The interaction of the Chrna5 D398N variant with developmental nicotine exposure

A single nucleotide polymorphism (SNP) in CHRNA5 (rs16969968, change from an aspartic acid [D] to asparagine [N] at position 398 of the human α5 nicotinic acetylcholine receptor subunit) has been associated with increased risk for nicotine dependence. Consequently, carriers of the risk variant may be at elevated risk for in utero nicotine exposure. To assess whether this gene-environment interaction might impact nicotine intake in developmental nicotine-exposed offspring, we utilized a mouse expressing this human SNP. D and N dams drank nicotine (100 μg/mL) in 0.2% saccharin water or 0.2% saccharin water alone (vehicle) as their sole source of fluid from 30 days prior to breeding until weaning of offspring. The nicotine (D Nic, N Nic) or vehicle (D Veh, N Veh) exposed offspring underwent a 2-bottle choice test between postnatal ages of 30 to 46 days. N Nic offspring consumed the most nicotine at the highest concentration (400 μg/mL) compared with all other groups. In contrast, D Nic offspring drank the least amount of nicotine at all concentrations tested. Nicotine-stimulated dopamine (DA) release measured from striatal synaptosomes was increased in D Nic offspring, while decreased in N Nic offspring relative to their genotype-matched controls. These data suggest that the α5 variant influences the effect of developmental nicotine exposure on nicotine intake of exposed offspring. This gene-environment interaction on striatal DA release may provide motivation for increased nicotine seeking in N Nic offspring and reduced consumption in D Nic offspring.

Distinct In Vitro Myelopoiesis is Dependent on the Self-Renewal of Hematopoietic Progenitors

Spleen and bone marrow (BM) have been shown to contain the progenitors of a novel dendritic-like antigen-presenting cell type (L-DC). These progenitors are also maintained in both long-term spleen cultures and co-cultures of spleen or BM over the stromal cell line STX3. We examined mouse foetal liver (FL), rich in hematopoietic stem/progenitor cells (HSC/HPC) after embryonic day (E) 12.5, for the presence of L-DC progenitors by testing their capacity to colonize STX3 and produce L-DC. E14.5 FL from wild-type C57BL/6J mice was found to colonize STX3 and produce L-DC for 28 days. By contrast, E14.5 FL from Ikaros Plastic mice gave only short-term production of low numbers of L-DC between 7 and 14 days of co-culture. The transient and weak production of L-DC by FL from Plastic E14.5 mice maps to the loss of self-renewal capacity amongst HSC. L-DC progenitors are, therefore, closely aligned with a subset of self-renewing HSC/HPC in FL.

The 5-HT1A receptor active compounds (R)-8-OH-DPAT and (S)-UH-301 modulate auditory evoked EEG responses in rats

Schizophrenics commonly demonstrate abnormalities in central filtering capability following repetitive sensory stimuli. Such sensory inhibition deficits can be mirrored in rodents following administration of psycho-stimulatory drugs. In the present study, male Sprague-Dawley rats were implanted with brain surface electrodes to record auditory evoked EEG potentials in a paired-stimulus paradigm, using 87 dB clicks delivered 0.5 s apart. Amphetamine (1.83 mg/kg, i.p.) produced the expected loss of sensory inhibition, as defined by an increase in the ratio between test (T) and conditioning (C) amplitudes at N40, a mid-latency peak of the evoked potentials. Also, the 5-HT(1A) agonist (R)-8-OH-DPAT caused a significant increase in the TC ratio at the highest dose studied (0.5 mg/kg s.c.), while the 5-HT(1A) antagonist (S)-UH-301 did not significantly affect the TC ratio at any dose studied (0.1-5 mg/kg s.c.). When administered with amphetamine, a lower dose of 8-OH-DPAT (0.1 mg/kg) and the highest dose of UH-301 tested (5 mg/kg, s.c.) were able to reverse the amphetamine-induced increase in TC ratio. The findings suggest that 5-HT(1A) signaling is involved in sensory inhibition and support the evaluation of 5-HT(1A) receptor active compounds in conditions with central filtering deficits, such as schizophrenia.

Development of dendritic cells from GM-CSF-/- mice in vitro : GM-CSF enhances production and survival of cells

The production of dendritic cells (DC) from haemopoietic progenitors maintained in long term stroma-dependent cultures (LTC) of spleen or bone marrow (BM) occurs independently of added granulocyte/macrophage colony stimulating factor (GM-CSF). The possibility that cultures depend on endogenous GM-CSF produced in low levels was tested by attempting to generate LTC from spleen and BM of GM-CSF-/- mice. Multiple cultures from GM-CSF-/- and wild type mice were established and compared for cell production. GM-CSF-/- LTC developed more slowly, but by 16 weeks produced cells resembling DC in numbers comparable to wild type cultures. LTC maintained distinct populations of small and large cells, the latter resembling DC. Cells collected from GM-CSF-/- LTC were capable antigen presenting cells (APC) for T cell stimulation and morphologically resembled DC. Large cells expressed the CD11b, CD11c, CD86, 33D1 and Dec-205 markers of DC. Addition of GM-CSF to GM-CSF-/- LTC increased the proportion of large, mature DC present in culture. Stromal cells from GM-CSF-/- LTC could support the differentiation of DC from early progenitors maintained in LTC without addition of GM-CSF. However, GM-CSF is not a critical factor in the in vitro generation of DC from progenitors. It can, however, substitute for stromal cells in increasing the survival of mature DC.

Improved FACS analysis confirms generation of immature dendritic cells in long-term stromal-dependent spleen cultures

Cells produced in spleen stroma-dependent long-term cultures (LTC) have now been clearly defined as dendritic cells (DC). Characterization of cells by antibody staining and FACS analysis has only been possible using a procedure to quench the high autofluorescence of DC produced in LTC (LTC-DC). The population of large cells produced by the established LTC-X1 culture are homogeneously positive for a number of cell-surface markers expressed by DC. These include CD11c, CD11b, Dec-205, Fc receptor and CD86. They also express markers detectable with the F4/80 and 33D1 antibodies. Cells produced in LTC do not uniformly express the MHC II marker, consistent with an immature DC phenotype. Most cells are weakly positive for MHC II with a small subset of highly positive cells. The quenching method involves staining cells with crystal violet dye, which is taken up within the cell. The importance of optimizimg fluorescent antibody staining assays for delineating DC subsets is indicated and the LTC system is established as a valuable and continuous source of DC precursors.

Identification of progenitor cells in long-term spleen stromal cultures that produce immature dendritic cells

Dendritic cells (DC) are produced continuously by a unique, long-term culture (LTC) system in which hemopoiesis is supported by a splenic stromal cell layer in the absence of added growth factors. Flow cytometric analysis reveals the production of two distinct cell subsets. The more predominant large-cell subset resembles highly endocytic DC that are large, granular, and possess membrane extensions. They also express high levels of the DC markers CD11c, CD11b, DEC-205, and CD80 on their cell surface. They do not resemble mature DC because they express low levels of MHC type II and CD86 molecules, as well as c-kit and Fc receptor (FcR). These are known characteristics of immature DC. Small cells are smaller and less granular than large cells, with negative to low expression of CD11c, DEC-205, and CD86. A majority of small cells express varying levels of CD11b and CD80. Subpopulations of small cells express low levels of c-kit, FcR, and MHC type II, and only a 20% subpopulation is weakly endocytic. Upon transfer to an irradiated stromal layer, cells within the small subset proliferate and differentiate to resemble the large cells in size, complexity, membrane extensions, and CD11c and CD86 expression. The two cell subsets produced in LTC are developmentally linked, with the heterogeneous small-cell subset containing progenitors of the larger homogeneous, immature DC subset. LTC represent a valuable model system for studying DC development from hemopoietic progenitors.

Review: the application of dendritic cell-derived exosomes in tumour immunotherapy

Cancer arises from the aberrant proliferation of a single transformed cell. This population acquires the ability to metastasis. An effective way to remove cancer cells from the body is to activate tumour-specific cytotoxic T cells (CTL). Activation of naive T cells depends on the unique antigen presenting capacity of DC. Activated tumour antigen-specific CTL can destroy cancer cells without harm to normal tissue. Their ability to stimulate antigen specific T cell responses makes DC attractive candidates to potentiate anti-tumour immunity. Several studies have demonstrated the efficacy of DC based anti-tumour immunotherapy and the goal now is to optimise immune responses induced by DC, so that effective strategies in treating cancer may be realised. One way to do this is to identify DC characteristics which make them more effective in T cell stimulation. Another is to use exosomes, the antigen presenting vesicles secreted by DC, in order to induce potent anti-tumour immune responses. The non-cellular nature of exosomes offers several advantages for use in tumour immunotherapy.

Proliferation of dendritic cell progenitors in long term culture is not dependent on granulocyte macrophage-colony stimulating factor

A unique long term culture (LTC) system has been developed which supports the production of dendritic cells (DC). Cell production is dependent on a stromal cell layer derived from murine spleen. This LTC system produces a high turnover of non-adherent cells that express DC morphology, cell-surface markers, and antigen-presenting capacity.

OBJECTIVE

The long term production of these cells suggests that the LTC system supports hemopoiesis. It was of interest to examine the number and nature of hemopoietic progenitors present in LTC.

MATERIALS AND METHODS

A combination of approaches, including FACS analysis, spleen colony-forming unit assays, and in vitro colony assays were undertaken.

RESULTS

Pluripotent haemopoietic stem cells are not detectable among the non-adherent cell population produced in LTC. Instead, LTC support a replicating c-kit+ progenitor population, which generates only dendritic-like colonies in in vitro colony assays. In addition, this population does not respond to combinations of growth factors thought to stimulate DC proliferation, including granulocyte macrophage-colony stimulating factor (GM-CSF) and Flt3L. Production of DC occurs only in the presence of LTC-derived culture supernatant or a confluent stromal cell layer.

CONCLUSIONS

These results suggest that LTC contain a dendritic progenitor that is dependent upon the stromal cell network for proliferation and differentiation. The development of only DC within LTC allows easy collection of cells for experimentation. This, in combination with the fact that DC development occurs in the absence of exogenous growth factors, makes the LTC system a practical model for the study of DC function and development.

Long-term stroma-dependent cultures are a consistent source of immunostimulatory dendritic cells

A long-term culture (LTC) system has been established that supports the continuous production of dendritic cells (DC) from haemopoietic cells present in the culture. The production of cells depends on the presence of an intact stromal cell layer containing a mixture of fibroblasts and endothelial cells. Cells are shed from foci of dividing cells in contact with the stromal cell matrix. They resemble DC in terms of morphology and cell surface marker expression. The LTC can be derived from different lymphoid tissues, but most success has been achieved with murine spleen. Different LTC vary in capacity to produce immunostimulatory DC. Some LTC produce DC that are very effective APC and can stimulate both mixed lymphocyte and antigen-specific T cell responses. The DC produced in others are weak APC. Different LTC appear to produce DC reflecting different stages of maturation or development, reflected by different phenotypic and functional characteristics. The production of cells within LTC occurs independently of added cytokines and is dependent on maintenance of the stromal cell layer and the presence of a subset of smaller progenitor cells. Long-term cultures remain a valuable source of cells for study of DC development and function.

Immunotherapeutic potential of dendritic cells generated in long-term stroma-dependent cultures

Long term cultures (LTC) producing dendritic cells (DC) have been established from spleen. A well developed stromal cell layer supported production of DC in numbers suitable for experimentation. Cells had obvious membrane pseudopodia and could be collected from culture every 2-3 days. Large cells produced in LTC stained with fluorescently labelled monoclonal antibodies specific for DC such as 33D1, and M1/70 which is specific for DC and myeloid cells. These staining patterns confirmed the presence of DC within the LTC population. LTC-DC were tested and shown capable of migration in vivo in B10.A(2R) mice following footpad inoculation. Most cells entered the spleen and a small number entered popliteal lymph node. LTC-DC have migratory capacity comparable with control spleen lymphocytes. LTC-DC were tested for capacity to induce an anti-tumour immune response after exposing cells to tumour cell membranes. LTC-DC pulsed with BL/VL3 tumour antigens were able to induce a BL/VL3-specific primary cytotoxic T lymphocyte (CTL) response detectable in popliteal lymph nodes and spleen of C57BL/6J mice within 6 days of priming. BL/VL3 tumour cells grew in sublethally irradiated C57BL/6J mice giving 100% mortality. Adoptive transfer of spleen cells from mice given BL/VL3 antigen-pulsed LTC-DC, two weeks previously, significantly slowed the growth of BL/VL3 tumour cells in mice. DC produced in LTC can function as antigen presenting cells (APC) when adoptively transferred into animals. Their capacity to migrate effectively, to induce a CTL response and to reduce tumour load suggests that DC grown using this in vitro system may have valuable clinical potential in humans.

Hemopoiesis in long-term stroma-dependent cultures from lymphoid tissue: production of cells with myeloid/dendritic characteristics

A long-term stroma-dependent culture system (LTC) has been developed which continuously produces hemopoietic cells providing an in vitro system for the study of cell differentiation. These nonadherent cell populations contain a large subpopulation of dendritic cells (DC). LTC producing DC were easily generated from spleen, but could also be established from bone marrow (BM) and lymph node with less success. It was difficult to establish DC-producing LTC from thymus. The properties of splenic and thymic stroma have been compared. Spleen stroma developed more complicated networks of fibroblasts, endothelial cells, macrophages, and DC. Thymic stromal monolayers were dominated by epithelial cells and fibroblasts, with a lower proportion of macrophages and endothelial cells. They had a relatively sparse structure of cell networks compared with spleen stroma. Cells with dendritiform morphology first appeared in cultures by 2-3 wk. The majority of cells produced were large cells which expressed DC-specific cell surface markers, major histocompatibility complex (MHC) Class II molecules, and the CD80/CD86(B7) costimulator. A high proportion of cells also expressed myeloid cell markers. No T or B lymphoid cells or granulocytes were present in the cultures. LTC continued to produce nonadherent cells resembling myeloid/DC for long periods, even after passage of stromal cells and stem cells at about 3-4 mo. after culture establishment. The LTC system offers potential to study the in vitro differentiation of myeloid/DC.

Long-term stromal cultures produce dendritic-like cells

A stromal cell-dependent long-term culture (LTC) system has been developed from spleen which continuously generates non-adherent cells with dendritic cell (DC) characteristics. Bioassays using factor-dependent cell lines have revealed that both spleen and thymic stromal cultures secrete interleukin (IL)-3 and IL-6-like growth factors. Conditioned medium from LTC also contains factors which appear to be unrelated to IL-3 and induces growth of stromal cells from bone marrow. Non-adherent cells generated in LTC were not T or B lymphoid cells or granulocytes, nor were mast cells detectable. Morphological and electron microscopic examination has also excluded the presence of macrophages (Mo). Cells with DC morphology have been detected by both light and electron microscopy. The majority of cells in the non-adherent population were found to have multiple membrane pseudopodia, with a small acentric nucleus. These appear to be the precursors of DC. They expressed cell surface markers detectable with DC-specific antibodies and antibody specific for major histocompatibility complex Class II molecules. A proportion of cells also expressed myeloid markers, but since this expression was not supported by histochemical staining for myeloperoxidase or non-specific esterase, it was concluded that the cells produced are not typical of the myeloid lineage. Cells generated in LTC were shown to be potent stimulators for allogeneic and syngeneic MLR and for antigen-specific T-cell proliferation.

The role of dendritic cells in T cell activation

Dendritic cells (DC) are distinguishable from other antigen-presenting cells by their potent antigen-presenting capacity. They are not only efficient at presenting peptide antigen but can also process and present soluble protein antigen sto antigen-specific T cells and cloned T cell lines. They are very strong stimulators of both allogeneic and syngeneic mixed lymphocyte reactions and have a unique capacity to stimulate naive T cells. The potent functional capacity of DC is related to a high-level expression of major histocompatibility complex class I/II molecules and constitutive expression of costimulatory molecules, such as CD80/CD86, as well as heat stable antigen, CD40 and the leucocyte function antigen (LFA) family of adhesion molecules. Recent studies have shown that DC are also involved in regulation of the immune response via induction of both central and peripheral tolerance.

Specific transcription of the unrearranged TCR V beta 8.2 gene in lymphoid tissues occurs independently of V(D)J rearrangement

A truncated T cell receptor (TCR) V beta 8.2 polypeptide expressed on the surface of a precursor lymphoid cell line and on a subset of mesenteric lymph node cells has previously been shown to be encoded by transcripts from unrearranged V beta 8 genes. Germline V beta 8 transcription has now been demonstrated in multiple lymphoid and non-lymphoid tissues in mice of varying ages and in cultured cell lines by reverse transcription-polymerase chain reaction (RT-PCR). Significant levels of V beta 8 germline transcription were found in thymus, spleen, liver and bone marrow and in all lymphoid cell lines studied. Germline V beta 8 transcription in the liver dropped as mice aged, and increased in the bone marrow. Germline V beta 8 transcription was also detectable in thymus, spleen, liver and bone marrow of RAG-1-/- mice. This indicated that it is not dependent upon the presence of mature lymphoid cells, nor necessarily related to V(D)J rearrangement events. Semi-quantitative polymerase chain reaction (PCR) and hybridization with oligonucleotides specific for V beta 8.1, 8.2 and 8.3 showed that the V beta 8.2 gene produced at least 90% of all the germline V beta 8 transcripts in all of the tissues examined. The significance of these results in lymphoid cell development and for models of the regulation of V(D)J rearrangement are discussed.

Association of repeat sequences with integrated retroviruses in a murine leukaemia cell line

An analysis was made of the retroviral integration sites for retroviruses in a murine lymphoid precursor cell line, C1-V13D, derived following in vitro infection with RadLV, an ecotropic murine retrovirus. A genomic library was constructed and lambda clones were selected for their capacity to hybridize with the specific RadLV gp70 ecotropic env probe. Analysis of these clones by a combination of approaches, including subcloning, partial restriction mapping and sequencing, has confirmed the existence of multiple recombinant and defective viruses in C1-V13D. To check for the presence of coding sequences in flanking genomic DNA, 32P-labelled cDNA from C1-V13D was used to probe HindIII- and Psti-digested virus-positive lambda clones by Southern analysis. Regions hybridizing specifically with 32P-labelled C1-V13D cDNA were subcloned and analysed. A notable feature of these cDNA+ regions was the frequent presence of B1, B2 and simple repeats. These repeat elements were found to be present in high frequency in the genomic regions flanking the proviruses, in numbers higher than expected for the genome as a whole. All full-length viruses isolated appeared to represent integration events into regions rich in repeat elements. Some B1 and B2 repeats have been shown to code for functional proteins and to play regulatory roles. Viral integration in the vicinity of these genetic elements could contribute to oncogenesis if the integration event were to disrupt normal gene function.

Germline transcription and expression of Tcrb-V8 genes in peripheral mouse lymphoid tissues

Germline transcription of the Tcrb-V8.2 gene has been recently shown to occur in a lymphoid precursor cell line and to result in weak expression of an aberrant T-cell receptor (Tcr) beta chain on the cell surface. An investigation into the expression of a similar Tcr structure in normal lymphoid sites has involved antibody staining and sorting to identify a minor subset of Tcr-Vbeta+ Cbeta- cells in mesenteric lymph node and thymus. These cells have been analyzed by reverse transcriptase-polymerase chain reaction for the presence of transcripts encoded by bV8 genes in rearranged vs germline configuration in subsets of cells sorted on the basis of Tcrb-V8 and Tcrb-C gene expression. Germline transcripts were found in the Tcr-Vbeta- Cbeta- subset of cells in bone marrow, thymus, and mesenteric lymph node. They were also found to be present in the Tcr-Vbeta8(+) Cbeta+ subset of cells in thymus and mesenteric lymph node. Cells in the Tcr-Vbeta8(+) Cbeta- subset of mesenteric lymph node contained germline but no rearranged bV8 transcripts. The same thymus subset expressed high levels of both rearranged and germline bV8 transcripts. The presence of germline bV8 transcripts in Tcr-alphabeta- cells in bone marrow and mesenteric lymph node suggests that germline Tcrb-V8 gene transcription is unrelated to the differentiation of mature T cells. The possible function and significance of the expression of a truncated Tcr beta chain is discussed.

Expression of a TCR V beta 8.2 polypeptide from the unrearranged gene in a murine lymphoid precursor cell line

The TCR in a mature T cell is a multimeric complex of TCR alpha and beta chains, and CD3 subunits. Functional TCR alpha and beta chains are encoded by genes that result from developmentally controlled somatic rearrangement events. By FACS analysis, we have detected a TCR V beta 8 protein on the surface of an immature lymphoid cell line, C1-V13D, that has all of its TCR genes in germline (unrearranged) configuration. RNA blot analysis detected a 1.4 kb polydenylated V beta 8 RNA in C1-V13D cells, but no expression of C beta was detected. Rapid amplification of 3' cDNA ends was used to clone an RNA that was initiated from the leader exon of the V beta 5.1 gene and spliced to the V exon of the V beta 8.2 gene. The putative sequence of the mature 10.8 kDa protein was entirely encoded by the V beta 8.2 exon. RT-PCR analysis confirmed that 97% of the V beta 8 RNA detected in C1-V13D cells was encoded by the V beta 8.2 gene, and only 3% by V beta 8.1 and V beta 8.3 genes. Furthermore, most of the V beta 8.2 RNA was spliced to the leader exon of the V beta 5.1 gene and not to the leader exon of the V beta 8.2 gene. The implications of preferential transcription from particular germline TCR genes for repertoire diversity and possible functions for proteins translated from germline TCR V beta genes are discussed.

Leukaemogenic progression: the importance of differentiation and associated genetic events

A feature common to many blood cell cancers is the uncoupling of normal proliferative and differentiative events, both of which are intimately linked in the cell's developmental programme. In some cancers, further differentiative events have been associated with oncogenic progression and, in other cancers, terminal differentiation of cells has been shown to result in reversal of malignancy and death of the cancer cell. Clearly the development of cancer is not the result of a single oncogenic event, but rather a myriad of events which appear to proceed in concert in a step-wise fashion and which are likely to be influenced by the cellular environment. Here we review some of the major genetic changes which occur in leukaemogenesis and discuss the possible role of differentiative events in the development of leukaemia.

Induction of leukemia in mice using a radiation leukemia virus-induced cell line: a model system for studying oncogenic progression

Leukemogenesis induced by slowly transforming retroviruses is a multistep process which is difficult to dissect because of its long latency and the problem of distinguishing oncogenic from differentiative events. A method for leukemia induction in mice has been developed using a cell line isolated following in vitro infection with the slowly transforming murine radiation leukemia virus (RadLV). The CI-V13D cell line represents a lymphoid precursor cell type at an early stage in cell transformation and can develop subcutaneous tumors in irradiated syngeneic hosts but not in allogeneic mice even after sublethal irradiation. Selective growth in allogeneic (CBA/H) mouse thymus has been demonstrated, but this requires preirradiation of the recipient. Upon reisolation from CBA/H thymus, C1-V13D progeny clones displayed increased tumorigenic potential in comparison to the 'parental' CI-V13D cell line. Tumorigenicity was shown to increase with serial passage through thymus and electron micrographs of clones also revealed increased production of C-type retroviruses. This new model for oncogenic progression should be more amenable to analysis of early genetic changes occurring during replication of leukemia in the thymus.

Analysis of oncogenic progression in a radiation leukemia virus model

The mechanism by which non-oncogene-bearing, slowly transforming retroviruses induce leukemia is not well understood, but appears to represent a multi-step process. Cell lines have been isolated following in vitro infection of lymphoid cells with radiation leukemia virus (RadLV) and they have been used to develop a two-step model for leukemia development. Thymic tumors were induced when one of the cell lines, C1-V13D, was inoculated into CBA/H mouse thymus. Upon reisolation of C1-V13D cells after one, two and three passages through thymus, individual cloned cell lines displayed increased tumorigenic potential compared with the non-tumorigenic parental line. Southern analysis has been used to track any genetic changes occurring while cells undergo further transformation and become increasingly tumorigenic. Specifically, retrovirus integration has been monitored in clones derived from C1-V13D at the primary, secondary and tertiary passage through thymus using probes specific for long terminal repeat (LTR), gag, pol and env genes of RadLV. The data indicate multiple ecotropic retrovirus integration sites in C1-V13D cells. Primary thymic tumors also showed the integration of a new recombinant or defective virus. There was no evidence that new ecotropic retrovirus integration had occurred during subsequent passage of primary tumors through the thymus, i.e. during the progression to oncogenesis. All data indicate an important role for the thymic environment in the development of a fully transformed cell.

The lineage relationship of dendritic cells with other haematopoietic cells

The lineage relationship of dendritic cells with other haematopoietic cells and within the broader class of dendritic cells is not well understood. Dendritic cells in different tissue sites and having slightly different characteristics all play a specialized role in maintaining self tolerance by the endocytosis and presentation of antigens within their environment. Recent evidence now suggests a possible lineage relationship between T cells and lymphoid dendritic cells and appears to conflict with the view that dendritic cells have a common origin with myeloid cells. One possibility is that dendritic cells mature in different tissue sites from bone marrow-derived precursors and develop region-specific characteristics which could reflect lineage differences.

Growth regulation of a T-cell lymphoma via the T-cell receptor

Autocrine stimulation is described for a Radiation leukaemia virus (RadLV)-induced T-cell lymphoma, C6VL/1. The proliferation of this tumour cell line can be regulated by several agents, including interleukin-2 (IL-2), antibodies to the IL-2 receptor and the T-cell antigen-specific receptor (TCR), as well as RadLV retrovirus particles produced by the cell itself. This information has been gained using various procedures to slow or arrest C6VL/1 proliferation, including the addition of gamma interferon (gamma-IFN) and cell culture at low density. All data suggest that these cells can receive growth stimulation via the T-cell receptor (TCR) and IL-2 receptor, implicating autocrine stimulation of growth involving IL-2 and retroviral gene products.

T-cell differentiative capacity of haematopoietic stem cells immortalized in vitro with radiation leukemia virus

The differentiative capacity of a unique haematopoietic cell type has been investigated. These cells have been found to be a common target in vitro to infection and immortalization by radiation leukemia viruses (RadLVs). Many continuous lines of these cells have been generated. Since RadLV retroviruses are known to be strictly T-cell-tropic in vivo, we have questioned whether these cells are precursors of T cells. To this end, the RadLV-induced C1-V13D cell line has been inoculated into thymus of sublethally irradiated syngeneic CBA/H mice and tested for capacity to proliferate and differentiate, i.e. express T-cell markers. When inoculated in high number, C1-V13D cells can induce a thymic tumour within 14 to 21 days. Expression of T-cell markers on these cells was determined by fluorescence-activated cell sorting (FACS) analysis, after gating out C1-V13D cells on the basis of their high 90 degree scatter and their high forward scatter. They can also be distinguished by their unique expression of RadLVgp70 envelope (env) protein, B220, CD44, and aberrant expression of a class I epitope. Explanted primary thymomas from many animals showed no evidence of T-cell marker expression on C1-V13D cells upon reisolation. However, when C1-V13D was further passaged intrathymically, there was clear expression of Thy-1, CD4, CD8, and TCR-alpha beta on C1-V13D cells reisolated from these tumours. Two-colour FACS analysis and fluorescent antibody staining have confirmed the acquisition of T-cell surface markers by C1-V13D cells growing in this environment. Northern analysis confirmed endogenous expression of T-cell receptor beta chain genes in C1-V13D cells isolated after the third passage. All data indicate that RadLV preferentially infects a unique haematopoietic precursor cell in spleen which can differentiate along the T lineage once located within the thymic environment. The cell lines described here represent valuable models for studying T-cell differentiation from lymphoid stem cells, and for dissecting the early events in leukemogenesis.

Characterization of unique lymphoid cells derived from murine spleen which constitutively produce interleukin-6

Attempts have been made to isolate continuous lines of rare subsets of lymphoid cells present in murine spleen in order to analyse their function and lineage relationship with respect to other lymphoid cells. Mitogenic stimulation was used to expand the lymphoid cells remaining in spleen following depletion of CD4+ and CD8+ T cells by antibody and complement treatment. Cells were cultured in the presence of concanavalin A (Con A), interleukin-2 (IL-2) and syngeneic irradiated spleen feeder cells. This procedure expanded a population of non-T-, non-B-lymphoid cells bearing a common, unique phenotype resembling lymphoid precursors. Eight cloned lines from B10.A(2R) and B10.A(5R) strains of mice have been analysed here. Analysis of cell surface marker expression has revealed positive expression of class I and class II major histocompatibility complex (MHC) antigens, CD44, CD45 (T200 and B220) but expressing no markers unique to T, B or myeloid cells. All cell lines represent agranular lymphoblasts and show no evidence of early T-cell receptor (TcR) or Ig heavy chain gene rearrangements, suggesting no commitment to T-or B-lymphoid lineage. Despite expression of the NK1.1 marker for natural killer (NK) cells, none of the cell lines has been shown to have cytotoxic function for NK targets, nor could cytotoxic function be induced following various activation procedures. Analysis of lymphokine production has revealed no detectable IL-1, IL-2, IL-3, IL-4, IL-5, tumour necrosis factor-alpha (TNF-alpha) or granulocyte-macrophage colony-stimulating factor (GM-CSF) in cell supernatants. However, all but one of these cell lines constitutively produce IL-6. Each cell line has been shown to induce T-cell proliferation independently in mixed lymphocyte reactions, implicating the capacity of these cells to act as antigen-presenting cells. Consistent with this hypothesis is the observation that these cells also demonstrate endocytic activity for foreign proteins. This was visualized by their uptake of fluoresceinated albumin into cytoplasmic granules. Since they express many cell surface markers common to described isolates of spleen dendritic cells, including both class I and class II major histocompatibility molecules, they would appear to represent the first example of continuous lines of this rare cell subset.

A murine retrovirus induces proliferation of unique lymphoid cell lines expressing T-cell-receptor structures utilizing common variable region alpha and beta chain genes

A murine radiation leukemia virus (RadLV) has been shown to induce in vitro proliferation of an unusual subset of lymphoid cells from spleen. They have the unusual property of expressing CD3/T-cell receptor alpha and beta chains (TCR-alpha beta) in the absence of other T-cell markers such as Thy-1, CD4, and CD8. Cell lines induced in two mouse strains with RadLV produced by the C6VL/1 thymoma all specifically utilize common V alpha 3 and V beta 8.2 variable region genes in the formation of a TCR structure. Each of these cell lines has now been found to express both class I and class II major histocompatibility antigens and the beta 2 integrin specific for spleen dendritic cells. Analysis of functional properties of these cells has revealed a subset that can endocytose proteins and function alone as antigen-presenting cells. They have therefore been called D-T cells (i.e., dendritic cells expressing TCR-alpha beta). A retroviral-driven event has been implicated in the proliferation of dendritic-like cells expressing a common TCR epitope.

A gamma model for extra-binomial variation in dilution assays

Dilution assays are widely used to estimate the concentration of a particular type of cell, called a limiting cell, in a population of cells from an animal. For each animal, the response vector is a set of binomial variables derived at different plating frequencies. Often extra-binomial variation is found when dilution assay data are analysed. This paper proposes a mixture model where the animal level effects are assumed to have a gamma distribution. This leads to more realistic standard errors for the estimates of the limiting cell concentrations.

Proliferation of the BCL1 B cell lymphoma induced by IL-4 and IL-5 is dependent on IL-6 and GM-CSF

Lymphokine requirements for the in vitro proliferation of the spleen-dependent B cell lymphoma BCL1 have been analysed. Cells were found to respond by proliferation to added recombinant (r) interleukin-4 (IL-4), r-IL-5 and recombinant granulocyte-macrophage colony-stimulating factor (r-GM-CSF). Inhibition by antibodies specific for each of these lymphokines has confirmed growth factor-dependent growth. Anti-GM-CSF has, however, been found to inhibit the proliferation of BCL1 cells induced by r-IL-4 and r-IL-5, as well as r-GM-CSF, suggesting that BCL1 cells may express receptors for GM-CSF and that GM-CSF may be able to act synergistically with IL-4 and IL-5 in promoting cell proliferation. Anti-IL-6 antibody was also found to be a very effective inhibitor of BCL1 proliferation induced by either IL-4 or IL-5 but not by GM-CSF. Added IL-6 did not stimulate BCL1 proliferation, suggesting that endogenous IL-6 may regulate the autocrine growth of BCL1 cells. BCL1 cell proliferation in vitro appears to be regulated by interactions between multiple growth factors.

Lymphoid precursor cell lines have capacity to migrate to multiple lymphoid sites

Cell lines have been isolated which phenotypically resemble natural killer (NK)/lymphoid precursor cells. These cell lines were derived by in vitro culture and represent continuously replicating cell lines. Since they do not grow as tumours in vivo, it was anticipated that they may have maintained the migratory capacity of their normal cell counterpart. Capacity to migrate to various lymphoid sites, i.e. spleen, bone marrow, thymus and mesenteric lymph node, has been analysed in a short-term 3-hr homing assay following intravenous injection of cells into a syngeneic irradiated host. Frequency of cells localizing in these organs was estimated by limit dilution cloning analysis. Three out of four cell lines were found to migrate to all four organs, while the C6VL/1 T-cell lymphoma was detected in spleen and bone marrow only, and did not enter thymus and mesenteric lymph nodes. This suggests that NK/lymphoid precursor cells may exist which have capacity to recirculate widely through the lymphoid system.

The diversity of retroviral diseases of the immune system

Retroviruses have been implicated as causative agents for a range of diseases including neoplasia, autoimmunity and immunosuppression. No two retroviruses carry the same complement of genes and for this reason it is not surprising that they induce a variety of different disease states. One common element in retroviral evolution has been the need to avoid immune recognition in order to persist within the host. A comparative approach, looking at various persistent retroviruses, has been used to pin-point the types of genetic adaptations adopted by retroviruses to remain hidden, often within the T cell compartment. Most of these retroviruses are T-cell-tropic and the diseases which they induce usually reflect the effect of the retrovirus on normal lymphocyte function.

Lymphocyte recirculation: the need for site-specific receptors to dictate T-lymphocyte localization into different tissue sites

This paper addresses the need for receptors involved in recirculation of T lymphocytes both during development and during an immune response or inflammation. Some known receptors present on T lymphocytes which are important in maintaining normal T-cell localization and function, i.e. the integrins, LECAMs, LPAM-1 and H-CAM (CD44) are considered in terms of the specificity which they confer on lymphocyte recirculation. A clear understanding of lymphocyte trafficking patterns and of the receptors involved may provide, for example, novel therapies for treatment of malignant cancer, alleviation of damage caused by lymphocytes during inflammatory responses, and targeting of cells to sites of infection.

Unique lymphoid cell subset target to infection and proliferation induced in vitro by a murine leukemia virus

The mechanisms by which non-oncogene bearing, slowly transforming T-cell-tropic retroviruses induce leukemia is not well understood. Viruses such as the murine radiation leukemia virus (RadLV) induce oncogenic transformation of T-cells in the thymus only in vivo and after a long latency. The capacity of RadLV to induce proliferation of lymphoid cells in vitro has been analysed here as a first attempt at mapping oncogenic transformation. Autonomously replicating cell lines have been isolated following exposure of splenic lymphocytes to two different isolates of RadLV, following in vitro culture in the presence of T-cell growth factors. Cells of similar precursor lymphoid morphology and phenotype have been isolated and cloned from cultures established from different animals. These cell lines all grow independently of exogenous growth factors in vitro, but are not tumorigenic in mice. Exposure to RadLV under the culture conditions provided has allowed integration of a new retroviral genome into each cell line, but no active replication of virus has been detected in any of the cell lines analysed. A common cell type resembling a lymphoid precursor has been induced to proliferate. These cell lines express cell surface markers attesting to their bone marrow origin, such as CD44 (Pgp-1), Gr-1, B220 and NK1.1, but they do not show the characteristics of T cells which have undergone differentiation within the thymus. They do not express the Thy-1 marker, nor show rearrangement involving any of the T-cell receptor (TCR) alpha, beta gamma or sigma genes. These cells bind several antibodies specific for the CD3-epsilon and TCR-alpha beta structures, and there appears to be aberrant expression of TCR proteins in cells bearing fully rearranged TCR genes. Precursor lymphoid cells and not mature T-cells in spleen, appear to be appropriate targets for RadLV-induced proliferation/immortalisation in vitro. Oncogenic transformation induced by RadLV in vivo may occur within precursor lymphoid cells and must be a complex process dependent on both the differentiation events which occur within the thymus, as well as the thymic environment of stromal cells.

Characterization of lymphoid cell lines from murine spleen which can localize in thymus

Several murine lymphoid cell lines have been tested for specific capacity to localize in thymus. These are all continuous, cloned Radiation leukemia virus-induced cell lines which have a common phenotype resembling lymphoid stem cells or immature T cells. Since each of these cell lines has a cloning efficiency approaching 100%, the number of cells which enters thymus during a 3 h homing assay has been estimated by limit dilution cloning analysis taking into account extra-binomial variation caused by individual mice. Only two out of seven of these cell lines have been found to have this specific property. These two cell lines, 16C1 and 5C2B, have been characterized as immature lymphoid cells, bearing no rearrangement at the TCR gamma and beta loci, and having the phenotype of CD3+CD4-CD8-, immature T cells. A maximum number of 2000 16C1 cells and 2500 5C2B cells can enter thymus during a 3 h homing assay, suggesting a limited number of sites in thymus to which these cells can bind. The capacity of 16C1 to enter thymus in low frequency has been found to be a stable property and was not increased by repetitive passage through mouse thymus. Using this assay, we have also been able to confirm that entry of 16C1 cells into thymus can be inhibited by antibody specific for the Ly24 (Pgp-1) molecule.

Radiation leukemia virus-induced T-cell lymphomas with common T-cell receptor variable region structure and similar binding specificity for retrovirus

The 5C2 cell line was derived following culture of mouse spleen cells exposed in vivo and in vitro to radiation leukemia virus (RadLV) containing supernatants from the C6VL/1 T cell lymphoma. This cell line has been found to express an alpha beta T-cell receptor (TCR) identifiable with the Mab124-40 anti-clonotypic antibody which is specific for C6VL/1. It has been shown to be genetically and phenotypically distinct from C6VL/1 with a unique phenotype, i.e. CD4-, CD8-, CD3+, TCR-alpha beta. 5C2 has been shown to express high levels of alpha and beta chain mRNA and to utilize the same or similar V alpha and V beta region genes as C6VL/1. Whereas C6VL/1 binds cross-reactively to both RadLV/C6VL and an unrelated isolate RadLV/VL3, 5C2 has binding specificity for only RadLV/C6VL, which induced its proliferation. The anti-clonotypic antibody Mab124-40 specifically and completely inhibits binding of 5C2 to RadLV/C6VL at concentrations as low as 300 ng/ml. The 5C2 cell line can also be stimulated to increased proliferation by RadLV/C6VL. All of these data are consistent with the role of a TCR alpha beta heterodimer in binding and stimulation by RadLV and satisfy one prediction of the receptor-mediated leukemogenesis hypothesis that T-cell clones identifiable by their T-cell receptor clonotype may be targets for transformation by a particular retrovirus.

Identification of molecules detected by three different anti-H-2Kk monoclonal antibodies

Three different monoclonal antibodies specific for murine Class I H-2Kk-encoded determinants have been found to bind to molecules other than the classical 45 Kd Class I glycoprotein. These results were obtained after electrophoresis of a detergent lysate of spleen cells, and extraction of molecules present in multiple gel fractions. The antigenic activity in each gel fraction was assessed after removal of detergent by capacity to inhibit the binding of each of these antibodies to Ig-capped spleen cells in a rosetting assay. Only the H100-27R9 antibody was inhibited by an extract representing 45-50 Kd proteins resembling Class I molecules. This antibody also bound material extracted from a higher 65-70 Kd fraction of the gel. The binding of the 11-4.1 and H100-30R3 antibodies was inhibited by unique molecules in the molecular weight range of less than 20 Kd. The inhibitory material was not sensitive to pronase but was sensitive to glycosidases. This material could be absorbed by each of the H100-30R3 and 11-4.1 antibodies but not by H100-27R9. All data are consistent with unique, low molecular weight carriers of carbohydrate-defined epitopes which can bind monoclonal antibodies having specificity for H-2K-encoded gene products. It is predicted that these are glycolipids, but it is not yet known whether they are cell-surface or cytoplasmic molecules.

Resistance to ectromelia virus infection in mice. Analysis of H-2-linked gene effects

The mechanism for resistance to ectromelia infection has been investigated in B6 and B10 congenic strains of mice which carry different alleles at the H-2 major histocompatibility locus. Greater susceptibility in some B10 congenic strains of mice has been associated with higher viral titres in the draining popliteal and inguinal lymph nodes as well as spleen at 3 days post infection. T cells which develop cytotoxic function following in vitro culture in the presence of T cell growth factors have also been detected in the popliteal lymph nodes of B6/B10 congenic strains of mice as early as 3 days post infection. Greater cytotoxicity has been detected in cultures of cells from resistant B6/B10 mice than from the susceptible B10 congenic strain B10.G, or other semi-resistant B10 congenic strains which differ at the H-2 locus. The early activation of T cells appears to be under H-2 gene control and activated T cells may play an "early" role in controlling viral replication within the lymphoid system.

Preferential expression of a common T cell receptor structure by T cells induced to proliferate in vitro with a murine retrovirus

We have successfully isolated continuous T cell lines from murine spleen which have been induced to proliferate after in vitro exposure to the murine leukemia virus RadLV. Cell lines isolated from several strains of mice have an "immature" phenotype and are immortalized CD4- CD8- CD3+ cell lines. Cell lines of similar phenotype have now been derived from many individual mice, after spleens have been infected with two different RadLV viruses, a leukemogenic and a nonleukemogenic isolate. Among cell lines induced with RadLV/C6VL, an unusually high proportion of cells was found to bind the 124-40 anticlonotypic antibody specific for the alpha beta TCR expressed by C6VL/1 cells which produces RadLV/C6VL. This was not reflected in cell lines induced with the RadLV/V13 isolate nor in various lymphocyte subsets freshly isolated from normal mice, or induced to proliferate in culture. Cells expressing a common TCR structure would appear to be appropriate targets for in vitro proliferation and transformation induced by RadLV.

Binding of the BL/VL3 murine T cell lymphoma to radiation leukaemia virus is specific for viral env determinants

Molecularly cloned radiation leukaemia viruses (RadLVs) isolated from the BL/VL3 radiation-induced thymoma have been used in assays to compare the binding specificity of the BL/VL3 cell line for different retroviruses. BL/VL3 cells bound well to two of three thymotropic, leukaemogenic viruses produced by this cell line. BL/VL3 did not bind to a cloned fibrotropic, non-leukaemogenic RadLV. BL/VL3 appears to have receptor specificity for only some of the leukaemogenic RadLVs, and this appears to be related to differences in the viral env sequence.

Monoclonal antibodies which identify carbohydrate-defined MHC class I epitopes

Eleven different monoclonal antibodies specific for H-2K- and H-2D-encoded Class I molecules have been screened to determine Class I epitopes dependent on both carbohydrate and protein structures. Monoclonal antibodies have been identified which bind to carbohydrate-defined antigens encoded by both the H-2K and H-2D gene regions. Sensitivity to glycosidases versus pronase has been used to classify antigens both expressed as cell surface molecules and when prepared as detergent solubilized antigen. Several simple sugars have also been found to act as inhibitors of antibodies which bind to carbohydrate-defined sites. The genetic control of carbohydrate antigen expression by H-2K- and H-2D-linked genes has been verified since a specific antibody does not bind to H-2Kb or H-2Db molecules encoded by several mutant strains of mice containing single amino acid substitutions in their protein product. All of these data are consistent with Class I antigenic structures being encoded in carbohydrate as well as protein moieties.

Identification of class I H-2Db molecules primarily expressed by B lymphocytes in murine spleen

Evidence is presented which supports the phenomenon of heterogeneity amongst H-2Db-encoded Class I molecules. Two monoclonal antibodies (MoAb) called H141-31 and B22-249 were used in these studies. Both bind to the 'private' H-2.2 site of H-2Db-encoded molecules, but the binding of B22-249 is determined by carbohydrate moieties, whereas H141-31 appears to bind to a protein-defined epitope. Some H-2Db molecules, identified by the H141-31 MoAb, are primarily expressed on B lymphocytes and not T lymphocytes in spleen. The number of H-2Db molecules which bind H141-31 on B cells was also found to be three- to four-fold less than the number which bound the B22-249 MoAb. B cells of two mutant strains of mice, B6-C.H-2bm13 and B6-C.H-2bm14 which harbour very few nucleotide changes in the H-2Db gene, also show marked reduction in the binding of both antibodies. This suggests that a single common gene encodes both target molecules and that post-translational modifications such as differential glycosylation may account for heterogeneity amongst H-2Db molecules. This would explain the presence of the different H-2Db molecules defined here. It follows that differences in glycosylation evidently occur both within the B cell population, since H141-31 binds to only a subset of H-2Db molecules on B cells, and between T and B lymphocytes, since resting T cells do not bind H141-31 MoAb.

Detection of class I MHC antigens on glycosidase-treated cells

Several Class I molecules encoded by the murine H-2K gene have been found to express epitopes with different sensitivities to glycosidases. This result was found to be variably represented by different assays used to measure the binding of monoclonal antibodies (MoAb) specific for Class I H-2Kk molecules.

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.

Natural anti-self reactivity which maps to MHC class I genes

Responder spleen cells of [B10.A(5R) x B10.A(2R)]F1 hybrid mice cultured in vitro with irradiated parental spleen cells, generate a cytotoxic T cell response which maps to the H-2Dd and H-2(K-I)b genes of the B10.A(5R) parent. Specific reactivity of (5R x 2R) cells to B10.A(5R) parental (P) stimulators and not to F1 hybrid or B10.A(2R) stimulators was also demonstrated as an F1 anti-P proliferative response. Generation of a (5R x 2R) anti-5R response has also been noted during 2 degrees in vitro anti-viral cytotoxic responses where (5R x 2R) cells from either ectromelia or Sendai virus primed mice have been stimulated in vitro with infected 5R cells, but not when stimulated with infected 2R or (5R x 2R) cells. The generation of these responses is dependent on the use of parental stimulators for F1 hybrid cells during in vitro culture. All data is consistent with the hypothesis that (5R x 2R) F1 cells are not tolerant of 5R cells, and of the 4-fold higher level of Class I H-2Kb/Dd antigens which they express.

Preferential usage of the V beta 8 gene family by CD4-CD8-T cell lines derived from spleen

Receptors encoded by the V beta 8 gene family and identified by the F23.1 antibody are commonly expressed amongst the CD4-CD8-T cell lines isolated from spleen cells infected in vitro with the RadLV retrovirus. All but one out of 12 cell lines showed between 50 and 85% F23.1+ cells in the uncloned cell population which is noticably higher than the approximately 13% level amongst the Ig- normal spleen cell population. There was a high frequency (approximately 50%) of F23.1+ clones from five of these cell lines. The frequency of F23.1 binding cells in the Ig-, CD4/CD8-depleted spleen population is only 0.2%, which gives a precursor frequency in spleen of less than 0.002%. This reflects selective isolation of CD4-CD8- alpha beta+ cells which express V beta 8 gene products by this culture scheme. The requirement for RadLV in induction of these cell lines has been established, suggesting that this retrovirus may selectively stimulate CD4-CD8-F23.1+ T cells. These cells may represent an autoimmune subset present in peripheral lymphoid tissue.

Unique role for the T cell receptor in retrovirus binding by the C6VL thymoma

Binding of cognate Radiation leukemia virus (RadLV) by the C6VL/1 thymoma involves a subset of TCR molecules in association with CD4 molecules expressed by that cell line. A CD4- variant of C6VL/1 has now been isolated which also has RadLV binding capacity. Stable expression of the TCR, class I, and CD5 molecules but not Thy1.2 and CD4 molecules has been demonstrated, and the C6VL/1 origin of this cell has been confirmed by Southern blot analysis using probes specific for the TCR beta chain gene. This cell line has maintained binding capacity for RadLV/C6VL prepared as an immunoabsorbent matrix, but unlike the parent C6VL/1 cell line, binds significantly less well to the related RadLV/VL3 isolate. Binding of the variant cell line to RadLV/C6VL can be completely inhibited by anti-clonotypic antibody to the TCR but only weakly by anti-H-2Kb antibody used at the same concentration. These data suggest that the TCR on C6VL/1 can interact with RadLV in the absence of any co-receptor function of CD4 and implicates the TCR as a sufficient receptor for retrovirus.

Antibody which defines a subset of bone marrow cells that can migrate to thymus

A T-cell line of immature phenotype, 16C1, has been shown to have specific capacity to migrate to and localize in the thymus of irradiated mice. Several antibodies specific for the Pgp-1 molecule have been tested for their capacity to inhibit the migration of 16C1 and of bone marrow to thymus in just a 3-hr double-label migration assay. Analysis of Pgp-1 expression has revealed that 16C1, derived from C57BL mice, characteristically binds antibodies specific for the Pgp-1.1 and not the Pgp-1.2 allelic determinant, which is normally expressed by cells from C57BL mice. This unusual epitope expression has also been demonstrated for several other cell lines of similar origin to 16C1. A 5% subpopulation of C57BL bone marrow has also been defined which binds both the allele-specific antibodies. These cells exist amongst the class I+, Thy-1+, T200+ subpopulation of bone marrow. Anti-Pgp-1 antibodies have been shown to inhibit the thymus-homing capacity of both 16C1 and of bone marrow and have been used to deplete bone marrow of cells capable of reconstituting the T-cell compartment of irradiated mice. All of this indicates at least two distinct Pgp-1 determinants can be expressed by cells from C57BL mice and that antibody specific for either of these determinants can inhibit thymus homing capacity. T-cell precursors which can migrate to thymus would appear to exist amongst the subset of bone marrow cells which express both the Pgp-1.1 and Pgp-1.2 determinants.

Measurement of binding specificity between T cell lymphomas and murine leukemia viruses

We have previously reported the presence of receptors on radiation leukemia virus (RadLV)-induced thymomas and malignant thymocytes from AKR mice which specifically bind retrovirus produced by these T cell clones. These receptors have been shown to have specificity for virus reminiscent of an immune-specific receptor. Previous studies on T cell lymphoma binding to retroviruses have involved measurement of the interaction of labelled virus with cells using fluorescence-activated cell sorter (FACS) analysis (McGrath et al., J. Virol. (1978) 25, 923; McGrath and Weissman, Cell (1979) 17, 65; Weissman and McGrath, Curr. Top. Microbiol. Immunol. (1982) 98, 103). Here we report development of an assay for measuring lymphoma binding to virus, prepared as an immunoabsorbent adhered to a microtiter plate. Using this assay, we have shown that only T and not B cell lymphomas can bind to T cell-tropic viruses, and some cell lines have greatest specificity for homologous virus. The AKR-derived T cell lymphomas, SL3 and KKT-2, show greater specificity for leukemogenic AKR viruses, than for an AKR xenotropic virus or the recombinant AKR virus, MCF247. The RadLV-induced T cell lines, C6VL/1 and BL/VL3, have been found to bind cross-reactively to several different murine leukemia viruses (MuLVs). RadLV-induced T cell lymphomas do have greater specificity for their cognate retroviruses since free, homologous retrovirus can best block the interaction between cells and virus adhered to the wells of a microtiter plate. Cross-reactive interactions are more easily demonstrated by this assay, probably because low avidity interactions are stabilized as a result of the mode of virus presentation. Binding specificity for retroviral envelope determinants has been demonstrated using a rat anti-retroviral antiserum prepared as an F(ab)1 fragment. This antiserum can inhibit the interaction between the C6VL/1 thymoma and its RadLV virus. Specificity of this antibody for a gp70-like protein was confirmed by NaDodSO4-polyacrylamide gel electrophoresis (PAGE) and by loss of this activity after absorption of antibody on virus. Antibodies specific for RadLV/VL3 gp70 determinants can inhibit the interaction of C6VL/1 with RadLV/VL3 suggesting that cross-reactive binding to heterologous virus is also specific for a gp70 viral env determinant.

Internalization of IL-2 by an IL-2-dependent murine T cell lymphoma expressing no detectable cell surface receptors for IL-2

A murine Radiation leukemia virus-induced T cell lymphoma, 5C2, which is dependent on interleukin-2 (IL-2) for proliferation has been analyzed for interleukin-2 receptor (IL-2R) expression. Using fluorescence-activated cell sorter and electron microscopic analysis together with antibody specific for the known p55 chain of the murine IL-2R, no evidence has been obtained to suggest that these cells express detectable numbers of receptors with high affinity for IL-2. However, two different antibodies with specificity for the p55 chain of the IL-2R have been shown to inhibit 5C2 proliferation. An analysis of 125I-IL-2 binding has precluded a cell surface receptor density of greater than 80 molecules per cell. A temperature-dependent, nonspecific uptake of 125I-IL-2 has been described for 5C2. Uptake is saturated at 8.5 nM 125I-IL-2 with equilibrium being established within 60 min. When incubated at 37 degrees C in the presence of 400 pM 125I-IL-2, a maximum of approximately 2,000 molecules are internalized within 40 min. Uptake of other iodinated proteins by 5C2 was not observed. This property is unique to 5C2 and not to the control C6VL/1 cell line. Intracellular vesicles have also been found in 5C2 cells by electron microscopy which stain positively with gold-conjugated antibody specific for the p55 chain of the IL-2R. 5C2 appears to exhibit unique IL-2 regulatory characteristics.

Monosaccharide inhibition of cytotoxic T-cell function: demonstration of clone-specific effects

A range of monosaccharides has been tested for their capacity to influence the induction and effector function of alloreactive cytotoxic T (Tc) cells. Strain-specific differences in the capacity of monosaccharides to inhibit Tc cell induction have been demonstrated. Monosaccharides can also inhibit effector function of target cell lysis, but this could only be demonstrated by assessing the effect of sugars added to limiting dilution cultures of alloantigen-stimulated T cells. B10.A(4R) anti-BALB/c Tc cells have been reproducibly inhibited by D-glucosamine and D-galactosamine, as well as D-galacturonic acid, at both the induction and effector phases of the Tc cell response. Analysis of monosaccharide inhibition of cytotoxicity in limiting dilution cultures has confirmed that D-glucosamine is the most effective inhibitor of B10.A(4R) anti-BALB/c Tc cells, while D-galactosamine and D-galacturonic acid inhibit cytotoxicity in only some limiting dilution wells. Analysis of several B10.A(4R) anti-BALB/c Tc cell clones has revealed at least two different 'clone-specific' patterns of inhibition by D-glucose, D-glucuronic acid and D-galacturonic acid. Since Tc cell recognition of antigen is generally specific for class I major histocompatibility complex (MHC) antigens, this data implicates a role for MHC-associated carbohydrate structures expressed by target cells in T-lymphocyte interactions with antigen.

Effects of anti-class I antibodies on proliferation of murine T lymphocytes

Antibodies specific for the murine Class I H-2K/D molecules have been analyzed for their effect on the proliferation of murine T cells. Several antibodies specific for both private and public determinants have been found to inhibit lectin-mediated T-cell proliferation. These same antibodies do not noticeably effect growth factor-dependent proliferation of activated T cells and have been found to stimulate rather than inhibit alloantigen-induced proliferation of T cells. Taken together these results suggest that Class I molecules may have some functional role in the early events of T-cell stimulation/proliferation, although the mechanisms for antibody effect may be different for T cells stimulated in different ways.