Cell surface antigen marking the stages of murine T cell ontogeny and its functional subsets

The role of gamma delta T cells in priming macrophages to produce tumor necrosis factor-alpha

The secretion of tumor necrosis factor (TNF)-alpha from macrophages is regulated by both priming and triggering signals. We found that macrophages from mice lacking gamma delta T cells [T cell receptor (TCR) delta-/- mice], which lack the gene encoding the delta chain, produced only small amounts of TNF-alpha in response to lipopolysaccharide (LPS) and showed a reduced level of expression of CD14. Pre-incubation of macrophages from TCR delta-/- mice with gamma delta T cells from their TCR delta +/- littermates restored their capacity to produce TNF-alpha in response to LPS. The priming activity of gamma delta T cells was in part inhibited by neutralizing anti-interferon (IFN)-gamma monoclonal antibodies. Collectively, these results suggest that gamma delta T cells play a role in priming macrophages to a steady state of activation via IFN-gamma secretion, which allows them to produce TNF-alpha when exposed to LPS.

Ontogenic development of murine fetal thymocytes is accelerated by 3,3',4,4'-tetrachlorobiphenyl

Polychlorinated hydrocarbons such as biphenyls or dioxins interfere with cellular processes by gene induction via ligand-activated binding of the cytosolic Ah-receptor to specific DNA elements. The thymus is a target organ for these processes and immunosuppression a hallmark of polychlorinated hydrocarbon toxicity. Using flow cytometry we analysed the development of thymocytes in fetal thymus organ cultures (FTOC) exposed to tetrachlorobiphenyl (TCB) for up to one week. We show that exposure to TCB changes the normal developmental pathways of fetal thymocytes within days. Overall fewer thymocytes are found in TCB-treated cultures from day 4 on, and significantly more CD8 positive thymocytes are detectable. These cells express the T-cell receptor, but not heat-stable antigen or IL2-receptor, giving them a mature phenotype. Moreover, relatively more CD4/CD8 double-negative thymocytes express CD44, a molecule involved in lymphocyte-epithelial interaction. We suggest that, at least for the CD8 single-positive thymocyte population, maturation is accelerated, and this may be due to TCB interference with physiological thymocyte-epithelial interactions.

CD4+CD8+ cells lacking self-Mls reactive T cells are induced in mesenteric lymph nodes of Salmonella enteritidis-infected mice

The percentage of mesenteric lymph node (MLN) cells that co-expressed both CD4 and CD8 was found to be from 5 to 7% in BALB/c and AKR/N mice bred under conventional conditions. In mice maintained under specific pathogen-free (SPF) conditions, the percentage fell below 2%. When mice were infected with an attenuated strain of Salmonella enteritidis (SER), the percentage of CD4+CD8+ cells in MLN rose to 20-30% transiently. In these mice, the total cell number and the percentage of CD8+ cells were not changed, but the CD4+ cell percentage was decreased. The expression intensity of TCR-alpha beta on CD4+CD8+ cells in the infected mice was higher in the MLN than in the thymus, but was similar to that of mature peripheral T cells. Among the CD4+CD8+ cell population in MLN, TCR-V beta 3+ cells were deleted but V beta 6+ cells were present in BALB/c mice which possess endogenous superantigen Mls-2a, but lack Mls-la. In AKR mice with the inverse of the occurrence of the superantigens, TCR-V beta 3+ cells were present and V beta 6+ cells were absent. These data suggest that CD4+CD8+ cells in the MLN of SER-infected mice may belong to thymus-derived mature T cells undergoing negative selection and that they may appear following exogenous stimulation.

Analysis of intraepithelial lymphocytes from major histocompatibility complex (MHC)-deficient mice: no evidence for a role of MHC class II antigens in the positive selection of V delta 4+ gamma delta T cells

Three-color flow cytometric analysis was carried out with intraepithelial lymphocytes from mice deficient in expression of major histocompatibility complex (MHC) antigens. These experiments were done to address the possible role of MHC class II molecules in the positive selection of V delta 4+ gamma delta T cells. By analyzing mice deficient MHC class II antigens alone or in combination with MHC class I antigens, no evidence was found for positive selection of V delta 4+ cells among CD8 alpha + or CD4-CD8- subpopulations of gamma delta T cell receptor-positive cells. Because V delta 4+, CD8 alpha + cells were reported to be positively selected on I-Ek and hybrid I-Ek/b molecules, class II-deficient animals were crossed with I-Ek transgenic mice and progeny examined for V delta 4 expression. Again, no evidence for positive selection was found. Interestingly, in MHC class I-deficient animals, the total number of gamma delta T cells was about twofold higher than in control and MHC class II-deficient mice and the proportion of V delta 4-expressing cells was correspondingly decreased. Taken together, these results cast doubt on a major role for conventional MHC antigens in shaping the gamma delta T cell repertoire of intraepithelial lymphocytes.

Immortalization of human T lymphocytes by oncogenes

Immortalized human T cell lines were established by cotransfecting c-Ha-ras and c-myc oncogenes to lymph node lymphocytes. The cell lines kept growing for 3 months after establishment without a decrease in growth rate. The cells did not require interleukin-2 (IL-2) for their growth, but addition of IL-2 stimulated the growth of these cells. Flow cytometric analysis revealed that these cells were T cells expressing CD4 or CD8 antigens. A CD4 positive (CD4+) cell line produced IL-6, indicating that the cell line belongs to helper T cells. The CD8 positive (CD8+) cell line possessed cytotoxicity to tumor cells, indicating that the cell line were killer T cells. Both cell lines were able to proliferate in serum-free medium indefinitely.

Two gut intraepithelial CD8+ lymphocyte populations with different T cell receptors: a role for the gut epithelium in T cell differentiation

Mouse gut intraepithelial lymphocytes (IEL) consist mainly (90%) of two populations of CD8+ T cells. One bears heterodimeric alpha/beta CD8 chains (Lyt-2+, Lyt-3+), a T cell receptor (TCR) made of alpha/beta chains, and is Thy-1+; it represents the progeny of T blasts elicited in Peyer's patches by antigenic stimulation. The other bears homodimeric alpha/alpha CD8+ chains, contains no beta chain mRNA, and is mostly Thy-1- and TCR-gamma/delta + or -alpha/beta +; it is thymo-independent and does not require antigenic stimulation, as shown by its presence: (a) in nude and scid mice; (b) in irradiated and thymectomized mice repopulated by T-depleted bone marrow cells bearing an identifiable marker; (c) in thymectomized mice treated by injections of monoclonal anti-CD8 antibody, which lead to total depletion of peripheral CD8+ T lymphocytes; and (d) in germ-free mice and in suckling mice. In young nude mice, alpha/alpha CD8 chains, CD3-TCR complexes, and TCR mRNAs (first gamma/delta) are found on IEL, while they are not detectable on or in peripheral or circulating lymphocytes or bone marrow cells. IEL, in contrast to mature T cells, contain mRNA for the RAG protein, which is required for the rearrangement of TCR and Ig genes. We propose that the gut epithelium (an endoderm derivative, as the thymic epithelium) has an inductive property, attracting progenitors of bone marrow origin, and triggering their TCR rearrangement and alpha/alpha CD8 chains expression, thus giving rise to a T cell population that appears to belong to the same lineage as gamma/delta thymocytes and to recognize an antigenic repertoire different from that of alpha/beta CD8+ IEL.

Culture conditions dictate whether mouse fetal thymus lobes generate predominantly gamma/delta or alpha/beta T cells

Thymus lobes from 14 day-old mouse embryos cultured submerged in r-IL-2 generated a mixture of CD8 alpha+/CD4- and CD8-/CD4- gamma delta TcR expressing cells (Ceredig et. al. 1989). Based upon Northern analysis with TcR constant region probes, no alpha beta T cells could be identified in these cultures. Submerged lobes also showed responsiveness to IL-7. In contrast, when cultured at an air liquid interface as organ cultures (OC), most cells appeared to express alpha beta TcR (Ceredig 1988). Thus depending on the mode of culture, fetal thymus lobes generate predominantly gamma delta or alpha beta T cells; it is unclear how this difference is regulated. Previous phenotypic and functional experiments suggested that gamma delta T cells may be present in OC. In order to study gamma delta T cells in both submerged lobe and OC, we have carried out three colour flow microfluorimetric analysis of gamma delta TcR, abTcR, CD3, J11d and CD8 beta expression by subpopulations of CD8 alpha and CD4 defined thymocytes. In addition, using V gamma-specific oligonucleotides and the polymerase chain reaction, we have begun identifying and sequencing the V gamma repertoire of gamma delta T cells in these mouse fetal thymus cultures.

In vivo treatment with anti B-220 monoclonal antibody affects T and B cell differentiation

The B220 cell marker is expressed on B cells and on T cell precursors. In order to determine the involvement of the B220 antigen on murine lymphoid differentiation, we treated 5-10-week-old mice periodically with a specific anti-B220 antibody, RA3-6B2, a non-cytolytic IgG2b. After the third injection, a significant reduction (P less than 0.02) in the number of thymocytes and less dramatically in the number of splenocytes was observed. This reduction was predominantly due to a decrease of cells carrying the following markers: Thy-1.2+, Lyt-1+, Lyt-2.3+, L3T4+, and asGM1+. Mitogenic response to concanavalin A, phytohaemagglutinin and lipopolysaccharide, mixed lymphocyte reaction, cytotoxic T cell activity, and plaque-forming cell generation were significantly decreased after the treatment (P less than 0.01). These results show that the in vivo treatment with anti-B220 monoclonal antibody reduced the number of T and B cells and modified their functional activity. This suggests that the B220 antigen is involved in the maturation of both T and B cells.

Differences in the phenotypes of cells mediating anti-tumour immunity at various stages of tumour progression in mice

In Winn assays, T cells from donors immunized by tumour excision, or from mice with small tumours, mediate rejection of the metastasizing murine fibrosarcoma MC-2. As the mean size of primary tumours in spleen donors increases, the strength of anti-tumour activity declines, until it is frequently undetectable in spleen cells from mice with very large tumour burdens. Loss of splenic anti-tumour activity is coincident with the appearance of cells capable of suppressing an otherwise protective anti-tumour response in Winn assays. This paper defines the phenotypes of T cells mediating immunity against MC-2. Eleven or more days after tumour inoculation the proportions of tumour-bearer splenic leucocytes expressing Ly 1.2 (CD5), Ly 2.2 (CD8a) or L3T4 (CD4) surface antigens were significantly less than similar preparations from normal animals. Depletion of Ly 1.2+ or L3T4+ cells from spleen cells of donors with small tumours, or from donors immunized by tumour excision, diminished protection in the Winn assay. Depletion of Ly 2.2+ cells from these donors had no effect on immunity. In contrast, spleen cells taken from donors with large tumors lost all anti-tumour activity if pretreated with any one of anti-Ly 1.2 or anti-Ly 2.2 or anti-L3T4 antibodies in the presence of complement. These results suggest that cells bearing the Ly 2.2 marker may be important to weak immunity remaining in the spleens of mice with large tumours, but are not critical to strong immunity generated early in tumour growth, nor to that following tumour excision. That is, in addition to an Ly 1.2+, Ly 2.2-, L3T4+ spleen cell subset also seen early in the growth of the MC-2 tumour, a cell population which expresses the Ly 2.2 marker and which is important to anti-tumour immunity emerges late in tumour growth.

In vivo influence of the anti-B220 monoclonal antibody administration of the T cell differentiation in mice

B220, a pan-B marker, is known to be also expressed on immature T cells of MRL/1pr or other congenic 1pr mice and minor population of immature thymocytes but not on peripheral T cells. In this study, we investigated in vivo the possibility whether B220 is one kind of premature T or prethymic T precursor cell marker as well as a pan-B cell marker. A monoclonal antibody against B220 glycoprotein was intravenously injected every 2 days into various strains of mice. After the third administration of this antibody, thymocytes decreased remarkably compared with those from the rat IgG-treated group, and spleen cells were also reduced significantly. Further, the number of cells expressing Thy-1, Ly-1, Lyt-2, and asialo GM1 (asGM1) in the spleen were significantly reduced. On the contrary, the number of cells expressing surface IgM (sIgM) or B220 were increased by this treatment, especially after the 8th treatment. Some T-dependent immunological functions including mitogenic responses to lectins and cytotoxic T cell activity were markedly suppressed but mixed lymphocyte reaction (MLR) and natural killer (NK) activity were rather augmented. Thus, B220 may be expressed on some kinds of T cell progenitor. Taken together, in vivo treatment with anti-B220 antibody may influence differentiating stages of some T cells from bone marrow progenitors before or just after their homing into the thymus.

CD4+CD8+ thymocytes develop into CD4 or CD8 single-positive cells in athymic nude mice

A differentiation pathway from CD4+CD8+ cells to CD4+CD8- or CD4-CD8+ cells was investigated in athymic nude mice. Using fluorescence-activated cell sorter, CD4+CD8+ cells were sorted out from AKR thymocytes (H-2k, Thy-1.1) stained with two monoclonal antibodies against CD4 and CD8 (anti-L3T4 and anti-Ly-2). These CD4+CD8+ AKR thymocytes were injected i.v. into CBA or C3H nude mice (H-2k, Thy-1.2) which had received 650 rads and had been reconstituted with syngeneic nude bone marrow cells. The lymph node cells of the nude recipients at 4 wks post-thymocyte transfer were shown to contain 50% AKR-derived Thy-1.1+ cells. The majority of the Thy-1.1+ cells were found to express either CD4 or CD8 alone but not to express both CD4 and CD8. These findings indicate that CD4+CD8+ thymocytes can develop into CD4+CD8- and CD4-CD8+ single-positive cells in extrathymic tissues.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. III. Genetic restriction of delayed hypersensitivity augmentation factor (DAF)

We found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the culture supernatant of the mixture of immune T cells and specific antigen, or in the serum of mice immunized with xenogeneic erythrocytes and elicited for DTH footpad reaction. Previous experiments on the genetic restriction of this factor (DTH-augmentation factor; DAF) indicated that DAF activity was effective across the MHC-barrier in C3H/He (H-2k)--BALB/c (H-2d) system. The genetic restriction between DAF and its acceptor cells was then investigated precisely using Igh (immunoglobulin heavy chain locus)-congeneic mice: 1) Expression of DAF activity was MHC-nonrestricted, 2) but was restricted by the Igh-linked gene on the 12th chromosome, 3) such Igh-linked gene restriction was also demonstrated by an absorption test with normal spleen cells. The acceptor cells for DAF were Thy-1+,L3T4+,Lyt-2- T cells.

Differentiation of B cell progenitors in vitro: generation of surface IgM+ B cells, including Ly-1 B cells, from Thy-1- asialoGM1+ cells in newborn liver

We have established a stromal adherent cell line (ST2) from fetal liver that promotes growth and differentiation of early B lineage cells. Many cells in the "null population" (3-5%) from newborn liver that lack antigens found on mature erythroid, myeloid or lymphoid cells proliferate extensively on this ST2 layer. Further division of this cell fraction on the basis of Thy-1 and asialoGM1 (aGM1) expression discriminates cells that predominantly proliferate from those that differentiate on the ST2 layer. Among four populations, Thy-1+ aGM1- cells proliferate most but yield few B220+ cells. In contrast, Thy-1- aGM1+ cells proliferate to a very limited extent, but most (greater than 90%) start to express B220 and a large fraction (up to 50%) become surface IgM+ after 2 weeks of culture. These B cells include cells expressing the pan-T cell molecule Ly-1, that is, Ly-1 B cells. Curiously, this Thy-1- aGM1+ cell population is largely absent from bone marrow in adult mice.

Three-cell-type clusters of T cells with antigen-presenting cells best explain the epitope linkage and noncognate requirements of the in vivo cytolytic response

Using an established i.p. adoptive transfer system in which primed precursors of cytolytic (Tc) cells are combined with primed helper (Th) cells and alloantigen, the three-cell-type hypothesis of T-T cooperation has been tested. This hypothesis assumes that cooperation takes place through the formation of clusters, consisting of one or more Tc precursors plus one or more Th cells binding to antigen on the surface of antigen-presenting cells (APC). By using antigens in which the H-2Db epitopes recognized by the Tc precursors are presented either on the same cell as the BALB minor histocompatibility epitopes recognized by the Th cells, or a different one, the value of epitope-linkage has been explored. Epitope-linkage is found to enhance the response at low concentrations of antigen but not at high ones, in accordance with the prediction that at low concentrations individual APC will usually take up either one antigen or the other but not both from an unlinked mixture, while at high concentrations most APC will take up both whether they are linked or not. In a further test of this hypothesis, no requirement for a cognate T-T interaction could be detected. With the three-cell-type interaction thus better established, its implications in terms of efficiency compared with linked-cognate interactions and its evolution are discussed.

Correlation of T cell receptor gene rearrangements to T cell surface antigen expression and to serum immunoglobulin level in scid mice

The severe combined immunodeficient (scid) mouse which has undetectable serum immunoglobulin (Ig) contains a small number of thymic lymphocytes which express Thy-1 and IL2 receptors (IL2R) but not Lyt-2 or L3T4 molecules. These thymocytes did not show any rearrangement of T cell receptor (TCR) beta-chain genes. Such thymocyte characteristics in the scid mouse were similar to the 15-day embryonic thymocytes in ordinary mice, indicating that the scid mouse thymocytes are arrested in the early stage of intrathymic differentiation. However, low or medium level serum Ig was occasionally found in the littermates of the scid mouse. The thymocytes of these mice showed some evidence of TCR beta-chain gene rearrangement and the presence of Lyt-2+/L3T4+ cells in correlation with the serum Ig level. In the mice with some serum Ig the thymocyte cell number was increased and the proportion of IL2R+ cells was decreased. Collectively, these results suggest that the rearrangement of TCR beta-chain genes is associated with the expression of Lyt-2 and L3T4 molecules in intrathymic differentiation and probably with cell proliferation of the migrated lymphoid cells in the scid mouse.

Immuno-electron microscopic characterization of large granular lymphocytes (natural killer cells) from rat liver

The immunocytochemical characteristics of large granular lymphocytes (LGL), isolated from the liver sinusoids of euthymic and athymic (nude) rats, were investigated in electron microscopy by the immunoperoxidase technique. The LGL were found positive for MRC OX-8 (natural killer cells and cytotoxic/suppressor T cells) and negative for MRC OX-19 (pan-T marker) in both rat strains. The LGL were heterogeneous in the expression of the natural killer cell marker asialo-GM1 which was found on 56% of the LGL from euthymic and on 71% of the LGL from athymic rats. LGL were easily distinguished from the other cells in the preparations, "conventional" lymphocytes and monocytes, thanks to their highly characteristic ultrastructural features, in particular by the presence of specific electron-dense cytoplasmic granules and rod-cored vesicles. These features have been described formerly for the so-called "pit cells" and are more reliable than the classical LGL characteristics at the light microscopic level, i.e. the presence of azurophilic granules. Our results give further support for the existence of an important population of natural killer cells in the liver sinusoids.

Expression of muscarinic cholinergic receptors during T cell maturation in the thymus

Thymocytes at various stages of their ontogeny have been studied in relation to their ability to bind [3H]quinuclidinyl benzilate [( 3H]QNB), a specific radioligand of the muscarinic cholinergic receptors. [3H]QNB-specific binding to thymocytes from 15-19-day fetal, newborn and adult thymuses of mice and rats was compared and correlated. Our experiments showed that the kinetics of [3H]QNB binding to thymocytes at 37 degrees C was similar to that of the lymph node lymphocytes (LNL) with maximum after 5 min of incubation and subsequent decrease to 10% of the maximum after 90 min of incubation. Maximal binding for the entire thymocyte population was twice lower than for the cortisone-resistant thymocytes (CRT) or for LNL. Binding of [3H]QNB carried out at 4 degrees C resulted in disappearance of the maximum, but did not alter the difference between CRT and entire thymocyte population. Depletion of CRT detectable [3H]QNB-specific binding to thymocytes until 18th day of gestation but the maximal binding increased up to 20% at the day 19 and reached 90% of adult level on the third day after birth. Moreover, carbamylcholine (a muscarinic agonist) treatment in vivo induced a significant decrease in [3H]QNB binding to the thymocytes. We thus suggest that a subpopulation of thymocytes bearing muscarinic receptors in the periphery acquired these receptors in the thymus as one of the last steps of their maturation. We cannot exclude the possibility that cholinergic stimulation might trigger these lymphocytes to leave the thymus.

A programmed functional and phenotypic development of bone marrow-derived cytotoxic cell precursors in vitro

An analysis of function and marker expression during cytotoxic cell differentiation in vitro from T cell-depleted bone marrow precursors is described. Cytotoxic activity is not detectable during the first five days of culture, but rises abruptly soon after. Antibody plus complement depletion studies show that cytotoxic cells derive from Thy-1-negative precursors and undergo a continual increase in Thy-1 and Lyt-2 marker expression as the culture progresses. A reciprocal decrease in asialo-GM1 antigen expression on effector cells is seen. The J11d-negative precursor cells acquire J11d (an antigen known to mark cortical thymocytes) at an intermediate stage of culture, but revert to the J11d-negative phenotype prior to functional acquisition. At least some effectors are T cell receptor positive as illustrated by an anti-T cell receptor antibody-mediated killing assay. These patterns precisely correlate with those detected among developing T cells in vivo. Results may indicate that a programmed course of differentiation inherent to bone marrow cells may be triggered in the absence of a thymic environment.

Molecular cloning of Lyt-3, a membrane glycoprotein marking a subset of mouse T lymphocytes: molecular homology to immunoglobulin and T-cell receptor variable and joining regions

Lyt-3 is a membrane glycoprotein expressed on thymocytes and class I major histocompatibility complex-restricted cytotoxic T cells. Lyt-3 is expressed as a heterodimer with Lyt-2, and this complex is considered to be a homologue of the human Leu-2/T8 (CD8) that has been postulated to be a receptor for the class I major histocompatibility complex. We have determined the complete primary structure of Lyt-3 from the nucleotide sequence of its cDNA clones. Analysis of the predicted amino acid sequence indicates that the Lyt-3 polypeptide has a 21-amino acid leader peptide, and the mature protein consists of an NH2-terminal region of 146 amino acids, a transmembrane region of 27 residues, and a C-terminal region of 19 amino acids. The NH2-terminal 110 residues show clear homology to the T-cell receptor and immunoglobulin variable region sequences. In addition, Lyt-3 has 11 residues that have strong homology to the joining region sequences of the T-cell receptor and the immunoglobulin heavy and light chains. The presence of immunoglobulin variable- as well as joining-region-related sequences in Lyt-3 further supports the idea that these molecules may be recognition molecules belonging to the immunoglobulin super gene family.

Differential expression of surface markers on thymic lymphomas induced by two carcinogenic agents in different mouse strains

Expression of several thymocyte surface antigens was monitored in a murine model system of thymic lymphoma induction in two different strains of mice. RF/J mice are sensitive to tumor induction by N-nitrosomethylurea (NMU) and by gamma-irradiation, while 129/J mice form tumors only upon NMU treatment. Latency periods for tumor formation were characteristically different depending upon the inducing agent and the mouse strain. We observed differences in thymic leukemia antigen and H-2K expression according to the mode of tumor induction and in relation to the mouse strain, implying multiple factors involved in target cell selection and tumor progression.

Differences in Ly 2- L3T4- thymocytes from foetal and adult murine thymus

The thymus is the major site of mammalian T cell production. The exact steps which occur in the thymus and give rise to mature T cells have not been defined, but there is general agreement that the earliest T cells are included in the group of thymic lymphoid cells lacking Ly 2 (CD8) and L3T4 (CD4). This population represents 2-6% of adult thymocytes and the vast majority of thymocytes in the mouse embryo until about day 16 of gestation. It has often been assumed that the foetal and adult CD4- CD8- thymocytes are equivalent. This paper shows that there are significant differences between the CD4- CD8- cells from these sources, in that the adult includes at least two subsets which are undetectable in the embryo. These two subsets of CD4- CD8- cells are both Ly 1high, B2A2- and M1/69-; one is Thy 1+ and one is Thy 1-. Each represents 20-25% of adult CBA double negative thymocytes. Both these populations are excluded from analyses of CD4- CD8- thymocytes which have been further selected as Ly 1low, a procedure adopted in several studies of early thymocytes. Even those subpopulations of CD4- CD8- cells which appear to express similar markers in adult and embryo thymus are quite different when analysed for cell size (forward light scatter), with the embryonic forms being much larger.

Two natural killer cell populations which belong to T cell lineage in nude mice

Enriched natural killer (NK) cell populations from BALB/c nude mice obtained by using nylon wool column (NWC) separation were stained with anti-Thy-1 and anti-asialo GM1 (GA1), and then were fractioned by flow cytometry into 4 cell populations: Thy-1+GA1+ cells, Thy-1+GA1- cells, Thy-1-GA1+ cells and Thy-1-GA1- cells. These cell populations were sorted out by flow cytometry and were examined for NK activity. Of the sorted cells, high NK activity was found in the two populations, Thy-1+GA1+ cells and Thy-1-GA1+ cells. In the other populations expressing Thy-1 antigen alone or expressing neither GM1 nor Thy-1, NK activity was almost undetectable. The two cell populations with NK activity were lineaged with respect to rearrangement of the T cell receptor genes. Southern gel analysis using a cDNA probe containing the D beta 1, J beta 1.3 and C beta 1 genes of the T cell receptor showed a reduction of the germ-line band of DNA in the 3 fractionated populations other than Thy-1-GA1- cells. Since these observations were demonstrated in nude spleen cells, it is indicated that the cells with NK activity belong to T cell lineage even if they lack Thy-1 expression and that they may develop out of the thymus, if they express Thy-1 antigen.

Binding and internalization of interleukin 1 by T cells. Direct evidence for high- and low-affinity classes of interleukin 1 receptor

In this report we describe, on the basis of direct IL-1 binding assays and IL-1 internalization studies, the existence of two classes of IL-1-R on a variety of T cell types. Cells of the EL4-6.1 thymoma express large numbers (approximately 20,000 per cell) of IL-1-R that have a Kd of approximately 300 pM for IL-1. Even though these receptors make up 98-99% of the total IL-1-R per cell, they appear to be nonfunctional, based on their inability to endocytose IL-1. A minor class of IL-1-R (200-400/cell) has an approximately 100-fold higher affinity for IL-1 (Kd, approximately 5 pM) and can rapidly internalize the ligand upon binding. All of the biological activity of IL-1 can be shown to occur via binding to high-affinity IL-1-R since the IL-1 concentration giving half-maximum biological activity in EL4-6.1 cells corresponds precisely to the Kd of this class of receptor. Other cell types, including normal T cells, also express both high- and low-affinity IL-1-R, but the absolute number of receptors per cell is considerably less.

The embryonic thymus produces chemotactic peptides involved in the homing of hemopoietic precursors

During ontogeny, T cell precursors must colonize the thymus to acquire immunocompetency. Using migration assays, a chemotactic activity was detected in conditioned media from avian embryonic thymic epithelial cells. The responding cells were shown to acquire T lymphocyte markers after homing into the thymus. Absorption experiments demonstrated surface receptors for the chemotactic substance on these hemopoietic precursors, which were not found on thymus-derived lymphocytes. Two peaks of chemotactic activity in the 1 kd-4 kd molecular weight range were detected after fractionation of thymic epithelial cell-conditioned medium. One of these activities was retained after heating to 95 degrees C but was destroyed after proteolytic treatment. Thus chemotactic peptides may be responsible for the thymic recruitment of the first hemopoietic precursors and may also be involved in the renewal of these precursors throughout adult life.

Interleukin 2 promotes growth and cytolytic activity in human T3+4-8- thymocytes

Human thymocytes bearing T3 but neither T4 nor T8 antigens (T3+4-8- cells) were obtained after negative selection of thymocytes, either fresh or cultured in medium containing recombinant interleukin 2 (IL-2), by treatment with Na1/34, OKT4A and B9.4 monoclonal antibodies (which recognize T6, T4, and T8 antigens, respectively) and complement. Quantitative flow cytometry showed a 98% pure population of T3+4-8- lymphocytes, which included proliferating cells. The growth and maturation requirements of these thymocytes were characterized and related to the T3-receptor complex and IL-2 pathways, thought to be used by mature lymphocytes. The results show that addition of recombinant IL-2 promotes, in a dose-dependent way, proliferation and acquisition of effector functions by cultured T3+4-8- thymocytes, the growth being inhibitable by monoclonal antibody 33B73 (anti-Tac). Furthermore, cytolytic activity of T3+4-8- cells induced by recombinant IL-2 is specifically blocked by monoclonal antibody OKT3, showing that it operates via the T3-receptor complex and does not require either T4 or T8 molecules. The finding of in vitro responsiveness to recombinant IL-2 in T3+4-8- thymocytes suggests a role of IL-2 in the growth and maturation of cells committed to the T-cell lineage, during intrathymic differentiation, prior to expression of T4 and T8 molecules.