Genetic nomenclature for loci controlling mouse lymphocyte antigens

ROR agonist hampers the proliferation and survival of postactivated CD8+ T cells through the downregulation of cholesterol synthesis-related genes

Cholesterol is a major component of the lipid bilayers of cellular membranes. The synthesis of cholesterol is acutely elevated during T-cell activation to support T-cell growth and proliferation. There is a limited understanding of cholesterol metabolism reprogramming during T-cell activation. Retinoic acid receptor-related orphan receptors (RORs) are ligand-activated nuclear receptors that regulate the transcription of target genes. In this study, we demonstrated that the activation of RORs by a synthetic agonist (SR1078) impairs the proliferation and survival of postactivated CD8⁺ T cells. The inhibitory effects of SR1078 on CD8⁺ T-cell proliferation and survival were attributed to cholesterol depletion and downregulated expression of cholesterol metabolism-related genes. The overexpression of RORα or RORγt promoted apoptosis in the postactivated CD8⁺ T cells in vitro. The expression of RORα (but not that of RORγt) was markedly upregulated in the CD8⁺ T cells upon stimulation with an antigen in vivo. The functional deficiency of RORα enhanced CD8⁺ T-cell expansion during the response to bacterial infection. These results suggest that RORs are involved in the regulation of CD8⁺ T-cell-mediated immune response through the regulation of cholesterol metabolism, which can be modulated by a synthetic ROR agonist. The findings of this study can aid in the development of immunotherapeutic methods that target nuclear receptors.

A System to Study Aneuploidy In Vivo

Aneuploidy, an imbalanced chromosome number, is associated with both cancer and developmental disorders such as Down syndrome (DS). To determine how aneuploidy affects cellular and organismal physiology, we have developed a system to evaluate aneuploid cell fitness in vivo. By transplanting hematopoietic stem cells (HSCs) into recipient mice after ablation of recipient hematopoiesis by lethal irradiation, we can directly compare the fitness of HSCs derived from a range of aneuploid mouse models with that of euploid HSCs. This experimental system can also be adapted to assess the interplay between aneuploidy and tumorigenesis. We hope that further characterization of aneuploid cells in vivo will provide insight both into the origins of hematopoietic phenotypes observed in DS individuals as well as the role of different types of aneuploid cells in the genesis of cancers of the blood.

TCR affinity for thymoproteasome-dependent positively selecting peptides conditions antigen responsiveness in CD8(+) T cells

In the thymus, low-affinity T cell antigen receptor (TCR) engagement facilitates positive selection of a useful T cell repertoire. Here we report that TCR responsiveness of mature CD8(+) T cells is fine tuned by their affinity for positively selecting peptides in the thymus and that optimal TCR responsiveness requires positive selection on major histocompatibility complex class I-associated peptides produced by the thymoproteasome, which is specifically expressed in the thymic cortical epithelium. Thymoproteasome-independent positive selection of monoclonal CD8(+) T cells results in aberrant TCR responsiveness, homeostatic maintenance and immune responses to infection. These results demonstrate a novel aspect of positive selection, in which TCR affinity for positively selecting peptides produced by thymic epithelium determines the subsequent antigen responsiveness of mature CD8(+) T cells in the periphery.

Thymoproteasomes produce unique peptide motifs for positive selection of CD8(+) T cells

Positive selection in the thymus provides low-affinity T-cell receptor (TCR) engagement to support the development of potentially useful self-major histocompatibility complex class I (MHC-I)-restricted T cells. Optimal positive selection of CD8(+) T cells requires cortical thymic epithelial cells that express β5t-containing thymoproteasomes (tCPs). However, how tCPs govern positive selection is unclear. Here we show that the tCPs produce unique cleavage motifs in digested peptides and in MHC-I-associated peptides. Interestingly, MHC-I-associated peptides carrying these tCP-dependent motifs are enriched with low-affinity TCR ligands that efficiently induce the positive selection of functionally competent CD8(+) T cells in antigen-specific TCR-transgenic models. These results suggest that tCPs contribute to the positive selection of CD8(+) T cells by preferentially producing low-affinity TCR ligand peptides.

Commonly used mouse strains

This appendix lists commonly used mouse strains and selected cell-surface molecules expressed by these strains. H-2 is the gene locus residing on chromosome 17 of the mouse which encodes major histocompatibility proteins. Only those H-2 loci involved in immunologic interactions frequently cited in this manual are listed here--i.e., Aa-, Ab-, Ea-, and Eb--region-encoded MHC class II molecules, and K-and D-region-encoded MHC class I molecules. In addition to H-2 loci, others are listed that encode immunologically important proteins. Congenic strains listed in this appendix represent inbred strains that were derived from their origin (BALB/c, C57Bl/10, and C3H) by selective matings, such that they differ from that originating strain at only one independently segregating genetic locus. The locus of choice in these cases was H-2; thus, these strains differ from their strain of origin only in their H-2 complex, but not in any other loci. During the production of the congenic lines, several strains were derived that had undergone intra-H-2 recombination events. These strains are listed here and have been invaluable in defining the major roles of various MHC glycoproteins.

TGF-beta in allogeneic stem cell transplantation: friend or foe?

Donor treatment with granulocyte-colony-stimulating factor (G-CSF) attenuates the ability of donor T cells to induce acute graft-versus-host disease (aGVHD) but increases the severity of chronic GVHD (cGVHD). We investigated the role of the regulatory cytokine transforming growth factor beta (TGF-beta) in this paradox in well-established murine models of aGVHD and cGVHD wherein recipients undergo transplantation with splenocytes from donors treated with G-CSF. Neutralization of TGF-beta after stem-cell transplantation (SCT) significantly increased the severity of aGVHD, and the concurrent prevention of interleukin-10 (IL-10) production further exaggerated this effect. Early after SCT, donor T cells were the predominant source of TGF-beta and were able to attenuate aGVHD in a TGF-beta-dependent fashion. Although the neutralization of TGF-beta augmented the proliferation and expansion of donor T cells after SCT, it paradoxically impaired cellular cytotoxicity to host antigens and associated graft-versus-leukemia (GVL) effects. In cGVHD, neutralization of TGF-beta from day 14 after SCT attenuated histologic abnormalities, and CD11b+ mononuclear cells infiltrating sclerodermatous skin produced 50-fold more TGF-beta than corresponding T cells. Thus, though the production of TGF-beta by donor T cells early after transplantation attenuates aGVHD and is required for optimal GVL, the production of TGF-beta late after SCT is preferentially from mononuclear cells and mediates cGVHD. These data have important implications for the timing of therapeutic TGF-beta neutralization to prevent cGVHD after allogeneic SCT.

Behavior of transplanted bone marrow-derived GFP mesenchymal cells in osteochondral defect as a simulation of autologous transplantation

To elucidate the behavior of autologously transplanted mesenchymal cells in osteochondral defects, we followed transplanted cells using green fluorescent protein (GFP) transgenic rats, in which all cells express GFP signals in their cytoplasm and nuclei as transplantation donors. Bone marrow-derived mesenchymal cells, which contain mesenchymal stem cells (MSCs), were obtained from transgenic rats. Then, dense mesenchymal cell masses created by hanging-drop culture were transplanted and fixed with fibrin glue into osteochondral defects of wild-type rats. At 24 weeks after surgery, the defects were repaired with hyaline-like cartilage and subchondral bone. GFP positive cells, indicating transplanted mesenchymal-derived cells, were observed in the regenerated tissues for 24 weeks although GFP positive cells decreased in number with time. Because GFP causes no immunological rejection and requires no chemicals for visualization, transplantation between transgenic and wild-type rats can be regarded as a simulation of autologous transplantation, and the survivability of transplanted cells are able to be followed easily and reliably. Thus, the behavior of transplanted mesenchymal cells was able to be elucidated in vivo by this strategy, and the results could be essential in future tissue engineering for the regeneration of osteochondral defects with original hyaline cartilage and subchondral bone.

Heat shock protein 10 inhibits lipopolysaccharide-induced inflammatory mediator production

Heat shock protein 10 (Hsp10) and heat shock protein 60 (Hsp60) were originally described as essential mitochondrial proteins involved in protein folding. However, both proteins have also been shown to have a number of extracellular immunomodulatory activities. Here we show that purified recombinant human Hsp10 incubated with cells in vitro reduced lipopolysaccharide (LPS)-induced nuclear factor-kappaB activation and secretion of several inflammatory mediators from RAW264.7 cells, murine macrophages, and human peripheral blood mononuclear cells. Induction of tolerance by contaminating LPS was formally excluded as being responsible for Hsp10 activity. Treatment of mice with Hsp10 before endotoxin challenge resulted in the reduction of serum tumor necrosis factor-alpha and RANTES (regulated upon activation, normal T cell expressed and secreted) levels and an elevation of serum interleukin-10 levels. Hsp10 treatment also delayed mortality in a murine graft-versus-host disease model, where gut-derived LPS contributes to pathology. We were unable to confirm previous reports that Hsp10 has tumor growth factor properties and suggest that Hsp10 exerts anti-inflammatory activity by inhibiting Toll-like receptor signaling possibly by interacting with extracellular Hsp60.

Fate of transplanted bone-marrow-derived mesenchymal cells during osteochondral repair using transgenic rats to simulate autologous transplantation

OBJECTIVE

The fate of transplanted cells used in tissue engineering strategies should be followed. With this aim in view, the survival of transplanted bone-marrow-derived mesenchymal cells within osteochondral defects was determined using transgenic rats to simulate autologous transplantation.

DESIGN

An autologous transplantation model was simulated using transgenic rats - whose transgenes produce no foreign proteins - as donors, and wild-type rats as recipients. Dense masses of mesenchymal cells were prepared from the transgenic rats using the hanging-drop culture technique. These cell masses were then transplanted into osteochondral defects created within the medial femoral condyle of wild-type rats, wherein they are affixed with fibrin glue. The course of repair was assessed histologically. The survival of the transplanted cells was ascertained by in situ hybridization of the transgenes.

RESULTS

Twenty-four weeks after transplantation, the defects were repaired with hyaline-like cartilage, which was thicker than normal, and with subchondral bone. Using the in situ hybridization technique, cells derived from the transplanted ones were detected within both the cartilaginous and the subchondral bone layers.

CONCLUSION

Using this simulated autologous transplantation model, the survival of transplanted mesenchymal cells was monitored in vivo. The findings indicate that the transplanted mesenchymal cells contributed to the repair of the osteochondral defects.

Beta-galactosidase of ROSA26 mice is a useful marker for detecting the definitive erythropoiesis after stem cell transplantation

BACKGROUND

Hematopoietic reconstitution after stem cell transplantation has been analyzed by using stem cells of Ly5 congenic mice. However, the early erythropoiesis has never been analyzed because this marker is not expressed on all of the erythroid lineage cells. The transgenic mouse expressing beta-galactosidase (beta-gal) or green fluorescent protein (GFP) has been reported. Using these markers, we analyzed the early erythropoiesis after stem cell transplantation.

METHODS

The beta-gal activity and GFP were examined in the hematopoietic cells of ROSA26 and GFP transgenic mice, respectively, by flow cytometry. The primitive hematopoietic stem cell fraction (Lin(-)c-kit(+)Sca-1(+)) in bone marrow (BM) cells of ROSA26 mice was transferred into lethally irradiated mice. The kinetics of hematopoietic reconstitution was analyzed in the BM and spleen after transplantation.

RESULTS

The beta-gal activity, but not the GFP and Ly5, was detected in all of the erythroid (TER119+) cells. The beta-gal activity was also detected in the donor-derived myeloid (Mac-1+), B lymphoid (B220+), and T lymphoid (Thy-1+) cells in the BM and spleen after stem cell transplantation. The kinetics of the hematopoietic reconstitution demonstrated that early erythroid (TER119(low)CD71(med)) cells were developed in the BM and spleen within 2 days after transplantation before development of proerythroblasts (TER119(+)CD71(high)), and that massive erythropoiesis and myelopoiesis were observed in the spleen until 2 and 4 weeks after transplantation, respectively. Conclusions. The beta-gal of ROSA26 mice can be a useful marker to identify the donor-derived hematopoietic cells, including early erythroid cells, and the first major wave of erythropoiesis occurring in the spleen after stem cell transplantation.

Donor treatment with pegylated G-CSF augments the generation of IL-10-producing regulatory T cells and promotes transplantation tolerance

We investigated whether the protection from graft-versus-host disease (GVHD) afforded by donor treatment with granulocyte colony-stimulating factor (G-CSF) could be enhanced by dose escalation. Donor treatment with human G-CSF prevented GVHD in the B6 → B6D2F1 murine model in a dose-dependent fashion, and murine G-CSF provided equivalent protection from GVHD at 10-fold lower doses. Donor pretreatment with a single dose of pegylated G-CSF (peg-G-CSF) prevented GVHD to a significantly greater extent than standard G-CSF (survival, 75% versus 11%, P < .001). Donor T cells from peg-G-CSF-treated donors failed to proliferate to alloantigen and inhibited the responses of control T cells in an interleukin 10 (IL-10)-dependent fashion in vitro. T cells from peg-G-CSF-treated IL-10-/- donors induced lethal GVHD; T cells from peg-G-CSF-treated wild-type (wt) donors promoted long-term survival. Whereas T cells from peg-G-CSF wt donors were able to regulate GVHD induced by T cells from control-treated donors, T cells from G-CSF-treated wt donors and peg-G-CSF-treated IL-10-/- donors did not prevent mortality. Thus, peg-G-CSF is markedly superior to standard G-CSF for the prevention of GVHD following allogeneic stem cell transplantation (SCT), due to the generation of IL-10-producing regulatory T cells. These data support prospective clinical trials of peg-G-CSF-mobilized allogeneic blood SCT. (Blood. 2004;103:3573-3581)

Local irradiation enhances congenic donor pluripotent hematopoietic stem cell engraftment similarly in irradiated and nonirradiated sites

Long-term multilineage chimerism is achieved in CD45 congenic mice receiving high bone marrow doses with or without mediastinal irradiation (MI). Increased donor chimerism results in MI-treated compared with nonirradiated animals, suggesting that MI makes "space" for engraftment of donor pluripotent hematopoietic stem cells (PHSCs). We have now examined whether space is systemic or whether increased engraftment of donor marrow in locally irradiated mice is confined to the irradiated bones. While increased donor chimerism was observed in irradiated bones compared with nonirradiated bones of MI-treated animals 4 weeks following bone marrow transplantation (BMT), these differences were minimal by 40 weeks. MI-treated chimeras contained more adoptively transferable donor PHSCs in the marrow of both irradiated and distant bones compared with non-MI-treated chimeras. Similar proportions of donor PHSCs were present in irradiated and nonirradiated bones of locally irradiated mice at both 4 and 40 weeks. Irradiated bones contained more donor short-term repopulating cells than distant bones at 4 weeks, but not 40 weeks, after BMT. Our study suggests that local proliferation of donor PHSCs in mice receiving local irradiation rapidly leads to a systemic increase in donor PHSC engraftment.

Differential roles of IL-1 and TNF-alpha on graft-versus-host disease and graft versus leukemia

We demonstrate an increase in graft-versus-host disease (GVHD) after experimental bone marrow transplant (BMT) when cyclophosphamide (Cy) is added to an otherwise well-tolerated dose (900 cGy) of total body irradiation (TBI). Donor T cell expansion on day +13 was increased after conditioning with Cy/TBI compared with Cy or TBI alone, although cytotoxic T lymphocyte (CTL) function was not altered. Histological analysis of the gastrointestinal tract demonstrated synergistic damage by Cy/TBI and allogeneic donor cells, which permitted increased translocation of LPS into the systemic circulation. TNF-alpha and IL-1 production in response to LPS was increased in BMT recipients after Cy/TBI conditioning. Neutralization of IL-1 significantly reduced serum LPS levels and GVHD mortality, but it did not affect donor CTL activity. By contrast, neutralization of TNF-alpha did not prevent GVHD mortality but did impair CTL activity after BMT. When P815 leukemia cells were added to the bone marrow inoculum, allogeneic BMT recipients given the TNF-alpha inhibitor relapsed at a significantly faster rate than those given the IL-1 inhibitor. To confirm that the role of TNF-alpha in graft versus leukemia (GVL) was due to effects on donor T cells, cohorts of animals were transplanted with T cells from either wild-type mice or p55 TNF-alpha receptor-deficient mice. Recipients of TNF-alpha p55 receptor-deficient T cells demonstrated a significant impairment in donor CTL activity after BMT and an increased rate of leukemic relapse compared with recipients of wild-type T cells. These data highlight the importance of conditioning in GVHD pathophysiology, and demonstrate that TNF-alpha is critical to GVL mediated by donor T cells, whereas IL-1 is not.

IL-11 separates graft-versus-leukemia effects from graft-versus-host disease after bone marrow transplantation

We recently showed that IL-11 prevents lethal graft-versus-host disease (GVHD) in a murine bone marrow transplantation (BMT) model of GVHD directed against MHC and minor antigens. In this study, we have investigated whether IL-11 can maintain a graft-versus-leukemia (GVL) effect. Lethally irradiated B6D2F1 mice were transplanted with either T cell-depleted (TCD) bone marrow (BM) alone or with BM and splenic T cells from allogeneic B6 donors. Animals also received host-type P815 mastocytoma cells at the time of BMT. Recipients were injected subcutaneously with recombinant human IL-11 or control diluent twice daily, from 2 days before BMT to 7 days after BMT. TCD recipients all died from leukemia by day 23. All control- and IL-11-treated allogeneic animals effectively rejected their leukemia, but IL-11 also reduced GVHD-related mortality. Examination of the cellular mechanisms of GVL and GVHD in this system showed that IL-11 selectively inhibited CD4-mediated GVHD, while retaining both CD4- and CD8-mediated GVL. In addition, IL-11 treatment did not affect cytolytic effector functions of T cells after BMT either in vivo or in vitro. Studies with perforin-deficient donor T cells demonstrated that the GVL effect was perforin dependent. These data demonstrated that IL-11 can significantly reduce CD4-dependent GVHD without impairing cytolytic function or subsequent GVL activity of CD8(+) T cells. Brief treatment with IL-11 shortly after BMT may therefore represent a novel strategy for separating GVHD and GVL.

Granulocyte Colony-Stimulating Factor–Mobilized Allogeneic Stem Cell Transplantation Maintains Graft-Versus-Leukemia Effects Through a Perforin-Dependent Pathway While Preventing Graft-Versus-Host Disease

Minimization of graft-versus-host disease (GVHD) with preservation of the graft-versus-leukemia (GVL) effect is a crucial step to improve the overall survival of allogeneic bone marrow transplantation (BMT) for patients with hematological malignancies. We and other investigators have shown that granulocyte colony-stimulating factor (G-CSF)–mobilized allogeneic peripheral stem cell transplantation (PBSCT) reduces the severity of acute GVHD in murine models. In this study, we investigated whether G-CSF–mobilized PBSC maintain their GVL effect in a murine allogeneic transplant model (B6 → B6D2F1). B6 mice (H-2b) were injected subcutaneously with human G-CSF (100 μg/kg/d) for 6 days and their splenocytes were harvested on day 7 as a source of PBSC. G-CSF mobilization dramatically improved transplant survival compared with nonmobilized controls (95% v0%, P < .001). Systemic levels of lipopolysaccharide and tumor necrosis factor- were markedly reduced in recipients of allogeneic G-CSF–mobilized donors, but cytolytic T lymphocyte (CTL) activity against host tumor target cells p815 was retained in those recipients. When leukemia was induced in recipients by coinjection of p815 tumor cells (H-2d) at the time of transplantation, all surviving recipients of G-CSF–mobilized B6 donors were leukemia-free at day 70 after transplant, whereas all mice who received T-cell–depleted (TCD) splenocytes from G-CSF–mobilized B6 donors died of leukemia. When splenocytes from G-CSF–mobilized perforin-deficient (pfp−/−) mice were used for transplantation, 90% of recipients died of leukemia, demonstrating that perforin is a crucial pathway mediating GVL effects after G-CSF–mobilized PBSCT. These data illustrate that G-CSF–mobilized allogeneic PBSCT separate GVL from GVHD by preserving perforin-dependent donor CTL activity while reducing systemic inflammation.

Granulocyte Colony-Stimulating Factor–Mobilized Allogeneic Stem Cell Transplantation Maintains Graft-Versus-Leukemia Effects Through a Perforin-Dependent Pathway While Preventing Graft-Versus-Host Disease

Minimization of graft-versus-host disease (GVHD) with preservation of the graft-versus-leukemia (GVL) effect is a crucial step to improve the overall survival of allogeneic bone marrow transplantation (BMT) for patients with hematological malignancies. We and other investigators have shown that granulocyte colony-stimulating factor (G-CSF)–mobilized allogeneic peripheral stem cell transplantation (PBSCT) reduces the severity of acute GVHD in murine models. In this study, we investigated whether G-CSF–mobilized PBSC maintain their GVL effect in a murine allogeneic transplant model (B6 → B6D2F1). B6 mice (H-2b) were injected subcutaneously with human G-CSF (100 μg/kg/d) for 6 days and their splenocytes were harvested on day 7 as a source of PBSC. G-CSF mobilization dramatically improved transplant survival compared with nonmobilized controls (95% v0%, P < .001). Systemic levels of lipopolysaccharide and tumor necrosis factor- were markedly reduced in recipients of allogeneic G-CSF–mobilized donors, but cytolytic T lymphocyte (CTL) activity against host tumor target cells p815 was retained in those recipients. When leukemia was induced in recipients by coinjection of p815 tumor cells (H-2d) at the time of transplantation, all surviving recipients of G-CSF–mobilized B6 donors were leukemia-free at day 70 after transplant, whereas all mice who received T-cell–depleted (TCD) splenocytes from G-CSF–mobilized B6 donors died of leukemia. When splenocytes from G-CSF–mobilized perforin-deficient (pfp−/−) mice were used for transplantation, 90% of recipients died of leukemia, demonstrating that perforin is a crucial pathway mediating GVL effects after G-CSF–mobilized PBSCT. These data illustrate that G-CSF–mobilized allogeneic PBSCT separate GVL from GVHD by preserving perforin-dependent donor CTL activity while reducing systemic inflammation.

Development of intraepithelial T lymphocytes in the intestine of irradiated SCID mice by adult liver hematopoietic stem cells from normal mice

BACKGROUND/AIMS

We recently reported the adult mouse liver to contain c-kit+ stem cells that can give rise to multilineage leukocytes. This study was designed to determine whether or not adult mouse liver stem cells can generate intraepithelial T cells in the intestine as well as to examine the possibility that adult liver c-kit+ stem cells originate from the fetal liver.

METHODS

Adult liver mononuclear cells, bone marrow (BM) cells, liver c-kit+ cells or bone BM c-kit+ cells of BALB/c mice were i.v. transferred into 4 Gy irradiated CB17/-SCID mice. In other experiments, fetal liver cells from Ly5.1 C57BL/6 mice and T cell depleted adult BM cells from Ly5.2 C57BL/6 mice were simultaneously transferred into irradiated C57BL/6 SCID mice (Ly5.2). At 1 to 8 weeks after cell transfer, the SCID mice were examined.

RESULTS

Not only BM cells and BM c-kit+ cells but also liver mononuclear cells and liver c-kit+ cells reconstituted gamma delta T cells, CD4+ CD8+ double-positive T cells and CD8 alpha+beta- T cells of intestinal intraepithelial lymphocytes of SCID mice. Injection of a mixture of fetal liver cells from Ly5.1 C57BL/6 mice and adult BM cells from Ly5.2 C57BL/6 mice into Ly5.2 C57BL/6 SCID mice induced both Ly5.1 and Ly5.2 T cells, while also generating c-kit+ cells of both Ly5.1 and Ly5.2 origins in the liver.

CONCLUSIONS

Adult mouse liver stem cells were able to generate intestinal intraepithelial T cells of the SCID mice, and it is thus suggested that some adult liver stem cells may indeed be derived from the fetal liver.

Marrow Ablative and Immunosuppressive Effects of131I-Anti-CD45 Antibody in Congenic and H2-Mismatched Murine Transplant Models

Targeted hematopoietic irradiation delivered by131I-anti-CD45 antibody has been combined with conventional marrow transplant preparative regimens in an effort to decrease relapse. Before increasing the proportion of therapy delivered by radiolabeled antibody, the myeloablative and immunosuppressive effects of such low dose rate irradiation must be quantitated. We have examined the ability of 131I-anti-CD45 antibody to facilitate engraftment in Ly5-congenic and H2-mismatched murine marrow transplant models. Recipient B6-Ly5a mice were treated with 30F11 antibody labeled with 0.1 to 1.5 mCi 131I and/or total body irradiation (TBI), followed by T-cell–depleted marrow from Ly5b-congenic (C57BL/6) or H2-mismatched (BALB/c) donors. Engraftment was achieved readily in the Ly5-congenic setting, with greater than 80% donor granulocytes and T cells after 0.5 mCi 131I (estimated 17 Gy to marrow) or 8 Gy TBI. A higher TBI dose (14 Gy) was required to achieve engraftment of H2-mismatched marrow, and engraftment occurred in only 3 of 11 mice receiving 1.5 mCi131I delivered by anti-CD45 antibody. Engraftment of H2-mismatched marrow was achieved in 22 of 23 animals receiving 0.75 mCi 131I delivered by anti-CD45 antibody combined with 8 Gy TBI. Thus, targeted radiation delivered via131I-anti-CD45 antibody can enable engraftment of congenic marrow and can partially replace TBI when transplanting T-cell–depleted H2-mismatched marrow.

Marrow Ablative and Immunosuppressive Effects of131I-Anti-CD45 Antibody in Congenic and H2-Mismatched Murine Transplant Models

Targeted hematopoietic irradiation delivered by131I-anti-CD45 antibody has been combined with conventional marrow transplant preparative regimens in an effort to decrease relapse. Before increasing the proportion of therapy delivered by radiolabeled antibody, the myeloablative and immunosuppressive effects of such low dose rate irradiation must be quantitated. We have examined the ability of 131I-anti-CD45 antibody to facilitate engraftment in Ly5-congenic and H2-mismatched murine marrow transplant models. Recipient B6-Ly5a mice were treated with 30F11 antibody labeled with 0.1 to 1.5 mCi 131I and/or total body irradiation (TBI), followed by T-cell–depleted marrow from Ly5b-congenic (C57BL/6) or H2-mismatched (BALB/c) donors. Engraftment was achieved readily in the Ly5-congenic setting, with greater than 80% donor granulocytes and T cells after 0.5 mCi 131I (estimated 17 Gy to marrow) or 8 Gy TBI. A higher TBI dose (14 Gy) was required to achieve engraftment of H2-mismatched marrow, and engraftment occurred in only 3 of 11 mice receiving 1.5 mCi131I delivered by anti-CD45 antibody. Engraftment of H2-mismatched marrow was achieved in 22 of 23 animals receiving 0.75 mCi 131I delivered by anti-CD45 antibody combined with 8 Gy TBI. Thus, targeted radiation delivered via131I-anti-CD45 antibody can enable engraftment of congenic marrow and can partially replace TBI when transplanting T-cell–depleted H2-mismatched marrow.

Interleukin-11 promotes T cell polarization and prevents acute graft-versus-host disease after allogeneic bone marrow transplantation

Administration of IL-11 prevented lethal graft-versus-host disease (GVHD) in a murine bone marrow transplant (BMT) model (B6 --> B6D2F1) across MHC and minor H antigen barriers (survival at day 50: 90 vs 20%, P < 0.001). Surpisingly, IL-11 administration polarized the donor T cell cytokine responses to host antigen after BMT with a 50% reduction in IFNgamma and IL-2 secretion and a 10-fold increase in IL-4. This polarization of T cell responses was associated with reduced IFNgamma serum levels and decreased IL-12 production in mixed lymphocyte cultures (MLC). In addition, IL-11 prevented small bowel damage and reduced serum endotoxin levels by 80%. Treatment with IL-11 also reduced TNFalpha serum levels and suppressed TNFalpha secretion by macrophages to LPS stimulation in vitro. IL-11 thus decreased GVHD morbidity and mortality by three mechanisms: (a) polarization of donor T cells; (b) protection of the small bowel; and (c) suppression of inflammatory cytokines such as TNFalpha. We conclude that brief treatment with IL-11 may represent a novel strategy to prevent T cell-mediated inflammatory processes such as GVHD.

Thymic Lineage Commitment Rather Than Selection Causes Genetic Variations in Size of CD4 and CD8 Compartments

During their development, immature CD4+CD8+ thymocytes become committed to either the CD4 or CD8 lineage. Subsequent complete maturation of CD4+ and CD8+ cells requires a molecular match of the expressed coreceptor and the MHC specificity of the TCR. The final size of the mature CD4+ and CD8+ thymic compartments is therefore determined by a combination of lineage commitment and TCR-mediated selection. In humans and mice, the relative size of CD4+ and CD8+ peripheral T cell compartments shows marked genetic variability. We show here that genetic variations in thymic lineage commitment, rather than TCR-mediated selection processes, are responsible for the distinct CD4/CD8 ratios observed in common inbred mouse strains. Genetic variations in the regulation of lineage commitment open new ways to analyze this process and to identify the molecules involved.

Hydroxyurea Can Be Used to Increase Mouse c-kit+Thy-1.1loLin−/loSca-1+ Hematopoietic Cell Number and Frequency in Cell Cycle In Vivo

The DNA synthesis inhibitor hydroxyurea (HU) was administered to determine whether it induces changes in the cell-cycle status of primitive hematopoietic stem cells (HSCs)/progenitors. Administration of HU to mice leads to bone marrow accumulation of c-kit+Thy-1.1loLin−/loSca-1+ (KTLS) cells in S/G2/M phases of the cell cycle. HU is a relatively nontoxic, reversible cell-cycle agent that can lead to approximately a threefold expansion of KTLS cells in vivo and approximately an eightfold increase in the number of KTLS cells in S/G2/M. HSCs in HU-treated mice have undiminished multilineage long-term and short-term clonal reconstitution activity.

Hydroxyurea Can Be Used to Increase Mouse c-kit+Thy-1.1loLin−/loSca-1+ Hematopoietic Cell Number and Frequency in Cell Cycle In Vivo

The DNA synthesis inhibitor hydroxyurea (HU) was administered to determine whether it induces changes in the cell-cycle status of primitive hematopoietic stem cells (HSCs)/progenitors. Administration of HU to mice leads to bone marrow accumulation of c-kit+Thy-1.1loLin−/loSca-1+ (KTLS) cells in S/G2/M phases of the cell cycle. HU is a relatively nontoxic, reversible cell-cycle agent that can lead to approximately a threefold expansion of KTLS cells in vivo and approximately an eightfold increase in the number of KTLS cells in S/G2/M. HSCs in HU-treated mice have undiminished multilineage long-term and short-term clonal reconstitution activity.

Total Body Irradiation and Acute Graft-Versus-Host Disease: The Role of Gastrointestinal Damage and Inflammatory Cytokines

The influence of bone marrow transplantation (BMT) conditioning regimens on the incidence and severity of graft-versus-host disease (GVHD) has been suggested in clinical BMT. Using murine BMT models, we show here an increase in GVHD severity in several donor-recipient strain combinations after intensification of the conditioning regimen by increasing the total body irradiation (TBI) dose from 900 cGy to 1,300 cGy. Increased GVHD was mediated by systemic increases in tumor necrosis factor α (TNFα). Histologic analysis of gastrointestinal tracts showed synergistic damage by increased TBI and allogeneic donor cells that permitted increased translocation of lipopolysacharide (LPS) into the systemic circulation. In vitro, LPS triggered excess TNFα from macrophages primed by the GVH reaction. In addition, macrophages isolated within 4 hours of conditioning were primed in proportion to the TBI dose itself to secrete TNFα. Thus, the higher TBI dose increased macrophage priming and increased gut damage after allogeneic BMT, causing higher systemic levels of inflammatory cytokines and subsequent severe GVHD. These data highlight the importance of conditioning in GVHD pathophysiology and suggest that interventions to prevent LPS stimulation of primed macrophages may limit the severity of GVHD after intensive conditioning for allogeneic BMT.

In Vitro Maintenance of Highly Purified, Transplantable Hematopoietic Stem Cells

The cellular and molecular mechanisms that regulate the most primitive hematopoietic stem cell are not well understood. We have undertaken a systematic dissection of the complex hematopoietic microenvironment to define some of these mechanisms. An extensive panel of immortalized stromal cell lines from murine fetal liver were established and characterized. Collectively, these cell lines display extensive heterogeneity in their in vitro hematopoietic supportive capacity. In the current studies, we describe a long-term in vitro culture system using a single stromal cell clone (AFT024) that qualitatively and quantitatively supports transplantable stem cell activity present in highly purified populations. We show multilineage reconstitution in mice that received the equivalent of as few as 100 purified bone marrow and fetal liver stem cells cultured for 4 to 7 weeks on AFT024. The cultured stem cells meet all functional criteria currently ascribed to the most primitive stem cell population. The levels of stem cell activity present after 5 weeks of coculture with AFT024 far exceed those present in short-term cytokine-supported cultures. In addition, maintenance of input levels of transplantable stem cell activity is accompanied by expansion of other classes of stem/progenitor cells. This suggests that the stem/progenitor cell population is actively proliferating in culture and that the AFT024 cell line provides a milieu that stimulates progenitor cell proliferation while maintaining in vivo repopulating activity.

Graft-versus-host-disease-associated lymphoid hypoplasia and B cell dysfunction is dependent upon donor T cell-mediated Fas-ligand function, but not perforin function

Allogeneic bone marrow transplant recipients often exhibit a graft-versus-host-disease (GVHD)-associated immune deficiency that can be prolonged and lead to life-threatening infections. We have examined the role of donor T cell-mediated cytotoxic function in the development of GVHD-associated immune deficiency. A major histocompatibility complex-matched model of allogeneic bone marrow transplantation was employed in which lethally irradiated C3H.SW mice received a nonlethal dose of T cells from either perforin-deficient (B6-perforin 0/0), Fas-ligand (FasL)-defective (B6-gld), or normal (B6) allogeneic donor mice. T cell-depleted marrow from B6-Ly-5.1 congenic donor mice was transplanted along with the donor T cell populations to determine the effects of donor T cell-mediated cytotoxicity on engraftment. Our results demonstrate that recipients of perforin-deficient or normal allogeneic T cells exhibit profound lymphoid hypoplasia and severely reduced splenic proliferative responses to lipopolysaccharide in vitro. In contrast, GVHD-associated lymphoid hypoplasia is dramatically reduced and in vitro B cell function is intact in recipients of FasL-defective allogeneic T cells. Engraftment of myeloid and erythroid lineage cells occurs irrespective of donor T cell cytotoxic function. Although recipients of perforin-deficient or normal allogeneic T cells exhibited hematopoietic engraftment exclusively of donor origin, recipients of FasL-defective donor T cells exhibited significant mixed chimerism (Ly-5.1/Ly-5.2). Because only marrow of donor origin was transplanted, this finding suggests that Fas-mediated antirecipient cytotoxicity is required for clearance of residual hematopoietic stem cells of host origin that persist following lethal irradiation.

The Unexpected G0/G1 Cell Cycle Status of Mobilized Hematopoietic Stem Cells From Peripheral Blood

Treatment with a combination of cytokines and chemotherapy can effectively stimulate the release of hematopoietic stem cells (HSC) into the peripheral blood (PB), which can then be harvested for transplantation. The cell cycle status of the harvested HSC from mobilized PB (MPB) is of interest because of the impact that cell cycling may have on optimizing the conditions for ex vivo expansion, retrovirus-mediated gene transfer, and the engraftment of transplanted tissues. Therefore, we characterized the cell cycling status of mobilized HSC from mice and humans. The murine HSC, which express the phenotype c-kit+ Thy-1.1lo Lin−/lo Sca-1+, were purified from PB, bone marrow (BM), and spleen after the mice were treated with the mobilizing regimen of granulocyte colony-stimulating factor (G-CSF ) or a combination of cyclophosphamide (CTX) and G-CSF. Human HSC (CD34+ Thy-1+ Lin−) and progenitor cells (CD34+ Thy-1− Lin−) were isolated from the BM of untreated healthy volunteers and from MPB of healthy volunteers and patients treated with G-CSF or a combination of CTX and GM-CSF. Cell cycle status was determined by quantitating the amount of DNA in the purified cells after staining with the dye Hoechst 33342. Fluorescence-activated cell sorting analysis of the progenitor cells from the murine and human samples showed an unexpected finding, ie, virtually none of the cells from the MPB was cycling. The G0/G1 status of HSC from MPB was surprising, because a significant proportion of HSC from BM are actively proliferating and, after mobilization, the HSC in the spleen and BM were also actively cycling.

Presence of hematopoietic stem cells in the adult liver

Recently, cases have been reported in which a mixed chimeric state of blood cells is established after liver transplantation. Because the established chimerism may have aided in the induction of donor-specific tolerance, the mechanism responsible for this chimerism is of clinical importance. To establish this, we examined cells in adult mouse liver and identified the presence of c-kit+ Sca-1+ Lin(lo/-) cells. These cells were capable of forming in vivo as well as in vitro colonies. Furthermore, the cells could reconstitute bone marrow of lethally irradiated recipient mice for at least 12 months. These data obtained from the mouse study strongly suggest that hematopoietic stem cells residing in the donor liver are responsible for mixed chimerism and maintenance of tolerance after liver transplantation.

Mobilization of long-term reconstituting hematopoietic stem cells in mice by recombinant human interleukin 7

Administration of recombinant human interleukin 7 (rh)IL-7 to mice has been reported by our group to increase the exportation of myeloid progenitors (colony-forming unit [CFU]-c and CFU-granulocyte erythroid megakarocyte macrophage) from the bone marrow to peripheral organs (blood, spleen[s], and liver). We now report that IL-7 also stimulates a sixfold increase in the number of more primitive CFU-S day 8 (CFU-S8) and day 12 (CFU-S12) in the peripheral blood leukocytes (PBL) of mice treated with rhIL-7 for 7 d. Moreover, > 90% of lethally irradiated recipient mice that received PBL from rhIL-7-treated donor mice have survived for > 6 mo whereas none of the recipient mice that received an equal number of PBL from diluent-treated donors survived. Flow cytometry analysis at 3 and 6 mo after transplantation revealed complete trilineage (T, B, and myelomonocytic cell) repopulation of bone marrow, thymus, and spleen by blood-borne stem/progenitor cells obtained from rhIL-7-treated donor mice. Thus, IL-7 may prove valuable for mobilizing pluripotent stem cells with long-term repopulating activity from the bone marrow to the peripheral blood for the purpose of gene modification and/or autologous or allogeneic stem cell transplantation.

Simultaneous detection of beta-galactosidase activity and surface antigen expression in viable haematopoietic cells

The quantitation of intracellular beta-galactosidase activity has been described for viable cells. By using the fluorogenic substrate fluorescein-di-beta-D-galactopyranoside (FDG) in conjunction with flow cytometry, the proportion of positive cells as well as the level of expression can be determined. In this paper we describe beta-galactosidase expression in lymphoid and myeloid cells from transgenic mice that widely express beta-galactosidase from an inserted lacZ transgene. Both foetal and adult haematopoietic tissues are able to express beta-galactosidase. The intracellular fluorescence reflecting beta-galactosidase activity can be readily combined with fluorescently labelled antibodies against cell surface antigens. Thus, beta-galactosidase can be used as a marker in transplantation experiments to study the development of lymphoid and myeloid precursor cells.

The murine NK2.1 antigen: a 130 kD glycoprotein dimer expressed by a natural killer cell subset of the spleen, thymus and lymph nodes

Murine natural killer (NK) cells express a few antigens not found on other leukocyte subsets. The NK1.1 antigen, that is present in only a few mouse strains, has been extensively characterized whereas our knowledge of the NK2.1 antigen, which is more commonly expressed, remains, as yet, limited. Our laboratory has previously reported the production of a mAb (4LO3311) recognizing a murine NK cell-specific molecule with a similar strain distribution as the NK2.1 antigen formerly defined with an NZB anti-BALB/c antiserum. In this study, we demonstrate by sequential immunoprecipitation that 4LO3311 represents the first NK2.1 antigen-specific mAb. This reagent was used to immunoprecipitate the NK2.1 antigen from 125I-labeled lysates of fresh NK-enriched spleen cells. SDS-PAGE analyses revealed that the NK2.1 antigen is expressed at the cell surface as a N-glycosylated disulfide-linked protein dimer with approximately 65 kD subunits. The NK2.1 antigen is likely to be anchored in the plasma membrane by a peptide moiety since its expression on NK cells was not affected by treatment with phosphatidylinositol-specific phospholipase C. In addition to be present on a splenic NK cell subset, the NK2.1 antigen is shown to be expressed by a small number of CD4-CD8-thymocytes and by a subset of CD4-CD8-IgG- lymph node cells. Finally, it is shown here that unlike the NKR-P1, the rat homologue of the murine NK1.1 antigen, neither the NK2.1 nor the NK1.1 antigen is expressed by polymorphonuclear leukocytes.

Donor CD8 cells prevent allogeneic marrow graft rejection in mice: potential implications for marrow transplantation in humans

Numerous experimental models have demonstrated that graft-vs.-host disease (GVHD) does not occur in irradiation chimeras when the graft does not contain mature, immunocompetent T lymphocytes, but clinical studies have shown that T cell depletion of donor marrow can be associated with a greatly increased risk of graft failure. We have developed a model where engraftment of (C57BL/6J x C3H/HeJ)F1 (B6C3) marrow in 800-cGy-irradiated (BALB/cJ x C57BL/6J)F1 (CB6) recipients depends on the presence of donor T cells in the graft. Recipients transplanted with 5.0 x 10(6) marrow cells depleted of T lymphocytes showed host lymphoid and myeloid reconstitution, whereas recipients transplanted with the same marrow plus 2.5 x 10(5) purified donor T cells showed donor reconstitution. Adding as few as 0.5 x 10(5) CD8-enriched donor T cells to marrow grafts containing 5.0 x 10(6) T cell-depleted donor cells was sufficient to enable donor reconstitution, while surviving recipients transplanted with the same marrow and 0.5-2.5 x 10(5) CD4-enriched donor cells showed only host reconstitution. To address the question of whether donor CD4 cells could facilitate engraftment under conditions where GVHD would not represent a limiting factor, engraftment of bm1 marrow was tested in major histocompatibility complex (MHC) class I-disparate B6.Ly5a recipients. Results indicated that the donor CD8-enriched population was at least fivefold more active than the CD4-enriched population for facilitating allogeneic marrow engraftment in this strain combination. Thus, the lymphokines and MHC class II-specific cytotoxic T cells generated by CD4 cells were relatively ineffective for enhancing engraftment, possibly reflecting the fact that the host T cells that contain effectors responsible for causing rejection do not express MHC class II antigens. The ability of donor CD8 cells to facilitate engraftment could reflect the activity of a cytokine uniquely elaborated after recognition of an MHC class I disparity. More likely, the graft-enhancing effect of donor CD8 cells may result from the generation of MHC class I-specific or class I-restricted cytotoxic T cells that recognize the host CD4 and CD8 cells responsible for causing rejection. The possibility remains that other mechanisms such as veto inactivation of host T cells by donor CD8 cells may also contribute to the graft-enhancing effect.

Cellular enzyme-linked immunocircle assay. A rapid assay of hybridomas produced against cell surface antigens

A novel method has been developed for the initial screening of hybridomas produced against cell surface antigens. Glutaraldehyde-fixed cells were immobilized as targets on the lid of a 96-well tissue culture plate which had been precoated with poly-L-lysine. Antibody binding was determined by an immunoenzymatic method in an arrangement permitting both macro- and microscopic examination. After optimization with mouse thymus cells using existing rat monoclonal antibodies, new rat-mouse hybridoma cell lines against mouse thymocytes and bone marrow cells were screened. The antibodies could be characterized immediately both by the localization of the immune reaction (surface or intracellular) or as estimated by the frequency of positive cells recognized by the antibody in the sample.

Heterogeneity of natural killer cell subsets in NK-1.1+ and NK-1.1- inbred mouse strains and their progeny

The 4LO3311 monoclonal antibody, a new NK-specific reagent recently produced in our laboratory, reacts with spleen cells of 11 mouse strains, most of which do not express the NK-1.1 alloantigen recognized by the PK136 mAb. Among positive strains, the susceptibility of spleen cells to the complement-dependent NK-inhibiting activity of the 4LO3311 mAb was variable but independent of the initial NK cell activity level of cells tested. This property was furthermore not modified after poly(I:C) stimulation. The susceptibility of spleen cells to the in vitro 4LO3311 mAb plus complement treatment is however influenced by the absolute number of 4LO3311+ cells as well as by the density of the corresponding alloantigen at the cell surface. Moreover, it was established that the strain-related variations observed also depended upon the relative size of the 4LO3311 cell subset within the lytic NK cell population. Indeed, when C3H (NK-1.1-4LO3311+) mice were inoculated with the 4LO3311 mAb, the lytic activity of their spleen cells was almost unaltered but 4LO3311-reactive cells were no longer detected in the spleen of treated animals and remaining NK cells were totally resistant to the in vitro 4LO3311 mAb plus complement treatment. These findings indicate that the 4LO3311 mAb identifies a subset rather than all NK cells, even in a NK-1.1- strain. Since a NK-1.1-unreactive cell subset was identified in NZB (NK-1.1+4LO3311-) mice inoculated with the PK136 mAb, the NK-1.1+ cell population is not necessarily responsible for all the splenic NK cell activity in all NK-1.1+ strains. In B6C3F1 hybrid mice, a relatively large subset of NK-1.1-4LO3311- cells was found in addition to those expressing the NK-1.1, the 4LO3311 alloantigen, or both. According to these results, NK cell heterogeneity should thus be taken as an evolving concept whose resolution appears more and more complex with the identification of new NK-specific reagents.

Identification of murine natural killer cell subsets with monoclonal antibodies derived from 129 anti-C57BL/6 immune spleen cells

Two hybridomas producing monoclonal antibodies reactive with natural killer cells were selected after fusion of 129 anti-C57BL/6 immune spleen cells with P3X63-Ag8.653 myeloma cells. Treatment of normal or stimulated cells with the 4LO3311 or the 4LO439 mAb and rabbit complement inhibited natural killer and antibody-dependent cellular cytotoxicities, whereas cell lysis mediated by natural cytotoxic cells, cytotoxic T lymphocytes, or activated macrophages was unaffected. Lymphokine-activated killer activity was reduced after complement-mediated treatment of interleukin-2-stimulated spleen cells with the 4LO3311 mAb but not after treatment with the 4LO439 mAb. Similar treatment of spleen cells with either mAb had no effect on the mitogen-induced proliferation of T and B lymphocytes and did not alter the frequency of antibody plaque-forming cells in immune spleen cell suspensions. The 4LO3311 and 4LO439 mAbs thus appear to be specific for NK cells and their progeny. Flow cytometry analysis confirmed that 4LO3311+ and 4LO439+ cells are phenotypically identical to NK-1.1+ cells. The epitope recognized by the 4LO3311 mAb has the same strain distribution as the NK-2.1 alloantigen previously detected with NZB anti-BALB/c antiserum, whereas the 4LO439 mAb appears to identify a new NK cell marker exclusively expressed in mice of C57BL lineage. The relationship of the molecules detected with either the 4LO3311 or the 4LO439 mAb to polymorphic antigens of the Ly series is discussed.

Ontogeny and expression of non-MHC-restricted T cell antigen-binding molecules by thymocytes and peripheral T cell subsets

The ontogeny of T cells which express major histocompatibility complex (MHC)-unrestricted T cell antigen-binding molecules (TABM) on the cell membrane was investigated. We used a rabbit anti-mouse TABM antiserum to investigate the expression of TABM by subsets of adult thymocytes, peripheral T cells, and thymocytes during gestation. TABM are expressed by CD4+, CD8-, CD4+, CD8+ thymocytes and single-positive thymocytes. During gestation, TABM are expressed as early as Day 16, and at birth the expression of TABM on thymocytes has reached adult levels. Data are also presented which suggest that the expression of membrane TABM (mTABM) on peripheral T cells can be upregulated during T cell activation. The results suggest that TABM are expressed by different T cell subsets and that TABM+ cells may utilize the same intrathymic developmental pathway as that of T cells which express the alpha/beta T cell receptor.

cDNA cloning and localization of the mouse leukosialin gene (Ly48) to chromosome 7

Mouse leukosialin, previously known as the 3E8 antigen, is expressed primarily on cells of the hematopoietic and lymphoid lineages and is shown to be the mouse homologue to the human leukosialin/sialophorin and rat W3/13 molecules. A partial leukosialin cDNA clone was isolated via cross-species hybridization with a portion of a human leukosialin cDNA. This mouse cDNA clone was used to demonstrate that the leukosialin isoforms are encoded by a single mRNA species of approximately 4.2 kilobases (kb) and that the leukosialin gene is located on chromosome 7. Based on these results, mouse leukosialin is given the designation Ly48.

Murine natural killer cells express the Ly24 (Pgp-1) marker on their surface

The Ly24 (Pgp-1) marker is expressed on some, but not all, mature T lymphocytes. It has recently become apparent that the development of Ly24- T lymphocytes is dependent on the presence of an intact thymus and that virgin Ly24- T cells rapidly acquire this marker upon antigenic or mitogenic stimulation. Although natural killer (NK) cells can develop and function in the absence of an intact thymus, some NK cell subsets express certain markers normally associated with T lymphocytes. The experiments in this report were undertaken to determine if NK cells express Ly24 and whether such an expression could be used to delineate distinct NK cell subsets. We found that mature functional NK cells expressed the Ly24 marker as defined by the monoclonal antibody 9F3. Double-color fluorescence analysis using C57BL/6 splenocytes (whose NK cells express the NK1.1 marker) showed all the NK1.1+ cells to be Ly24+ as well. For C3H/HeN (an NK1.1- strain), double-color fluorescence analysis utilizing asialo GM1 and Ly24 revealed a distinct subset positive for both markers and containing most of the functional NK cell activity. Whereas the Ly24 marker did not illuminate an NK cell subset, these findings demonstrate that this determinant can be useful for the further characterization and isolation of NK cells.

Very early (VEA) and very late (VLA) activation antigens have distinct functions in T lymphocyte activation

We have described in detail the properties of two types of murine T-cell activation antigen. mAbs to these cell surface antigens were initially identified because they demonstrated apparent selective reactivity with a number of cloned cell lines derived from dendritic epidermal T cells. After careful study, both of these antigens were also found to be expressed by normal T cells. The dimer recognized by mAb H1.2F3 which we have termed Very Early Activation (VEA) antigen, is rapidly and transiently expressed during the process of normal T-cell activation. It is likely that the VEA antigen plays a major role in T-cell activation as mAb H1.2F3 is a potent stimulator of T-cell proliferation in the presence of PMA and accessory cells. The second cell surface antigen recognized by mAbs H9.2B8 and 8.18E12 is a Very Late Activation (VLA) antigen that has biochemical, tissue distribution, and functional properties which resemble the human VLA antigens, which have been recently shown to be members of the integrin superfamily of cell surface receptors. While the physiologic ligand for the VEA antigen has yet to be identified, the integrin identified by mAbs H9.2B8 and 8.18E12 mediates cell adhesion to a well-defined group of ligands consisting of the ECM-proteins fibronectin, fibrinogen, and vitronectin. We postulate that the VEA and VLA antigens have distinctly different functions and that further detailed analysis of these dimers will further elucidate the role of these cell surface antigens in T-cell activation and function.

Organization of the Ly-5 gene

A single Ly-5 gene is known to generate a variety of transmembrane glycoprotein isoforms that distinguish various cell lineages and stages of differentiation within the hematopoietic developmental compartment of the mouse. Systems homologous to Ly-5 are known in rats and in humans. The complete exon-intron organization of the Ly-5 gene is described in this report. The Ly-5 gene occupies about 120 kilobases of chromosome 1 and comprises 34 exons, of which 32 (Ex-3 to Ex-34) are protein coding. Ex-1, Ex-2, and parts of Ex-3 and Ex-34 are untranslated. In all cDNA clones examined, either Ex-1 or Ex-2 was represented, but not both, implying that Ex-1 and Ex-2 in Ly-5 mRNA may be mutually exclusive. Primer extension and S1 nuclease protection mapping were used to identify initiation (cap) sites for transcription. The finding of putative cap sites for Ex-1 and Ex-2, and of corresponding TATA-like sequences, suggests the presence of two promoters. In both Ex-1+ and Ex-2+ cDNA clones the next exon is Ex-3, which has a translation-initiating codon. The intron between Ex-3 and Ex-4 is unusually long, about 50 kilobases. Evidence is given that Ex-5, like Ex-6 and Ex-7 (studied previously), is another alternative exon that is selectively programmed, alone or together with Ex-6 or Ex-7 or both, to generate actual or potential Ly-5 isoforms by alternative splicing.

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.

Organization of the Ly-5 gene

A single Ly-5 gene is known to generate a variety of transmembrane glycoprotein isoforms that distinguish various cell lineages and stages of differentiation within the hematopoietic developmental compartment of the mouse. Systems homologous to Ly-5 are known in rats and in humans. The complete exon-intron organization of the Ly-5 gene is described in this report. The Ly-5 gene occupies about 120 kilobases of chromosome 1 and comprises 34 exons, of which 32 (Ex-3 to Ex-34) are protein coding. Ex-1, Ex-2, and parts of Ex-3 and Ex-34 are untranslated. In all cDNA clones examined, either Ex-1 or Ex-2 was represented, but not both, implying that Ex-1 and Ex-2 in Ly-5 mRNA may be mutually exclusive. Primer extension and S1 nuclease protection mapping were used to identify initiation (cap) sites for transcription. The finding of putative cap sites for Ex-1 and Ex-2, and of corresponding TATA-like sequences, suggests the presence of two promoters. In both Ex-1+ and Ex-2+ cDNA clones the next exon is Ex-3, which has a translation-initiating codon. The intron between Ex-3 and Ex-4 is unusually long, about 50 kilobases. Evidence is given that Ex-5, like Ex-6 and Ex-7 (studied previously), is another alternative exon that is selectively programmed, alone or together with Ex-6 or Ex-7 or both, to generate actual or potential Ly-5 isoforms by alternative splicing.