Thymocyte clones from 14-day mouse embryos. I. State of T cell receptor genes, surface markers, and growth requirements

TCRalpha enhancer activation occurs via a conformational change of a pre-assembled nucleo-protein complex

The TCR alpha enhancer (Ealpha) has served as a paradigm for studying how enhancers organize trans-activators into nucleo-protein complexes thought to recruit and synergistically stimulate the transcriptional machinery. Little is known, however, of either the extent or dynamics of Ealpha occupancy by nuclear factors during T cell development. Using dimethyl sulfate (DMS) in vivo footprinting, we demonstrate extensive Ealpha occupancy, encompassing both previously identified and novel sites, not only in T cells representing a developmental stage where Ealpha is known to be active (CD4(+)CD8(+)-DP cells), but surprisingly, also in cells at an earlier developmental stage where Ealpha is not active (CD4(-)CD8(-)-DN cells). Partial occupancy was also established in B-lymphoid but not non-lymphoid cells. In vivo DNase I footprinting, however, implied developmentally induced changes in nucleo-protein complex topography. Stage-specific differences in factor composition at Ealpha sequences were also suggested by EMSA analysis. These results, which indicate that alterations in the structure of a pre-assembled nucleo-protein complex correlate with the onset of Ealpha activity, may exemplify one mechanism by which enhancers can rapidly respond to incoming stimuli.

Cross talk between alpha(v)beta3 and alpha4beta1 integrins regulates lymphocyte migration on vascular cell adhesion molecule 1

Local inflammation leads to increased expression of the vascular cell adhesion molecule (VCAM)-1 on vascular endothelium which contributes to the encapture of leukocytes from the circulating blood through the leukocyte ligand alpha4beta1 integrin. Inflammatory vascular endothelium expresses VCAM-1 at high density. We found that the speed of locomotion of activated lymphocytes migrating along surfaces coated with recombinant VCAM-1 at a comparable density to that found on inflammatory endothelium was slow. However, lymphocytes do migrate and extravasate rapidly under inflammatory conditions, indicating that there must be mechanisms that regulate the interaction between alpha4beta1 and VCAM-1 in vivo. Here we show that the lymphocyte alpha(v)beta3 integrin and integrin-associated protein (IAP) is able to regulate this interaction. The occupancy of lymphocyte alpha(v)beta3 integrin by platelet cell adhesion molecule-1 or vitronectin regulated the speed of alpha4beta1 integrin-dependent locomotion of lymphocytes on recombinant VCAM-1. This allowed rapid lymphocyte migration at VCAM-1 densities which are typical of inflammatory vessels. This alpha(v)beta3-mediated enhanced migration of lymphocytes via alpha4beta1 is likely to depend on the interaction of alpha(v)beta3 integrin with the IAP. Furthermore, this motile process correlates with polarization of the actin cytoskeleton in lymphocytes. Our results suggest that cross talk between alpha(v)beta3 integrin and alpha4beta1 integrin is a mechanism in the regulation of lymphocyte locomotion along inflammatory endothelium and subsequent transendothelial migration. This can explain how lymphocytes overcome tight adhesion to the vascular endothelium and start rapid migration along and through the endothelial lining of blood vessels into inflammatory tissue.

HEMCAM, an adhesion molecule expressed by c-kit+ hemopoietic progenitors

We have characterized the adhesion molecule HEMCAM, which is expressed by hemopoietic progenitors of embryonic bone marrow. HEMCAM belongs to the immunoglobulin superfamily and consists of the V-V-C2-C2-C2 Ig domains. There are three mRNA splice variants. One has a short cytoplasmic tail; another has a long tail; while the third seems to lack transmembrane and cytoplasmic regions. Except for the NH2-terminal sequence, HEMCAM is identical to gicerin, a molecular involved in neurite outgrowth and Wilm's kidney tumor progression in the chicken and it is significantly homologous with MUC18 a molecule involved in melanoma progression and metastasis in human beings. In the bone marrow the HEMCAM+ cell population contains c-kit+ subsets. HEMCAM+ cells coexpressing the receptor tyrosine kinase c-kit give rise to T cells at a frequency of 0.17 when injected intrathymically in congenic animals. As HEMCAM+, c-kit+ cells differentiate into myeloid and erythroid CFU's the double-positive cell population seems to contain precursors for multiple lineages. HEMCAM promotes cell-cell adhesion of transfected cells. Cross-linking of murine HEMCAM leads to cell spreading of T-lymphocyte progenitors adhering to the vascular adhesion molecules, PECAM-1 and VCAM-1. Thus, HEMCAM is likely to be involved in cellular adhesion and homing processes.

Vanin-1, a novel GPI-linked perivascular molecule involved in thymus homing

Migration of hematopoietic precursor cells to the thymus is shown to depend upon a novel molecule called Vanin-1 expressed by perivascular thymic stromal cells. An anti-Vanin-1 antibody blocks the binding of pro-T cells to thymic sections in vitro, the in vivo accumulation of bone marrow cells around cortical thymic vessels, and long-term thymic regeneration. Thus, it interferes with the entry, and not the differentiation, of hematopoietic precursor cells. The Vanin-1 gene codes for a GPI-anchored 70 kDa protein that shows homology only with human biotinidase. Transfection of thymic stromal cells with the Vanin-1 cDNA enhances thymocyte adhesion in vitro. These data suggest that Vanin-1 regulates late adhesion steps of thymus homing under physiological, noninflammatory conditions.

Tumor necrosis factor-alpha (TNF-alpha) induces a reversible, time- and dose-dependent adhesion of progenitor T cells to endothelial cells

Recent in vivo studies suggest that tumor necrosis factor-alpha (TNF-alpha) is involved in the development of the thymus. We postulated that this inflammatory mediator could regulate the influx of progenitor T cells into the thymus. Using an in vitro static adhesion system, we found that TNF-alpha increases the adhesion of a murine progenitor T cell line (FTF1) to a bovine aortic endothelial cell line (1F8), human umbilical vein endothelial (HUVE) cells, and a murine arterial endothelial (MAE) cell line. TNF-alpha treatment of the 1F8 cells resulted in a time- and dose-dependent increase in the adherence of FTF1 cells. Adherence increased during the first 6 hr of treatment with TNF-alpha concentrations ranging from 10(-11) to 10(-9) M. Maximal adherence (6 hr treatment with 10(-10) M of TNF-alpha) was approximately 4.5-fold larger than that of untreated monolayers. A slow decrease in adherence, down to approximately 2-fold at 48 hr, was observed beyond 12 hr of TNF-alpha treatment; in contrast, removal of TNF-alpha after 6 hr of continued stimulation caused the adherence to return to pre-stimulation levels within 24-30 hr. Adhesion of FTF1 cells to TNF-alpha treated 1F8 cells was almost completely blocked by a monoclonal antibody against murine CD49d (very late antigen-4) expressed on FTF1 cells. TNF-alpha-induced adhesion of FTF1 cells to MAE cells was also blocked by monoclonal antibodies against murine CD49d and CD106 (vascular cell adhesion molecule-1). These results support the notion that local secretion of TNF-alpha could modulate the dynamics of adhesion of progenitor T cells to the thymic endothelium.

CD31/PECAM-1 is a ligand for alpha v beta 3 integrin involved in adhesion of leukocytes to endothelium

To protect the body efficiently from infectious organisms, leukocytes circulate as nonadherent cells in the blood and lymph, and migrate as adherent cells into tissues. Circulating leukocytes in the blood have first to adhere to and then to cross the endothelial lining. CD31/PECAM-1 is an adhesion molecule expressed by vascular endothelial cells, platelets, monocytes, neutrophils, and naive T lymphocytes. It is a transmembrane glycoprotein of the immunoglobulin gene superfamily (IgSF), with six Ig-like homology units mediating leukocyte-endothelial interactions. The adhesive interactions mediated by CD31 are complex and include homophilic (CD31-CD31) or heterophilic (CD31-X) contacts. Soluble, recombinant forms of CD31 allowed us to study the heterophilic interactions in leukocyte adhesion assays. We show that the adhesion molecule alpha v beta 3 integrin is a ligand for CD31. The leukocytes revealed adhesion mediated by the second Ig-like domain of CD31, and this binding was inhibited by alpha v beta 3 integrin-specific antibodies. Moreover alpha v beta 3 was precipitated by recombinant CD31 from cell lysates. These data establish a third IgSF-integrin pair of adhesion molecules, CD31-alpha v beta 3 in addition to VCAM-1, MadCAM-1/alpha 4 integrins, and ICAM/beta 2 integrins, which are major components mediating leukocyte-endothelial adhesion. Identification of a further versatile adhesion pair broadens our current understanding of leukocyte-endothelial interactions and may provide the basis for the treatment of inflammatory disorders and metastasis formation.

Developmentally regulated cell surface expression and function of c-kit receptor during lymphocyte ontogeny in the embryo and adult mice

We have used a c-kit-specific monoclonal antibody, immuno-fluorescence staining and flow fluorocytometry or microscopy analysis to assess the cell surface expression of the c-kit receptor on a panel of non-transformed clones representing different stages of T- and B-lymphocyte development, freshly isolated lymphoid cells from thymus, bone marrow and spleen of young adult C57BL/6 mice and cells from yolk sac, thymus and liver of developing C57BL/6 mouse embryos. Pro-T, Pro-B and Pre-B clones derived from thymus or liver of 14-day embryos are c-kit+. Starting at day 8 to 8.5 in yolk sac, day-10 in fetal liver, and day 11 to 12 in fetal thymus, there are many c-kit+ cells. The number of c-kit+ cells in liver and thymus increases up to day 15 and progressively decreases thereafter. Cell sorter purified c-kit+ day 14 fetal liver cells fully reconstitute the T and B cell compartments of immunodeficient Scid mice. Stromal cells or epithelial cells derived from fetal thymus or liver, which can support growth and differentiation of c-kit+ lymphocyte progenitor clones, synthesize mRNA for Steel Factor (SF), the ligand of c-kit. In the adult mouse, however, c-kit expression is restricted to very early stages of T- and B-lymphocyte development (multipotent progenitors, B-cell/myelocytic progenitors, Pro-T and Pro-B lymphocyte progenitors). Most cells at the Pre-T, Pre-B and later stages of development do not bear detectable c-kit. Using Cos-1 cells transfected with mouse SF-cDNA and an antagonistic c-kit receptor-specific antibody, we show that the c-kit/SF system contributes to the survival of lymphocyte progenitors and enhances the proliferative responses of these cells to other growth factors (i.e. IL2, IL3, IL4, IL7). However, the c-kit receptor/SF ligand pair is neither sufficient nor necessary for the differentiation of lymphocyte progenitors into mature T- or B-lymphocytes. Finally, in stromal cell lines from fetal liver and adult bone marrow and thymic epithelial cell lines the level of steady state SF-RNA transcripts is inversely correlated with that of IL-7-mRNA. Moreover, IL7 inhibits the synthesis of SF-mRNA in stromal cells and rIL6 abrogates this inhibitory effect of rIL7. Thus, the expression of SF in stromal cells is subjected to complex regulation by other cytokines produced by the same stromal cells or by neighboring cells in a given microenvironment.(ABSTRACT TRUNCATED AT 400 WORDS)

Transcription of germ line V alpha segments correlates with ongoing T-cell receptor alpha-chain rearrangement

M14T is a virally transformed immature T-cell line which continues to rearrange its T-cell antigen receptor (TCR) alpha-chain genes in vitro and thus represents a dynamic system for studying TCR assembly. In an effort to investigate whether the TCR alpha locus is accessible for V(D)J rearrangement events, we examined M14T cells for the presence of germ line TCR alpha transcripts. Several unrearranged V alpha segments were found to be transcriptionally active in M14T cells. By comparison, germ line V alpha transcripts are absent in nonlymphoid and pro-T-cell lines and barely detectable in mature T-cell lines, suggesting that this phenomenon is likely stage and tissue specific. We demonstrate a perfect correlation between transcriptionally active V alpha segments and their involvement in ongoing V alpha-to-J alpha rearrangements. In addition, data suggesting that the unrearranged J alpha locus is also transcriptionally active in the M14T line are presented. Furthermore, the recombination-activating genes RAG-1 and RAG-2 are differentially expressed, with RAG-2 detectable only by polymerase chain reaction, implying that very low levels of one of these gene products are sufficient to complement the other to facilitate VJ rearrangements. These findings provide the first direct evidence for an accessibility model of antigen receptor rearrangement in T cells.

Transcription of germ line V alpha segments correlates with ongoing T-cell receptor alpha-chain rearrangement

M14T is a virally transformed immature T-cell line which continues to rearrange its T-cell antigen receptor (TCR) alpha-chain genes in vitro and thus represents a dynamic system for studying TCR assembly. In an effort to investigate whether the TCR alpha locus is accessible for V(D)J rearrangement events, we examined M14T cells for the presence of germ line TCR alpha transcripts. Several unrearranged V alpha segments were found to be transcriptionally active in M14T cells. By comparison, germ line V alpha transcripts are absent in nonlymphoid and pro-T-cell lines and barely detectable in mature T-cell lines, suggesting that this phenomenon is likely stage and tissue specific. We demonstrate a perfect correlation between transcriptionally active V alpha segments and their involvement in ongoing V alpha-to-J alpha rearrangements. In addition, data suggesting that the unrearranged J alpha locus is also transcriptionally active in the M14T line are presented. Furthermore, the recombination-activating genes RAG-1 and RAG-2 are differentially expressed, with RAG-2 detectable only by polymerase chain reaction, implying that very low levels of one of these gene products are sufficient to complement the other to facilitate VJ rearrangements. These findings provide the first direct evidence for an accessibility model of antigen receptor rearrangement in T cells.

Fetal liver pro-B and pre-B lymphocyte clones: expression of lymphoid-specific genes, surface markers, growth requirements, colonization of the bone marrow, and generation of B lymphocytes in vivo and in vitro

We describe here the development and characterization of the FLS4.1 stromal line derived from 15-day fetal liver of BALB/c embryos and defined culture conditions that efficiently support the cloning and long-term growth of nontransformed B-220+ 14-day fetal liver cells at two stages of B-cell development, namely, pro-B lymphocytes (immunoglobulin [Ig] genes in germ line configuration) and pre-B cells (JH-rearranged genes with both light-chain Ig genes in the germ line state). All B-cell precursor clones require recombinant interleukin-7 (rIL-7) and FLS4.1 stromal cells for continuous growth in culture, but pro-B lymphocyte clones can also proliferate in rIL-3. None proliferate in rIL-1, rIL-2, rIL-4, rIL-5, rIL-6, or leukemia inhibitory factor. FLS4.1 stromal cells synthesize mRNA for Steel factor but not for IL-1 to IL-7; all pro-B and pre-B clones express c-Kit, the receptor for Steel factor, and a c-Kit-specific antibody inhibits the enhanced proliferative response of fetal liver B-220+ B-cell precursors supported by FLS4.1 stromal cells and exogenous rIL-7 but does not affect that promoted by rIL-7 alone. Northern (RNA) blot analysis of the expression of the MB-1, lambda 5, Vpre-B, c mu, RAG-1, and RAG-2 genes in pro-B and pre-B clones show that transcription of the MB-1 gene precedes IgH gene rearrangement and RNA synthesis from c mu, RAG-1, RAG-2, lambda 5, and Vpre-B genes. All clones at the pre-B-cell stage synthesize mRNA for c mu, RAG-1, and RAG-2 genes; transcription of the lambda 5 and Vpre-B genes seems to start after D-to-JH rearrangement in B-cell precursors, indicating that the proteins encoded by either gene are not required for B-cell progenitors to undergo D-to-JH gene rearrangement. These findings mark transcription of the MB-1 gene as one of the earliest molecular events in commitment to develop along the B-lymphocyte pathway. Indeed, both pro-B and pre-B clones can generate in vitro and in vivo B lymphocytes but not T lymphocytes; moreover, these clones do not express the CD3-gamma T-cell-specific gene, nor do they have rearranged gamma, delta, or beta T-cell antigen receptor genes.

Fetal liver pro-B and pre-B lymphocyte clones: expression of lymphoid-specific genes, surface markers, growth requirements, colonization of the bone marrow, and generation of B lymphocytes in vivo and in vitro

We describe here the development and characterization of the FLS4.1 stromal line derived from 15-day fetal liver of BALB/c embryos and defined culture conditions that efficiently support the cloning and long-term growth of nontransformed B-220+ 14-day fetal liver cells at two stages of B-cell development, namely, pro-B lymphocytes (immunoglobulin [Ig] genes in germ line configuration) and pre-B cells (JH-rearranged genes with both light-chain Ig genes in the germ line state). All B-cell precursor clones require recombinant interleukin-7 (rIL-7) and FLS4.1 stromal cells for continuous growth in culture, but pro-B lymphocyte clones can also proliferate in rIL-3. None proliferate in rIL-1, rIL-2, rIL-4, rIL-5, rIL-6, or leukemia inhibitory factor. FLS4.1 stromal cells synthesize mRNA for Steel factor but not for IL-1 to IL-7; all pro-B and pre-B clones express c-Kit, the receptor for Steel factor, and a c-Kit-specific antibody inhibits the enhanced proliferative response of fetal liver B-220+ B-cell precursors supported by FLS4.1 stromal cells and exogenous rIL-7 but does not affect that promoted by rIL-7 alone. Northern (RNA) blot analysis of the expression of the MB-1, lambda 5, Vpre-B, c mu, RAG-1, and RAG-2 genes in pro-B and pre-B clones show that transcription of the MB-1 gene precedes IgH gene rearrangement and RNA synthesis from c mu, RAG-1, RAG-2, lambda 5, and Vpre-B genes. All clones at the pre-B-cell stage synthesize mRNA for c mu, RAG-1, and RAG-2 genes; transcription of the lambda 5 and Vpre-B genes seems to start after D-to-JH rearrangement in B-cell precursors, indicating that the proteins encoded by either gene are not required for B-cell progenitors to undergo D-to-JH gene rearrangement. These findings mark transcription of the MB-1 gene as one of the earliest molecular events in commitment to develop along the B-lymphocyte pathway. Indeed, both pro-B and pre-B clones can generate in vitro and in vivo B lymphocytes but not T lymphocytes; moreover, these clones do not express the CD3-gamma T-cell-specific gene, nor do they have rearranged gamma, delta, or beta T-cell antigen receptor genes.

The development of functionally responsive T cells

The work reviewed in this article separates T cell development into four phases. First is an expansion phase prior to TCR rearrangement, which appears to be correlated with programming of at least some response genes for inducibility. This phase can occur to some extent outside of the thymus. However, the profound T cell deficit of nude mice indicates that the thymus is by far the most potent site for inducing the expansion per se, even if other sites can induce some response acquisition. Second is a controlled phase of TCR gene rearrangement. The details of the regulatory mechanism that selects particular loci for rearrangement are still not known. It seems that the rearrangement of the TCR gamma loci in the gamma delta lineage may not always take place at a developmental stage strictly equivalent to the rearrangement of TCR beta in the alpha beta lineage, and it is not clear just how early the two lineages diverge. In the TCR alpha beta lineage, however, the final gene rearrangement events are accompanied by rapid proliferation and an interruption in cellular response gene inducibility. The loss of conventional responsiveness is probably caused by alterations at the level of signaling, and may be a manifestation of the physiological state that is a precondition for selection. Third is the complex process of selection. Whereas peripheral T cells can undergo forms of positive selection (by antigen-driven clonal expansion) and negative selection (by abortive stimulation leading to anergy or death), neither is exactly the same phenomenon that occurs in the thymic cortex. Negative selection in the cortex appears to be a suicidal inversion of antigen responsiveness: instead of turning on IL-2 expression, the activated cell destroys its own chromatin. The genes that need to be induced for this response are not yet identified, but it is unquestionably a form of activation. It is interesting that in humans and rats, cortical thymocytes undergoing negative selection can still induce IL-2R alpha expression and even be rescued in vitro, if exogenous IL-2 is provided. Perhaps murine thymocytes are denied this form of rescue because they shut off IL-2R beta chain expression at an earlier stage or because they may be uncommonly Bcl-2 deficient (cf. Sentman et al., 1991; Strasser et al., 1991). Even so, medullary thymocytes remain at least partially susceptible to negative selection even as they continue to mature.(ABSTRACT TRUNCATED AT 400 WORDS)

EA-1, a novel adhesion molecule involved in the homing of progenitor T lymphocytes to the thymus

The mouse progenitor T lymphocyte (pro-T) cell line FTF1 binds in vitro to thymus blood vessels, the thymic capsule, and liver from newborn mice. A mAb, EA-1, raised against an embryonic mouse endothelial cell line, blocked adhesion. The antibody also interfered with pro-T cell adhesion to a thymus-derived mouse endothelial cell line; it had no effect on the adhesion of mature T lymphocytes and myeloid cells. The antigen recognized by EA-1 is located on the vascular endothelium of various mouse tissues and absent on pro-T cells. EA-1 antibody precipitates molecules with apparent molecular weights of 110,000, 140,000, 160,000, and 200,000. Immunoclearing and binding-inhibition studies with antibodies against known adhesion molecules suggest that the EA-1 antigen is a novel adhesion molecule involved in colonization of the embryonic thymus by T cell progenitors.

A differentially expressed murine RNA encoding a protein with similarities to two types of nucleic acid binding motifs

Using differential screening, a murine cDNA, termed X16, was isolated corresponding to an mRNA which is more strongly expressed in pre-B cell lines relative to mature B-cell lines. The complete coding sequence of the mRNA predicts a 19kD protein with two domains connected by a proline-rich spacer. The N-terminal domain of about 90 amino acids encodes an RNA binding motif including the ribonucleoprotein consensus octapeptide found in one class of RNA-binding proteins and highly conserved from yeast to man. Within the very basic C-terminal domain of about 60 amino acids, several copies of two different peptides are found which are also present in several proteins which bind DNA or RNA. The expression of X16 is not limited to the lymphoid lineage. In adult mice, although the strongest expression was seen in thymus, mRNA was also found in testis, brain, spleen, and very low in heart. X16 mRNA was not detected in liver and kidney. In tissue culture, the expression of X16 mRNA can be induced by serum. The conserved protein motifs and expression pattern suggest that X16 could be involved in RNA processing correlating with cellular proliferation.

Rearrangement patterns of T-cell receptor genes in the spleen of athymic (nu/nu) young mice

Although the athymic nude mouse is grossly deficient in peripheral T cells, the number of lymphocytes bearing T-cell markers (L3T4, LyT2) and the alpha beta or gamma delta T-cell receptor (Tcr) increases steadily with age. The anatomical site(s) where these cells arise are unknown. Splenocytes from 3-5-week-old C57BL/6 (nu/nu) mice contain 2%-5% Pro-T cell progenitors identified with the Joro 37-5 and Joro 75 antibodies, but not mature T cells. To study Tcr gene rearrangement outside the thymus, we fused splenocytes from 3-5-week-old C57BL/6 nude mice with the T-cell lymphoma BW 100.129. Of 22 hybrids that grew stably in culture, four had Tcrd-VD1-D2-J1, two had Tcrd-VD2-J1, and seven had Tcrd-D1-D2 types of rearrangement. Eight hybrids had rearranged the Tcrg-2 gene cluster, but none had rearranged Tcrg-1, -3, or -4. None of the hybrids had rearranged the Tcrb gene cluster and 13 contained DJ rearrangements at the Igh locus. We conclude that the spleen is one of the extrathymic sites where T-cell progenitors can rearranged Tcrd and Tcrg genes. However, there was no evidence for Tcrb gene rearrangements in this organ. Furthermore, the analysis of this limited number of hybrids suggests that extrathymic Tcr gene rearrangements seem to be distinct and much less diverse than those found in the developing thymocytes.

Cloning and characterization of a protein binding to the J kappa recombination signal sequence of immunoglobulin genes

A protein with molecular weight of 60,000 that binds to the recombination signal sequence (RS) of the immunoglobulin J kappa segment was purified from the nuclear extract of a murine pre B cell line 38B9. This binding protein was found in lymphoid cell lines but not in non-lymphoid cell lines. The Kd value of the J kappa RS binding protein to the J kappa RS was 1 nM. The cDNA clone (RBP-2) was isolated based on partial amino-acid sequence of this protein. This cDNA encodes 526 amino-acid residues, and its sequence does not show extensive overall homology with any known proteins, but displays an interesting homology to a 40-residue region that is conserved among a subset of site specific recombinase (integrase family).

Characterization of triple negative clones isolated from post-natal human thymus

Human triple negative (CD3- CD4- CD8-) thymocytes and double negative (CD4- CD8-) thymocytes purified from post-natal thymus were cloned with a feeder cell mixture of irradiated PBL, irradiated JY cells and PHA and expanded with IL-2. The cloning efficiency of triple negative thymocytes was less than 1% and the majority of the clones were triple negative. One out of 11 clones was TCR alpha beta+ CD4+. No TCR gamma delta+ clones were isolated. On the other hand, the cloning efficiency of double negative thymocytes was about 10% and most of the clones isolated were TCR gamma delta+. We could not find any evidence of in vitro differentiation of triple negative thymocytes into TCR gamma delta+ cells. Some of the triple negative clones expressed CD16 brightly and were apparently NK cells. All CD16- clones isolated from triple negative thymocytes, however, expressed NKH1, which is also an NK cell marker. Cytoplasmic CD3-delta and CD3-epsilon Ag which have been reported to be expressed in the most immature thymocytes were not detected in any of these clones. Furthermore, the CD16- triple negative clones exhibited significant cytolytic activity against K562. Phenotype of the clones seems to be stable under various conditions in vitro including coculture with human thymic epithelial cells. These data indicate that the CD16- triple negative clones isolated from triple negative thymocytes are similar to a minor subset of NK cells which is CD16- NKH-1+. It is not clear whether they originated from a distinct subset of mature or immature NK cells resident in the thymus tissue or from common precursors of both T and NK lineage.

IL-3 and IL-4 affect thymocyte differentiation in organ culture

The ability of lymphokines to affect the development and differentiation of mouse thymocytes in vitro was evaluated in a carefully controlled 3-day organ culture system. Concanavalin A (Con A)-induced supernatant (SN) from the T-cell clone D10.G4, which contains high concentrations of interleukin-3 (IL-3), IL-4 and IL-5, but lacks IL-1, IL-2 and interferon (IFN), markedly increased the proportion of CD4+CD8- cells, and decreased the proportion of CD4+CD8+ cells. These effects were unaffected by dialysing the SN, showing them to be caused by macromolecular factors. Highly purified recombinant IL-3 and IL-4 could exert similar effects, rIL-3 and rIL-4 both increasing the proportion of CD4+CD8- cells, and rIL4 in addition reducing the proportion of CD4+CD8+ cells. In conjunction with the findings of other investigators, these results indicate that at least four lymphokines (IL-1, IL-2, IL-3 and IL-4) can control T-cell development in the thymus.

Endogenously secreted IL-4 is required for mouse thymocytes to become cytotoxic. Human, but not mouse, IL-2 induces a functionally immature thymic subset to secrete IL-4 and become CTL

Experiments described here demonstrate that the differentiation of mouse thymocytes into cytotoxic T lymphocytes (CTL) requires interleukin-4 (IL-4). To reach this conclusion, we took advantage of our discovery that human and mouse IL-2 have very different effects on the development of CTL from a functionally immature subset of thymocytes. The lobster agglutinin 1 (LAg1)-negative subpopulation of thymocytes proliferated when cultured with concanavalin A (Con A)+ human or mouse IL-2, but these cells became CTL only when cultured with Con A+ human IL-2. Furthermore, Con A+ human IL-2, but not mouse IL-2, stimulated IL-4 production by cells within this population. Con A-induced cytotoxicity by mature LAg1-positive thymocytes and normal thymocytes was also accompanied by secretion of IL-4. The anti-IL-4 mAb 11B11 inhibited induction of cytotoxicity by all thymocyte populations tested. Taken together these experiments indicate that stimuli which induce cytotoxicity by mouse thymocytes also induce the secretion of IL-4, which is necessary for the differentiation of thymocyte CTL precursors into CTL.

A role for interleukin 4 in the differentiation of mature T cell receptor gamma/delta + cells from human intrathymic T cell precursors

We have analyzed the effect of human recombinant interleukin 4 (rIL-4) on the growth and differentiation of human intrathymic pre-T cells (CD7+2+1-3-4-8-). We describe that this population of T cell precursors proliferates in response to rIL-4 (in the absence of mitogens or other stimulatory signals) in a dose-dependent way. The IL-4-induced proliferation is independent of the IL-2 pathway, as it cannot be inhibited with an anti-IL-2 receptor alpha chain antibody. In our culture conditions, rIL-4 also promotes the differentiation of pre-T cells into phenotypically mature T cells. Although both CD3/T cell receptor (TCR)-alpha/beta + and CD3-gamma/delta + T cells were obtained, the preferential differentiation into TCR-gamma/delta + cells was a consistent finding. These results suggest that, in addition to IL-2, IL-4 plays a critical role in promoting growth and differentiation of intrathymic T cell precursors at early stages of T cell development.

Identification and characterization of pro-T lymphocytes and lineage-uncommitted lymphocyte precursors from mice with three novel surface markers

The study of prethymic stages of T cell development has been limited because specific markers for mouse pro-T lymphocytes were not available. We developed a panel of rat monoclonal antibodies (mAbs) that bind to our pro-T lymphocyte clones obtained from bone marrow of young adult mice and the thymus of 14-d-old embryos. The mAbs, called Joro 30-8, Joro 37-5, and Joro 75, were found to bind to all pro-T clones tested but not to cell lines representing later stages of T cell development, B lymphocyte, or myeloid lineages. We determined the frequency and tissue distribution in normal and immunodeficient mouse strains as well as the ontogeny in liver and thymus of cells positive for these mAbs. The results were consistent with the pattern of reactivity observed with cell lines. We isolated Joro 30-8+, Joro 37-5+, and Joro 75+ bone marrow cells by cell sorter and found that: (a) phenotypically, they are Thy-1+, CD4-, CD8-, CD3-, B-220-, IgM-, F4/80-, and PgP-1+; (b) they grew in response to the combination of interleukin 3 (IL-3) + IL-4 or IL-3 + IL-4 + IL-6; and (c) Joro 37-5+ and Joro 75+ marrow cells gave rise to mature T lymphocytes but not to B lymphocytes, while Joro 30-8+ marrow cells generated both T and B lymphocytes after 8-12 wk of transfer into severe combined immunodeficient (Scid) mice. In normal mice subjected to 600 rad of irradiation to induce a wave of thymus recolonization, we found by flow fluorocytometry analysis that Joro+ cells entered the thymus 2 d after irradiation, expanded during the next 4 d, and underwent further differentiation, and from day 8 up to day 21, post-irradiation Joro+ cells were no longer detectable in the thymuses. Immunohistochemical analysis of normal thymus shows the presence of very few Joro 30-8+, Joro 37-5+, and Joro 75+ lymphoid cells in the subcapsular area and outer cortex but not in the medulla. The kinetic analysis of tissue sections from thymuses at various days post-irradiation suggests that Joro+ cells enter the thymus via blood vessels through the subcapsular and outer cortex areas; subsequently, these cells seem to migrate to the inner cortex without reaching the medulla, and give rise to Joro- thymocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

T cell receptor-negative thymocytes from SCID mice can be induced to enter the CD4/CD8 differentiation pathway

In order to investigate the role of T cell receptor (TcR) expression in thymocyte maturation, we have analyzed thymocytes from C.B-17/SCID mice, which are unable to productively rearrange their antigen receptor genes and fail to express TcR. Despite this defect, SCID thymocytes are functional as they produce lymphokines and proliferate in response to a variety of stimuli. Phenotypic analysis revealed that thymocyte populations from young adult SCID mice resemble thymocyte populations from normal embryonic mice in that they are large, Thy-1.2+, CD4-, CD8-, TcR- and enriched in CD5lo, IL2R+ and Pgp1+ cells. However, other TcR- populations normally present in adult mice (i.e., CD4-CD8+ cells and CD4+CD8+ cells) are absent from the thymus of TcR- adult SCID mice. To understand the basis of the developmental arrest of TcR- SCID thymocytes at the CD4-CD8- stage of differentiation, we analyzed thymi from the occasional "leaky" SCID mouse which possesses small numbers of TcR+ thymocytes. We found that the presence of TcR+ cells within a SCID thymus was invariably associated with the presence of CD4+ and/or CD8+ SCID thymocytes. Interestingly, however, the CD4+/CD8+ SCID thymocytes were not themselves necessarily TcR+. That is, emergence of SCID thymocytes expressing CD4/CD8 was tightly linked to the presence of TcR+ cells within that SCID thymus, but the SCID thymocytes that expressed CD4/CD8 were not necessarily the same cells that expressed TcR. Finally, we found that the introduction into TcR- SCID mice of normal bone marrow cells that give rise to TcR+ cells within the SCID thymus promoted the differentiation of SCID thymocytes into CD4-CD8+ and CD4+CD8+ TcR- cells. These data indicate that TcR+ cells within the thymic milieu provide critical signals which promote entry of CD4-CD8-TcR- precursor T cells into the CD4/CD8 differentiation pathway. When applied to differentiation of normal thymocytes, these findings may imply a critical role for early appearing CD4-CD8- TcR (gamma/delta)+ cells in initiating normal thymic ontogeny.

Purification and characterization of a protein that binds to the recombination signal sequence of the immunoglobulin J kappa segment

A protein that binds to the recombination signal sequence (RS) of the immunoglobulin J kappa segment was purified almost to homogeneity from the nuclear extract of a murine pre-B cell line 38B9. A similar binding protein was found in lymphoid cell lines but not in non-lymphoid cell lines. The binding activity was associated with a polypeptide with a molecular weight of 60,000. DNase I footprinting analysis demonstrated that this binding protein interacted with the heptamer and several 3' bases close to the heptamer. The Kd value of the J kappa RS binding protein to the J kappa RS was 1 nM. One base substitution in the heptamer of the J kappa RS greatly reduced the affinity of the J kappa RS binding protein. The high specificity of the binding site of the J kappa RS binding protein suggests that this protein may be involved in V-J recombination.

Factor requirements for activation and proliferation steps of human CD2+CD3-CD4-CD8- early thymocytes

Human CD2+CD3-CD4-CD8- thymocytes were shown to display high in vitro growth ability although their factor requirements for activation and proliferation are not fully known. We have thus isolated these precursors and assayed their activation and proliferation potentials in response to various factors. Our results indicate that these cells proliferate in response to phytohemagglutinin (PHA), recombinant interleukin 2 (rIL 2) and rIL 4. Simultaneous addition of anti-CD2I + III monoclonal antibodies (mAb) and rIL 2 highly increased cell growth while IL 4-induced proliferation was not enhanced upon addition of anti-CD2. Anti-CD2 and PHA, but not IL 2, induced intracytoplasmic Ca2+ influx phosphatidyl inositol turnover as well as IL 2 receptor expression. Sequential studies indicated that CD2 triggering enable many more CD2+ precursors to respond to rIL 2. Endogenous IL 2 synthesis was necessary for PHA-induced cell growth. Neither of these in vitro treatment were able to induce membrane expression of CD3, CD4 or CD8 on CD2+ cells.

Monoclonal antibodies reactive with the mouse interleukin 5 receptor

The rat mAbs R52.120 and R52.625 inhibit the action of IL-5 on both IL-5-sensitive cell lines and freshly isolated splenic B lymphocytes. Neither antibody inhibits the proliferative cell responses promoted by IL-2, IL-3, or IL-4. Purified R52.120+ lymphoid spleen cells contain 15-20-fold higher numbers of B lymphocytes responding to IL-5 in the form of maturation into antibody-producing cells. By immunofluorescence staining and flow fluorocytometry, the R52.120 and R52.625 antibodies bound to all 12 IL-5-sensitive cell lines tested. Both antibodies react with 2-4% cells in the spleen, 5% lymphoid cells, and 10-15% myeloid cells in the bone marrow, and 10-14% in the peritoneum of C57BL/6, DBA/2, and BALB/c adult mice. No positive cells for either antibody were detected in the thymus and lymph nodes of these mice. Both R52.120 and R52.625 antibodies specifically inhibit the binding of radiolabeled IL-5 to its receptor. Finally, R52.120 and R52.625 antibodies precipitate from 35S-methionine-labeled IL-5-R+ cell lysates three proteins with Mr 46,000, 130,000, and 140,000. Taken together from these results, we conclude that the R52.120 and R52.625 mAbs recognize epitopes on the IL-5-R complex very close or identical to the IL-5 binding sites.

In vitro effects of recombinant interleukin 7 on growth and differentiation of bone marrow pro-B- and pro-T-lymphocyte clones and fetal thymocyte clones

We have studied the effects of recombinant (r) interleukin 7 (IL-7) on growth and differentiation of marrow pro-B-lymphocyte clones (CB/Bm7, LyD9, LyB9), marrow pro-T-lymphocyte clones (C4-77/3, C4-86/18, C4-95/16), and fetal thymocyte clones (FTH5, FTA2, FTD5) in the presence or absence of the bone marrow stroma clone RP.0.10, which was selected for its ability to promote differentiation of the pro-B clones. rIL-7 alone stimulated some DNA synthesis (measured by [3H]thymidine uptake) but not actual growth (increase in cell number) of the pro-B clones. Antibodies against IL-4 and IL-6 or against receptors for IL-2, IL-3, and IL-5 did not inhibit this effect of rIL-7 on the pro-B clones. rIL-7 alone or in various combinations with other cytokines (from rIL-1 alpha to rIL-6) could not induce differentiation of the pro-B clones into IgM+ B cells regardless of the presence of lipopolysaccharide (LPS). The RP.0.10 marrow stroma cells by themselves do not support the growth of the pro-B clones. However, the pro-B clones grew when cultured with rIL-7 and monolayers of the RP.0.10 stroma cells. While the RP.0.10 stroma cells induced the pro-B clones to differentiate into IgM+ B cells but not T3+ T cells when cultured in the presence of LPS and rIL-3, the B-cell progenitor clones gave rise to significantly higher numbers of IgM+ B cells (up to 63%) and to many more B cells expressing higher levels of surface IgM when cocultured with rIL-7, LPS, and RP.0.10 stroma cells. The pro-B clones also generated IgM+ B cells (up to 20%) when cocultured with RP.0.10 stroma cells and rIL-7 in the absence of LPS. By using culture plates designed for testing requirements for cell-cell contact, we found that cell interactions between the pro-B cell and the marrow stroma cell are essential to induce rearrangement and expression of the immunoglobulin genes in the pro-B clones. Possible mechanisms to account for the remarkable effects of rIL-7 in the presence of RP.0.10 stroma cells on both growth and differentiation of the pro-B clones are discussed. Finally, rIL-7 alone or together with RP.0.10 stroma cells neither supported proliferation nor induced differentiation into T3+ T cells or IgM+ B cells of the marrow pro-T clones or the fetal thymocyte clones. In light of these findings, we postulate that the interaction of the pluripotential stem cell with marrow stroma cells like RP.0.10 and the availability of IL-7 could play a critical role in the commitment to develop along the B-lymphocyte pathway.

Thymocyte clones from 14-day mouse embryos. II. Transcription of T3 gamma gene may precede rearrangement of TcR delta and expression of T3 delta, T3 epsilon and T11 genes

We have studied the state of TcR delta gene and the expression of T3 delta, T3 epsilon, T3 gamma and T11 (CD2) genes in the fetal thymocyte (FT) clones A2, G15, H5, E10, D5, H12, F1 and D11 obtained from a 14-day B10.BR mouse fetal thymus. The eight FT clones contain the TcR delta gene in the germ-line configuration as determined by Southern blot analysis. With the exception of clones E10 and D5, the other six FT clones express normal sized transcripts for T3 gamma gene and none of the eight FT clones produced detectable RNA transcripts for T3 delta, T3 epsilon and T11 genes as assessed by Northern blot analysis. Together with our previous work showing that all eight FT clones contain the TcR gamma and the TcR beta gene clusters in the germ-line configuration, the data indicate that the FT clones represent the earliest stage of T cell development identified within the thymus. Our results provide evidence that (a) the T3 gamma gene is the first of the genes that encode components of a TcR/T3 complex to be expressed in ontogeny within the thymus; (b) the T3 (delta, epsilon, gamma) genes are switched on asynchronously and their expression must be differentially regulated, and (c) the T11 gene product may not be involved in early stages of T cell development within the thymus.

Differentiation of thymocytes in fetal organ culture: lack of evidence for the functional role of the interleukin 2 receptor expressed by prothymocytes

Thymic rudiments of 14-day-old mouse embryos were put into organ culture in the presence of interleukin 2 (IL2) and PC.61, a monoclonal antibody that binds to the IL2 receptor (IL2R). After 5 and 7 days of culture, we found no influence of PC.61 on the growth of the thymus and the composition of the thymocyte subpopulations as studied with a panel of monoclonal antibodies. High-dose IL2 treatment of the organ culture resulted in a reduction of the number of thymocytes and a decrease in the single CD4+ and CD4+CD8+ thymocytes, whereas the number of CD8+Ly-1+ thymocytes and the number of CD4-CD8-Ly-1- IL2R+ thymocytes increased. The effect of high-dose IL2 treatment was ascribed to the induction of a nonspecific LAK activity. Our findings argue against a functional role of IL2R on prothymocytes during early T cell development.