Identification of thymocyte progenitors in hemopoietic tissues of the rat. II. Enrichment of functional prothymocytes on the fluorescence-activated cell sorter

Age-related changes of naive and memory CD4 rat lymphocyte subsets in mucosal and systemic lymphoid organs

The purpose of this study was to investigate in rats, by double-label immunofluorescence and flow cytometric analysis, the age related changes in the CD4 subset of gut-associated lymphoid tissues and spleen. We found that the percentage of CD4+ T cells in Peyer's patches (PP) and spleen (SP) increased during the first 6 weeks after weaning. An age-related decrease of the CD4 subset was observed in SP of aged rats, but not in their PP. In all lymphoid tissues studied, an age-related decrease of the Thy-1+ subset was observed from weaning to 2 years of age. Analysis of the naive CD4 subset (CD45RC+) showed that in SP this subset increased during the first 9 weeks of age, and declined in aged rats. However, in PP this subset presented a slow decrease from weaning until 2 years of age. Together with the decrease of the naive subset, a sharp increase of the memory/activated CD4+ cells (CD45RC- Thy-1-) was observed in PP, and to a lesser extent in SP. When the maturation of the CD4 T cells in PP was followed during the first week after weaning, we found that an important proportion of this subset changes its phenotype at this time, from recent thymic emigrant (CD45RC- Thy-1+) to naive T cell (CD45RC+ Thy-1-) and then to activated/memory cell (CD45RC- Thy-1-). Therefore it appeared that CD4 T cells from PP mature faster than SP CD4 T cells, and they are not subject to the deleterious effect of aging. One surprising point was the different kinetics of the CD4 T cells observed in mesenteric lymph nodes (MLN). No age-related changes were observed in the CD4 subset at this site. Furthermore, the percentage of the CD45RC+ cells did not decrease in aged rats, and in the first 9 weeks of life an increase of this subset was observed.

Impairment of B and T cell maturation in gut associated lymphoid tissues due to malnutrition during lactation

Previously we found that malnutrition during lactation in rats produces an impairment in the immune response to cholera toxin. In this report we found that malnutrition during lactation provokes in 28-day-old rats an increase of Thy1+ c mu+ cells in gut associated lymphoid tissues concomitantly with a decrease of sIgA+ B cells. No differences were found in the percentages of the IgM+ B cell populations. Furthermore, no differences were found in the Peyer's patch (PP) and mesenteric lymph node (MLN) T cell subsets in weaning rats when compared to controls. However, after 1 week of refeeding a higher percentage of the Thy1+ c mu- subset together with a lower percentage of CD5+, CD4+, and CD8+ T cells, were found in malnourished rats when compared to controls. The above results may indicate that B-cell maturation is delayed in malnourished rats at two stages of differentiation: (a) in the passage of pre-B cells (Thy1+ c mu+) to immature B cells (s mu+), and (b) in the switch from s mu+ B cells to s alpha+ B cells. The decrease of CD5+, CD4+, and CD8+ T cells together with an increase of the Thy1+ c mu- subset in gut-associated lymphoid tissues (GALT) may indicate that T-cell maturation is also delayed. Results obtained at weaning may be due to an engraftment by maternal milk-derived lymphocytes in the pups.

Isolation of rat bone marrow mast lineage cells using Thy 1.1 and rat stem cell factor

Recent reports have shown that various marrow-derived cell populations respond vigorously to recombinant rat stem cell factor (rrSCF164), one form of the kit-ligand. In the present study, we isolated cell populations from rat bone marrow using the Thy 1.1 antigen (an antigen that in the rat is differentially expressed on primitive hemopoietic progenitor cells) and fluorescently conjugated rrSCF164 (rrSCF164-PE). We show that rrSCF164 only stimulates cells that are enriched in the brightest Thy 1.1 populations (Thy 1.1bright). Numerous cell lines were generated by serial passage in rrSCF164 containing medium, and the prototypic cell lines have been designated SRT002 and SRT003. Each cell line retains the Thy 1.1bright phenotype and does not respond to interleukins (IL) 1-8, IL-10, granulocyte (G) colony-stimulating factor (CSF), granulocyte macrophage (GM) CSF, M-CSF, or crude preparations of mitogen-stimulated T-cell supernatants. The Thy 1.1bright population of rat marrow was subdivided into a subset that binds rrSCF164-PE (Thy 1.1bright, rrSCF164+). The majority of these cells possess certain characteristics in common with marrow-derived mast cells and the Thy 1.1bright, rrSCF164 responsive cell lines, having similar granule morphology, being metachromatic, and reacting positively with alcian blue. Moreover, rats treated with rrSCF164 displayed significant increases in Thy 1.1bright, rrSCF164+ cells in the bone marrow. These studies show that the combination of Thy 1.1 and rrSCF164 makes possible the isolation of a unique subset of rat bone marrow cells that differentially express the Thy 1.1 antigen and the cell surface receptor c-kit, the majority of which are morphologically similar to marrow-derived mast cells.

The role of hematogenous and intrinsic precursor cells in lymphocyte production in murine bone marrow and thymus

It is well recognized that the bone marrow contains cells that can repopulate a depleted thymus as well as cells that can be induced to express phenotypic markers characteristic of T cells. It is not known, however, to what extent thymocytopoiesis in the normal thymus relies on immigrant, bone marrow-derived cells, nor whether some T cell precursors have entered the bone marrow from the circulation. We used the parabiotic system to test whether thymocytopoiesis relies on progenitors intrinsic to the thymus or on cells that enter the organ from the circulation. In the same system, we have also investigated whether Thy-1- bone marrow lymphocytes that respond to phytohemagglutinin (PHA) by proliferation and Thy-1 expression are produced by myelogenous or hematogenous progenitors. Syngeneic CBA/HT6 and CBA/CaJ mice were joined in parabiotic union at 4-6 weeks of age. Cross circulation between the two partners was verified by the equilibration of Evans' blue dye injected into one partner and by the equilibration of PHA-responsive T cells in the spleen of the parabionts. Chromosome spreads were prepared from the PHA-stimulated T cell-depleted bone marrow and from spontaneously proliferating thymocytes as well as from thymocytes stimulated by PHA or Concanavalin A (Con A). The exchange of spleen colony-forming units (CFU-S) in the femoral marrow was assessed by karyotyping individual spleen colonies. Regardless of the length of parabiotic union, ranging from 4 to 20 weeks, Thy-1-, PHA-responsive bond marrow lymphocytes remained predominantly of the host type with only 3% being derived from the opposite partner.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of a marrow stroma and thymus-associated antigen (ST3) in the rat brain: comparison with Thy-1

Cells of the immunohemopoietic and nervous systems express certain molecules that generally are not found in other tissues. One example is the 'ST3' antigen, which is present on the major population of fibroblastoid cells grown from rat bone marrow, but is not detected on adherent cells from most peripheral organs (e.g. lung). An immunohistological survey revealed ST3 also in the thymic cortex, the glomerular mesangial area, and the brain. Because this pattern of distribution is similar to that described for Thy-1, we compared the localization of the two antigens in the adult rat brain and found that there were areas where it was congruent and others where it was distinct. Staining for ST3 was absent from the white matter, but was especially notable in discrete layers of the frontal, orbital, parietal, and cingulate cortices, the substantia nigra, the inferior olivary nuclei, and the deep molecular layer of the cerebellum, as well as other scattered regions in the gray matter. This is in contrast to Thy-1, which stained more diffusely throughout the gray zones. In further experiments using primary brain cell cultures, ST3 was demonstrated on neurons, but not on oligodendrocytes or astrocytes. Similarly, it was found on the surface of cells of the PC12 neuronal line, but not on the C6 astrocytoma. This restricted distribution on a subpopulation of neurons raises the possibility that the ST3 epitope might be part of a cell interaction molecule of the marrow stroma, thymus, and brain.

Characterization of rat T cell precursors sorted by chemotactic migration toward thymotaxin

An established rat thymic cell line secretes a peptide in the 11 kd range called thymotaxin that attracts a small subset of juvenile rat bone marrow cells via a chemotactic mechanism. The selected cell subset (0.1% of the total bone marrow) is composed of low-density lymphoid cells that do not replicate, and display an immature Thy-1+T-B- phenotype. Thymotaxin-responding cells do not grow in semi-solid cultures under hemopoietic growth factors stimulation, and survive only in coculture with thymic stroma under steroid-free conditions. This stroma mimics the thymic microenvironment and allows a fraction of responding bone marrow cells to acquire T cell differentiation markers and to synthesize transcripts of the TCR alpha and beta chains. Chemotactic migration toward thymic epithelial cell peptides can be used in vitro to sort pre-T cells from the rat bone marrow. The sorted T cell precursors are resting stem cells possibly committed to lymphoid lineage.

Thymotaxin: a thymic epithelial peptide chemotactic for T-cell precursors

The embryonic thymus is seeded by invading hemopoietic precursor cells that differentiate intrathymically into T lymphocytes. We have recently reported that avian thymic epithelial cells secrete chemotactic peptides, which provoke oriented migration of hemopoietic precursor cells in vitro. The established rat thymic epithelial cell line IT-45 R1 produced a polypeptide that resolves as a single band in the region of 11 kDa on NaDodSO4/polyacrylamide gels. This molecule, which we have named thymotaxin, induced a chemotactic response in a subpopulation of hemopoietic cells from juvenile rat bone marrow. Responding cells were generated by short-term coculture of rat bone marrow hemopoietic cells with mouse bone marrow stroma in a steroid-free medium. Cells selected in a chemotactic chamber have a lymphoid or blast cell morphology. The phenotype of the responding cells is Thy-1+, CD4- [corrected] and CD8-. In contrast, CD8 T-lymphocyte differentiation antigen was expressed after coculture with embryonic thymic monolayers, suggesting that the responding cells correspond to the precursors colonizing the thymus.

Analysis of the development of cellular subsets present in the neural crest using cell sorting and cell culture

We have tested the hypothesis that developmentally significant cellular subsets are present in the early stages of neural crest ontogenesis. Cultured quail trunk neural crest cells probed with the monoclonal antibodies HNK-1 and R24 exhibited heterogeneous staining patterns. Fluorescence-activated cell sorting was used to isolate the HNK-1+ and HNK-1- cell populations at 2 days in vitro. When these cell populations were cultured, the HNK-1+ sorted cells differentiated into melanocytes, unpigmented cells, and numerous catecholamine-positive (CA+) cells. In contrast, the HNK-1- sorted cells gave rise to melanocytes and unpigmented cells, but few, if any, CA+ cells. When neural crest cells at 2 days in vitro were labeled with R24 and sorted, both the R24+ the R24- sorted cell populations produced numerous CA+ cell, melanocytes, and unpigmented cells. These results provide evidence for the existence of developmental preferences in some subsets of neural crest cells early in embryogenesis.

Characterization of RT6 bearing rat lymphocytes. I. Ontogeny of the RT6+ subset

The RT6 alloantigen is present on approximately 70% of peripheral T cells in the rat, but is absent from thymocytes and bone marrow lymphocytes. The results of further phenotypic analysis in the present study demonstrated that the RT6 alloantigen is expressed on approximately 45% of the helper/inducer (CD4; W3/25+) and 80% of the cytotoxic/suppressor (CD8; OX8+) peripheral T-cell subsets. Ontogenetic and thymus ablation studies indicated that the RT6+ T-cell subset is thymus-dependent and normally develops after the appearance of RT6-T cells in neonatal rats, and that the expression of RT6 is a post-thymic maturational event. Furthermore, intrathymic adoptive transfer of bone marrow cells demonstrated that RT6+ T cells are thymus-derived cells. These results show that most if not all RT6+ T cells are the progeny of RT6- T cells. However, they do not exclude the possibility that a separate lineage of RT6- T cells exists, which also has OX8+ and W3/25+ subsets. The possible developmental and functional relationships of RT6- and RT6+ T cells in the rat are discussed.

Characterization of rat prothymocyte with monoclonal antibodies recognizing rat lymphocyte membrane antigenic determinants

Utilizing the technique of fluorescence-activated cell sorting and monoclonal antibodies directed at rat membrane antigens, various subpopulations of Lewis bone marrow cells were isolated and subsequently transfused into sublethally irradiated, histocompatible NBr recipient rats by either intravenous or intrathymic inoculation. Recipient rats were sacrificed and cell suspensions from thymus and other lymphoid tissue were examined for the presence of the RT7.1 marker on Lewis thymus-derived lymphocytes by fluorescence-activated cell analysis. From these studies, the population of Lewis bone marrow cells that could reconstitute T cells in the NBr rats was found to be Ox-22 negative, Ox-7 positive, W3/13 positive, and Ox-18 positive. Further analysis characterized the prothymocyte as being Ox-7 upper 20% positive and W3/13 weakly positive. In addition this marrow cell population was able to protect lethally irradiated Lewis rats (9.5 Gy) in 30-day survival tests. These studies have indicated that the prothymocyte either has been derived from the Ox-22 negative, Ox-7 upper 20% positive, and W3/13 positive marrow cells or, like the hematopoietic stem cell, this cell has also been characterized by this phenotype.

The effects of leukemosuppressive immunotherapy on bone marrow infectious cell centers in AKR mice

The bone marrow of AKR mice is the richest source of infectious ecotropic cell centers (ICCs) during the neonatal period. The bone marrow ICCs reside in a low-density population expressing high levels of viral glycoprotein (gp71) and Class I histocompatibility antigens (H-2Kk). In addition, ICCs are enriched in the lymphoid band of Ficoll-Hypaque-fractionated bone marrow, the adherent population of nylon wool separated cells and among the low-density subpopulation of Percoll-fractionated marrow. The observed dichotomy between viral antigen expression and actual virus production suggests that actively cycling cells may be the primary virus producers in the AKR bone marrow. The phenotypic and physical data indicate that bone marrow stem cells and/or prothymocytes may be among the initial virus producing cells in the AKR bone marrow. Leukemosuppressive antiviral immunotherapy delays the appearance of ICCs in the bone marrow but does not exert any major long-term changes on the populations of cells present.

An attempt to produce "pre-T" cell hybridomas and to identify their antigens

With the aim of identifying some of the stages in the development of pre-T cells (cells of the T cell lineage before they enter the thymus), we have produced a large number of hybridomas by the fusion of BALB/c bone marrow cells, bone marrow cells from BALB/c-nu/nu mice, BALB/c fetal liver cells and BALB/c fetal thymocytes with the AKR thymoma BW5147. The hybridomas were selected for the expression of the Thy-1.2 antigen of the normal cell donor and for their ability to produce interleukin 2 (IL 2) upon co-culture with irradiated normal spleen cells. A set of these hybridomas is described in this communication. The hybridomas were then used to immunize rats and to generate monoclonal antibody-producing B cell hybridomas. Most, if not all, of the immunizing hybridomas were derived from pre-T cells as evidenced by the fact that they produce IL 2, and express some of the T cell markers (the Thy-1.2, Ly-1, Ly-2 or L3T4 antigens). The monoclonal antibodies were tested on a panel of pre-T cell hybridomas and on normal cells obtained from spleen, lymph nodes, thymus and bone marrow. The testing was carried out by the microcytotoxicity assay and flow cytometric analysis. Three groups of antibodies could be distinguished. Some antibodies were broadly reactive, being positive with virtually all the clones in the pre-T cell panel and with a substantial fraction of normal lymphoid cells. The identity of the antigens detected by these antibodies remains unknown but they do not seem to correspond to any of the known cell surface markers. Other antibodies reacted only with some of the pre-T cell clones and did not react at all with normal lymphoid cells obtained from adult animals. Finally, other antibodies still reacted only with a minor subpopulation of thymocytes or of thymocytes and bone marrow cells, as well as some of the pre-T cell clones; they did not react with spleen and lymph node cells. These antibodies might be specific for cells in the prethymic phase of the T cell differentiation pathway. They should prove useful for the identification of pre-T cell markers and hence for the isolation of pre-T cells and their functional analysis.

Defective lymphopoiesis in bone marrow of motheaten (me/me) and viable motheaten (mev/mev) mutant mice. I. Analysis of development of prothymocytes, early B lineage cells, and terminal deoxynucleotidyl transferase-positive cells

This study identifies defects in the early stages of lymphopoiesis that may contribute to the abnormalities in the development and/or function of peripheral T and B lymphocytes in mice homozygous for the motheaten (me/me) and viable motheaten (mev/mev) mutations. The results indicate that in me/me and mev/mev mice prothymocytes in bone marrow are present in essentially normal numbers, as determined by intrathymic injection, but apparently lack the ability to home effectively to the thymus, as determined by intravenous transfer; early B lineage cells in bone marrow, identified by the B220 antigen, are markedly depleted, including immature B cells (sIg+), pre-B cells (cIg+, sIg-), and pro-B cells (B220+, cIg-, sIg-); TdT+ bone marrow cells, especially a subset that expresses the B220 B lineage antigen, are markedly depleted by two weeks of age; normal numbers of TdT+ thymocytes are present during the first 3 wk of postnatal life, but rapidly decrease thereafter. The results further indicate that neither the defective thymus homing capacity of prothymocytes nor the deficiency of TdT+ bone marrow cells is due to autoantibodies. The possible relationship of the defective development of lymphoid precursor cells to the premature onset of thymic involution and to the abnormalities of peripheral T and B lymphocytes in me/me and mev/mev mice is discussed; as are the results of in vitro studies (presented in a companion paper), which suggest that a primary defect in the stromal microenvironment of the bone marrow is responsible for the abnormal development of the lymphoid precursor cells.

Isolation of cell lines possessing functional and serological properties resembling those of thymocyte precursors

Thymocytes develop from a committed haematopoietic progenitor, referred to as a prothymocyte. They are uniquely capable of migrating to and restoring the thymus of a lethally irradiated host, a property which has been exploited as a specific assay for these cells. Like other committed haematopoietic progenitors, prothymocytes are found only in small numbers in even the richest sources (0.05-1.0% of the nucleated cells in bone marrow). Purification has proved difficult both in terms of finding a suitable starting material and in the degree of enrichment achieved. We now report the isolation of cloned lines of cells with some of the serological and functional properties of prothymocytes. One of these lines has been in continuous culture for almost 2 years. When injected into irradiated recipients, cells from this line migrate to the thymus and there develop into cells which resemble normal cortical thymocytes.

Dynamics of early T cells: prothymocyte migration and proliferation in the adult mouse thymus

The object of this review has been to consider precursor cell migration into the normal adult thymus, using the mouse model. We have presented a series of experiments and discussed them in the context of other relevant experiments in the literature. The conclusions, qualified in the text, can be summarized as follows: There is a continual input of precursor cells into the normal undepleted adult thymus. The daily input of precursors under normal circumstances is very low (e.g. several per day). Once a precursor enters the pool of proliferating cells inside the thymus, its proliferation is limited to only several weeks. There is no permanent endogenous stem cell. There are a number of different precursor microenvironments in the thymus with different controls, since the kinetics of early (bone marrow-derived) and late (thymus-derived) precursors is quite different. All of these points require further analysis, and we have presented a minimal model as a basis for further experiment.

Frequency of 6-thioguanine-resistant T cells is inversely related to the declining T-cell activities in aging mice

The frequency of clonable 6-thioguanine-resistant (6-TGr) splenic T cells increased moderately with age in female BALB/c mice ranging in age from 3 to 32 months; however, the correlation between the frequency of clonable 6-TGr cells and age was weak. Those clonable 6-TGr T cells were deficient in hypoxanthine/guanine phosphoribosyltransferase (HGPRT) activity and sensitive to hypoxanthine/aminopterin/thymidine medium, as in the case of HGPRT-deficient L5178Y mouse lymphoma cells. When splenic T cells of individual aging mice were assessed simultaneously for the frequency of clonable 6-TGr T cells and for their ability to produce interleukin 2 or to proliferate in response to mitogenic stimulation, an inverse correlation was observed. These results indicate that the frequency of 6-TGr T cells is more closely related to physiologic age than chronologic age. This would mean that the frequency could be used as an index of physiologic age and that the T cells could serve as a cellular model relating gene alterations to physiologic age.

Studies of thymocytopoiesis in rats and mice. I. Kinetics of appearance of thymocytes using a direct intrathymic adoptive transfer assay for thymocyte precursors

We describe a quantitative intrathymic (i.t.) adoptive transfer system for detecting thymocyte precursor cells in rats and mice. In this system, the generation of donor-origin thymocytes is analyzed on the FACS after the injection of test cells directly into the thymus of sublethally irradiated, histocompatible, RT-7 (rat) or Ly-1 (mouse) alloantigen-disparate recipients. Like the standard i.v. adoptive transfer assays for prothymocytes, the i.t. transfer assay is time, dose, and irradiation dependent. However, unlike the i.v. assays, the i.t. assay is highly sensitive, independent of cell migration, and specific for T-lineage precursor cells. Thus, the i.t. system requires between 25- and 50-fold fewer precursor cells than do the i.v. systems to generate a given number of donor-origin thymocytes; it detects nonmigratory as well as migratory subsets of precursor cells; it detects prethymic and intrathymic precursor cells with equal facility; and it produces a discrete, self-limited wave of donor-origin thymocytes and peripheral T cells. Moreover, neither hemopoietic nor lymphopoietic stem cell chimerism occurs at extrathymic sites. Comparison of the kinetics of thymocytopoiesis in the i.t. and i.v. transfer systems suggest that the seeding efficiency of prothymocytes in the i.v. assay approximates 0.04; the lag phase of the time-response curve is not due to a delay in the entry of prothymocytes into the thymus; and the relative amount of thymocyte precursor activity in various lymphohemopoietic tissues is highest in bone marrow, lowest (or absent) in lymph node, and intermediate in spleen, blood, and thymus. Moreover, the occurrence of saturation kinetics in the dose-response curve of the i.t. system supports the hypothesis that a finite number of microenvironmental niches for prothymocytes may exist in the thymus. These initial observations will require confirmation and extension in future studies. However, based on the present findings and related observations, we anticipate that the i.t. adoptive transfer system will contribute importantly to the definitive analysis of both normal and abnormal thymocytopoiesis.

Phenotypic heterogeneity of Gross virus-induced thymic lymphomas in the rat: cellular origins and migratory properties

Neoplastic thymocytes from rat thymic lymphoma-leukemias induced by the rat-adapted Gross leukemia virus (RAGV) were analyzed for a variety of differentiation markers. The neoplasms from individual rats all expressed the antigenic phenotype MP+, W3/13+, Thy-1+, RT-1+, RT-7+, W3/25-. However, approximately two-thirds of the neoplasms were positive for the OX 8 antigen, and one-third were negative. The OX 8- neoplasms only involved the thymus, whereas approximately 40% of the OX 8+ neoplasms involved the spleen as well as the thymus. Virtually all OX 8+ and OX 8- neoplastic cells contained terminal deoxynucleotidyl transferase (TdT), and both OX 8+ and OX 8- lymphomas expressed the lactate dehydrogenase (LDH)-5' isozyme and the primary, but not the secondary, ADA isozyme. This enzymatic phenotype is characteristic of thymocyte precursors, but not thymocytes. Our results therefore indicate that RAGV-induced lymphomas arise from transformed prethymic TdT+ cells which contain the LDH-5' and the primary ADA isozymes. These preleukemic cells presumably migrate to the thymus where they express the RT-7 pan-T-cell antigen and, in some instances, the OX 8 antigen during the development of overt leukemia. The OX 8+ neoplasms, being more differentiated than their OX 8- counterparts, then migrate to peripheral lymphoid tissues.

Characterization of thymocytes expressing the common acute lymphoblastic leukemia antigen

We studied the relationship between CALLA + thymocytes and two known markers of T-lymphocyte differentiation, Tdt and the sheep erythrocyte receptor. Thymocytes were studied using double fluorochrome analysis (with monoclonal anti-CALLA antibody and anti-Tdt) before and after E rosette separation. We found that approx. 4% of unseparated thymocytes were CALLA + and that most CALLA + cells were also Tdt +. After E rosettes separation CALLA + Tdt + cells were found mostly in the ER- fraction (20% of ER- cells) while only 1.0% of ER + cells were CALLA +. The expression of CALLA on ER- Tdt + thymocytes suggests that CALLA may define cells early in T-cell differentiation.