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P L Witte

Publications and source records attributed to P L Witte.

At least 19 recordsLinked to original sources
PubMed1995

Vascular cell adhesion molecule 1-positive reticular cells express interleukin-7 and stem cell factor in the bone marrow.

In vitro studies have defined an essential role for stromal cells in supporting B-cell development, including production of lymphopoietic cytokines. It has been suggested that stromal cells are equivalent to adventitial reticular cells in the marrow; however, evidence of reticular cells producing cytokines has been difficult to obtain. Staining of bone marrow (BM) sections with antibodies to interleukin-7 (IL-7) showed a reticular pattern, mimicking that obtained using antibodies to vascular cell adhesion molecule 1 (VCAM-1), a molecule present on both stromal cells in vitro and reticular cells. To more closely examine cytokine production within normal marrow, an immunomagnetic separation scheme was devised to directly enrich VCAM-1+ stromal cells. Twenty to thirty percent of cells isolated in the VCAM-1+ fraction shared characteristics with stromal cells from long term BM cultures, including cellular morphology and expression of alkaline phosphatase and alpha actin. These were termed "reticular stromal" cells. Immunohistochemical staining showed that virtually all of the latter cells possessed cytoplasmic IL-7 protein, and about half expressed stem cell factor. In contrast with cultured stromal cells, very few had detectable macrophage-colony-stimulating factor. These data constitute the first report of cytokine expression by marrow reticular cells in vivo. The implications of this data with respect to the existence of stromal cell subsets and their regulation of lymphopoiesis is discussed.

Actins↗
PubMed1995

Apoptosis and interleukin 7 gene expression in chronic B-lymphocytic leukemia cells.

mRNA for interleukin 7 (IL-7) was readily detected in leukemic cells immediately upon their removal from patients with chronic B-lymphocytic leukemia (B-CLL). IL-7 mRNA expression and IL-7 gene transcription were down regulated, however, when B-CLL cells were placed in culture at 37 degrees C for 4 hr. Down regulation of the IL-7 gene was prevented in cells maintained at 4 degrees C. Continued culture of B-CLL cells at 37 degrees C resulted in programmed cell death, or apoptosis, as evidenced by DNA fragmentation. The coincident kinetics of IL-7 gene down regulation and apoptosis suggested that IL-7 gene expression may be required for maintenance of CLL viability in vivo. Signals for IL-7 gene regulation and apoptosis induction were thus examined. Activation of normal B cells through their immunoglobulin receptors did not result in upregulation of IL-7 gene expression. Reagents required for CLL cell purification and culture also did not contribute to IL-7 gene regulation and apoptosis induction. IL-7 gene expression was retained and apoptosis was prevented, however, in CLL cells cultured on a monolayer of EA.hy926 human umbilical cord endothelial hybrid cells. Signals specifically presented by EA.hy926 cells supported both CLL cell viability and IL-7 gene expression, whereas culture of CLL cells on A549/8 carcinoma cells, the fusion partner used to generate the EA.hy926 cells, did not. Cell-cell contact was required, as culture supernatants did not prevent apoptosis. Specifically, IL-7 mRNA expression was retained and apoptosis was prevented only by contact with the endothelial cell hybrids. Preliminary data indicated that integrins expressed on CLL cells affected modulation of apoptosis and IL-7 gene regulation, suggesting that integrins may play significant roles in regulating viability of CLL cells.

Apoptosis↗
PubMed1994

Native associations of early hematopoietic stem cells and stromal cells isolated in bone marrow cell aggregates.

In suspensions of murine bone marrow, many stromal cells are tightly entwined with hematopoietic cells. These cellular aggregations appear to exist normally within the marrow. Previous studies showed that lymphocytes and stem cells adhered to stromal cells via vascular cell adhesion molecule 1 (VCAM1). Injection of anti-VCAM1 antibody into mice disrupts the aggregates, showing the importance of VCAM1 in the adhesion between stromal cells and hematopoietic cells in vivo. Early hematopoietic stem cells were shown to be enriched in aggregates by using a limiting-dilution culture assay. Myeloid progenitors responsive to WEHI-3CM in combination with stem cell factor (c-kit ligand) and B220- B-cell progenitors responsive to insulin-like growth factor-1 in combination with interleukin-7 are not enriched. We propose a scheme of stromal cell-hematopoietic cell interactions based on the cell types selectively retained within the aggregates. The existence of these aggregates as native elements of bone marrow organization presents a novel means to study in vivo stem cell-stromal cell interaction.

Animals↗
PubMed1993

Activity of stem cell factor and IL-7 in combination on normal bone marrow B lineage cells.

The production of B cells is regulated by soluble and cell contact signals presumably provided by bone marrow stromal cells. Among these is IL-7, a well characterized proliferative stimulus for a subset of pre-B cells. Stem cell factor (SCF), a stromal cell-derived cytokine with broad hemopoietic effects, has been reported to synergize with IL-7 to drive the proliferation and differentiation of B220- bone marrow cells into B220+ B cell precursors in long term culture. A subsequent report has cast doubt on this result by showing that SCF and IL-7 were incapable of producing mu+ pre-B cells after short term culture. Here, using the cell sorter to assure discrete separation of B220+ and B220- cells followed by soft agar culture to prevent interaction with accessory cells, we demonstrate that the combination of SCF and IL-7 does not stimulate the expansion or differentiation of B220- lymphoid precursors but can act synergistically in the clonal proliferation of B220+ cells.

Animals↗
PubMed1993

Cytokine production and heterogeneity of primary stromal cells that support B lymphopoiesis.

Many reports document that bone marrow stromal cells or their cytokine products can influence the formation of B cells in vitro. Most of this data comes from studies using lines or clones of stromal cells after multiple passage in culture, which could alter gene expression. Our aim in the present study was to determine which cytokines are produced by normal stromal cells under conditions that promote B lymphopoiesis. Primary cultured stromal cells were isolated on FACS from active Whitlock cultures. These cells proved to be relatively homogeneous in expression of cell surface antigens (CD44, VCAM-1, MECA10, and a molecule marked by hamster anti-mouse 8.28 monoclonal antibody). RNA from unselected Whitlock cultured adherent cells and sorted stromal cells from the same cultures were subjected to reverse transcriptase polymerase chain reaction to assess constitutive expression of several cytokine genes. Transcripts for interleukin-1 beta (IL-1 beta), IL-7, macrophage (M)-colony-stimulating factor (CSF), stem cell growth factor (SCGF), insulin-like growth factor 1 (IGF-1) and occasionally leukemia inhibitory factor were detected in RNA from intact cultures. Messages for IL-7, M-CSF, and SCGF were selectively contained within the isolated stromal cell fraction; whereas, IL-1 beta was found solely within the non-stromal cell fraction. IGF-1 was transcribed by both stromal cells and macrophages in Whitlock cultures. No evidence was found for constitutive expression of IL-1 alpha, IL-4, IL-6, or granulocyte-macrophage-CSF. This is in contrast to some reported stromal cell lines and clones. To determine if all primary stromal cells from active lymphopoietic cultures produced IL-7, the isolated cells were stained to reveal cytoplasmic IL-7 protein. A majority of the cells produced IL-7, but about 20% had no detectable IL-7 protein. Taken together, our results suggest that the primary stromal cells are a distinguishable cell type but functional subsets may exist. In regard to the differences in IL-7 production, the primary cell phenotype appears to mirror at least one division noted among the stromal cell lines.

Animals↗
PubMed1992

Enrichment of primary lymphocyte-supporting stromal cells and characterization of associated B lymphocyte progenitors.

Studies of Whitlock/Witte long-term bone marrow cultures have revealed the necessity of two cell types for B lymphopoiesis, a stem cell and the stromal cell. While a number of stromal cell lines exist they have been found to be heterogeneous with respect to cell surface marker expression and growth factor production. Separation and analysis of fresh bone marrow stromal cells is, therefore, necessary to understand the regulation of lymphopoiesis in vivo. Here we report the early stages of such studies. We demonstrate that stromal cells, as assessed by morphology and alkaline phosphatase reactivity after short-term culture, are enriched in cellular aggregates that can be separated from bone marrow suspensions. Stromal cells are present in aggregates at a frequency of one per thousand cells, whereas marrow from which the aggregates have been removed contains only one stromal cell per fifty-thousand cells. These aggregates are able to form Whitlock cultures from greatly reduced numbers of initiating cells, indicating that they contain culturable B lineage precursors as well as stromal cells capable of supporting B lymphopoiesis. The aggregates appear to be naturally formed and provide a means to examine native B cell precursor-stromal cell contacts. We find little evidence for sequestering of late-stage B cell precursors within the aggregates. Terminal deoxynucleotidyl transferase-positive cells, on the other hand, are approximately three times more frequent in bone marrow aggregates, suggesting close contact between very early B cell progenitors and stromal cells within the aggregates. The finding that stromal cells are enriched in cellular aggregates is an important first step in the ultimate isolation of these cells from marrow suspensions, which is vital to understanding stromal cell function in vivo.

Animals↗
PubMed1990

Further studies on growth factor production by the TC-1 stromal cell line: pre-B stimulating activity.

Adherent murine stromal cells support long-term in vitro lymphopoiesis or myelopoiesis dependent on the culture conditions used. A cell line, TC-1, isolated from long-term liquid murine marrow cultures under conditions approaching those permissive for lymphoid growth, has been found to produce an activity that acts synergistically with interleukin-3 (IL-3) or colony-stimulating factor-1 (CSF-1) to stimulate in vitro myeloid colonies, but which has no intrinsic colony-stimulating activity. We report here the presence of multiple growth factors in conditioned medium (CM) from the TC-1 line, including granulocyte-macrophage colony-stimulating factor (GM-CSF) (bioassay with antibody blocking and messenger RNA [mRNA] analysis), granulocyte CSF (G-CSF) and IL-4 (factor-dependent cell line bioassay), and CSF-1 (radioimmunoassay, mRNA) along with a pre-B cell inducing activity, which appears separate from these CSFs and segregates with the myeloid synergizing activity through anion exchange, sizing, and Conconavalin A chromatography. Because these activities are not yet purified to homogeneity, their identity or lack of identity remains an open question. Assays of TC-1 CM or cellular mRNA analysis have given negative results for IL-1, IL-2, IL-3, IL-6, and IL-7, and IL-6 does not stimulate pre-B cells in this assay. However, IL-4 and G-CSF do stimulate in vitro induction of pre-B cells from pre-B and B-cell-depleted Balb/C marrow and are present in CM by selective cell line assay. A monoclonal antibody to IL-4 that inhibited its pre-B inducing activity did not inhibit pre-B inducing activity of TC-1 CM. These data suggest the existence of a unique synergizing and pre-B inducing factor(s) in TC-1 CM. Given the known capacity of subliminal levels of growth factors to act synergistically, an alternate possibility is that these biologic phenomena represent the actions of low concentrations of growth factors acting synergistically and possibly associated with some core protein.

Animals↗
PubMed1990

Natural killer cells in the thymus. Studies in mice with severe combined immune deficiency.

The relationship between NK cell and T cell progenitors was investigated by using mice with severe combined immune deficiency (scid). Scid mice are devoid of mature T and B cells because they cannot rearrange their Ig and TCR genes. However, they have normal splenic NK cells. Thymus of scid mice, although markedly hypocellular, contains cells that lyse YAC-1, an NK-sensitive tumor cell. By flow cytometry, two populations of cells were identified in the scid thymus. Eighty percent of the cells were Thy-1+, IL-2R(7D4)+, J11d+, CD3-, CD4-, CD8- whereas the remaining were IL-2R-, J11d-, CD3-, CD4-, and CD8-. By cell sorting, all NK activity was found in the latter population, which is phenotypically similar to splenic NK cells. To determine if the thymus contains a bipotential NK/T progenitor cell, J11d+, IL-2R+ cells were cultured and analyzed for the generation of NK cells in vitro. These cells were used because they resemble 15-day fetal and adult CD4- CD8- thymocytes that are capable of giving rise to mature T cells. Cultured J11d+ thymocytes acquired non-MHC-restricted cytotoxicity, but in contrast to mature NK cells, the resulting cells contained mRNA for the gamma, delta, and epsilon-chains of CD3. This suggests that J11d+ cells are early T cells that can acquire the ability to kill in a non-MHC-restricted manner, but which do not give rise to NK cells in vitro. The differentiative potential of scid thymocytes was also tested in vivo. Unlike bone marrow cells, scid thymocytes containing 80% J11d+ cells failed to give rise to NK cells when transferred into irradiated recipients. Together these results suggest that mature NK cells reside in the thymus of scid mice but are not derived from a common NK/T progenitor.

Animals↗
PubMed1989

The xid mutation affects hemopoiesis in long term cultures of murine bone marrow.

Cells of the humoral immune system are particularly affected by a mutation at the X chromosome linked immunodeficiency disease (xid)locus. Although B cells are made in normal numbers, they fail to become phenotypically and functionally diverse. Consequently, poor antibody responses are mounted to certain types of Ag. There have been some indications that other types of hemopoietic cells may be influenced by the mutation and development of the humoral immune system is unusually dependent on the presence of T lymphocytes. We now describe an analysis of the lympho-hemopoietic environment studied with long term bone marrow cultures. Contrary to expectations, cultures initiated with cells from homozygous female or hemizygous male mice with the mutant allele established more quickly than normal. The accelerated initial growth pattern was clearly linked to the xid mutation. Artificial mixtures of marrow exhibited intermediate growth kinetics. Experiments with H-2 congenic and T6 chromosome marked cells did not reveal an intrinsic dominance of growth in nonadherent xid cells. Similar results were obtained with culture conditions which favored production of myeloid or lymphoid cells. These findings would be consistent with subtle changes in the bone marrow microenvironment resulting from the xid mutation. The pedigree of the mouse strains had a significant influence on lymphopoiesis in long term bone marrow cultures. Lymphocytes of BALB/c origin dominated over CBA/H background cells in cultures established from mixtures of the two, but this did not correlate with any functional deficiency in CBA/H stromal cells. In fact, establishment of an adherent layer was a rate-limiting step in initiating long term cultures and this could be achieved with a low dose inoculum of CBA/H marrow. Even more dramatic effects were found in hemopoietic cells from doubly defective C3H.nu/nu-xid mice. The bone marrow of these athymic animals contained normal numbers of granulocyte/macrophage progenitors. However, lymphoid cultures could not be reproducibly established with their cells and myelopoiesis was never observed in vitro. The relatively simple conditions which pertain in culture make it possible to appreciate effects of mutations and pedigree on hemopoiesis which are unremarkable in intact animals.

Animals↗
PubMed1988

Transcriptional regulation of mu and delta gene expression in bone marrow pre-B and B lymphocytes.

Newly formed B cells first express IgM and subsequently display IgD on the cell surface. This is an ontologically, as well as developmentally, regulated process because IgD is virtually absent on neonatal splenic B cells. In the present studies we have examined, by means of nascent RNA chain labeling, the relative levels of mu to delta gene transcription in bone marrow B cells, pre-B cells, and earlier progenitors of B cells. Pre-B cells were obtained from Whitlock-type long term cultures of bone marrow cells from normal and C.B17 scid mice. Both populations were found to transcribe the delta gene at very low but detectable levels. A similarly low level of delta transcription was found to occur in surface IgM-positive cells from both cultured and freshly isolated bone marrow B cells. In all populations analyzed, termination of the majority of polymerases occurred within a discrete 1-kb region located between the microM and C delta I exons. Analysis of steady state RNA indicated that long term cultured bone marrow cells from normal mice produced both 2.7-kb normal sized microM mRNA as well as 2.9-kb aberrantly spliced I mu-mRNA, whereas those from C.B17 scid mice contained only aberrant sized mu-mRNA. In contrast to these results, our previous findings with spleen cells obtained from both neonatal and adult animals showed that delta gene transcription occurs at a relatively high level. Therefore, it is possible that activation of regulatory signals that allow polymerases to progress beyond the termination site 3' of the microM exons may occur when newly formed B cells migrate from the bone marrow to the splenic environment.

Animals↗
PubMed1988

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.

Animals↗
PubMed1987

Lack of dendritic Thy-1+ epidermal cells in mice with severe combined immunodeficiency disease.

C.B-17 scid (severe combined immunodeficiency disease) mice were used to evaluate the relationship of dendritic Thy-1+ epidermal cells (EC) to T lymphocytes (deficient in scid) and to NK cells (replete in scid). Epidermis from scid mice was deficient in dendritic Thy-1+ cells as determined by immunofluorescent staining of epidermal whole mounts. Similarly, epidermal cell suspensions from scid mice failed to proliferate in response to Con A, as compared with epidermal cell suspensions from C.B-17 control mice. Transplantation of normal bone marrow into scid mice reconstituted morphologically identifiable dendritic Thy-1+ EC in whole mounts, as well as Con A responsiveness of EC suspensions, thus indicating that the deficiency in dendritic Thy-1+ EC in scid mice is at the precursor level. These studies demonstrate that Thy-1+ EC are more closely related to T lymphocytes than to NK cells.

Animals↗
PubMed1987

Characterization of B lymphocyte lineage progenitor cells from mice with severe combined immune deficiency disease (SCID) made possible by long term culture.

A single gene mutation results in near absence of B and T lymphocytes and their immediate progenitors in mice with severe combined immunodeficiency disease (SCID). However, long term culture conditions allowed rapid outgrowth of lymphocytes from SCID bone marrow suspensions, and this permitted their detailed analysis. The cells were judged to be committed to the B lymphocyte lineage on the basis of expression of the BP-1 antigen, as well as by the density and pattern of expression of other markers. Cultured SCID lymphocytes were indistinguishable from control BALB/c cells in terms of morphology, typing for 13 cell surface markers, and changes in cell surface antigen expression with time in culture. In contrast to cultures of normal cells, which always included IgM synthesizing cells, SCID lymphocytes rarely expressed mu heavy chains. Southern blot analysis demonstrated that at least the first Ig gene rearrangement step had occurred in most of the cultured cells. The patterns of JH gene rearrangements suggested that relatively limited population diversity existed in individual cultures of SCID and normal BALB/c marrow. In addition, there was evidence that abnormal Ig heavy chain gene rearrangements had taken place in lymphocytes from approximately 25% of the SCID cultures. These cells were distinguished by the absence of detectable JH gene segments. kappa light chain genes appeared to be unrearranged in SCID cultured lymphocytes. We conclude that the lymphopoietic microenvironments of SCID mice are probably normal, and the animals have infrequent progenitors of B cells. Aberrant or nonproductive IgH gene rearrangements may account for the absence of pre-B and B cells in SCID mice. This study demonstrates the usefulness of long term culture methodology for isolating rare subsets of non-transformed lymphoid cells from normal and genetically defective hemopoietic tissues.

Animals↗
PubMed1987

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

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

Animals↗
PubMed1986

Effects of 5-fluorouracil on B lymphocyte lineage cells.

The aim of these studies was to determine the sensitivity of B lymphocyte lineage precursor cells in mice to 5-fluorouracil (5-FU). Selective effects could be very helpful in dissecting precursor-product relationships between these and the rare multipotential stem cells from which they derive. Numbers and functions of particular types of cells were determined at intervals after a single treatment (3 mg) and, as expected, myeloid-committed stem cells were very severely affected. Day 8 spleen colony-forming cells (CFU-S) and colony-stimulating factor-responsive macrophage progenitors were reduced by 98% within 24 hr, whereas presumptive early stem cells (day 14 CFU-S) were much more resistant. B cells, which were probably recently formed in bone marrow and which are not thought to be actively dividing, were also 5-FU-sensitive, but perhaps less so than pre-B cells and immunoglobulin-negative lymphocytes bearing a B lineage marker. Approximately 5 wk were required for the normal cellular composition of marrow to return to normal. Transplantation of marrow from 5-FU-treated mice suggested that the slow regeneration of B lymphocytes might partially result from residual drug effects or damage to microenvironmental elements which are required for B lineage differentiation. Acute reductions of lymphocytes in the thymus were also documented, and the larger cells declined most rapidly and regenerated most slowly in that tissue. Of particular interest was the differential susceptibility of B cells in various lymphoid tissues to 5-FU. Whereas lymph node B cells were minimally affected, one-half of the splenic B cells disappeared within 48 hr of drug injection. Intrinsic differences in 5-FU sensitivity were confirmed by treatment of lymphocytes in vitro, and this suggests that particular B cell sets may be metabolically distinct. This drug should find additional experimental application in studies of B lymphocyte formation and functional heterogeneity.

Animals↗
PubMed1986

Development and ontogeny of hamster T cell subpopulations.

The Syrian hamster is unique among laboratory animals because products of class I MHC genes are monomorphic. Thus, this species may be a model in which to test the relationship between MHC polymorphism and the T cell antigen receptor repertoire. Recently, cytotoxic and helper T cell subpopulations have been distinguished on the basis of cell surface phenotype detected with monoclonal antibodies (mAb). We used these reagents (mAb 110 detects all peripheral T cells and mAb 38 detects cytotoxic T cells) to dissect and categorize thymic populations according to relative maturational status. The two mAb divide thymocytes into four subpopulations in the young adult. Two (110+ 38+, 110+ 38-) were peripheral-like and were housed in the medulla, exclusively; another subset (110- 38+) consisted almost entirely of TdT+ cortical thymocytes. The fourth subset (110- 38-), bearing neither marker, was heterogeneous and consisted mostly of medium-large-size thymocytes, including cells with an early phenotype (nuclear TdT+). Cells with the cortical phenotype proved to be the most sensitive to cortisone treatment, whereas those which expressed the medullary marker, 110, were most resistant. To ascertain the relationship between 110- and 110+ T lineage cells, we followed the appearance of the four thymic subpopulations during ontogeny of the hamster thymus. Adult-like thymic architecture (delineation of cortex and medulla) as well as the two 110- subsets were established before expression of 110 antigen was apparent in the thymus. However, lymphocytes bearing the 110 antigen were found in lymph nodes prior to thymus during ontogeny, concomitant with developing T cell function in peripheral tissue. This finding implies that cells lacking 110 antigen were exported from the thymus and subsequently acquired expression of the molecule in the periphery, and we suggest that acquisition of 110 antigen may be a stage of postthymic maturation. Although 110+ cells appeared to be the most mature subset by several criteria, all functional thymocytes of adults or neonates were not 110+. Thus, we conclude that the 110 marker is acquired after T cells reach functional maturity. Moreover, the response profile of isolated 38+ thymocytes was analogous to peripheral 38+ T cells, suggesting that the dichotomy of function detected with our mAb also occurs before acquisition of 110 antigen. We have modeled what is known about hamster T cell development into a hypothetical scheme.

Animals↗