory activities of IFN-gamma.

Interferon-alpha/beta enhances the expression of Ly-6 antigens on T cells in vivo and in vitro

Interferons (IFN) have been shown to modulate the expression of a number of cell surface antigens on macrophages and lymphocytes. Because such phenotypic alterations may be involved in the functional effects of IFN, it appears important to characterize further these alterations. In the present work, we evaluated the response to IFN of Ly-6-encoded molecules on murine T cells. Two types of Ly-6 antigens, Ly-6A and Ly-6C, normally present on minor subsets of mature T cells were studied. It was found that in vivo treatment of mice with the IFN inducer poly(I . C) or with purified IFN-alpha/beta resulted two days later in augmented expression of these antigens. Purified T cells cultured in vitro for 2 days in the presence of 5% serum from poly(I . C)-treated mice or of 10(4) units/ml IFN-alpha/beta also displayed dramatically increased (4-12-fold) amounts of Ly-6 antigens. Under the same conditions, the T cell markers Thy-1, Ly-1, Lyt-2 and MT4 were unaffected or slightly diminished while surface expression of H-2 or beta 2-microglobulin antigens was increased by only 10-36%. Therefore, poly(I . C)-induced or purified IFN interacts with resting T cells to selectively enhance Ly-6 antigen expression. This phenomenon was found to correlate functionally with increased proliferative response of the T cells, in presence of phorbol myristate acetate, to anti-Ly-6 antibodies cross-linked on their surface. Enhancement of Ly-6 antigen expression on T cells may thus play a role in IFN-mediated immunoregulation.

Gene encoding T-cell-activating protein TAP maps to the Ly-6 locus

Recently we described two murine T-cell membrane proteins, TAP (T-cell-activating protein) and TAPa (TAP-associated protein). Previous experiments suggested that TAP is involved in physiologic T-cell activation. The subject of this report is a genetic analysis of these molecules. TAP and TAPa map to the Ly-6 locus. The relationship of these molecules to other antigens encoded in this locus is examined. Based on tissue distribution, molecular structure, and functional properties, TAP is distinct from any previously described Ly-6 antigen, whereas TAPa is probably identical to the 34-11-3 antigen. TAP and TAPa are coexpressed on all cell types examined so far. Moreover, comparative studies demonstrate a complex developmentally regulated pattern in the expression of molecules encoded in this locus.

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 greater than 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-6D.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.

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.

Identification of two forms of the Ly-6.2 antigen showing differential expression

A monoclonal antibody to the Ly-6.2 specificity, defined by strain and tissue distribution, was used to identify the cellular antigens of lymphocytes and tumor cell lines. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immune precipitates demonstrated that the Ly-6.2 antigen on the surface of thymus and the T lymphoma EL-4 was a protein of 34 kd, whereas spleen cells showed two Ly-6.2 molecules of 34 kd and 56 kd. In vitro translation of EL-4 T-lymphoma poly A+ RNA followed by immunoprecipitation showed the synthesis of two Ly-6.2 precursor polypeptides. These two precursors were translated from separable mRNA molecules; the larger encoded a 54 kd polypeptide, while the second, smaller one translated a 36 kd polypeptide. Thus, the T lymphoma EL-4 contains two distinct mRNA, but only one is seen on the surface, while spleen cells contain and translate both mRNAs and both surface forms are detected. What determines the utilization of the two mRNAs and the surface expression of the two different proteins in the different tissues is not known. Whether the two mRNAs are the transcripts of one gene or arise by transcription of two separate but closely linked genes remains to be determined.

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.

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.

A monoclonal anti-HLA antibody recognizes a mouse tumor-associated antigen

The monoclonal antibody W6/32.1 recognizes a public determinant on the HLA-A, B and C antigens of all tested human haplotypes. Though the antibody does not bind to normal mouse cells of any H-2 haplotype, it does show an unexpected specificity for the T cell leukemia line MBL-2 from a C57BL/6 mouse. It is shown that the murine antigen recognized by W6/32.1 is on an H-2-like molecule which also carries the determinant recognized by the monoclonal antibody B22-249 R1, specific for the H-2Db antigen. Unlike B22-249 R1, however, W6/32.1 does not bind to normal H-2b lymphocytes, nor to a variety of tumor cell lines of the H-2b haplotype. This cross-reaction is specific to W6/32.1, and is not shared by other monoclonal antibodies of similar anti-HLA specificities. Moreover, the affinity of W6/32.1 for its human antigen is substantially higher than for its mouse antigen. We conclude that W6/32.1 fortuitously recognizes a novel determinant on the H-2Db antigen of MBL-2, rather than an extensive region of structural homology shared between HLA and H-2. Thus for cells of the H-2b allotype this determinant is detected only on MBL-2, and by definition is thus an example of a tumor-associated antigen.

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.

Evidence for a major cluster of lymphocyte differentiation antigens on murine chromosome 2

The region of chromosome 2 between H-13 and H-3 has been shown to contain loci coding for a variety of other alloantigens, including Ly-4 and the locus coding for beta 2-microglobulin. Herein we show that Ly-6 and Ly-11 are coded for by genes in a segment of chromosome 2 adjacent to the H-3-H-13 region and that this segment of chromosome also contains the tightly linked loci coding for antigens Ala-1, DAG, H9/25, H-30, Ly-8, and ThB. In addition, at least one locus (and probably more) affecting susceptibility to leukemia induction is found within this gene cluster.

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.

Hybridomas: a new dimension in biological analyses

Since the first report of hybridomas producing monoclonal antibodies by Kohler and Milstein in 1975, this technique has spread to nearly all areas of biological, biochemical, and biomedical research. Watching the use of these methods spread from immunologists to cell biologists, developmental biologists, biochemists and to other biological disciplines and observing the nearly logarithmic increase in publications using these reagents has been in itself fascinating and informative. An overview of the development of this technology and its applications is presented including the use of monoclonal antibodies to study cell surface molecules, differentiation antigens, receptors, and histocompatibility antigens. The use of these antibodies to analyze microorganisms and parasitic antigens as well as their use in the genetic analysis of human cell surface antigens and the detection of polymorphic variation in enzymes and other proteins is discussed. Examples of the application of monoclonal reagents to the study of tumor cell biology including the labeling of metastatic tumor cells and the detection of cell surface molecules implicated in the regulation of growth control and cell division are provided.

A new mouse cell-surface antigen (Ly-m18) defined by a monoclonal antibody

Spleen cells from C3H/An mice immunized with spleen cells of C57BL/6-H-2k mice were fused with myeloma cell line NS.1. One established hybrid cell line continuously secreted antibody that recognized a new surface antigen provisionally called Ly-m18. The new alloantigen is expressed on 90 percent of thymus cells, 55 percent of spleen cells, and 45 percent of either lymph-node or bone-marrow cells. It is also expressed on cells derived from brain, kidney, and liver. Fifty percent of either peripheral T or B cells express the Ly-m18 antigen, and some tumor cell lines with T, B, pre-B or stem cell characteristics are Ly-m18 (+). The strain distribution pattern distinguishes Ly-m18 antigen from all other murine lymphocyte alloantigens. The typing data of two sets of CXB and AKXL recombinant inbred strains indicate that the Ly-m18 gene is linked to the Ltw-2 locus which has not yet been assigned to a chromosome.

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.

Monoclonal antibody H9/25 reacts with functional subsets of T and B cells: killer, killer precursor and plaque-forming cells

Monoclonal antibody (McAb) H9/25 has previously been shown to react with an alloantigen expressed on subpopulations of mouse lymphocytes. We here investigated the expression of the antigen (H9/25 Ag) on functional subsets of T and B cells. Lymphocytes were depleted of H9/25 Ag-bearing cells by complement-dependent cytolysis or by the affinity to immobilized McAb H9/25, and the residual immunological functions were tested. In these tests, killer T cells generated in mixed lymphocyte cultures and their precursors were found to express H9/25 Ag. In contrast, the activity and frequency of helper T cells specific to keyhole limpet hemocyanin carrier were not decreased by the depletion of H9/25 Ag-bearing cells. On the other hand, IgG and IgM anti-TNP plaque-forming cells were found to express H9/25 Ag, while it was not detected on unprimed B cells, as tested by using TNP-Ficoll and TNP-lipopolysaccharide. Only a small proportion of TNP memory B cells seemed to express the antigen. These results revealed significant differences between H9/25 Ag and other known alloantigens in the distribution among functional subsets of lymphocytes.

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.