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

Ly6d marks the earliest stage of B-cell specification and identifies the branchpoint between B-cell and T-cell development

Common lymphoid progenitors (CLPs) clonally produce both B- and T-cell lineages, but have little myeloid potential in vivo. However, some studies claim that the upstream lymphoid-primed multipotent progenitor (LMPP) is the thymic seeding population, and suggest that CLPs are primarily B-cell-restricted. To identify surface proteins that distinguish functional CLPs from B-cell progenitors, we used a new computational method of Mining Developmentally Regulated Genes (MiDReG). We identified Ly6d, which divides CLPs into two distinct populations: one that retains full in vivo lymphoid potential and produces more thymocytes at early timepoints than LMPP, and another that behaves essentially as a B-cell progenitor.

Expression of Ly-6D on the surface of normal and neoplastic mammary epithelial cells of the mouse

Rat were immunized with mouse mammary epithelial cells and monoclonal antibodies (MAbs) were obtained to identify antigens stably expressed on the surface of both normal and neoplastic mammary epithelial cells of the mouse. Examination of the reactivities of the MAbs by immunofluorescence staining of tissue sections showed that one of the antibodies, MAb 2A2, reacted with luminal epithelium of the mammary gland and spontaneous mammary carcinomas of SHN mice. Further examination of the tissue lysates by western blot analysis revealed that MAb 2A2 reacts with a 17-kDa antigen expressed in normal mammary epithelial cells and mammary carcinoma cells. The antigen recognized by MAb 2A2 was absent in the lysates of liver, lung, salivary gland, kidney, small intestine, ovary and uterus. After immunoaffinity purification of the MAb 2A2-recognized antigen and determination of its N-terminal amino acid sequence, we identified the antigen as Ly-6D, also known as ThB, which belongs to a family of glycosyl-phosphatidylinositol-anchored cell surface proteins. Northern blot analysis further demonstrated that Ly-6D mRNA is expressed in the mammary gland. Based on these observations we concluded that Ly-6D is stably expressed on the surface of both normal and neoplastic mammary epithelial cells of the mouse. Ly-6D will serve as a useful epithelial cell surface marker for the study of mammary gland development, as well as for breast cancer research.

Ly6C expression differentiates plasma cells from other B cell subsets in mice

Plasma cell differentiation is induced in vitro by lipopolysaccharide (LPS) stimulation but can be blocked by including anti-CD40 antibodies. Using subtractive cDNA hybridization we have identified the cell surface protein Ly6C as differentially expressed on B cells stimulated with LPS only. Ly6C has been shown to be expressed on certain T cell subsets and on subsets of macrophages and NK cells, but not on resting B cells. We show that Ly6C is up-regulated upon LPS stimulation of B cells in vitro and that this up-regulation is blocked by anti-CD40 or anti-Ig antibodies. Furthermore, ELISPOT analysis of cells sorted by magnetic-activated cell sorting show that Ly6C is expressed on ex vivo plasma cells from the spleen and bone marrow. Flow cytometric analysis showed that Ly6C is expressed on splenic plasma cells as well as on lamina propria plasma cells. Finally, Ly6C cross-linking positively up-regulated the amount of immunoglobulin produced by LPS-stimulated splenic B cells in vitro.

Panning T cells on vascular endothelial cell monolayers: a rapid method for enriching naive T cells

A key functional/phenotypic difference between naive and memory T cells is the ability of memory and activated T cells to home to sites of inflammation by adhering to vascular endothelial cells. To determine if this trait could be used to separate naive T cells from memory T cells, CD4+ T cells were incubated with monolayers of IFN-gamma-primed vascular endothelial cells after which the phenotypic and functional characteristics of the nonadherent population were assayed. The nonadherent population 1) contained a five-fold decrease in the frequency of cells displaying the CD44(high)/CD45RB(low) "memory" phenotype and 2) responded well to allostimulation but displayed a reduced ability to respond to immobilized anti-CD3 antibody and, when isolated from ovalbumin-immunized mice, displayed a reduced recall response to ovalbumin in vitro. These studies demonstrate that rwo brief incubations of T cells with monolayers of IFN-gamma-primed endothelial cells can significantly enrich for naive T cells as determined by both phenotypic and functional analyses.

LPS stimulation of TNF-receptor deficient macrophages: a differential role for TNF-alpha autocrine signaling in the induction of cytokine and nitric oxide production

To evaluate the role of autocrine TNF-alpha signaling in macrophage activation, immortalized macrophages from normal mice (B6/J2) and from mice containing gene targeted disruptions of the type 1 and type 2 TNF-receptor genes (TRN) were stimulated under CD14-dependent or serum-free conditions. Although the B6/J2 and TRN clones mounted similar nitric oxide responses to LPS in the presence of serum, the TRN macrophages responded poorly when stimulated with LPS under serum free conditions. LPS stimulation of TRN and B6/J2 under serum-free conditions resulted in equivalent levels of IL-1beta, TNF-alpha, and iNOS gene expression. However, Western blot analysis revealed that iNOS protein production by TRN was 2-fold lower than that produced by B6/J2. These results indicate that autocrine TNF-alpha stimulation contributes to the signaling pathways initiated by ligation of LPS receptors in the absence of LBP and is involved in iNOS post-transcriptional regulation.

Prevention of experimental autoimmune encephalomyelitis by encephalitogenic epitope sequence simplified derivatives

The encephalitogenic epitope P81-100 from mouse myelin basic protein was used to generate two simplified derivatives with glycine substitutions in alternating positions which were tested for their biological activity in a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis. While both derivatives were unable to induce in mice the disease at the same parent peptide P81-100 dosage, T cell proliferation assays demonstrated their ability to compete with the parental peptide in a dose related manner. Experiments of cell surface binding and T cell tolerance revealed a different behavior of the two derivatives, suggesting different roles in the MHC blockade or T cell tolerance. On induction of encephalomyelitis in animals by P81-100 treatment, one variant proved in vivo to be very effective in protecting from the disease.

A monoclonal antibody against the 66-kDa protein expressed in mouse spleen and thymus inhibits Ly-6A.2-dependent cell-cell adhesion

The Ly-6 locus encodes several cell surface proteins of 10-12 kDa. Some members of this multigene family may function in cell signaling and/or cell adhesion processes. T lymphocytes overexpressing Ly-6A.2 (one member of the Ly-6 gene family) protein homotypically aggregate when cultured in vitro. Further analysis of this homotypic aggregation suggests that Ly-6A.2 participates in cell-cell adhesion. These observations indicated the presence of a Ly-6 ligand(s) on the surface of lymphoid cells. In this study we report generation of a hamster mAb, 9AB2, that blocks Ly-6A.2-dependent cell-cell adhesion. The 9AB2 Ab recognizes a 66-kDa glycoprotein with unique tissue expression. The 9AB2 mAb does not bind Ly-6A.2, but coimmunoprecipitates Ly-6A.2 molecule. Moreover, 9AB2 Ag-expressing thymocytes specifically bind to Chinese hamster ovary cells overexpressing Ly-6A.2 protein, and this binding is specifically blocked by 9AB2 and anti-Ly-6A.2 Abs. These results suggest that the 66-kDa protein recognized by 9AB2 mAb is the putative ligand for Ly-6A.2.

Ly6d-L, a cell surface ligand for mouse Ly6d

The mouse Ly6 gene family encodes proteins found in lymphocytes and other cells. Some are involved in cell activation; no ligands have been found. A ligand for Ly6d (ThB) was identified on lymphocytes using microspheres loaded with Ly6d and the cDNA isolated from a spleen/thymus library by panning on Ly6d. The Ly6d ligand (Ly6d-L) is a nonglycosylated protein of 9 kDa of broad distribution, rich in cysteine, with no discernable transmembrane sequence. Its N and C termini are on the cell surface, where it associates with a 30 kDa protein. Ly6d-L is homologous with an EGF repeat of Notch.

Genes Encoding Three New Members of the Leukocyte Antigen 6 Superfamily and a Novel Member of Ig Superfamily, Together with Genes Encoding the Regulatory Nuclear Chloride Ion Channel Protein (hRNCC) and a Nω-Nω-Dimethylarginine Dimethylaminohydrolase Homologue, Are Found in a 30-kb Segment of the MHC Class III Region

Many of the genes in the class III region of the human MHC encode proteins involved in the immune and inflammatory responses. We have sequenced a 30-kb segment of the MHC class III region lying between the heat shock protein 70 and TNF genes as part of a program aimed at identifying genes that could be involved in autoimmune disease susceptibility. The sequence analysis has revealed the localization of seven genes, whose precise position and order is cen-G7-G6-G6A-G6B-G6C-G6D-G6E-tel, five of which are fully encoded in the sequence, allowing their genomic structures to be defined. Three of them (G6C, G6D, and G6E) encode putative proteins that belong to the Ly-6 superfamily, known to be GPI-anchored proteins attached to the cell surface. Members of the family are specifically expressed and are important in leukocyte maturation. A fourth gene, G6B, encodes a novel member of the Ig superfamily containing a single Ig V-like domain and a cytoplasmic tail with several signal transduction features. The G6 gene encodes a regulatory nuclear chloride ion channel protein, while the G6A gene encodes a putative homologue of the enzyme Nω,Nω-dimethylarginine dimethylaminohydrolase, which is thought to be involved in regulating nitric oxide synthesis. In addition, three microsatellite markers, 9N-1, 82-2, and D6S273 are contained within the sequence, the last two of which have been reported to be strongly associated with the autoimmune disease ankylosing spondylitis.

Asymmetric Contribution to Ig Repertoire Diversity by Vκ Exons: Differences in the Utilization of Vκ10 Exons

The mouse has approximately 140 germline Vκ genes, and functional Vκ exons are expressed at roughly equivalent levels in the preimmune repertoire. We have examined the expression of individual members of the Vκ10 family. Vκ10A and Vκ10B genes have been utilized in numerous hybridomas and myelomas, while Vκ10C has not. In this study, we have cloned the Vκ10C gene and shown that it is structurally functional, has the expected promoter elements and recombination signal sequences, and that it is capable of recombination. Vκ10C mRNA, however, is present at levels at least 1000-fold lower than Vκ10A and Vκ10B in adult spleens. While there are no sequence differences in the octamer or TATA box between Vκ10C and Vκ10A, there are three nucleotide changes in the promoter region. These promoters equally drive the expression of a reporter gene in B cells or plasma cells, but the Vκ10A promoter is able to drive expression in pre-B cell lines significantly better than the Vκ10C promoter (p < 0.05). Vκ10C rearrangements can be detected in bone marrow and splenic DNA. Therefore, the lack of Vκ10C expression may reflect the inability of Vκ10C-rearranged cells to undergo positive or negative selection. Our results suggest that the available Ab repertoire is shaped not only by the number of structurally functional genes, but also by the ability of assembled genes to be expressed at critical points during B cell maturation.

Characterization and Mapping to Human Chromosome 8q24.3 of Ly-6-Related Gene 9804 Encoding an Apparent Homologue of Mouse TSA-1

The 9804 gene, which encodes a human Ly-6 protein most similar to mouse differentiation Ag TSA-1/Sca-2, has also been called RIG-E. Like mouse TSA-1, it has a broad tissue distribution with varied expression levels in normal human tissues and tumor cell lines. Like some members of the murine Ly-6 family, the 9804 gene is responsive to IFNs, particularly IFN-α. Overlapping genomic fragments spanning the 9804 gene (5543 bp) have been isolated and characterized. The gene organization is analogous to that of known mouse Ly-6 genes. The first exon, 2296 bp upstream from exon II, is entirely untranslated. The three coding exons (II, III, and IV) are separated by short introns of 321 and 131 bp, respectively. Primers were developed for specific amplification of 9804 gene fragments. Screening of human-hamster somatic cell hybrids and yeast artificial chromosomes (YACs) indicated that the gene is distal to c-Myc, located in the q arm of human chromosome 8. No positives were detected from the Centre d′Etude du Polymorphisme Humain mega-YAC A or B panels, nor from bacterial artificial chromosome libraries; two positive cosmids (c101F1 and c157F6) were isolated from a human chromosome 8 cosmid library (LA08NC01). Fluorescence in situ hybridization of metaphase spreads of chromosome 8, containing hybrid cell line 706-B6 clone 17 (CL-17) with cosmid c101F1, placed the 9804 gene close to the telomere at 8q24.3. This mapping is significant, since the region shares a homology with a portion of mouse chromosome 15, which extends into band E where Ly-6 genes reside. Moreover, the gene encoding E48, the homologue of mouse Ly-6 molecule ThB, has also been mapped to 8q24.

Tissue expression, structure and function of the murine Ly-6 family of molecules

Murine Ly-6 molecules are a family of cell surface glycoproteins which have interesting patterns of tissue expression during haematopoiesis from multipotential stem cells to lineage committed precursor cells, and on specific leucocyte subpopulations in the peripheral lymphoid tissues. These interesting patterns of tissue expression suggest an intimate association between the regulation of Ly-6 expression and the development and homeostasis of the immune system. Ly-6 molecules are low molecular weight phosphatidyl inositol anchored glycoproteins with remarkable amino acid homology throughout a distinctive cysteine rich protein domain that is associated predominantly with O-linked carbohydrate. These molecules are encoded by multiple tightly linked genes located on Chr. 15 which have conserved geneomic organization. The in vivo functions of Ly-6 molecules are not known although in vitro studies suggest a role in cellular activation. This review will summarize our understanding of Ly-6 with regard to tissue expression, molecular structure, gene organization and function.

Overexpressed Ly-6A.2 mediates cell-cell adhesion by binding a ligand expressed on lymphoid cells

The Ly-6 locus encodes several cell surface proteins whose functions are unknown. Although it is hypothesized that these proteins may be receptors, there is no direct evidence that they bind a ligand. Herein we present evidence that Ly-6A.2, a Ly-6 protein expressed on T lymphocytes, binds a ligand expressed on normal thymocytes and splenic B and T cells. We find that transgenic thymocytes that overexpress Ly-6A.2 spontaneously aggregate in culture. This homotypic adhesion requires the overexpression of Ly-6A.2 because it is not observed in cultures of nontransgenic thymocytes. The aggregation of Ly-6A.2 transgenic thymocytes is inhibited by phosphatidylinositol-specific phospholipase C (which removes Ly-6A.2 and other glycosylphosphatidylinositol-anchored proteins from the membrane). Some anti-Ly-6A.2 monoclonal antibodies, including nonactivating ones and Fab' fragments, inhibit this aggregation. In contrast, other anti-Ly-6A.2 monoclonal antibodies increase the aggregation of transgenic but not nontransgenic thymocytes. To further examine whether Ly-6A.2 mediates adhesion (versus inducing another adhesion pathway) reaggregation assays were performed with paraformaldehyde-fixed Tg+ thymocytes. Paraformaldehyde-fixed Tg+ thymocytes reaggregate in culture and this aggregation is also blocked by phosphatidyl-inositol-specific phospholipase C and anti-Ly-6A.2 monoclonal antibodies. These results indicate that the homotypic adhesion of cultured Ly-6A.2 transgenic thymocytes is directly mediated by Ly-6A.2 and, more importantly, strongly suggests that Ly-6A.2 binds a ligand that is expressed on thymocytes. Tg+ thymocytes also bind to nontransgenic thymocytes, B cells, and T cells, indicating that normal cells naturally express the Ly-6A.2 ligand.

Polymorphism at the mouse Thb locus

Mouse ThB is a 15,000 M(r) glycosyl phosphatidyl inositol anchored cell surface glycoprotein that shares amino acid homology with Ly-6 molecules; the gene is closely linked to Ly-6 on chromosome 15. The Thb locus has two alleles, Thbh and Thbl, which control the level of expression of ThB molecules on thymocytes (as shown herein) and on splenic B cells, and is therefore different from the usual polymorphisms of other Ly loci which give an all or none serological reaction. The reason for the expression polymorphism is unknown and could include a different protein structure in ThB molecules, altered glycosylation, or differences in transcriptional control. To determine the reason for the differences in expression, we examined the RNA (cDNA) sequence of Thbh and Thbl alleles: there was complete nucleotide identity in the cDNA sequence in both ThB(high) (C57BL/6)- and ThB(low) (BALB/c)-expressing strains; the RNA and protein sequences would therefore be identical. In addition to the difference in the amount of cell surface glycoprotein, there was also a difference in the level of ThB mRNA in ThB(high) and ThB(low) strains; thus the differences in ThB expression are likely to be due to different rates of transcription of the two alleles.

Functional and molecular characterization of single, (4-hydroxy-3-nitrophenyl)acetyl (NP)-specific, IgG1+ B cells from antibody-secreting and memory B cell pathways in the C57BL/6 immune response to NP

We have used multiparameter flow cytometry to identify a population of IgG1+ IgM- antigen-specific B cells which emerges in spleens of C57BL/6 mice following immunization with the hapten, (4-hydroxy-3-nitrophenyl)acetyl (NP). Characterization of the specificities of IgG1 antibodies produced by single, sorted IgG1+ NP+ cells in both Elispot assays and in microcultures containing lipopolysaccharide, interleukin (IL)-2, IL-4 and IL-5 indicates that the splenic IgG1+ NP+ B cell population includes both IgG1 anti-NP antibody-secreting cells and non-secreting, IgG1+ memory B cells. Each functionally discrete population of IgG1+ B cells expresses a distinctive surface phenotype defined by a wide range of B cell markers. In particular, antibody-secreting, IgG1+ cells were uniquely identified by co-expression of the matrix receptor, syndecan. The NP-specific B cell population emerging in the day 7 primary response was assessed for clonotypic diversity by amplification and direct sequencing of the rearranged V186.2 heavy chain variable region gene expressed by single, ex vivo IgG1+ NP+ lambda+ B cells. Memory B cell clones, distinguished by junctional diversity, carried either no mutation or a single mutation within rearranged V186.2, suggesting isolation of these cells at the onset of the hypermutation mechanism. This novel approach, therefore, allows the direct and unambiguous identification and characterization of individual B cell clonotypes during their initial selection and activation in antibody responses in vivo.

Diverse classes of T-cell lymphomas arise in T-lymphocyte-inductive epitheliomas of the mouse salivary gland

During the course of serial transplantations of polyomavirus-induced C3H-Bittner salivary gland epitheliomas in F1-hybrid mice, three tumor sublines were found which gave rise to T-cell lymphomas of host origin. The lymphomas resembled spontaneous AKR/J thymic lymphomas in their expression of lymphoid differentiation antigens, and they may represent sequential stages in the differentiation of immature T lymphocytes. We found no evidence that polyomavirus directly induced the lymphomas, rather, the lymphomagenic events paralleled those which occur in spontaneous AKR/J thymic lymphomas.

Identification of a surface protein (p100) associated with two glycosyl-phosphatidylinositol-linked molecules (Thy-1 and ThB) by natural anti-lymphocyte autoantibodies

Our previous study of natural autoantibodies showed that anti-lymphocyte antibodies are frequently produced by perinatal B cells from normal strains of mice. One-third of these monoclonal antibodies (mAb) recognized similar epitopes on the surface of thymocytes. In the present report, we have characterized the molecule recognized by three of these mAb (D10, G7, 22). These mAb identified a 100-kDa protein (p100) on the surface of thymocytes. This protein resolved into 70-kDa polypeptide chains under reducing conditions. Inhibition experiments as well as antibody immunoprecipitations in the presence of mild detergents revealed non-covalent association of the p100 with Thy-1 and ThB. A similar multimolecular complex was identified following chemical cross-linking of thymocyte surface proteins. Analysis of several Thy-1-defective mutant cells lines, and thymocytes treated with phosphatidylinositol-specific phospholipase C (PI-PLC) showed that the expression of p100 was strongly influenced by Thy-1 molecule. The p100 was resistant to PI-PLC treatment and was not released into the supernatant as was the case for Thy-1 and ThB molecules. These data lead us to propose that the p100 is a transmembrane protein, the expression of which in the plasma membrane is dependent on the association or presence of Thy-1 molecule.

T cells bearing the CD44hi "memory" phenotype display characteristics of activated cells in G1 stage of cell cycle

T cells capable of anamnestic proliferative responses to antigen in vitro (i.e., "memory" cells) have been shown to display the CD44hi CD45RBlo surface phenotype. To assess the state of activation of these T cells, CD4+ T cells expressing the CD44hi or CD45RBlo phenotype were compared to CD4+ T cells expressing the CD44lo or CD45RBhi phenotype in the context of expression of the "activated" (asialo-GM1hi) vs "resting" (asialo-GM1lo) phenotype and in the context of cell size, total protein content, and total RNA content. Dual fluorescence analysis demonstrated that all CD4+ T cells expressing the CD44hi phenotype also expressed the asialo-GM1hi phenotype associated with cell activation. In vitro proliferative assays confirmed that the CD4+ asialo-GM1hi, the CD4+ CD45RBlo, and the CD4+ CD44hi FACS-sorted populations displayed stronger in vitro responsiveness to stimulation with immobilized anti-CD3 mAB than the CD4+ asialo-GM1lo, CD45RBhi, or CD44lo populations. Acridine orange analysis of sorted CD44hi/lo fractions revealed that the diploid (G1) population of the CD44hi T cells displayed a higher mean RNA content than the CD44lo T cells. Similarly, the CD44hi T cells displayed a higher mean cell size and a higher mean total protein content than the CD44lo CD4+ T cells. Similar results were obtained with asialo-GM1 and CD45RB subsets of CD4+ T cells. The basal rate of protein synthesis, as determined by [3H]leucine incorporation, was approximately 50% higher in the CD44hi small CD4+ T cells than in the CD44lo CD4+ T cells. Based on the knowledge that cell size, total protein and RNA content, and responsiveness to signals inducing proliferation are lowest in G0 stage of cycle and increase through G1 stage of cycle, it appears that the CD44hi CD45RBlo T cells exist in a higher activation state than CD44lo CD45RBhi T cells. The previously demonstrated association of CD44hi CD45RBlo phenotype with memory T cells suggests that the CD44hi memory T cells are maintained in G1 (not necessarily cycling) rather than resting "out of cycle" in G0.

An early activation antigen of murine T cells recognized by monoclonal natural autoantibody NTA204 and the expression on T cells from aged NZB x NZW F1 mice with overt autoimmune disease

A monoclonal natural thymocytotoxic autoantibody NTA204 established from an autoimmune-prone NZB mouse reacted with the majority of thymocytes, all peripheral B cells, granulocytes and bone marrow myeloid cells, but not with peripheral resting T cells of normal mice. In aged NZB/W F1 mice with overt autoimmune disease, the population of NTA204+ CD4+ CD25- T cells was remarkably increased. The NTA204 antigen could be induced on splenic T cells from normal healthy mice as early as 3 hr after the initiation of culture with stimulant Con A, and was expressed on the vast majority in the 48-hr culture. The expression preceded that of other T cell activation antigens tested, CD25 and CD45R. Cell cycle analysis suggested that NTA204 is expressed at an early phase of G1A. T cells, particularly CD8+ T cells, in the allogeneic mixed lymphocyte culture (MLC) could be divided into two populations, NTA204+ and NTA204-. By immunohistochemical analysis, 30% of NTA204+ CD8+, but few NT204- CD8+ T cells were intensely positive for large cytoplasmic granules of perforin, an important cytolytic mediator of cytotoxic T cells. Thus the increased population of NTA204+ T cells in aged NZB/W F1 mice appear to be activated T cells and might be at least partly involved in the pathogenesis of disease in these mice. Immunoblotting analysis of Con A-activated splenic T cells showed that NTA204 molecules have a molecular mass of 49 Kd.

Long-range physical map of the Ly-6 complex: mapping the Ly-6 multigene family by field-inversion and two-dimensional gel electrophoresis

The Ly-6 proteins are encoded by a recently identified multigene family. Much attention has been focused on these proteins because they may be involved in lymphocyte activation, and expression of some of them occurs at critical times in the differentiation of lymphocytes. These features make it important to investigate and to characterize further this family of molecules and the genes that encode them. To aid our investigation of these issues, we have constructed a physical map of the entire Ly-6 complex in the C57BL/6 murine genome using the combined techniques of field-inversion gel electrophoresis (FIGE), phage and cosmid genomic library screening, and two-dimensional DNA electrophoresis. This map spans approximately 1600 kb, and comparison of the FIGE map and cosmids indicates that most of the Ly-6 complex has been isolated in the cosmid clones.

Effects of induced anemia in normal and autoimmune mice

Normal and autoimmune mice were studied with regard to signals eliciting differentiation and division of bone marrow stem cells. The erythropoiesis induced by anemia following serial bleedings was analyzed in young autoimmune New Zealand Black (NZB) mice and non-autoimmune strains. No difference in the response to the stimulus created by anemia was noted between the strains. After serial bleedings as a stimulus to stem cell proliferation, a five-fold increase in numbers of proliferating spleen cells occurred in both NZB and DBA/2 strains; the increased proliferating spleen cells in both strains were non-lymphoid. The bled animals had decreased percentages of B cells. The production of autoantibodies was not significantly altered by the experimentally induced anemia. In contrast, anti-immunoglobulin activation of resting B cells was increased in response to anemia. Young mice which had experimentally induced anemia had several characteristics in common with old autoimmune NZB mice. Both old NZB mice and young anemic animals had splenomegaly, increased numbers of proliferating spleen cells, decrease in splenic Ly 5+ cells and an increase in splenic colony forming units (CFUs). The anemic normal strains of animals lacked other characteristics of old NZB mice such as hyperimmunoglobulinemia or autoantibody production or elevated CD5+B cell numbers. This work supports the concept that the increase in spleen cell number, proliferating spleen cells, CFUs and the increased percentages of non-Ly-5 cells (which include erythroid precursors) found in the spleens of old NZB mice may in part result from their autoimmune hemolytic anemia.

Analysis of three distinct Ly6-A-related cDNA sequences isolated from rat kidney

Mouse Ly6A and Ly6C cDNA probes were hybridized to total RNA of rat tissues and, as in mouse, the highest level of Ly6-related transcripts was detected in kidney. Therefore, Ly6-related cDNA clones were isolated from a commercial rat kidney cDNA library in lambda gt11. Four of these (RK3, RK6, RK10, and RK11) have been fully characterized, and represent transcripts from three distinct genes. Each contains a reading frame encoding an amino acid sequence typical of the known Ly6 molecules: a 26aa leader (except in clone RK6 which has only two of its leader codons), followed by a sequence of 108 or 109aa containing 10 cysteines in excellent alignment with those of Ly6A. The three rat polypeptide sequences were more closely related to Ly6A than Ly6C, and more closely related to each other than to Ly6A. The most striking similarity between all these sequences is in the last 33aa at the C-terminal. Most of this is presumed to be cleaved off during post-translational addition of a phosphatidylinositol-glycan (PI-G) membrane anchor. Southern blot analysis of rat DNA probed with rat-Ly6 cDNA showed multiple band patterns indicative of a multigene family. No restriction fragment length polymorphism (RFLP) was evident amongst the six inbred rat strains tested. Anomalies in two of the rat cDNA clones, resulting from improper splicing of the original transcripts, correlated with Ly6Ca exon boundaries, thus suggesting conserved intron-exon organization.

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.

Cross-linking of Ly 6-linked alloantigens: association between ThB and Ly 5

The bifunctional cross-linking reagent dithiobis(succinimidyl propionate) (DSP) was used to cross-link 125I surface-labelled glycoproteins from viable thymocytes. The cells were solubilized, and the cross-linked material immunoprecipitated and analysed by SDS-PAGE. When DSP cross-linked thymocyte material was immunoprecipitated with either anti-ThB or anti-Ly 5 monoclonal antibodies, and then cleaved, molecules with masses identical to Ly 5 (Mr 180 kD) and ThB (Mr 16-18 kD) were obtained. However, if the cross-linker was not cleaved, the intact product had a molecular mass of greater than 200 kD. The identity of these co-precipitated, cross-linked moieties was formally proved by limited proteolysis peptide map analysis. The data indicated that the ThB and Ly 5 antigens were associated on the thymocyte cell surface but no such association could be found on peripheral lymphocytes. The ThB-Ly 5 interaction may indicate an association relevant to the differentiation of thymocytes.

Expression of Ly-6A/E alloantigens in thymocyte and T-lymphocyte subsets: variability related to the Ly-6a and Ly-6b haplotypes

We have studied the cellular basis for differential expression of the Ly-6A/E alloantigen on T cells obtained from mice of the Ly-6a (10-20% Ly-6A/E+) and Ly-6b (50-60% Ly-6A/E+) haplotypes. During T-cell ontogeny only a small fraction (less than 12%) of thymocytes expressed Ly-6A/E. By 4 weeks of age adult levels of Ly-6A/E bearing lymphocytes were seen in peripheral lymphoid tissue. Immunohistochemical studies of the thymus revealed that Ly-6A/E+ cells were located predominantly in the medulla with small clusters of Ly-6A/E+ cells throughout the cortex. Consistent with this result, phenotypic studies showed that in the adult thymus the majority of Ly-6A/E expression was on mature CD4+CD8- and CD4-CD8+ cortisone-resistant and precursor CD4-CD8- thymocytes. However, a much higher percentage of CD4+CD8- and CD4-CD8- thymocytes as well as CD4+CD8- peripheral T cells expressed Ly-6A/E from Ly-6b mice. Furthermore, although gamma interferon induced increased Ly-6A/E expression in certain thymocyte and T-cell subsets, this induction functioned preferentially for cells obtained from Ly-6b mice. Studies using F1 hybrid mice (Ly-6a x Ly-6b) indicated that the "basal" level of Ly-6A/E expression on these subsets appeared to be under codominant genetic control, whereas gamma interferon-induced regulation of Ly-6A/E expression appeared to be under dominant genetic control. Collectively, these results suggest that the expression of Ly-6A/E on a particular T-cell subset is established in the thymus and is a stable characteristic of each haplotype. In addition, the low levels of Ly-6A/E expression for the Ly-6a haplotype appear to be partially due to the inability of the majority of resting CD4+ T cells to express Ly-6A/E and to the relatively poor induction of this protein by gamma interferon.

Mouse strain variation in Ly-24 (Pgp-1) expression by peripheral T cells and thymocytes: implications for T cell differentiation

The cell surface glycoprotein Ly-24 has been proposed as a useful marker for the identification of in vivo-primed T cells. Analysis of Ly-24 surface expression by T cells from different mouse strains has shown variation in Ly-24 expression that is not H-2 linked; however, mice of the Ly-24.1 allele (e.g. BALB/c) express relatively high amounts, whereas Ly-24.2 strains (e.g. C57BL/6) are low expressors. In BALB/c (Ly-24 high) and C57BL/6 (Ly-24 low) mice, Ly-24 was expressed by both CD4- CD8+ and CD4+ CD8- subpopulations of single-positive T cells and thymocytes Among CD4- CD8- thymocytes, the overall expression of Ly-24 was similar in both mouse strains. Analysis of CD4+ and CD8+ single-positive thymocytes from newborn and adult BALB/c mice showed that the neonatal population contained fewer Ly-24+ cells. However, using the cell surface markers J11d and CD3, neonatal single-positive thymocytes were found to contain larger numbers of cells with the Ly-24-J11d+CD3 low to negative phenotype. Taken together, these results show that in BALB/c (Ly-24 high) mice, as soon as functional mature phenotype (CD3+) CD4+ and CD8+ single-positive thymocytes are generated, they already express Ly-24. These data cast doubt on the usefulness of Ly-24 expression as a universal marker of in vivo-primed T cells and suggest that in BALB/c mice thymus migrants may well be Ly-24+. Expression of Ly-24 by thymocytes is discussed in the context of current models of intrathymic T cell differentiation.

The 33,000 protein precipitated by Ly-6A.2-specific antibodies is not associated with the Ly-6 polymorphism

In this study, the relative mass of the Ly-6A.2 antigen was shown to be 12,000-14,000, in contrast to initial studies which showed the relative mass to be 33,000. Using polymorphic Ly-6-specific antibodies, the 33,000 molecules could be immunoprecipitated from surface-iodinated thymocytes of Ly-6A.2+, Ly-6A.2- strains and a Ly-6A.2- mutant cell line BW(Thy-1-e). This clearly demonstrated that 33,000 molecules were not associated with the Ly-6 polymorphism. By contrast, when biosynthetically labeled Ly-6A.2+ spleen cell lysates were analyzed, the major species immunoprecipitated by the polymorphic Ly-6A.2-specific antibody was 12,000-14,000, although a minor 33,000 species were also evident. The Ly-6A-specific antibody D7 which detects a monomorphic epitope on the Ly-6A molecule could immunoprecipitate the 12,000-14,000 molecules from surface-labeled cells. By contrast, the Ly-6A.2-specific antibodies detecting the polymorphic Ly-6A.2 determinant could not, though the reasons for this difference are not clear. Thus 12,000-14,000 molecules were only immunoprecipitated from Ly-6A.2+ cells, whereas 33,000 molecules were precipitated from both Ly-6A.2+ cells and Ly-6A.2- cells. These findings suggest that the 33,000 molecules immunoprecipitated by 5041-24.2 are most likely to be an unrelated protein, possibly cross-reactive with some Ly-6A.2 antibodies.

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.

N-methyl-N-nitrosourea-induced and spontaneous AKR/J thymic lymphomas express distinct differentiation antigen phenotypes

Spontaneous and N-methyl-N-nitrosourea (MNU)-induced AKR/J thymic lymphomas were characterized for expression of several lymphocyte differentiation antigens. The majority (53%) of spontaneous lymphomas expressed both Lyt-2 and L3T4 antigens, similar to the predominant normal thymocyte subset. In contrast, 63% of the thymic lymphomas induced by the chemical carcinogen MNU, expressed an Lyt-2+ L3T4- antigenic profile. Although this profile suggested that MNU-induced lymphomas are phenotypically similar to a mature thymocyte subset, the presence of ThB antigen on Lyt-2+ L3T4- lymphomas did not support this notion. Diagonal gel electrophoresis of 125I-labeled membrane extracts and immunoprecipitates revealed that 17 of 29 Lyt-2+ L3T4-MNU-induced lymphomas expressed cell surface T-cell receptor heterodimer components. Northern blot analyses confirmed that the T-cell receptor material was composed of alpha and beta polypeptide chains. The results from this study indicate a distinct origin or differentiation potential of the target cells involved in viral and chemical induced lymphomagenesis of AKR/J mice.

Evidence that murine hematopoietic cell subset marker J11d is attached to a glycosyl-phosphatidylinositol membrane anchor

Glycosyl-phosphatidylinositol (G-PI) has been shown to serve as membrane anchor for cell surface molecules such as Thy-1, Ly-6-controlled ThB and Qa antigens. Here, we present several lines of evidence indicating that the hematopoietic cell lineage (i.e. thymocytes, B cell subset and red blood cells) marker defined by the rat monoclonal antibody J11d is also a G-PI-linked structure. First, surface expression of the J11d-defined molecules, and that of the related antigen B2A2, was found to be specifically reduced by treatment of thymocytes and B lymphoma or hybridoma cells with excess of Staphylococcus aureus PI-specific phospholipase C; this enzyme also solubilizes a 35-40-kDa material from erythrocyte microsomal membranes corresponding to the predominant J11d-reactive red cell surface molecules. Second, Thy-1- mutants of the BW5147, T1M1, S1A or S49 murine T lymphoma cells of the complementary classes A, B, C and E (i.e. shown to be defective in the enzymatic machinery that posttranslationally modify Thy-1 molecules) also lack J11d, or express it at a very low level. Although directed at a G-PI-linked structure, the J11d monoclonal antibody, unlike other reagents to Thy-1 or Ly-6-controlled antigens, failed to induce thymocyte proliferation even in the presence of phorbol myristate acetate and cross-linker monoclonal antibody.

Relationships between B-lineage lymphocytes and stromal cells in long-term bone marrow cultures

In long-term culture of mouse bone marrow, the growth and differentiation of B-lineage lymphocytes depends on interaction with adherent cells or their products. The objectives of these studies were to characterize the types of cells present in the supporting adherent layer as well as the physical relationships of these cells with lymphocytes. With an extensive panel of antibodies against hemopoietic and lymphocyte antigens, two discrete nonlymphoid populations were identified: macrophages and undefined, large cells which we termed "stromal cells". Lymphocyte clusters grew in actual contact with the latter cells only. Stromal cells lacked expression of most hemopoietic antigens, including the common leukocyte antigen, J11d, heat stable antigen (M1/69), Thy-1 and BP 1. Antigens expressed by stromal cells were detected by AA4.1, our 94.2 antibody, and antibody to the Forsmann antigen, but the most distinguishing characteristics of the lymphocyte-binding stromal cells were production of basement membrane components, laminin and collagen IV, and the extremely low uptake of acetylated low density lipoprotein (LDL). Using acetylated LDL uptake as a sorting criterion, the lymphocyte-binding stromal cells were separated from the macrophages, recultured and shown to support lymphocyte proliferation. We found the binding between stromal cells and lymphocytes to be highly selective and dependent on divalent cations; hence, specialized adhesion mechanisms may have a role in B cell development. Moreover, our studies suggest that phosphatidylinositol-anchored cell surface molecules may be involved in this adhesion. Our findings demonstrate the possibility that a single cell type provides physical support and proliferation stimuli for early B-lineage cells. This accessory cell is not a macrophage; rather, it has features of an endothelial or epithelial cell.

In vivo localization and growth of the 70Z/3 pre-B-cell line

The 70Z/3 pre-B-cell line has long been used as a model for understanding the nature and mode of action of differentiation-inducing stimuli as well as mechanisms which control immunoglobulin light chain gene expression. This study is a first appraisal of the localization, growth, and differentiation of the cell line in vivo. At 24 hr after intravenous injection, radiolabeled 70Z/3 cells localized efficiently to the bone marrow and analysis by flow cytometry revealed that fluorescein isothiocyanate-labeled cells localized to bone marrow and spleen in a ratio of 2:1. Growth of the cell line paralleled the localization pattern. When the cells were given intravenously, bone marrow contained 100% of tumor cells at a time when a majority of spleen cells were still normal. Tumor cells were found in the blood only at end-stage disease in a minority of animals. Because 70Z/3 cells differentiate in vitro in response to a variety of factors, it is possible that exposure to the in vivo environment would have a similar effect. When blast cells from heavily infiltrated bone marrow and spleen were analyzed for the expression of a panel of B-lymphocyte lineage surface antigens, however, there was no evidence for surface kappa induction. Inductive stimuli may be present in limiting quantities in vivo or overridden by by negative feed-back control mechanisms. This information provides a basis for in vivo experimentation with the inducible 70Z/3 cell line and raises issues concerning normal mechanisms which control B-lineage cell differentiation.

Antigen-induced changes in B cell subsets in lymph nodes: analysis by dual fluorescence flow cytofluorometry

Changes in the representation and surface phenotype of defined B cell subsets in murine lymph nodes stimulated with keyhole limpet hemocyanin or sheep red blood cells have been analyzed by two-color immunofluorescence fluorocytometric analysis. Shortly after immunization with either antigen there is a dramatic increase in both the frequency and absolute number of IgM+, IgD+ B cells, which is followed by the formation of germinal centers. Germinal center cells, as soon as they appear on day 3 after primary immunization, bind high levels of peanut agglutinin, bear low levels of surface IgM but no detectable surface IgD, and are characterized by lack of staining with MEL-14, a monoclonal antibody which recognizes a lymphocyte surface receptor involved in lymphocyte homing. The level of I-A and H-2K region-encoded surface antigens on early germinal center cells is higher than on PNAlo B cells. During the first 7 days of the germinal centers there is a progressive decrease in the average level of H-2K but not of Ia antigens. A similar decrease was observed for ThB. It is confirmed that the germinal center cell population contains the majority of antigen-binding cells in the stimulated lymph node. These findings indicate that B cells are recruited nonspecifically to antigen-stimulated lymph nodes, and that the antigen-specific cells then selectively participate in the formation of germinal centers where they undergo specific differentiation events.

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.

Independent regulation of IgM, IgD, and Ia antigen expression in cultured immature B lymphocytes

Long-term cultured bone marrow cells were characterized with respect to a number of B and pre-B cell markers. Cells expressing ThB, B-220, and IgM were found within cultures set up according to the procedure of Whitlock and Witte. This culture system was modified by placing sorted pre-B cells (ThB+, IgM-) from bone marrow in culture with previously-established bone marrow adherent layers. These cultures commenced growth without the lag associated with the Whitlock cultures. These cultured nonadherent cells show a high frequency of IgM+ cells, but do not express either IgD or Ia, and we refer to them as immature B cells. Cells with a similar phenotype (IgM+, Ia-, IgD-) are found within the spleens of young but not adult mice. The phorbol ester PMA induces expression of IgD on the cultured immature B cells, but has no effect on Ia expression. This suggests that the processing of H chain RNA transcripts may be affected by protein kinase C. These results demonstrate that the appearance of IgM, IgD, and Ia are independently controlled in long-term cultured B-lineage cells.

Peritoneal Ly-1 B cells: genetic control, autoantibody production, increased lambda light chain expression

Previous studies demonstrate that Ly-1 B cells and their progenitors are clearly detectable in peritoneum in normal mice. In this publication, we show (a) that peritoneal Ly-1 B cells resemble splenic Ly-1 B cells with respect to surface marker expression and functional activity (autoantibody production); (b) that Ly-1 B frequencies in peritoneum are considerably higher than in spleen; and (c) that genetic mechanisms reduce peritoneal Ly-1 B frequencies to minimal levels in SJL-related mice and to below detectability in CBA/N and other mice with the X-linked immunodeficiency (Xid). In addition, we show that that peritoneal (and perhaps splenic) Ly-1 B populations demonstrate an unique bias in immunoglobulin commitment. That is, they are selectively enriched for cells that express IgM heavy chains in association with lambda light chains. Thus, as a whole, evidence presented here defines the peritoneum as a tightly regulated lymphocyte compartment that normally houses a large population of mature Ly-1 B cells with distinctive functional properties.