Thy-1 determinants are present on many murine hematopoietic cells other than T cells

The Benefits of Complement Measurements for the Clinical Practice

The complement cascade is an evolutionary ancient innate immune defense system, playing a major role in the defense against infections. Its function in maintaining host homeostasis on activated cells has been emphasized by the crucial role of its overactivation in ever growing number of diseases, such as atypical hemolytic uremic syndrome (aHUS), autoimmune diseases as systemic lupus erythematosus (SLE), C3 glomerulopathies (C3GN), age-related macular degeneration (AMD), graft rejection, Alzheimer disease, and cancer, to name just a few. The last decade of research on complement has extended its implication in many pathological processes, offering new insights to potential therapeutic targets and asserting the necessity of reliable, sensitive, specific, accurate, and reproducible biomarkers to decipher complement role in pathology. We need to evaluate accurately which pathway or role should be targeted pharmacologically, and optimize treatment efficacy versus toxicity. This chapter is an introduction to the role of complement in human diseases and the use of complement-related biomarkers in the clinical practice. It is a part of a book intending to give reliable and standardized methods to evaluate complement according to nowadays needs and knowledge.

Normal and Neoplastic Stem Cells

A stem cell is broadly defined as a cell that retains the capacity to self-renew, a feature that confers the ability to continuously make identical daughter cells or additional cells that will differentiate into downstream progeny. This highly regulated genetic program to retain "stemness" is under active investigation. Research in our laboratory has explored similarities and differences in embryonic, tissue-specific, and neoplastic stem cells and their terminally differentiated counterparts. In this review, we will focus on the contributions of our laboratory, in particular on the studies that identified the mouse hematopoietic stem cell (HSC) and the human leukemic stem cell. These studies have led to significant improvements in both preclinical and clinical research, including improved clinical bone marrow transplantation protocols, isolation of nonleukemic HSCs, a cancer immunotherapy currently in clinical trials, and development of a HSC reporter mouse. These studies and the current follow-up research by us and others will continue to identify the properties, function, and regulation of both normal and neoplastic stem cells.

Endothelial progenitor cell: a blood cell by many other names may serve similar functions

The first reports of circulating cells that displayed the capacity to repair and regenerate damaged vascular endothelial cells as progenitor cells for the endothelial lineage (EPC) were met with great enthusiasm. However, the cell surface antigens and colony assays used to identify the putative EPC were soon found to overlap with those of the hematopoietic lineage. Over the past decade, it has become clear that specific hematopoietic subsets play important roles in vascular repair and regeneration. This review will provide some overview of the hematopoietic hierarchy and methods to segregate distinct subsets that may provide clarity in identifying the proangiogenic hematopoietic cells. This review will not discuss those circulating viable endothelial cells that play a role as EPC and are called endothelia colony-forming cells. The review will conclude with identification of some roadblocks to progress in the field of identification of circulating cells that participate in vascular repair and regeneration.

Stems and standards: social interaction in the search for blood stem cells

This essay examines the role of social interactions in the search for blood stem cells, in a recent episode of biomedical research. Linked to mid-20th century cell biology, genetics and radiation research, the search for blood stem cells coalesced in the 1960s and took a developmental turn in the late 1980s, with significant ramifications for immunology, stem cell and cancer biology. Like much contemporary biomedical research, this line of inquiry exhibits a complex social structure and includes several prominent scientific successes, recognized as such by participating researchers. I use personal interviews and the published record to trace the social interactions crucial for scientific success in this episode. All recognized successes in this episode have two aspects: improved models of blood cell development, and new interfaces with other lines of research. The narrative of the search for blood stem cells thus yields a robust account of scientific success in practice, which generalizes to other scientific episodes and lends itself to expansion to include wider social contexts.

Genetic models to study quiescent stem cells and their niches

Hematopoietic stem cells (HSC) have been defined by their ability to establish long-term hematopoiesis in myelo-ablated hosts. Prospective isolation using combinations of cell-surface markers and/or dye exclusion can yield highly purified and nearly homogeneous phenotypically defined cells that repopulate irradiated hosts. Although highly informative, these types of analyses may not necessarily reflect ongoing homeostatic hematopoiesis. HSCs are also described as being quiescent. This has been demonstrated by cell cycle analysis of phenotypically defined HSCs. Some studies have challenged the existence of truly quiescent HSCs, suggesting that they continuously cycle, albeit with very slow kinetics. Here we present a pulse-chase system based on the controllable incorporation of H2B-GFP into nucleosomes, which allows the identification, purification, and functional analysis of viable label-retaining cells. Our data complement and extend recent studies using similar strategies. These, together with our present studies, find a rare, quiescent or dormant subset within the population of stringently defined HSC phenotypes. To date, three types of niches, endosteal, vascular, and reticular, have been described; herein we review the cellular and spatial nature of these microenvironments. We propose that HSC label-retention combined with genetically manipulated stem cell niches will allow us to determine their anatomical architecture, to address HSC cell fate proliferation kinetics, and to begin to dissect the molecular cross talk among stem cells and niche cells in vivo during both normal and perturbed homeostasis.

Freshly isolated bone marrow cells induce death of various carcinoma cell lines

In some carcinomas such as digestive tract carcinomas, bone marrow infiltration by tumor cells is a frequent event but usually remains a micrometastatic disease and rarely induces overt bone lesions. The mechanisms responsible for the control of these metastases in the bone marrow remain poorly known. We show that freshly isolated bone marrow cells from human, murine and rat origin rapidly kill a wide range of syngeneic or xenogeneic carcinoma cell lines in culture. Further analysis of this cytotoxic process in the rat indicated that neither resident bone marrow macrophages nor NK cells were responsible for this cytotoxic effect that was restricted to a subpopulation of bone marrow cells expressing CD90 (Thy-1), a marker of hemopoietic precursors. The tumoricidal activity of these cells did not require long-term culture nor addition of exogenous cytokines or growth factors. A subset of CD90+ cells that rapidly differentiates into CD163(ED2)-expressing macrophages was observed to be responsible for tumor cell killing. These macrophages induced a non-apoptotic death of tumor cells, a process that required both a direct interaction with the tumor cell and nitric oxide (NO) production through the activation of inducible nitric oxide-synthase (iNOS). This ability of pluripotent hemopoietic stem cells to rapidly differentiate into macrophages capable of killing invasive tumor cells may account for the limited expansion of micrometastases of some carcinomas in the bone marrow.

Blood cell progenitors: Insights into the properties of stem cells

Hematopoiesis is a dynamic process in which eight lineages of mature blood cells are derived from a common stem cell. Great progress has been made in identifying the functionally disparate progenitors that emerge from the stem cell and in elucidating the molecules required for their growth and survival. Further work will be required to understand the molecular mechanisms that regulate commitment of stem and progenitor cells to each stage of progenitor cell development and ultimately into the mature blood cells.

Nonatopic asthma: in vivo airway hyperreactivity adoptively transferred to naive mice by THY-1(+) and B220(+) antigen-specific cells that lack surface expression of CD3

To investigate the cellular immune events contributing to airway hyperreactivity (AHR), we studied an in vivo mouse model induced by the hapten picryl (trinitrophenyl) chloride (PCl). Mice were immunized by cutaneous contact sensitization with PCl and airway challenged subsequently with picryl sulfonic acid (PSA) antigen (Ag). Increased airway resistance was produced late (24 h) after Ag challenge, disappeared by 48 h, and was associated with no decrease in diffusion capacity. AHR could be produced in PCl immune/ PSA challenged mice on day 7 or even, with challenge, as early as 1 d after contact sensitization, after adoptive transfer of immune cells lacking CD3(+) contact sensitivity effector T cells, or after transfer of Ag-specific lymphoid cells depleted of conventional T lymphocytes with surface determinants for CD3, CD4, CD8, TCR-beta, or TCR-delta molecules. Further experiments showed that development of AHR depended upon transfer of immune cells expressing surface membrane Thy-1 and B220 (CD45RA) determinants. We concluded that a novel population of Ag-specific lymphoid cells with a defined surface phenotype (Thy-1(+), CD3(-), CD4(-), CD8(-), TCR-alphabeta-, TCR-gammadelta-, and CD45RA+) is required in a mouse model for the development of AHR.

Immunophenotyping of murine peritoneal macrophages and lymphocytes by flow cytometry

Peritoneal cells include mainly macrophages and both T and B lymphocytes. We describe a simple procedure to analyze by flow cytometry the antigens expressed on macrophage and/or lymphocyte membranes. F4/80 and CR3 macrophage antigens were detected with anti-F4/80 and anti-Mac-1 monoclonal antibodies (mAb) respectively, CD4 and THY1.2 T lymphocyte antigens with GK1.5 and J1j mAbs respectively, B CD5 lymphocytes were identified with LY1.2 mAb and Fc gamma RII/Fc gamma RIII were detected with 2.4G2 mAb.

Early thymic regeneration after irradiation

Whole body irradiation produces profound thymic atrophy. After sublethal irradiation, regeneration begins promptly and the earliest regeneration is from radioresistant intrathymic precursors. The progeny of these precursors expand rapidly and restore thymic cellularity to near normal within 2 weeks. We have used monoclonal antibodies specific for a variety of differentiation markers of the T lineage to analyze the early events in thymic regeneration. A three-color flow microfluorometric analysis revealed that the majority of the cells found early in the regenerative process have the phenotype of mature T cells. These include CD4-/CD8-; CD3hi as well as CD4+/CD8-; CD3hi and Cd4-/CD8+; CD3hi. The proportion of cells with mature phenotypes declines rapidly between day 6 and day 12. Not all of the early appearing cells have mature phenotypes. Among the early cells that do not express CD3 are both CD4 and CD8 single positive cells that express HSA and resemble the intrathymic precursors found in other systems. In these mice CD4 single positive predominate. There are other cells that are HSA positive but express low levels of CD4 and very low levels of Thy-1. These appear to include the earliest members of the T-lineage. In addition to relatively mature conventional T cells and early progenitors, the early developing population includes cells that express markers of the T-cell lineage including the T-cell receptor but do not express Thy-1. These Thy-1 negative T cells comprise a significant number of the earliest cells found after regeneration.

A novel macromolecular structure is a target of the promyelocyte-retinoic acid receptor oncoprotein

Acute promyelocytic leukemia (APL) is associated with a t(15;17) translocation that creates the promyelocyte-retinoic acid receptor alpha (PML-RAR alpha) fusion gene. Immunohistochemistry demonstrates that PML is a part of a novel macromolecular organelle (including at least three other nuclear proteins) referred to as PML oncogenic domains (PODs). In APL cells, the POD is disrupted into a microparticulate pattern as a consequence of the expression of the PML-RAR oncoprotein. RA treatment of APL cells triggers a reorganization of PML to generate normal-appearing PODs. We propose that PML-RAR is a dominant negative oncoprotein that exerts its putative leukomogenic effect by inhibiting assembly of the POD. According to this proposal, not only is the POD a novel structure, but it can be ascribed an imputed function such that its disruption leads to altered myeloid maturation; this may represent a novel oncogenic target.

Growth and differentiation signals mediated by different regions in the cytoplasmic domain of granulocyte colony-stimulating factor receptor

Granulocyte colony-stimulating factor (G-CSF) is a cytokine that regulates the proliferation and differentiation of neutrophils. The G-CSF receptor (G-CSFR) is a member of the hemopoietic growth factor receptor family. A G-CSFR expression plasmid was introduced into interleukin-3 (IL-3)-dependent mouse myeloid precursor FDC-P1 cells that normally do not respond to G-CSF. G-CSF stimulated proliferation of the transformants, down-regulated Thy-1 and F4/80 antigens on the cell surface, and induced expression of neutrophil-specific genes such as myeloperoxidase (MPO) and leukocyte elastase. On the other hand, neither granulocyte/macrophage colony-stimulating factor (GM-CSF) nor IL-3 induced MPO gene expression, but they inhibited G-CSFR-mediated MPO gene expression. These results suggested that the G-CSFR, but not the IL-3/GM-CSF receptors, transduced the neutrophilic differentiation signal into cells. Mutational analysis of the G-CSFR indicated that the N-terminal region of its cytoplasmic domain is sufficient to transduce the proliferation signal into cells, while the C-terminal region plays an essential role in transducing the differentiation signal.

Transitory expression of Thy-1 antigen in immature B cell lines

In cmu- B220+ Thy-1- murine immature B cells transformed with a temperature-sensitive mutant of Abelson murine leukemia virus, a low level of Thy-1 antigen was transitorily expressed after the shift of the culture temperature from the permissive (35 degrees C) to the non-permissive (39 degrees C) temperature. On the other hand, B220 antigen was persistently expressed regardless of whether the cells were cultured at the permissive or non-permissive temperature. No other T-lineage-specific antigens, CD3, CD4, and CD8 were induced during the culture at the non-permissive temperature. Expression of Thy-1 antigen was confirmed by the detection of a low level of Thy-1-specific mRNA. These results clearly showed that immature B cells could express Thy-1 antigen during proliferation and/or differentiation. The results imply a role for Thy-1 antigen in B cell proliferation and/or differentiation.

Perinatal thymocyte antigen expression and postnatal immune development altered by gestational exposure to tetrachlorodibenzo-p-dioxin (TCDD)

In utero exposure to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was found to alter expression of murine thymocyte fetal cell-surface markers. Pregnant mice were treated (via gavage) with 0, 1.5, or 3.0 micrograms TCDD/kg/day in corn oil on gestational days (gd) 6-14. Offspring were examined on gd 18 and postnatally on d6, d14, and d21, and at 7, 8, and 10 weeks of age. Severe thymic atrophy and cellular depletion were found both pre- and postnatally in TCDD-exposed mice. Immunocytochemical localization of the Thy 1.2 antigen on gd 18 thymocytes revealed no TCDD-related changes in cellular distribution. Flow cytometric analysis, however, indicated that the TCDD treatment resulted in a significant decrease in the percentage of CD4+8+ fetal thymocytes, as well as significantly increased CD4-8- and CD4-8+ thymocytes. The increased CD4-8+ population after TCDD was not from induction of Ts cells. At 7-8 weeks postnatally, no differences existed between control and treatment groups in mitogen responses and antibody plaque response. However, altered thymocyte antigen expression was found to correlate with altered postnatal immune function, as evidenced by decreased cytotoxic T lymphocyte response at 8 weeks of age. Taken together, these results indicate that immunosuppression following prenatal exposure to TCDD can be readily detected by qualitative and quantitative changes in the cell surface phenotype of fetal thymocytes. Furthermore, the observed altered distribution suggests that TCDD inhibits normal thymocyte maturational processes.

Immunological characterization of canine hematopoietic progenitor cells

Canine hematopoietic progenitor cells were characterized by separation with monoclonal antibodies. Depleted and enriched fractions were studied for growth of CFU-GM in semisolid agar and for repopulating capacity of lethally irradiated dogs. CFU growth was not reduced by depletion of marrow using monoclonal antibodies F 3-20-7 (anti-dog Thy-1), MT606 (anti-human CD 6), and IOT2a (anti-human DR). CFU growth was variable following treatment with the anti-canine T-cell antibody MdT-P 1 and immunomagnetic bead separation. It was regularly enriched when MdT-P 1 treatment was followed by immunorosetting with staphylococcal protein A-loaded sheep red blood cells and density gradient separation. Lethally irradiated dogs were reconstituted by autologous marrow depleted of MdT-P 1-positive cells using immunorosetting and density gradient centrifugation, whereas immunomagnetic bead-depleted marrow was ineffective. Fluorescence-activated cell sorting showed enrichment of hematopoietic progenitor cells in the weakly MdT-P 1-positive fraction.

Improved fixation of frozen lympho-haemopoietic tissue sections with hexazotized pararosaniline

In this study, a simple single-step fixation method for frozen tissue sections is introduced using the hexazotized salt of Pararosaniline as preservative agent. Tissue preservation by this method was shown to be superior to the commonly-used fixation with acetone. Fixation with hexazotized Pararosaniline caused a minimal loss of antigenicity as demonstrated using twenty-three monoclonal antibodies directed against lympho-haemopoietic and stromal cells.

Prothymocyte seeding in the thymus

A major gap in our understanding of T lymphocyte development is the process of stem cell differentiation into T lymphocyte precursors. An important question is whether bone marrow-derived stem cells become committed to T lymphoid lineage within the bone marrow, or whether this occurs once cells have entered the microenvironment of the thymus. Attempts to identify a haemapoietic precursor of thymocytes in mice, a "prothymocyte", have involved cell transfer experiments involving isolated and selected populations of bone marrow stem cells, as well as transformed or continuous cell lines representing early stage in mouse T cell development. Current information on the properties of stem cells which can seed the thymus is reviewed in this paper, and the possibility that progenitor T cells may be identified by their expression of receptor(s) which localise them into the thymus is considered.

Expression of the M-CSF receptor is controlled posttranscriptionally by the dominant actions of GM-CSF or multi-CSF

We have isolated a murine myeloid precursor cell line (FDC-P1/MAC) that simultaneously expresses receptors for multi-CSF, GM-CSF, and M-CSF (c-fms protooncogene). FDC-P1/MAC cells express high levels of c-fms mRNA and protein when grown in M-CSF, whereas growth in multi-CSF or GM-CSF caused a dramatic reduction of c-fms glycoprotein and mRNA. Nuclear run-off assays demonstrated that c-fms transcription was not growth factor dependent and the regulation occurred posttranscriptionally. Factor switching experiments have shown that both multi-CSF and GM-CSF act dominantly and in a factor concentration dependent manner to suppress c-fms expression. In vitro agar assays of bone marrow cells grown in the presence of GM-CSF and M-CSF, individually and in combination, support the concept that GM-CSF can act dominantly to prevent monocyte/macrophage development. These results suggest that GM-CSF and multi-CSF can suppress development along the monocyte/macrophage lineage and offer a simple stochastic mechanism governing myeloid lineage restriction.

Expression of CD4 by human megakaryocytes

The CD4 antigen, which serves as the receptor for human immunodeficiency virus type 1 (HIV-1) on T cells, has been detected on human megakaryocytes. Recent evidence of impaired thrombopoiesis in HIV-1-related thrombocytopenia suggested that these cells could be directly infected by the virus and prompted a search for a receptor on megakaryocytes of normal subjects that could permit entry of HIV-1. Bone marrow specimens from uninfected normal control subjects were centrifuged over Ficoll-Hypaque (1.077 g/ml) and analyzed by three-color analysis with a flow cytometer utilizing monoclonal antibodies against CD4 and a glycoprotein present on the surface of megakaryocytes and platelets (GPIIb/IIIa; CD41), as well as 7-aminoactinomycin D, a stain for DNA. Cells presumed to be megakaryocytes were identified by having a DNA content greater than tetraploid and staining brightly with anti-CD41. Approximately 0.4% of the nucleated cells of the marrow met these criteria. Twenty-five percent of these megakaryocytes stained as brightly as CD4+ T cells. Several clones of antibody recognizing different epitopes of the CD4 molecule gave similar results. Platelets were CD4-. Staining of megakaryocytes with anti-CD4 was confirmed by direct microscopic examination of Percoll-gradient-enriched megakaryocytes employing two-color (CD4-phycoerythrin and CD41-fluorescein) immunofluorescence analysis and phase-contrast microscopy. The proportion of double-labeled cells among 112 phase-contrast-identifiable megakaryocytes from five bone marrow specimens varied between 20% and 26% with a mean and SD of 22% +/- 2.5%. Thus some human megakaryocytes express CD4 on their surface that should be capable of binding the HIV-1 gp120 envelope protein. This could serve as a portal of entry for HIV-1.

Regulation of murine B cell Thy-1 expression by IL-4, IFN-gamma, and CD4+ T cell subsets

Interleukin 4 (IL-4) induces the expression of membrane Thy-1 on the vast majority of lipopolysaccharide (LPS)-stimulated normal murine B cells in vitro. This induction is inhibited by interferon-gamma (IFN-gamma). IL-4 and IFN-gamma are required late in culture to effect maximal induction and inhibition of Thy-1 expression by LPS- or LPS + IL-4-stimulated B cells, respectively. IFN-gamma suppresses IL-4-induced Thy-1 expression by inhibiting the induction of steady-state levels of Thy-1-specific mRNA. Three distinct CD4+ Th2 clones, through their release of IL-4, induce B cells to express high levels of Thy-1, by 24 hr, in striking contrast to the 3 days required to induce Thy-1 expression after stimulation with LPS and IL-4. This induction is abrogated by the addition of IFN-gamma. B cells stimulated with three distinct Th1 clones (IFN-gamma- and IL-2-producing) exhibit a modest, non-IL-4-dependent, expression of Thy-1. In contrast to intrinsic expression of Thy-1 by Th2-stimulated B cells. Thy-1 expressed by Th1-stimulated B cells is acquired, having the allotype specificity of the stimulating T cell.

Further enrichment and analysis of rat CFU-s

Using the monoclonal antibody W3/13, which recognizes a determinant expressed on a sialoglycoprotein, rat marrow cells with the phenotype Thy-1 antigen upper 20% positive (Ox720) and high molecular weight leukocyte common antigen negative (Ox22-) were separated into W3/13 dim (W3/13d) and W3/13 bright (W3/13b) subpopulations by single-laser cell sorting. The spleen colony-forming unit (CFU-s) was found in the W3/13d fraction. A 468-fold enrichment of CFU-s was achieved. Only 20% of the Ox720, Ox22-, and W3/13d cells were in the S phase of the cell cycle as compared to 56% of Ox720, Ox22-, and W3/13b cells. Using Indo-1, it was not possible to demonstrate increases in cytosolic Ca++ levels within the enriched CFU-s population by colony-stimulating factors (CSFs) or interleukins 1, 2, and 3. However, challenge with the Ca++ ionophore, ionomycin, demonstrated apparent heterogeneity of intracellular Ca++ management within the enriched CFU-s population. The source of this heterogeneity is not known. Only a 12-day CFU-s was detected in the rat, and it was predominantly, but not exclusively, a Rhodamine 123 (Rh123) dull cell.

Induction of macrophage colony-stimulating factor-dependent growth and differentiation after introduction of the murine c-fms gene into FDC-P1 cells

A system has been established for analyzing the functions of the c-fms/macrophage colony-stimulating factor (M-CSF) receptor gene product in hematopoietic growth and differentiation. The murine c-fms gene was introduced into the factor-dependent murine hematopoietic cell line FDC-P1 by retroviral infection, and conversion to M-CSF-dependent growth was assayed in agar cultures. Expression of the c-fms gene in FDC-P1 cells, which normally do not express this gene, resulted in the conversion of resultant FD(c-fms) cells to M-CSF-dependent growth. Stimulation of FD(c-fms) cells by M-CSF led to the formation of colonies of altered morphology and produced reversible morphological changes suggestive of myeloid differentiation. M-CSF also induced expression of mature myeloid surface marker proteins in the FD(c-fms) cells. Neither multi-CSF nor granulocyte-macrophage CSF induced similar phenotypic changes but remained able to stimulate the proliferation of undifferentiated FD(c-fms) cells. These results indicate that the c-fms gene was expressed functionally in FDC-P1 cells and transmitted signals for growth. Also, the interaction of M-CSF with the c-fms gene product generated an additional signal for myeloid differentiation but did not irreversibly commit FD(c-fms) cells to terminal differentiation. This system can be used for molecular analysis of the growth- and differentiation-promoting activities of the c-fms proto-oncogene.

Induction of macrophage colony-stimulating factor-dependent growth and differentiation after introduction of the murine c-fms gene into FDC-P1 cells

A system has been established for analyzing the functions of the c-fms/macrophage colony-stimulating factor (M-CSF) receptor gene product in hematopoietic growth and differentiation. The murine c-fms gene was introduced into the factor-dependent murine hematopoietic cell line FDC-P1 by retroviral infection, and conversion to M-CSF-dependent growth was assayed in agar cultures. Expression of the c-fms gene in FDC-P1 cells, which normally do not express this gene, resulted in the conversion of resultant FD(c-fms) cells to M-CSF-dependent growth. Stimulation of FD(c-fms) cells by M-CSF led to the formation of colonies of altered morphology and produced reversible morphological changes suggestive of myeloid differentiation. M-CSF also induced expression of mature myeloid surface marker proteins in the FD(c-fms) cells. Neither multi-CSF nor granulocyte-macrophage CSF induced similar phenotypic changes but remained able to stimulate the proliferation of undifferentiated FD(c-fms) cells. These results indicate that the c-fms gene was expressed functionally in FDC-P1 cells and transmitted signals for growth. Also, the interaction of M-CSF with the c-fms gene product generated an additional signal for myeloid differentiation but did not irreversibly commit FD(c-fms) cells to terminal differentiation. This system can be used for molecular analysis of the growth- and differentiation-promoting activities of the c-fms proto-oncogene.

Enrichment of murine haemopoietic stem cells: diverging roads

The cellular elements of the peripheral blood must be constantly replenished by the process of haemopoiesis, since most blood cells have a limited life span of only days or weeks. Although the developmental lineages of haemopoietic differentiation have been depicted in textbooks for decades, the actual details of the early stages of haemopoiesis are relatively unknown due to the very low numbers of haemopoietic stem cells in bone marrow or spleen. Only by isolating these rare stem cells and developing in-vitro culture systems to maintain them can a complete understanding of the early stages of haemopoiesis be achieved. This approach has already been successfully applied to the study of the later stages of haemopoiesis. In this review, Gerald Spangrude examines several experimental approaches that have been used to enrich murine haemopoietic stem cells.

Identification of a novel bone marrow-derived B-cell progenitor population that coexpresses B220 and Thy-1 and is highly enriched for Abelson leukemia virus targets

A novel stage in early B-lymphocyte differentiation has been identified in normal mouse bone marrow cells. Earlier work had demonstrated that bone marrow cells characterized by low levels of Thy-1 and lack of a panel of lineage markers (Thy-1lo Lin- cells) were highly enriched for pluripotent hematopoietic stem cells. In this paper, we present evidence that another bone marrow population, which expressed low levels of Thy-1 and coexpressed B220, a B-lineage-specific form of the leukocyte common antigen, contained early and potent precursors for B lymphocytes upon in vivo transfer to irradiated hosts. These Thy-1lo B220+ cells, comprising 1 to 2% of bone marrow cells, were enriched for large cells in the mitotic cycle; the population lacked significant pluripotent hematopoietic stem cell activity and myeloid-erythroid progenitors. Most strikingly, Thy-1lo B220+ cells represented a highly enriched population of bone marrow cells that could be targets of Abelson murine leukemia virus transformation. We propose that Thy-1lo B220+ bone marrow cells represent the earliest stage of committed lymphocyte progenitors, intermediate in differentiation between Thy-1lo Lin- pluripotent stem cells and, in the B lineage, Thy-1- B220+ pre-B cells.

Identification of a novel bone marrow-derived B-cell progenitor population that coexpresses B220 and Thy-1 and is highly enriched for Abelson leukemia virus targets

A novel stage in early B-lymphocyte differentiation has been identified in normal mouse bone marrow cells. Earlier work had demonstrated that bone marrow cells characterized by low levels of Thy-1 and lack of a panel of lineage markers (Thy-1lo Lin- cells) were highly enriched for pluripotent hematopoietic stem cells. In this paper, we present evidence that another bone marrow population, which expressed low levels of Thy-1 and coexpressed B220, a B-lineage-specific form of the leukocyte common antigen, contained early and potent precursors for B lymphocytes upon in vivo transfer to irradiated hosts. These Thy-1lo B220+ cells, comprising 1 to 2% of bone marrow cells, were enriched for large cells in the mitotic cycle; the population lacked significant pluripotent hematopoietic stem cell activity and myeloid-erythroid progenitors. Most strikingly, Thy-1lo B220+ cells represented a highly enriched population of bone marrow cells that could be targets of Abelson murine leukemia virus transformation. We propose that Thy-1lo B220+ bone marrow cells represent the earliest stage of committed lymphocyte progenitors, intermediate in differentiation between Thy-1lo Lin- pluripotent stem cells and, in the B lineage, Thy-1- B220+ pre-B cells.

L3T4 antigen expression by hemopoietic precursor cells

L3T4 (CD4) is expressed on immature hematopoietic cells. Sorting bone marrow cells on the basis of their expression of this antigen produces populations of cells that are markedly enriched for multipotential stem cells (CFU-s) and for myeloid precursors (CFU-c). We believe that L3T4 is transiently expressed by most, if not all, hematopoietic precursors early in their maturation. We suggest that the expression of CD4 molecules on the surface of immature precursors is required for their interaction with Ia bearing cells within the hemopoietic inductive microenvironment(s) of the marrow and thymus.

Changes in cell surface antigen expression during murine bone marrow cell regeneration in vivo and proliferation in vitro

Modulations in surface antigen expression during marrow regeneration in vivo, and proliferation in vitro in response to haemopoietic growth factors, were studied using a panel of monoclonal antibodies recognizing antigenic determinants expressed by primitive multipotential progenitor cells (Thy-1, Qa-m7), or lineage antigens restricted to committed progenitors and differentiated cells of the neutrophil/macrophage (7/4) and B lymphocyte (B220) lineages. These two categories of antigen exhibited differing responses to marrow perturbation and proliferation. Following administration of a cytotoxic dose of 5-fluorouracil, or lethal irradiation and transplantation of normal donor marrow, the levels of Thy-1 and Qa-m7 antigen expression rapidly increase, reaching a peak at the onset of regeneration: the nadir of marrow cellularity. Expression of these antigens returns to normal as regeneration proceeds and marrow is reconstituted. 7/4 and B220 antigen expression reflect the presence or absence of maturing cells bearing these markers: antigen expression declining following perturbation, and re-emerging during the course of regeneration. In vitro, when marrow cells taken from mice 8 days following treatment with 5-FU are grown in liquid culture in the presence of colony-stimulating factor-1 plus bladder cell carcinoma cell line 5637 conditioned medium, marrow cells are stimulated to proliferate and differentiate along the neutrophil/macrophage lineage. 7/4 antigen expression increases throughout the culture period, and B220 antigen is undetectable after the fifth day of culture. Thy-1 antigen expression also rises and remains elevated, and Qa-m7 antigen expression remains stable.

Thy-1 positive tingible body macrophages (TBM) in mouse lymph nodes

This study was prompted by the observation that cells in mouse lymph nodes (LN) with cytological characteristics of tingible body macrophages (TBM) appeared to be Thy-1 positive. The objective of this study was to determine if these large cells were TBM and to conclusively demonstrate their reactivity for Thy-1. The cells were studied using monoclonal antibodies (MoAb) against Thy-1 and macrophage markers including F4/80 and Ia antigens at both light microscopic (LM) and electron microscopic (EM) levels. Immunocytochemical reactivity by TBM for Thy-1 antigen specific MoAb was demonstrated by LM in both in situ and in vitro LN preparations. Furthermore, ultrastructural examination of these germinal center cells in situ demonstrated that the Thy-1 reactivity visualized at the LM level was associated with ribosomes and endoplasmic reticulum as well as their plasma membrane. Similarly, these cells expressed intracytoplasmic and membrane reactivity for Ia antigens and also for the macrophage specific antigen F4/80. This indicates that the reactivity is due to active synthesis of the Thy-1 antigen and not attributable to reactivity of any phagocytosed Thy-1 positive cells. As defined by their germinal center location and morphological characteristics, these Thy-1 reactive macrophages were identified as TBM. Germinal center TBM thus represent a unique, vigorously phagocytic subset of mature macrophages which express both macrophage and thymocyte markers.

Interleukin 4 induces membrane Thy-1 expression on normal murine B cells

Thy-1, a cell-surface glycoprotein of undetermined function, is expressed in relatively large amounts on mouse thymocytes, peripheral T cells, and neurons. It is widely used as a marker to distinguish peripheral T cells from B cells in mice. We show here that, in five distinct mouse strains, recombinant interleukin 4 (IL-4/B-cell stimulatory factor 1) strikingly induces membrane expression of Thy-1 on the vast majority of lipopolysaccharide (LPS)-stimulated normal murine B cells. Thy-1+ B cells are precursors for immunoglobulin-secreting cells. RNA blot analysis indicates that B cells express a Thy-1 mRNA of 1.8 kilobases, the same size as that found in T cells. Cell mixing experiments show that only cells derived from Thy-1.2+ donors express Thy-1.2, indicating that B cells expressing Thy-1 have not passively absorbed the glycoprotein from another cell source. Recombinant interferon-gamma inhibits Thy-1 induction by B cells stimulated with LPS and IL-4. Thy-1 is also induced on B cells that have been stimulated as a result of the specific activation of an IL-4-producing T-helper clone. Anti-IL-4 monoclonal antibody inhibits the induction of B-cell Thy-1 in this T-cell-B-cell interaction.

Relationships between B cell and myeloid differentiation. Studies with a B lymphocyte progenitor line, HAFTL-1

A cell line, HAFTL-1, derived by in vitro transformation of fetal liver cells with v-Ha-ras, was found to have molecular and phenotypic characteristics of pro-B cells recently committed to the Ly-1+ B cell differentiation pathway. Stimulation of these cells with LPS resulted in their differentiation within either the B or myelomonocytic lineages. Thus, lines derived from LPS-stimulated HAFTL-1 cells were shown to be clonally related, as evidenced by common v-ras integrations, but to exhibit characteristics of pre-B cells (ThB expression, continuing DJ heavy chain rearrangements) or mature macrophages (expression of Mac-1 and Mac-2, lysozyme and nonspecific esterase production, phagocytosis) while maintaining their Ly-1+ phenotype. These results suggest that events resulting in the irrevocable commitment to a single lineage occur late in differentiation, at least within the pathway yielding Ly-1+ B cells and a proposed subpopulation of Ly-1+ monocytes and macrophages. Final commitment to these lineages is carefully orchestrated, as evidenced by restricted expression of Ly-5 isoforms and production of IgH transcripts.

In vivo homing of thymus-enriched bone marrow cells

A population of adult CBA/J mouse bone marrow (BM) cells enriched by in vitro migration to supernatant prepared from neonatal thymus was labeled with a DNA-binding fluorochrome, Hoechst dye No. 33342 (H33342). Labeled cells were injected into irradiated recipients in order to compare the in vivo localization of the migration-enriched BM (MEBM) cells to the localization of injected nonenriched BM (NEBM) cell controls. A characteristic difference in the distribution of localized cells was observed in the spleen but not in other lymphoid organs. At 2 hr after injection the MEBM cells were located in the marginal zones surrounding the periarterial lymphoid sheaths (PALS) of the splenic white pulp. At 6 hr after injection the MEBM cells were seen distributed between marginal zones and the PALS and by 16 hr they had localized almost exclusively in the white pulp. In contrast, the NEBM cells were located in the marginal zones or red pulp for the duration of the experiment. These observations show that the MEBM cells home selectively to T-cell areas of the spleen. Direct immunofluorescent monoclonal antibody staining of H33342-labeled cells obtained from the recipient spleens at 16 hr demonstrated that the MEBM cells were negative for Thy-1 antigen, indicating that acquisition of Thy-1 was not prerequisite to the observed homing. The results are compared to known localization patterns of mature lymphocytes.

Development of autoreactive L3T4+ T cells from double-negative (L3T4-/Ly-2-) Thy-1+ spleen cells of normal mice

Thy-1+/L3T4-/Ly-2- spleen cells were purified from normal C57BL/6 (B6) and C,B-17 mice. Cells within this subset expressed the T cell receptor (TcR) for antigen: the majority of cells in this subset were CD3+; a fraction of the cells was stained with the monoclonal antibody (mAb) F23.1; and the TcR molecule was immunoprecipitable with mAb F23.1 from cells within this subset. In limiting dilution analyses, about 1/30 cells within this subset were growth inducible in vitro by stimulation with phorbol myristate acetate (PMA) plus ionomycin; conditioned media containing interleukin (IL) 1, IL2, IL3 or IL4 activity neither triggered nor promoted in vitro growth of these cells. The in vitro generated T cells displayed the Thy-1+/L3T4+/Ly-2- surface phenotype and were self-reactive, i.e., proliferated preferentially in response to syngeneic stimulator cells, and secreted IL2 and IL3 only in response to syngeneic but not allogeneic stimulator cells. The proliferative response of these cells to syngeneic stimulator cells was blocked by anti-self Ia mAb. This autoreactive helper T cell subset was not inducible in purified Thy-1+ spleen cell subsets from athymic nude mice or scid mice. Autoreactive helper T cells did not express detectable levels of the IL2 receptor (IL2R), and their proliferative response was not blocked by anti-IL2R mAb. From PMA plus ionomycin-stimulated double-negative Thy-1+ spleen cells, 14 T cell clones were established in long-term culture which displayed the CD3+CD4+CD8- surface phenotype and were self-reactive.

Proliferation and differentiation of highly enriched mouse hematopoietic stem cells and progenitor cells in response to defined growth factors

Three distinct hematopoietic populations derived from normal bone marrow were analyzed for their response to defined growth factors. The Thy-1loT- B- G- M-population, composing 0.2% of bone marrow, is 370-fold enriched for pluripotent hematopoietic stem cells. The two other populations, the Thy-1- T- B- G- M- and the predominantly mature Thy-1+ T+ B+ G+ M+ cells, lack stem cells. Thy-1loT- B- G- M- cells respond with a frequency of one in seven cells to IL-3 in an in vitro CFU-C assay, and give rise to many mixed colonies as expected from an early multipotent or pluripotent progenitor. The Thy-1- T- B- G- M- population also contains progenitor cells which responded to IL-3. However, colonies derived from Thy-1- T- B- G- M- cells are almost exclusively restricted to the macrophage/granulocyte lineages. This indicates that IL-3 can stimulate at least two distinct clonogenic early progenitor cells in normal bone marrow: multipotent Thy-1loT- B- G- M- cells and restricted Thy-1- T- B- G- M- cells. Thy-1loT- B- G- M-cells could not be stimulated by macrophage colony-stimulating factor (M-CSF), granulocyte CSF (G-CSF) or IL-5 (Eosinophil-CSF). The hematopoietic precursors that react to these factors are enriched in the Thy-1- T- G- B- M- population. Thus, multipotent and restricted progenitors can be separated on the basis of the expression of the cell surface antigen Thy-1.

Two rare populations of mouse Thy-1lo bone marrow cells repopulate the thymus

Two-color FACS analysis of mouse bone marrow reveals a rare population, comprising 0.1-0.3% of the total, that expresses low levels of the Thy-1 antigen but does not express any of five surface markers that characterize differentiated hematolymphoid cells. We demonstrate here that this fraction of mouse bone marrow is enormously enriched in cells that can home to the thymus and differentiate into mature T lymphocytes, subsequently migrating to peripheral lymphoid organs. Only a subset of the FACS-isolated fraction (1/90 after intrathymic injection) is capable of responding to the thymic microenvironment with a productive commitment to the T cell lineage. A second fraction of mouse bone marrow, which expresses how levels of Thy-1 but is also positive for at least one of five hematolymphoid lineage-specific markers, also contains cells that home to the thymus and establish colonies of thymocytes. The two fractions each contribute approximately equal amounts of thymic colony-forming units (CFUt) to the bone marrow, and together can account for at least half of the CFUt in whole bone marrow.

Sequential activation and loss of the pre-B cell Thy-1 gene in T-cell X pre-B cell somatic hybrids

In somatic cell hybrids between the pseudodiploid Thy-1- Abelson-leukemia-virus-induced pre-B cell lymphoma RAW 253.1 and the Thy-1+ T-cell lymphoma, AKR1 (Thy-1+), all cells express the Thy-1 allele of the T-cell parent but most hybrid cells do not express the Thy-1 allele of the pre-B cell lymphoma parent. The Thy-1 allele of the pre-B cell parent, however, is spontaneously activated in a minor proportion of hybrid cells. By sorting for cells expressing the Thy-1 allele of the pre-B cell parent, derivative clones in which 100% of cells express both parental Thy-1 alleles can be isolated. Revertants with a phenotype identical with that of the original hybrid cell line can be isolated from these derivatives by sorting for nonexpression of the Thy-1 allele of the pre-B cell parent. These first-generation revertant cell lines have lost one copy of the Thy-1 gene derived from the pre-B cell lymphoma parent. By a further cycle of sorting, derivatives in which 100% of cells express both parental Thy-1 alleles can again be obtained. Second-generation revertants isolated by sorting these Thy-1+ hybrid cells for nonexpression of the Thy-1 allele of the pre-B cell parent no longer contain a normal copy of the pre-B cell Thy-1 allele and this surface antigen is no longer expressed by any cells in the population. These results are consistent with a mechanism that sequentially activates each copy of the Thy-1 gene derived from the pre-B cell lymphoma parent. Hybrids between the class D Thy-1- mutant, AKR1 (Thy-1- d), in which the 5' region of the Thy-1 structural gene has been deleted, and RAW 253.1 cannot be activated to express either Thy-1 allele. This result indicates that a sequence upstream of exon 2 of the active Thy-1 allele is critical for the initial activation event.

Differentiation in vitro of T3+ large granular lymphocytes with characteristic cytotoxic activity from an isolated hematopoietic progenitor colony

Blast colonies were developed by rIL-3 from the spleen cells of mice pretreated with 5-fluorouracil (5-FU) in the methylcellulose cultures. When such IL-3-induced blast colonies were individually lifted up and recultured in the presence of rIL-3 and recombinant erythropoietin (rEpo), a variety of hematopoietic colonies developed from every single colony, including neutrophils, macrophages, eosinophils, megakaryocytes, mast cells, and erythroblasts. The results indicated that IL-3-induced blast colonies consisted of multipotential hematopoietic progenitor cells. By culturing individual IL-3-induced blast colonies in the presence of rIL-2 and irradiated peritoneal macrophages, on the other hand, the proliferation of homogeneous lymphoid cells was observed in 5 of 24 wells, each of which received a single blast colony. Morphologically, they were typical large granular lymphocytes (LGL), and thus it was indicated that LGL could be differentiated directly from the hematopoietic progenitor cells utterly in vitro by rIL-2 and accessory macrophages. From one of these culture wells, a continuous LGL line, IL3B1, was successfully obtained. The proliferation of IL3B1 was dependent on IL-2 in the presence of accessory macrophages, but they no longer responded to IL-3, nor to another T cell growth factor, IL-4. Flow cytometric analysis indicated that the phenotype of IL3B1 was Thy-1+,T3+,L3T4-,Lyt-2-,T200+ Asialo GM1+, whereas that of original IL-3-induced blast cells was Thy-1+,T3-,L3T4-,Lyt-2-,B220-. The results suggested that the expression of T3 molecules was induced in the process of LGL differentiation from the hematopoietic progenitor cells in vitro. Conforming to this, it was revealed that both gamma and beta chain genes of the TCR were rearranged in IL3B1. Northern blot analysis indicated that IL3B1 had abundant mRNA for gamma chain, while mRNA for beta chain was rather faint. Functionally, IL3B1 exhibited typical NK-patterned cytotoxic activity against a panel of tumor cell targets. In addition, they showed significant cytotoxic activity against normal bone marrow cells, as well as various factor-dependent myelogenous progenitor cell lines, all of which were resistant to endogenous NK activity of the fresh spleen cells. These results indicated that at least a set of T3+ LGL with rearranged TCR genes could be directly differentiated from isolated hematopoietic progenitor cells in vitro. Results also suggested that such a prethymically differentiated subset of T-lineage lymphocytes, namely T3+ double-negative LGL, had particular cytotoxic activity in addition to conventional NK activity, which might well contribute to feedback regulation of hematopoiesis.

Quantitative immunocytochemical characterization of four murine macrophage-like cell lines

The aim of the present study was to obtain quantitative data on the expression of seven cell-surface antigens by the murine macrophage-like cell lines WEHI-3, P388-D1, J774.1, and PU5-1.8, and to compare these data with those obtained for various mononuclear phagocytes. Binding of monoclonal antibodies F4/80, M1/70, 2.4.G.2., 30.G.12, M3/38, M3/84, and 59AD2.2 to cells from these four cell lines was detected by the biotin-avidin immunoperoxidase staining method and quantified by cytophotometry. The results are expressed as the percentage cells expressing a given antigen and the mean specific integrated absorbance per 0.25 micron2 cell-surface area. The results revealed that the phenotypes of the four macrophage-like cell lines differ markedly. Expression of the cell antigens by the cells of the various cell lines did not follow a normal distribution. Although the cell lines divide continuously and have certain characteristics in common with mature mononuclear phagocytes, none of the macrophage-like cell lines accurately resembles any of the mononuclear phagocyte populations. The strongest correlations for membrane were found between on the one hand WEHI-3 and P388-D1 cells and monoblasts and promonocytes (P greater than 0.011) on the other. P388-D1, J774.1 and PU5-1.8 cells expressed four of the six antigens to the same extent as skin macrophages (P greater than 0.012). With respect to expression of antigens recognized by antibodies 2.4.G.2., 30.G.12, M3/38, and M3/84 PU5-1.8 cells resembled activated peritoneal macrophages (P greater than 0.031). It is concluded that WEHI-3 is the most immature cell line, followed by the P388-D1 cell line, while J774.1, and PU5-1.8 are the most mature cell lines.

Monoclonal anti-Thy-1.2 antibody induced hematopoiesis in vivo

The intravenous injection of a monoclonal anti-Thy-1.2 alloantibody (IgM class) induced a rapid increase in the number, and the ratio, of multipotent hematopoietic stem cells (CFU-S) in S-phase. The onset of hematopoiesis was thymus-independent. Reconstitution of lethally-irradiated mice with bone marrow cells from mice injected with antibody augmented the T-cell responsiveness to mitogens. No activation was observed in granulocyte/macrophage progenitors. The monoclonal antibody did not directly stimulate CFU-S in vitro, although hematopoietic activity could be found in the sera of antibody-injected mice. Immediately after injection, the antibody was found bound on Thy-1+ cells in spleen. No decrease in the number of peripheral T cells was seen. These results seem to indicate that Thy-1.2-positive cells bound with anti-Thy-1.2 alloantibody may secrete a factor which induces the proliferation of hematopoietic stem cells.

The production of myeloid blood cells and their regulation during health and disease

The regulation of myelopoiesis in vivo most likely entails a complex set of interactions between cell-derived biomolecules and their target cells: hematopoietic stem and progenitor cells and accessory cells. Stimulating and suppressing factors have been characterized through in vitro studies, and their mechanisms of action in vitro and in vivo have begun to be elucidated. Among those factors being studied are the hematopoietic colony-stimulating factors (CSF): interleukin-3 (multi-CSF), granulocyte-macrophage-CSF, granulocyte-CSF, and macrophage-CSF; other molecules include erythropoietin, B-cell-stimulating factor-1, interleukin-1, interleukin-2, prostaglandin E, leukotrienes, acidic ferritins, lactoferrin, transferrin, the interferons-gamma, -alpha, and -beta, and the tumor necrosis factors-alpha and -beta (lymphotoxin). These factors interact to modulate blood cell production in vitro and in vivo. The proposed review characterizes these biomolecules biochemically and functionally, including receptor-ligand interactions and the secondary messengers within the cell which mediate their functional activity. The production and action of the molecules are described under conditions of hematopoietic disorders, as well as under normal conditions. Studies in vitro are correlated with studies in vivo using animal models to give an overall view of what is known about these molecules and their relevance physiologically and pathologically.

A molecular genetic approach to the identification of genes expressed predominantly in the neuroendocrine and immune systems

Our results demonstrate that expression of neuropeptide tyrosine, one of the most abundant and widespread peptides in the mammalian nervous system, occurs in non-neuronal cells, in keeping with the emerging view that neuropeptide synthesis is not restricted to cells of the nervous system. RNA blot analyses and radioimmunoassays detected both NPY mRNA and NPY peptide in rat and mouse spleen, bone marrow, and peripheral blood cells. Immunohistochemical staining of sections from rat bone marrow with an NPY-specific antiserum revealed NPY-like immunoreactivity in megakaryocytes. In situ hybridization confirmed that the NPY-like peptide detected in megakaryocytes was synthesized de novo from NPY mRNA present in these cells. Megakaryocytes, the platelet-forming cells, originate from pluripotent hematopoietic stem cells present in the bone marrow as well as in the spleen of rodents. During microvascular damage, platelets aggregate at the damaged site and release bioactive substances. NPY is known to be a potent vasoconstrictor. Therefore, we propose that megakaryocyte-derived NPY is stored in platelets and released during platelet aggregation, resulting in a long-lasting vasoconstriction. Greatly elevated levels of megakaryocyte-derived NPY, as compared to the level found in BALB/C mice, were found in several mouse strains (NZB, NZB x W, and BXSB) which develop an autoimmune disease resembling systemic lupus erythematosus. Whether the elevation of megakaryocyte-derived NPY plays a role in the autoimmune disease progression in these mice or whether it merely reflects a related hematopoietic abnormality remains to be determined. Subtractive hybridization was used to isolate two cDNA clones that are predominantly expressed in the brain and the immune system. These and similarly derived cDNA clones will be used as molecular probes to study the mechanisms governing tissue-specific expression in the nervous and immune systems. Discovering the function of the proteins encoded by such cDNA clones may reveal evolutionary mechanisms shared by the nervous and immune systems, as well as a molecular basis for the interaction between these systems.

Methods for the selection and growth of antigen-specific cytolytic T lines and clones bearing a defined T cell receptor beta chain marker

Murine cytolytic T lymphocyte (CTL) clones specific for type A influenza virus antigens were generated by in vitro stimulation with syngeneic virus-infected cells in the presence of T cell growth factor (TCGF). All CTL clones recognize viral determinants shared by PR8 and X31 influenza viruses in association with a class I antigen, coded either by the H-2K or H-2D end of the appropriate haplotype. All clones express the Lyt2 antigen marker. Two of five clones also express an antigenic determinant of the V beta chain of the T cell receptor (TCR) identified by F23.1 monoclonal antibody. To effectively generate F23.1+ and antigen-specific CTL clones, heterogenous CTL lines were expanded with F23.1 coated Sepharose beads in the presence of TCGF and then stimulated with PR8 virus-infected cells. Thus, both the proliferative activity to PR8 and the expression of the F23.1 marker was increased significantly. Alternatively, F23.1+ T cells were sorted from in vivo primed mice and expanded with PR8 virus-infected stimulator cells in the presence of TCFG. This F23.1+ T cell line exhibited antigen-specific cytotoxicity for PR8 virus-infected target cells. Additionally, in an 'FcR-focused killing' assay only the F23.1+ CTL line and F23.1+ clones lysed Fc receptor bearing target cells in the presence of F23.1 antibody. These findings indicate that antigen-specific and F23.1+ clones can be selected with high efficiency by alternating stimulation with influenza virus-infected cells and with F23.1-coated Sepharose beads or through the use of a cytofluorograph. The usefulness of antigen-specific and F23.1+ CTL clones and other possible strategies for their selection are discussed.

A lymphoproliferative abnormality associated with inappropriate expression of the Thy-1 antigen in transgenic mice

The Thy-1 antigen is a cell-surface glycoprotein of unknown function expressed on mouse T lymphocytes, neurons, and hematopoietic stem cells. To alter the normal pattern of Thy-1 expression during hematopoietic differentiation, we created transgenic mice using a hybrid Thy-1 gene containing a transcriptional enhancer of the mouse immunoglobulin heavy chain gene (E mu). Strains of mice bearing the Thy-1.2/E mu gene express the Thy-1.2 antigen on mature B lymphocytes and their progenitors, and develop a heritable lymphoid hyperplasia characterized by massive expression of the Thy-1.2 antigen in the bone marrow and lymph nodes. The phenotype associated with inappropriate developmental regulation of the Thy-1 gene suggests that the Thy-1 antigen may play a role in inducing activation or differentiation events on early lymphocyte progenitor cells.

Differential expression of surface markers on thymic lymphomas induced by two carcinogenic agents in different mouse strains

Expression of several thymocyte surface antigens was monitored in a murine model system of thymic lymphoma induction in two different strains of mice. RF/J mice are sensitive to tumor induction by N-nitrosomethylurea (NMU) and by gamma-irradiation, while 129/J mice form tumors only upon NMU treatment. Latency periods for tumor formation were characteristically different depending upon the inducing agent and the mouse strain. We observed differences in thymic leukemia antigen and H-2K expression according to the mode of tumor induction and in relation to the mouse strain, implying multiple factors involved in target cell selection and tumor progression.

Purification and analysis of rat hematopoietic stem cells by flow cytometry

The monoclonal antibody OX7 recognizes an epitope expressed on the Thy-1 glycoprotein, OX22 recognizes the high molecular weight form(s) on leukocyte common antigen, and W3/13 recognized determinants found on certain sialoglycoproteins. Recently, the rat colony-forming unit spleen (CFU-S) was characterized as being OX7 upper 20% positive (OX7u20%), OX22 negative (OX22-), and W3/13 weakly positive (W3/13+). In the present study these observations have been extended to include the hematopoietic stem cell (HSC). Rat marrow cells were incubated with allophycocyanine-OX7 Fab' (APC-OX7 Fab') and phycoerythrin B-OX22 Fab' (Phy B-OX22 Fab'). The cells were sorted with a FACS-II instrument by using a Krypton laser tuned to the 530 nm spectral line for phycobiliprotein excitation. It was found that marrow cells capable of protecting lethally irradiated Lewis rats (9.5 Gy total body radiation, 0.4 Gy/min Co60) had the phenotype OXu20%, OX22-. The percentage of cells in the marrow with this phenotype was found to be 0.34 +/- 0.01 (mean +/- S.E.). Three thousand of these cells were required to rescue 50% of lethally irradiated recipients (30-d survival), while the number of unsorted bone marrow cells required was 1.05 X 10(6). Thus, a 350-fold purification of the HSC was realized. Although CFU-S copurified with HSC, purification of only 105-fold was obtained. This might indicate that purified HSC have a reduced capacity to generate splenic hematopoietic colonies. The OX7u20%, OX22- -enriched HSC population could be further divided into W3/13 dim and W3/13+ subpopulations by three-parameter immunofluorescence analysis with the use of a new optical bench arrangement.