Thy-1 antigen expression by murine high-proliferative capacity hematopoietic progenitor cells. I. Relation between sensitivity to depletion by Thy-1 antibody and stem cell generation potential

Hematopoietic stem cells of high proliferative potential such as the giant macrophage colony-forming cell HPP-CFC, were present in the marrow of mice treated with high dose 5-fluorouracil (5Fu) (150 mg/kg i.v.), whereas most committed granulocyte-macrophage progenitors, GM-CFU-C, were depleted. Enrichment of primitive stem cells in post 5-Fu bone marrow (5FuBM) was reflected in an enhanced capacity to proliferate in suspension cultures stimulated by the mixture of lymphokines present in Con A spleen-conditioned medium supernatant (Con A CM) when compared to normal bone marrow. The population of blast-like cells harvested at 5 days from suspension cultures of 5FuBM with Con A CM showed marked increases in stem cells GM-CFU-C and HPP-CFC. For this reason, 5FuBM was utilized to study the cell surface characteristics of putative pluripotential stem cells capable of giving rise to committed stem cells in suspension cultures. Treatment of 5FuBM (BDF1 mice) before suspension culture with a high concentration of either of two cytotoxic monoclonal antibodies directed against the Thy-1.2 surface antigen in the presence of rabbit complement reduced or abrogated the generation of stem cells HPP-CFC and GM-CFU-C in suspension cultures, even though the input content of HPP-CFC and GM-CFU-C in treated 5FuBM compared with control 5FuBM showed little reduction by the antibody plus complement treatment. The Thy-1+ cell required for generation of stem cells was not a T cell, because reconstitution of Thy-1.2-depleted 5FuBM with spleen nylon nonadherent (T) cells did not reconstitute the generation of stem cells, even though T cells did grow in the suspension cultures. In addition, depletion from 5FuBM of cells expressing Lyt-1 and Lyt-2 antigens, unambiguous markers of T cell-thymocyte differentiation, did not ablate the generation of HPP-CFC and GM-CFU-C. Rather, performance of Thy-1 cell depletion at lower efficiency, which still abrogated T cell function, ablated generation of HPP-CFC but did not affect the generation of GM-CFU-C. It was concluded that 5FuBM contains distinct Thy-1+ primitive stem cells expressing different amounts of Thy-1 antigen correlating with their respective generation potentials. Some of these Thy-1+ progenitor cells may be pluripotential.     

Abnormalities of B lineage cells are demonstrable in long term lymphoid bone marrow cultures of New Zealand black mice

The formation of B lymphocytes in young New Zealand Black (NZB) mice proceeds at an accelerated rate resulting in a deficiency of B lineage precursors in adult (greater than 15 wk old) animals. To study the characteristics of B lineage cells in young (4 wk) and old (6 mo) NZB mice, bone marrow from these animals was used to initiate long term lymphoid bone marrow cultures (LBMC) that permit the long term maintenance of B cells and their precursors. Age-matched cultures from BALB/c mice and NZB.xid marrow were established in parallel. Primary LBMC were readily established from these strains and showed similar patterns of growth for the 3-mo observation period. No significant differences in numbers of 14.8 positive cells were observed. However, NZB mice at both ages had a higher percentage of membrane IgM (mIgM)-expressing cells. Significant levels of supernatant IgM were found only in cultures of 6-mo NZB and BALB/c mice; levels were highest in NZB culture supernatants and were often more than 500 ng/ml; significant, although much lower, levels of IgG were likewise detected. Lymphoid cells from NZB.xid mice were unable to generate significant levels of IgM in supernatant fluids indicating the effects of the xid gene were displayed in vitro. Autoantibodies were not detected in any of the culture supernatants. Additional evidence for NZB hyperactivity in primary B lymphopoiesis was observed upon initiation of primary myeloid bone marrow cultures (MBMC) from these strains of mice and subsequently transferring them to LBMC conditions. This results in the cessation of myelopoiesis at the initiation of B lymphopoiesis. At the time of converting MBMC to LBMC, cultures of NZB and BALB/c mice morphologically resembled myeloid cultures and had neither B cell colony-forming units nor cells that expressed 14.8 or mIgM. However, following the switch, NZB mice had a 5-fold higher number of B cell colony-forming units. Further, MBMC established from NZB bone marrow cells had a reduced capacity to form colonies in the granulocyte-macrophage colony-forming unit assay. These studies indicate that defects of NZB hemopoietic cells are manifest in vitro and suggest the use of in vitro long term cultures as a valuable technique to further dissect the hematopoietic abnormalities of NZB mice and possible underlying microenvironmental defects.     

In vitro studies on lymphocyte differentiation. II. Generation of terminal deoxynucleotidyl transferase-positive cells in long-term cultures of mouse bone marrow.

The enzyme TdT is the earliest known marker of lymphocytic differentiation in rodents. Cells containing this enzyme were demonstrated in suspension cultures of mouse bone marrow cells that had been maintained in vitro for periods of 7 to 45 days. The cells were detected by immunofluorescence using purified antibodies to homogeneous TdT. Between 0.04 and 2.0% of cultured bone marrow cells from a variety of mouse strains were positive. More than 40% of the TdT-positive cells incorporated 3H-thymidine during a 20-min pulse. Surface Ig and Thy-1 antigens were not detected on the TdT-positive cells. The prevalence of TdT-positive cells was decreased 10-fold in cultures that had been treated with 10(-6) M hydrocortisone 24 hr before harvesting. The results indicate that lymphoid progenitor cells can be generated in vitro.     

Mouse skin graft prolongation with donor strain bone marrow and anti-lymphocyte serum: surface markers of the active bone marrow cells

The survival of C3H/HeJ skin grafts on B6AF1 mice treated with anti-lymphocyte serum (ALS) can be significantly prolonged by the injection of the host with C3H/HeJ bone marrow. Although the prolongation is apparently due at least in part to the ultimate presence in the host of specific suppressor cells of donor origin, little is known about the nature of the cells in the marrow inoculum that are responsible for this effect. The present investigation was undertaken to characterize surface markers of the active bone marrow cells. Marker-positive populations were either depleted and enriched by panning techniques or depleted by killing with specific antibody and complement, and then were assayed for their ability to prolong graft survival. Cells that were adherent to anti-Ia-coated plates extended graft survival only slightly better than did treatment with ALS alone, whereas nonadherent (Ia-depleted) cells, as well as cells treated with anti Ia and complement, retained good prolonging activity. Similarly, panning on anti-immunoglobulin (Ig)-coated plates produced an active, Ig+-depleted population and an inactive adherent population, and killing of Thy-1+ cells with antibody and complement did not compromise the ability of the bone marrow inoculum to prolong graft survival. Complement receptor-positive (EAC+) and Fc gamma receptor-positive cells (EA+) were separated by panning on plates coated with sheep erythrocytes/antibody/complement and erythrocytes/7S antibody respectively. Adherent, EAC+-enriched cells were only slightly active, whereas the nonadherent, EAC-depleted population was fully active in graft prolongation. However, both Fc gamma R+ (EA+)-enriched and depleted populations were active, with the enriched fraction producing significantly better prolongation than the depleted population. Thus, the bone marrow cells that can prolong skin graft survival in ALS-treated mice appear to be Ia-, Thy-1+, largely complement receptor negative, and Ig-, but are largely positive for Fc gamma receptors.     

Induction and long-term maintenance of Thy-1 positive T lymphocytes: Derivation from continuous bone marrow cultures

In the present study we investigated the presence of T-lymphocyte progenitors in the long-term murine bone marrow culture system described by Dexter: mature Thy-1 antigen-bearing T lymphocytes are lost in these cultures after a few days. By culturing nonadherent cells from such cultures in the presence of a supernatant of concanavalin A-stimulated spleen cells, a source of T-cell growth factor, we found that Thy-1 positive blast cells proliferated together with a second population of Thy-1 negative cells. These two populations of cells have been maintained in long-term in vitro cultures by passaging the cells in fresh conditioned medium at regular intervals. Moreover, we have been able to establish pure cultures of the Thy-1-bearing blast cells after separating them from the non-T cells using their adherence property to plastic surfaces. Long-term cultures of T lymphocytes can thus be established from long-term marrow cultures as well as from the spleen, thymus or fresh bone marrow.     

Pluripotential hematopoietic stem cells in post-5-fluorouracil murine bone marrow express the Thy-1 antigen

Expression of the Thy-1 alloantigen by hematopoietic stem and progenitor cells in post-5-fluorouracil (5-FU) murine bone marrow was investigated. FACS analysis of BDF1 bone marrow stained for Thy-1.2 with a triple-layer amplified labeling technique demonstrated that 35% of the total bone marrow population expressed Thy-1.2 (Thy-1.2+). Two distinct size subpopulations were observed in post-5-FU BDF1 marrow. Thy-1.2+ cells were present in both the large and the small subpopulations. FACS-separated bone marrow cells were also plated in methylcellulose cultures. Ninety percent of all colony-forming cells surviving in vivo administration of 5-FU were Thy-1.2+. Replating of primary hemopoietic colonies and morphologic examination of primary and secondary colonies demonstrated that the most primitive stem cells including "stem" (S) cells were Thy-1.2+. These cells (Thy-1.2+) were capable of self-renewal in vitro and exhibited multiple differentiation potentials in comparison to Thy-1.2-cells, which lacked significant self-renewal capability and were mono- or bipotent progenitor cells. Separation of Thy-1.2+ cells into large or small Thy-1.2+ subpopulations showed that only the large Thy-1.2+ colony-forming cells possessed significant self-renewal capacity. Treatment of BDF1 bone marrow with anti-Thy-1.2 plus complement reduced primary colony formation by 67% and eliminated those colony-forming cells which had extensive self-renewal properties. In the presence of PWMSCM, depletion and reconstitution of T lymphocytes had no effect on primary or secondary colony formation. These data demonstrate that Thy-1 is present on primitive hematopoietic stem cells in post-5-FU bone marrow. In addition, they show that the murine S cell is Thy-1+.     

Rapid, B lymphoid-restricted engraftment mediated by a primitive bone marrow subpopulation

Utilizing multiparameter flow cytometry, we have defined a subset of bone marrow cells containing lymphoid-restricted differentiation potential after i.v. transplantation. Bone marrow cells characterized by expression of the Sca-1 and c-kit Ags and lacking Ags of differentiating lineages were segregated into subsets based on allele-specific Thy-1.1 Ag expression. Although hematopoietic stem cells were recovered in the Thy-1.1low subset as previously described, the Thy-1.1neg subset consisted of progenitor cells that preferentially reconstituted the B lymphocyte lineage after i.v. transplantation. Recipients of Thy-1.1neg cells did not survive beyond 30 days, presumably due to the failure of erythroid and platelet lineages to recover after transplants. Thy-1.1neg cells predominantly reconstituted the bone marrow and peripheral blood of lethally irradiated recipients with B lineage cells within 2 weeks, although a low frequency of myeloid lineage cells was also detected. In contrast, myeloid progenitors outnumbered lymphoid progenitors when the Thy-1.1neg population was assayed in culture. When Thy-1. 1low stem cells were rigorously excluded from the Thy-1.1neg subset, reconstitution of T lymphocytes was rarely observed in peripheral blood after i.v. transplantation. Competitive repopulation studies showed that the B lymphoid reconstitution derived from Thy-1.1neg cells was not sustained over a 20-wk period. Therefore, the Thy-1. 1neg population defined in these studies includes transplantable, non-self-renewing B lymphocyte progenitor cells.     

Stromal cells derived from spleen or bone marrow support the proliferation of rat natural killer cells in long-term culture.

Rat nylon wool nonadherent bone marrow cells were propagated for up to 75 days in co-culture with stromal cells derived from either spleen or bone marrow. Interleukin (IL) 1 enhanced the ability of spleen stroma to support the long-term culture of natural killer (NK) cells, ostensibly by inducing these support cells to synthesize other cytokines. Flow cytometry studies indicated that the nylon wool separation procedure enriched the concentrations of mature NK cells from 7.9% to 38.1% for splenocytes and from 3.8% to 19.5% for bone marrow cells. Analyses of the adherent zones of suspended nylon screen NK cell cultures revealed substantial numbers of large granular lymphocytes that expressed NK 323+/MOM/3F12/F2- phenotypes. The presence of both mature and immature cells of the NK lineage in this matrix was inferred by the presence of both IL-2 receptor (IL-2R) positive and IL-2R negative, and OX-8+ and OX-8- NK 323+ cells over the greater than 4-month experimental period. Suspended nylon screen cultures displayed a greater potential for producing cytolytic cells than either co-cultures of bone marrow nonadherent cells on stroma monolayers or suspension cultures. The large granular lymphocytes produced in suspended nylon screen cultures could be transformed into active killers of YAC-1 targets by IL-2. In contrast to bone marrow nonadherent cells, more splenic nylon-wool-passed cells displayed a mature NK phenotype, but their proliferative potential and ability to be transformed into cytolytic cells by IL-2 decreased rapidly in culture. In the suspended nylon screen culture system, NK cells migrate from the underlying stroma in stages as they mature, retain their cytolytic potential, and manifest a capacity for self-renewal. Cultured cells were routinely dissociated into single cell suspensions via enzyme treatment and were reinoculated onto "fresh" nylon screen/stromal cell templates after passage through nylon wool columns. These co-cultures continued to generate cytolytic cells in numbers greater than those of the initial inoculum.     

Feedback suppression of the immune response in vivo. III. Lyt-1+ B cells are suppressor-inducer cells

We previously demonstrated that injection of a high dose (4 X 10(9] of sheep erythrocytes (SRBC) into C57BL/6 mice results in the generation of splenic B cells (plastic nonadherent, Thy-1- and Ig+) which, when transferred to normal syngeneic recipients, subsequently induce antigen-specific suppressor T cells to suppress the recipient's plaque-forming cell (PFC) responses to SRBC. In the present study we characterized the suppressor-inducer B cells phenotypically. Cytotoxic treatment of the donor's immune spleen cells with anti-Lyt-1 antibody plus complement (C'), but not with anti-Lyt-2 antibody plus C', relieved the suppression of PFC responses in recipients. The FcRr+ population separated by EA-rosette formation showed enriched suppressor-inducing activity, whereas the FcRr- population showed no activity. Our findings, taken together with the previous ones, suggest that suppressor-inducer cells are Thy-1-, Lyt-1+, Lyt-2-, FcRr+, and Ig+.     

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.     

Isolation of two early B lymphocyte progenitors from mouse marrow: a committed pre-pre-B cell and a clonogenic Thy-1-lo hematopoietic stem cell

Two novel early B lymphocyte precursor populations have been identified by their capacity to differentiate in Whitlock-Witte bone marrow cultures. Cells expressing neither the B lineage antigen B220 nor Thy-1 contain committed B cell precursors which differentiate in short-term culture into pre-B and B cells. The other population expresses low levels of Thy-1, and lacks B220 as well as the T cell markers L3T4 and Lyt-2. The Thy-1+ cells which initiate long-term B cell cultures contain clonogenic B cell precursors at a frequency of 1 in 11, a 100-fold enrichment over unseparated bone marrow. Thy-1+ cells are also highly enriched for myeloid-erythroid precursors (CFU-S). Thy-1+ cells allow long-term survival of lethally irradiated mice and fully reconstitute the hematopoietic system, including T and B lymphocyte compartments. These results indicate that this population (approximately 0.1% of bone marrow) may contain the pluripotent hematopoietic stem cell.     

20 alpha hydroxysteroid dehydrogenase (20 alpha SDH) activity in New Zealand mice T lymphocytes and bone marrow cells: effect of age, sex, and castration.

The activity of 20 alpha hydroxysteroid dehydrogenase (20 alpha SDH), a T lymphocyte-associated enzyme, was measured in fetal liver, thymus, spleen, and bone marrow cells from NZB, NZW, and (NZB X NZW)F1 (B/W) mice. There was an age-dependent increase of 20 alpha SDH activity in bone marrow cells, and a decrease in thymocytes and splenic T lymphocytes. Treatment with anti-theta and complement did not reduce the 20 alpha SDH activity of bone marrow and fetal liver cells, but reduced the activity of spleen cells. PHA stimulates both 20 alpha SDH activity and thymidine incorporation in splenic, bone marrow, and fetal liver lymphocytes. The results suggest that the enzyme in the bone marrow and fetal liver is located in pre-T lymphocytes. Enzymatic activity in bone marrow cells taken from female B/W mice (older than 7 months) was 40 to 20% lower than in male mice. Orchidectomy, but not ovariectomy, caused a significant decrease in thymocyte 20 alpha SDH activity. Orchidectomy depressed and ovariectomy enhanced 20 alpha SDH activity of bone marrow cells. The 20 alpha SDH activity of fetal liver cells from B/W mice was twice as high as in either parent strain. No 20 alpha SDH activity was found in fetal liver cells taken from BALB/C SJL or C57BL/6 mice. A model is proposed to explain the age- and sex-related changes in 20 alpha SDH activity of pre-T and T lymphocytes in healthy and pathologic conditions.     

Effect of cyclosporin A on lymphopoiesis. III. Augmentation of the generation of natural killer cells in bone marrow transplanted mice treated with cyclosporin A

The effects of cyclosporin A (CsA) on the generation of NK cells were studied using syngeneic bone marrow transplanted mice subsequently treated with CsA (BMT/CsA mice). In contrast to a severe reduction in T cells that was reported previously, these mice exhibited a marked enhancement of splenic NK activity. The enhanced NK activity was mediated by NK1.1+, Thy-1- cells as assessed by antibody plus complement treatment, and was concomitant with an absolute increase in the numbers of NK1.1+ cells as assessed by flow cytometry. Because the depletion of host-derived, mature NK cells by injection of anti-asialo GM1 antibody before bone marrow reconstitution did not affect the enhancement of NK activity, CsA appeared to augment the generation of NK cells from bone marrow precursors. To investigate a possible relationship between the enhancement of NK activity and the maturational arrest of T cells in the thymus induced by CsA, mice were thymectomized, followed by irradiation, bone marrow reconstitution, and CsA treatment. These mice exhibited as strong enhancement of splenic NK activity as BMT/CsA mice, suggesting that the CsA-induced effect on NK cells is distinct from its effect on T cell development in the thymus. Taken together, these results are the first demonstration of the positive effect of CsA on NK cell generation and may be of importance in clinical bone marrow transplantation.     

High expression of the Thy-1 antigen on natural killer cells recently derived from bone marrow

The subset of murine natural killer (NK) cells that kills lymphoma targets contains about 50% cells expressing the Thy-1 antigen and this has been one of the reasons for assigning NK cells to the T-cell differentiation lineage. It has now been shown that the proportion of the Thy-1+ NK cells is not constant: ca. 90% of the NK cells appearing in the spleens of irradiated mice injected 10-14 days previously with bone marrow cells (anti-Thy-1 plus complement treated) express this antigen. The donor origin of these Thy-1+ NK cells was demonstrated by using semisyngeneic bone marrow cells in transfers but this same phenomenon could also be observed after entirely syngeneic transfers, excluding the possibilities that this Thy-1+ NK activity is due to activated T cells or to the effect of T-cell activation products on NK cells. Additionally, these early NK cells expressed the asialo-GM1 antigen, which is found on murine NK cells but not on cytotoxic T cells. These data suggest that the precursors for NK cells in the bone marrow are Thy-1-, and that the first splenic NK cells derived from these progenitors express this antigen.     

Comparison of response to stem cell differentiation signals between normal and autoimmune mouse strains

Normal DBA/2 and autoimmune NZB mice were studied with regard to signals eliciting differentiation and division of bone marrow stem cells. Irradiated (NZB X DBA/2)F1 mice were repopulated with various combinations of T-depleted bone marrow from NZB and DBA/2 mice. In response to the repopulation signal of irradiation, recipients of autoimmune NZB marrow initially demonstrated expansion of LY-5+ lymphoid and hemopoietic cells, particularly of the B cell lineage. The greater the proportion of NZB marrow, the higher the percentage of lymphoid cells observed 2 wk post-repopulation. B cells (ThB-positive cells) were increased in disproportionate numbers in recipients of NZB marrow, even those that had received as little as 20% NZB bone marrow cells. However, by 2 mo, the initially observed increase in lymphoid cells in recipients of NZB marrow was no longer observed. Up to 6 mo post-repopulation, cytogenetic analysis revealed that irradiated recipients were repopulated in the same proportion of DBA/2: NZB as was in the injected marrow. Endogenous colony formation assays indicated that recipients of 100% NZB, 80% NZB, and 20% NZB marrow all had greater numbers of splenic endogenous colonies than did recipients of DBA/2 marrow alone. These studies indicated that autoimmune NZB marrow repopulated irradiated mice in the proportion in which it was injected, but there was a disproportionate early increase in cells of the B lineage as well as a disproportionate increase in splenic colony formation.     

A role for the thymic epithelium in the selection of pre-T cells from murine bone marrow

A rat thymic epithelial cell line IT45-R1 has been previously described as secreting soluble molecules that in vitro chemoattract rat hemopoietic precursor cells. The development of such an in vitro migration assay was based on the ability of cells to migrate across polycarbonate filters in Boyden chambers. In the present paper, by using the same strategy, we studied murine bone marrow cells capable of migrating in vitro toward IT45-R1 conditioned medium. The responding cells were shown to represent a minor bone marrow subpopulation characterized by a low capacity to incorporate tritiated thymidine in vitro (less than 10% of control). Moreover, this cell subset was considerably impoverished with respect to granulocyte-macrophage CFU (less than 7% of control) and pluripotent hemopoietic stem cells (less than 12% of control). Potential generation of T cells of donor-type in the lymphoid organs of irradiated recipients was measured by using C57BL/Ka Thy-1.1 and Thy-1.2 congenic mice. Thy-1.1 irradiated mice were injected intrathymically or intravenously with the selectively migrated cell subset of Thy-1.2 donor-type bone marrow cells. The use of an i.v. transfer route allowed us to show that these cells possess thymus-homing and colonization abilities. In a time-course study after intrathymic cell transfer, these migrated cells were able to generate Thy-1.2+ donor-type thymocytes represented by all cortical and medullary cell subsets in a single wave of repopulation from day 20 to day 30 after transfer, with a peak around days 23 to 25. The degree of repopulation closely resembled that seen with unfractionated bone marrow cells in terms of absolute numbers of donor cells per thymus (82% of control, 22 x 10(6) Thy-1.2+ cells) as well as in percent donor cells per thymus (105% of control). Thy-1.2+ cells were also detected in the lymph nodes and the spleens of reconstituted recipient mice. Taken together, these results support the idea that the supernatant of the established thymic epithelium IT45-R1 induces the migration of a murine bone marrow subset that contains hemopoietic stem cells already committed to the lymphoid lineage (i.e., pre-T cells).     

Effects of B-lymphocytes from different organs on hemopoietic colony formation in the spleen by bone marrow cells]

The influence of B-lymphocytes from various sources on splenic colony formation was studied in the syngeneic system. B-lymphocytes were obtained by panning with IgG-fraction of rabbit anti-mouse Ig, absorbed on Petri dishes. In addition, adherent cells, Thy-1+ and SC-1+ were eliminated from the fraction of Ig(+)-cells. SC-1- and SC-1+ fractions, containing, respectively, stem cells and T-lymphocyte precursors, were obtained by panning with IgG-fraction of rabbit anti-SC-1 serum. SC-1- cells transferred to irradiated syngeneic mice did not induce colony formation in the spleen. Introduction of SC-1- and SC-1+ cells induced formation of colonies. A similar helper effect occurred when SC-1(-)-cells were introduced with bone marrow or lymph node B-cells, but not with splenic B-cells. Splenic, but not bone marrow and lymph node B-cells inhibited colony formation by combination of SC-1- and SC-1+ cells. All effects of Ig+ cells were abolished by treatment of cells with rabbit anti-MBLA serum. Thus, B-cells of various origin can either enhance or inhibit colony formation. The enhancing of inhibitory effect after B (MBLA+)-cells elimination from suspension of bone marrow and lymph node (but not spleen) Ig(+)-cells resulted from the activity of B-contrasuppressors.     

Lymphohemopoiesis in culture is prevented by interaction with adherent bone marrow cells from mutant viable motheaten mice

Mice with the recessive "motheaten" (me) or "viable motheaten" (mev) mutations have severe immunologic disturbances and die at an early age. The function of hemopoietic progenitor cells and microenvironmental elements that regulate their growth and differentiation were studied in mev mice with two types of long term bone marrow cultures. Cells from bone marrow of homozygous defective mev/mev mice were non-productive under conditions that normally support replication of stem cells and production of neutrophil granulocytes. Similarly, in a different culture system, lymphocytes were produced from normal littermate, but not mev/mev bone marrow. Initial overgrowth of cells having macrophage-like characteristics occurred in both culture systems with marrow from defective mice. Co-cultures of normal and defective bone marrow cells were always non-productive. In contrast, supernatants of mev/mev bone marrow cultures did not have a detrimental effect on cultures of normal cells, implying that the suppression was cell-associated. Furthermore, there was no evidence for abnormal release of granulocyte or macrophage growth factors in mev bone marrow cultures. A small population of cells in mev/mev bone marrow cultures were morphologically similar to "stromal" cells that support lymphohemopoiesis. Certain culture strategies could be used to enrich for these. mev/mev stromal cells had affinity for normal lymphocytes; however, they did not support lymphocyte growth. The long term bone marrow cultures thus reveal an apparent imbalance in the regulatory mechanisms affected by these single gene mutations. This is manifested by preferential or aberrant growth of one type of adherent cell and a possible functional abnormality of stromal cells. mev mice could provide an ideal model for investigating cell-associated molecules that normally limit progenitor cell replication.     

Interleukins 2 and 3 regulate the in vitro proliferation of two distinguishable populations of 20-alpha-hydroxysteroid dehydrogenase-positive cells

The ability of interleukin 2 (IL 2), interleukin 3 (IL 3), and granulocyte/macrophage colony-stimulating factor (GM-CSF) to induce the proliferation of cells from thymus, spleen, or bone marrow was examined and compared with their ability to induce expression of the enzyme 20-alpha-hydroxysteroid dehydrogenase (20 alpha SDH). In the thymus, the peanut agglutinin agglutinated cells (PNA+) lacked 20 alpha SDH and showed no detectable response to IL 2, IL 3, or GM-CSF in either proliferation or induction of 20 alpha SDH. In contrast, the PNA nonagglutinated (PNA-) subpopulation expressed 20 alpha SDH and proliferated in response to Con A and/or IL 2. The responding cells that could be expanded in vitro with IL 2 expressed high levels of 20 alpha SDH. Neither IL 3 nor GM-CSF in the presence or absence of Con A had a demonstrable effect on the PNA- population. In cultures of bone marrow cells, both IL 3 and GM-CSF induced proliferation, whereas IL 2 had no effect on proliferation in the presence or absence of Con A. Thy-1-depleted bone marrow cells, expanded in tissue culture with IL3, contained cells that co-expressed Thy-1 and 20 alpha SDH. In contrast, cells proliferating in vitro to GM-CSF did not expressed Thy-1 or 20 alpha SDH. In cultures of normal splenic lymphocytes, two populations of cells capable of expressing 20 alpha SDH were detected. One population could be expanded in vitro with IL 2 and Con A, whereas the second was responsive to IL 3. In spleens from athymic mice, only the latter cells were detected. These results demonstrate that IL 3 and IL 2 responsiveness distinguishes two populations of 20 alpha SDH cells. The relevance of these observations to the possible relationship of IL 3 and IL 2 in T cell differentiation is discussed.     

Synergy between spleen cells and bone marrow cells in mixed lymphocyte culture-induced cytotoxicity: Requirement for macrophages in the induction of synergy

Synergistic interaction between isogeneic spleen cells and bone marrow cells were induced during the in vitro generation of cytotoxic effector cells against alloantigens. The observed synergy occurs during the early sensitization period and not at the effector phase of cytotoxicity. The cytotoxic effector cells appear to be T cells provided by spleen cells. The synergizing cells are Thy-1-negative subpopulations of bone marrow cells have light to moderate densities on BSA gradient, and appear to interact with splenic T cells only in the presence of macrophages.