Signal requirements for the in vitro differentiation of cytotoxic T lymphocytes (CTL): distinct soluble mediators promote preactivation of CTL-precursors, clonal growth and differentiation into cytotoxic effector cells

There is more than one interleukin 1

In 1972, Gery and co-workers(1) detected a factor that promotes murine thymocyte proliferation in culture supernatants of human peripheral blood adherent leukocytes. This factor is active across species lines, does not support the growth of interleukin 2 (IL-2)-dependent lymphocyte lines, is produced by monocytic rather than lymphocytic leukocytes, and has subsequently been termed interleukin 1 (IL- 1)(2). More recently, it has become evident that IL-1 activities can be produced by virtually every nucleated cell type and, in addition, IL-1 has been reported to have stimulatory effects on the growth and differentiation of numerous cell types. In this review, Joost Oppenheim and his colleagues discuss the biochemical characteristics, gene cloning, cell sources, biological properties and actions of IL-1, and give reasons why this pleitotropic, nonspecific hormone-like cytokine is of considerable concern to immunologists.

Lytic granules from cytotoxic T cells exhibit kinesin-dependent motility on microtubules in vitro

One major mechanism of cell-mediated cytolysis is the polarized secretion of lytic granules, a process which is highly dependent on microtubules. We isolated lytic granules from murine cytotoxic T cells and tested their ability to bind to and move along microtubules in vitro. In the presence of a motor-containing supernatant, the granules bound to the microtubules and moved along them at an average maximal rate of 1 microns/second. Virtually every granule could bind to microtubules, and about half translocated within a few seconds of binding. Motility required exogenous cytosolic motors, hydrolyzable nucleotides, and an intact granule membrane. Although the motor preparation used to support granule movement contains both plus- and minus-end-directed motor proteins, granule movement was strongly biased toward microtubule plus-ends. Inactivation of cytoplasmic dynein had little effect on granule binding and movement, but immuno-depletion of kinesin from the motor preparation inhibited granule binding by 50%. These results indicate that most granule movement in this assay is mediated by kinesin. The speed and direction of granule movement in vitro are sufficient to account for the release of lytic granules in the intact T cell. This model system should be valuable for studying the interactions of secretory granules with microtubules, and for identifying the regulatory factors involved.

Modification of tumor cells by a low dose of Newcastle disease virus. III. Potentiation of tumor-specific cytolytic T cell activity via induction of interferon-alpha/beta

To investigate possibilities of augmenting tumor-specific immune responses against the highly metastatic murine lymphoma ESb, we tested the effects of the interferon inducer newcastle disease virus (NDV) or of interferon-alpha/beta as costimulator in mixed lymphocyte-tumor cell cultures (MLTC) on the tumor-specific cytolytic T cell (CTL) response. Both approaches, namely stimulation of ESb immune spleen cells with NDV-modified stimulator cells or with ESb stimulator cells and exogenous IFN-alpha/beta, led to a selective potentiation of tumor-specific CTL activity. The potent activation of tumor-specific CTL precursor (CTLP) required the simultaneous presence of the specific ESb tumor antigen--possibly to mediate a signal via the corresponding T cell receptor--and costimulators--possibly to mediate second activation signals. Increased CTL activity required only very low amounts of NDV or IFN-alpha/beta. The generation of CTL activity in the MLTC cultures could be blocked by antisera to IFN-alpha/beta, not, however by control sera. Similar effects were observed in vivo, suggesting that IFN-alpha/beta not only caused an increase in CTL activity, but was essential for the generation of CTL activity. The reduction of the generation of CTL by antiserum to IFN-alpha/beta could be overcome by excess interferon, especially when using ESb-NDV as stimulator cells.

Accessory factors involved in murine T cell activation. Distinct roles of interleukin 6, interleukin 1 and tumor necrosis factor

Interleukin (IL) 6 was compared to other macrophage-derived products for its capacity to support the proliferation of accessory cell-depleted T cells. Monoclonal anti-IL6 antibodies were found to inhibit completely the "accessory activity" of macrophage supernatants, thus demonstrating the central role played by IL6 in T cell activation. IL6 was apparently more critical for initiating than in maintaining T cell proliferation because anti-IL6 antibodies lost all inhibitory activity when added late to the culture. Moreover, IL6 was not the only accessory factor required for optimal T cell proliferation. Using low-density cultures to minimize the number of contaminating accessory cells, we found that significant proliferation of CD4 cells was obtained only in the presence of both IL6 and IL1. In contrast, with CD8 cells substantial proliferation was obtained with IL6 alone. This response could, however, be enhanced by IL1. Tumor necrosis factor (TNF) and granulocyte/macrophage colony-stimulating factor showed no activity in these assays. The concentrations of IL1 and of IL6 required to support optimal proliferation were 10 pg/ml and 1 ng/ml, respectively. Analysis of the mechanisms underlying T cell activation by IL1 and IL6 indicated that both cytokines were required for optimal production of IL2 but that IL6 alone was sufficient to confer IL2 responsiveness. For CD8 cells, this effect was observed with doses of IL6 about 100 times lower than those required for the induction of IL2 secretion (0.001 vs. 0.1 ng/ml). TNF, which was not capable of inducing IL2 secretion, was also found to induce IL2 responsiveness but only at a concentration approximately equal to 1000 times higher than that of IL6. In accordance with these observations, IL6 and to a lesser extent TNF were found to enhance IL2R expression by CD8 cells. Interestingly, this enhancing effect was totally dependent on the presence of IL2.

Interleukin 5 is a differentiation factor for cytotoxic T lymphocytes

The role of IL-5 on the generation of cytotoxic T lymphocytes (CTL) was analysed using a culture system in which production of T helper cell factors was abrogated by exposure of the stimulator cells to ultraviolet irradiation. Supernatants from a T helper cell line (2.19 sup), recombinant (r) IL-2, rIL-4 and rIL-5 were then tested for the capacity to replace T cell help, on the generation of CTL. The results showed that the specific CTL response, in unseparated spleen cells, could be reconstituted by either 2.19 sup, IL-2 or IL-4. However, if the responder cells were purified in nylon wool, only 2.19 sup or rIL-4 plus rIL-5, but not each lymphokine per se, reconstituted the CTL response. Because IL-5 does not support T cell proliferation, it is suggested that IL-5 induces differentiation of immature precursors into CTL. Based on these findings and in an attempt to conciliate the conflicting views that have emerged from different reports, as to whether IL-2 by itself could support generation of CTL in purified T cells, a hypothesis is formulated, suggesting that T cell at different stages of differentiation require distinct lymphokines to acquire CTL effector function.

Tumour-associated proliferative responses in vitro of regional lymph nodes draining solid cancers in man

The proliferative responses in vitro of tumour-draining lymph node lymphocytes were evaluated against autologous colon and lung carcinoma cells. The reactivity of lymphocytes appeared to be directed against tumour-associated rather than tumour-specific antigens. The lymphocyte reactivity detected was not due to an autologous mixed lymphocyte reaction. Recombinant interleukin-2 augmented the responses detected but not their tumour specificity. Phenotypic characterisation indicated the presence of T suppressor/cytotoxic (TS/C) cells as well as natural killer (NK) cells. Only the later, however, were active in functional cytotoxicity assays. The inability to generate both tumour-specific proliferation of tumour-draining lymph node lymphocytes and tumour-specific cytotoxic killer cells may be due to the presence of suppressor cells in the regional lymph nodes; preliminary data suggest the presence of such cells.

Cross-linking of T-cell receptors is insufficient to induce IL-2 responsiveness (activation) in resting Lyt-2+ T cells. IL-4 or RIF are essential as second signal

High-density (resting) murine Lyt-2+ T cells exposed in vitro to the ligand concanavalin A (Con A), or immobilized F23.1 monoclonal antibody (mAb) recognizing an allotypic determinant on the T-cell receptor (TCR), or high-density (resting) allogeneic B stimulator cells remain IL-2-unresponsive; such cells do not express functional IL-2 receptors unless reconstituted with accessory cells. We conclude that cross-linking of TCR is insufficient as signal to induce IL-2 responsiveness, that is, activation. Both the macrophage product RIF and the T-cell product interleukin-4 efficiently induce the IL-2 responsiveness in resting Lyt-2+ T cells exposed in vitro either to the ligand Con A, or to immobilized F23 mAb, or to nonimmunogenic allogeneic stimulator cells. We conclude that two restricting points control the induction of IL-2 responsiveness (activation) in antigen-driven Lyt-2+ T-cell responses, that is, cross-linking of TCR by way of presented antigen and "costimulator" activity expressed by accessory cells. Both RIF and IL-4 express costimulator activity, therefore replacing the requirement for accessory cells.

Cytokines involved in the generation of cytolytic effector T lymphocytes

The differentiation of precursor, antigen-competent, T cells into effective helper and/or cytolytic cells involves a number of different steps that are signaled by soluble molecules termed cytokines. We demonstrate here that subsets of T cells, distinguished on the basis of their expression of cell-surface markers, CD4 and CD8, receive distinct signals for differentiation. The precursor T cells of a T-cell subset that is MHC class II-restricted are readily activated by signals provided by rIL-1, rIL-2, rIL-3, or IFN-gamma. The precursor T cells of the MHC class I-restricted T-cell subset, on the other hand, are not readily activated by signals provided by rIL-1, rIL-3, or IFN-gamma. Recombinant IL-2 apparently functions in a nonrestricted manner, in that it can provide growth signals to both MHC class I- and class II-restricted T cells.

Dynamics of cytotoxic T lymphocyte precursors in vivo assessed by change in the radiation sensitivity. Evidence for development of radiation-sensitive memory cells without clonal expansion

The dynamics of cytotoxic T lymphocyte precursors (CTL-p) in mice injected with allogeneic spleen cells (SC) was studied with special reference to changes in their radiation sensitivity. Whole-body 400 rad X-ray irradiation of allo-SC-primed and unprimed mice virtually abolished the capacity of their SC to proliferate and to generate CTL in primary or secondary mixed leucocyte culture (MLC). However, the impaired ability of SC to generate CTL in the primary MLC was restored by interleukin 2 (IL-2). This showed that helper cells whose activity was replaceable with IL-2 (IL-2-producing cells) were functionally more radiation-sensitive than CTL-p in unprimed mice. In contrast, the radiation-impaired activity in secondary MLC was not restored by IL-2, suggesting that memory CTL-p in allo-SC-primed mice were unexpectedly sensitive to radiation. The D37 values determined from the percentage of residual CTL-p activity of SC in bulk cultures 1 day after irradiation were 525 rad for virgin CTL-p and 75 rad for memory CTL-p. Further studies demonstrated that the radiation-sensitive memory CTL-p were generated from relatively radiation-resistant precursors, largely independent of radiation-sensitive IL-2-producing cells and of cellular proliferation. The mean frequency of CTL-p in SC measured by limiting dilution assay was not significantly increased by the priming. This supports our conclusion that the development of the memory CTL-p activity in allo-SC-primed mice did not depend on clonal expansion. Whole-body 400 rad-irradiation reduced the frequency of CTL-p in SC from unprimed mice to 1/2-1/3 and that in SC from allo-SC-primed mice to 1/8-1/15. This supports the view that the majority of radiation-resistant virgin CTL-p functionally mature to radiation-sensitive memory CTL-p without cellular proliferation in allo-SC-primed mice.

CD4 cytotoxic T lymphocyte differentiation

In vitro allostimulated CD4+ human lymphocytes were cloned by micromanipulation and expanded for a short time in IL-2 conditioned medium. In the present study we observed that proliferative noncytotoxic cloned cells were able to acquire the specific cytolytic activity under some modification of the cloned cells restimulation cycle. We demonstrated that rIFN-alpha and -gamma are the agents responsible for the acquisition of specific lytic activity.

Primary activation of murine CD8 T cells via cross-linking of T3 cell surface structures: two signals regulate induction of interleukin 2 responsiveness

In the model system used here to study the minimal signal requirements for the activation of murine resting CD8 T cells, cross-linking of T cell receptor structures by antigen-presenting cells is substituted for by the use of anti-CD3 monoclonal antibodies immobilized in Sepharose beads. We show that cross-linking of CD3 structures, even in combination with CD8 structures, is necessary but insufficient to induce responsiveness to the growth-promoting effect of interleukin 2 (IL2), i.e. fails to induce expression of functional IL2 receptors. A macrophage cell line product termed IL2 receptor-inducing factor (RIF), but not IL1, IL3, IL4 or tumor necrosis factor, efficiently functions as costimulator. Once activated, growth of CD8 T cells is entirely driven by IL2. We conclude that two restriction points control the activation of resting CD8 T cells. While cross-linking of CD3 structures is essential as a first step, RIF is required as competence factor to induce IL2 responsiveness. We consider the possibility that the ability of antigen-presenting cells to produce RIF determines the immunogenicity of presented antigen towards antigen-reactive resting CD8 T cells.

Characterization of a factor(s) which synergizes with recombinant interleukin 2 in promoting allogeneic human cytolytic T-lymphocyte responses in vitro

Supernatants from PHA-activated human peripheral blood mononuclear cells, depleted of virtually all IL-2 activity by an anti-rIL-2 immunoadsorbent column, contain a factor(s) which synergizes with rIL-2 in facilitating the generation of allogeneic human CTL responses in vitro. This factor, provisionally termed CTL maturation factor (TcMF), did not appear to promote CTL responses in the absence of rIL-2. Furthermore, it acted later than IL-2 in facilitating CTL responses and could not be replaced by recombinant IFN-gamma. In this report we show that rIFN-alpha, rIL-1 alpha, and rIL-1 beta likewise lack TcMF activity. The TcMF activity in lymphokine-containing culture supernatants could be eliminated by trypsin or pronase but not by neuraminidase or RNase. Gel filtration revealed two peaks of TcMF activity, one at 12,000 to 25,000 Da and the other at 45,000 to 65,000 Da. Isoelectrofocusing demonstrated substantial charge heterogeneity. The majority of TcMF activity was recovered between pI 4.0 and pI 5.5 with a minor component at pI 6.5, corresponding to the areas in which IL-1 activity was also found. However, TcMF activity could be separated from IL-1 by reverse-phase HPLC. Moreover, TcMF recovered following reverse-phase HPLC was also found to be depleted of IL-4 activity. These studies suggest that TcMF activity is mediated by a protein(s) distinct from IL-1, IL-2, IL-4, and interferon-alpha or-gamma.

Activation of murine CD8+ lymphocytes: two distinct signals regulate c-myc and interleukin 2 receptor RNA expression

Resting cytotoxic T lymphocyte precursors (CTL-P; CD8+) constitutively express T cell receptors (TcR) on their cell surfaces. CTL-P are preactivated if binding of the corresponding antigen (mitogens, allogeneic major histocompatibility complex (MHC) determinants, viral proteins or haptens in conjunction with self MHC structures) to the TcR takes place. Using a myc-specific probe I show that within 12 h first antigen binding leads to optimal c-myc RNA expression which seems to be the first sign that resting CTL-P are preactivated. Thereafter, c-myc RNA expression was remarkably reduced only at day 5. Antigen alone, however, is not sufficient for interleukin 2 receptor (IL2R) RNA expression. A monocyte-derived, soluble mediator termed IL2R-inducing factor (RIF) acts in conjunction with antigen to induced the expression of IL2R RNA and functional IL2R on the cell surface. RIF is a 44-kDa heat-labile protein produced by accessory cells and its function is restricted to CD8+ lymphocytes. IL2R RNA is first expressed 12 h after onset of culture, maximally expressed on day 3 and it decreases thereafter. Cells kept in long-term culture without mitogen but in the presence of IL2 do not express high amounts of IL2R RNA. Expression of IL2R RNA can be very efficiently reinduced, however, by mitogenic stimulation. In contrast to primary cultures, IL2R RNA expression peaks earlier and is independent of RIF. The results obtained here show that (a) for CD8+ lymphocytes of primary cultures two distinct activation signals (mitogen and RIF) are necessary for c-myc and IL2R RNA expression and (b) for CD8+ lymphocytes of secondary cultures the mitogenic signal alone is sufficient for re-expression of IL2R RNA.

Regulation of helper T cell clone proliferation via the CD2 molecule

We have investigated the requirements for CD2-induced proliferation of a CD4+, CD8-, CD3+, CD2+ antigen-specific, class II-restricted proliferating cloned cell line. A combination pair of two monoclonal antibodies (MoAb) recognizing, respectively, TII1 and D66 epitopes on the CD2 molecule was used as a stimulus. The regulatory function of accessory cells and various interleukins in this proliferation was determined. The results show that although this clone was able to proliferate in the absence of accessory cells (AC) or interleukin 1 (IL-1) when stimulated by these MoAb, AC constantly enhanced the response to these MoAb. AC acted by increasing high-affinity IL-2 receptor expression. On the contrary they did not play any role in IL-2 production. This regulation of IL-2 receptor expression by AC was specific of adherent cells, did not involve Fc receptors, was impaired when AC were metabolically inactivated and did not require T cell-AC interaction via LFA1, CD4, or HLA molecules. The AC function was not abrogated by anti-IL-1 antibodies and could not be replaced by exogenous IL-1. These results were compared to previously described AC effects on resting T-cell proliferation when stimulated with the same pair of anti-CD2 MoAb. Clear differences in activation requirements in resting and activated T cells via CD2 molecules were found.

Identification of a major 50-kDa molecular weight human B-cell growth factor with Tac antigen-inducing activity on B cells

A bioassay was developed using human small B cells adherent to anti-human IgM (anti-mu)-coated wells. These B cells were stimulated to proliferate by culture supernatants of concanavalin A (Con A)-activated human peripheral blood lymphocytes (Con A Sup) even in the presence of high concentrations of anti-mu coated on assay wells. Human B-cell growth factor (BCGF) activities were partially purified from Con A Sup. Preparative chromatography (Sephacryl S-200 and isoelectrofocusing) yielded a major peak of BCGF activity for B cells adherent to anti-mu-coated wells with a molecular weight of 50,000 (50 kDa) and a pI 7.6. The 50-kDa BCGF was further purified by sequential chromatography using DEAE-Sephacel, CM-Sepharose, Sephacryl S-200, CM-high performance liquid chromatography (HPLC), and hydroxyapatite (HA)-HPLC. The HA-HPLC-purified 50-kDa BCGF was free of interleukin-1 (IL-1), interleukin-2 (IL-2), and interferon activities, but could support growth of BCL1 cells, similar to BCGF-II. Neither IL-1 nor interferon-gamma had any growth-stimulating effect in our B-cell proliferation assay with or without BCGF in Iscove's synthetic assay medium. BCGF-induced proliferation of B cells adherent to anti-mu-coated wells could be markedly augmented by the simultaneous or sequential addition of recombinant human IL-2 (rIL-2). When cultured for 3 days with 50-kDa BCGF, about 40% of B cells adherent to anti-mu-coated wells expressed Tac antigen, and monoclonal anti-Tac antibody inhibited rIL-2 enhancement of proliferation of 50-kDa BCGF-preactivated B cells. In addition, 50-kDa BCGF could induce Tac antigen on an Epstein-Barr virus-transformed B-cell line (ORSON) in the presence of a suboptimal dose of phorbol myristate acetate (PMA) and also on a natural killer-like cell line (YT cells). We have therefore identified a major 50-kDa BCGF activity with Tac antigen-inducing activity that also has a synergistic effect with IL-2 on normal B-cell proliferation.

Interleukin 5, a T-cell-derived B-cell differentiation factor also induces cytotoxic T lymphocytes

We describe an interleukin, termed interleukin 5, that is the recombinant product previously referred to as T-cell-replacing factor (TRF), B-cell growth factor II (BCGF II), or killer-helper factor (KHF). TRF has been defined as a T-cell-derived lymphokine that acts on activated B cells as a B-cell differentiation factor. We have previously demonstrated that TRF is identical to BCGF II and induces expression of receptors for interleukin 2 (IL-2) on activated B cells. We also have reported that KHF can induce not only expression of IL-2 receptors on peanut agglutinin-binding (PNA+) thymocytes but also generation of cytotoxic T lymphocytes (CTL) in PNA+ thymocytes in the presence of IL-2. We show here that culture supernatants of T-cell hybridomas that produce TRF as well as TRF purified by high-pressure liquid chromatography (HPLC-TRF) have KHF activity and generate CTL in PNA+ thymocytes in the presence of stimulator cells and IL-2. Moreover, translation products (recombinant TRF) of Xenopus oocytes injected with cDNA encoding for murine TRF (BCGF II) also exert KHF activity. A rat monoclonal anti-TRF antibody TB13 can block generation of CTL by HPLC-TRF or recombinant TRF. These results indicate that TRF acts not only on B cells as BCGF II but also on PNA+ thymocytes as KHF. In view of the diverse activities and targets of TRF, we propose that TRF refers to a different interleukin, interleukin 5.

An antigen-independent physiological activation pathway for L3T4+ T lymphocytes

The data presented in this report describe an antigen-independent activation pathway leading to reinduction of proliferation of class II major histocompatibility complex (MHC)-restricted murine T cell lines that after previous antigen-specific stimulation reverted to a resting state. Antigen-independent proliferation and interleukin 2 (IL2)-receptor expression occur in the presence of splenic accessory cells, exogenous IL2 and a soluble factor(s) provisionally termed T cell-stimulating factor(s) (TSF). Each of these components is essential for inducing growth. TSF is found in the supernatant of an autoreactive T cell line upon stimulation with syngeneic accessory cells. Neither TSF nor accessory cells can be replaced by IL1 and by some other cytokines. Monoclonal antibodies against class II MHC molecules, the T cell receptor and L3T4 do not block this antigen-independent stimulation. This demonstrates that the function of the accessory cell in this system is not MHC restricted and that the T cell receptor is also not involved. Furthermore, it is suggested that the blocking of L3T4 molecules by antibody will mediate a negative signal only if T cells are triggered via their antigen receptors.

Specificity repertoire of splenic Lyt-2+/F23+ cytotoxic lymphocyte precursors from B6 mice

As revealed by flow cytometric analysis, about 30% of nylon wool nonadherent Lyt-2+ B6 spleen cells were F23+, i.e., were stained with the monoclonal antibody F23.1 directed against an allotypic T-cell receptor determinant. The specificity repertoire of splenic Lyt-2+/F23+ cytotoxic lymphocyte precursors (CLP) from B6 mice was investigated in a limiting dilution (LD) system designed to support clonal expansion in vitro of a representative fraction of this T-cell subset: in highly purified Lyt-2+ responder cells cocultured with mitomycin-treated F23 hybridoma cells in the presence of (recombinant) interleukin 2 under LD conditions, one out of three Lyt-2+/F23+ CLP gave rise to a functional cytotoxic T lymphocyte (CTL) clone. The split-well analysis of individual CTL populations demonstrated a clear-cut segregation of the lytic reactivities toward different allogeneic Con A blast targets. A large fraction of B6-derived CTL clones (3-10%) specifically lysed fully H-2 allogeneic (H-2k, H-2d), or H-2K mutant (bm1) targets. Self-reactive and allorestricted lytic patterns were not found.

Functional and biochemical characteristics of a murine interleukin 2 receptor-inducing factor

High density (resting) murine Lyt-2+ T cells exposed in vitro to the ligand concanavalin A (Con A) remain interleukin 2 (IL 2) unresponsive, i.e. do not express functional IL 2 receptors, unless reconstituted with accessory cells. This finding provides a bio-assay to define functional and biochemical characteristics of an IL 2 receptor-inducing factor (RIF). RIF bioactivity as secreted from the macrophage cell line P388-D1 is associated with a trypsin-sensitive protein of 44 kDa which does not need to be glycosylated and which binds to and can be eluted from hydroxylapatite and phenyl-Sepharose. While both RIF and IL 1 are produced by accessory cells the lymphokines separate from each other according to functional and biochemical criteria. Either accessory cells, RIF or the protein kinase C activator phorbol myristate acetate can substitute for each other and are equally active for the induction of IL 2 responsiveness in high-density Lyt-2+ T cells exposed to Con A. To explain these results we conclude that in the mitogen system used, induction of IL 2 responsiveness (activation) represents a two-step event in which first cross-linking of cell surface structures by the ligand Con A excites the responder T cells, which subsequently respond to the accessory cell product RIF.

Accessory cell dependent T lymphocyte proliferation: potent activity of dendritic cells

The proliferative response of T lymphocytes to Concanavalin A (Con A) and the oxidative mitogens, sodium periodate (NaIO4) and neuraminidase plus galactose oxidase (NGO), requires the participation of dendritic cells (DC). High density cells (HDC) recovered from the fractionation of lymph node cells on a discontinuous gradient of bovine plasma albumin did not respond to NaIO4, but responded well above background levels to NGO or Con A. Addition of DC elevated these responses further. By an indirect panning technique, the HDC were exhaustively depleted of cells expressing Ia surface antigens. Ninety-nine percent of these HDC displayed T cell surface antigens. These Ia- T cells did not respond to any of the three mitogen treatments until DC were added, whereupon the proliferative responses were restored in a concentration-dependent manner, with maximal levels attained at a DC to T cell ratio of 1:200. The addition of a purified preparation of IL2 to untreated or mitogen-treated Ia- T cells increased the proliferative responses slightly and was unable to substitute for the potent activity of dendritic cells. Only the addition of DC was able to stimulate mitogen-induced proliferation to maximal levels. The limiting factor in these responses was the number of dendritic cells, which controlled the induction of both the release of IL2 and responsiveness to IL2 for the oxidative mitogens and Con A. Thus, DC function as potent accessory cells for each of the three mitogens.

Clonal activation of cytotoxic lymphocyte precursors by monoclonal anti-CD3 antibody: analysis of feeder cell requirements

Activation of cytotoxic lymphocyte precursors (CLP) by the mitogenic monoclonal anti-CD3 antibody OKT3 was studied under limiting dilution (LD) culture conditions. One out of 2-6 E-rosette-purified T cells gave rise to a cytotoxic T cell (CTL) clone when cultured in the presence of OKT3 (0.2-2 ng/ml), recombinant IL-2 (100 U/ml), and irradiated feeder cells. Clonal CLP activation was optimally supported by a combination of E-rosette-depleted non-T feeder cells with small numbers of T cells added back. Among the cell lines tested, Fc-receptor-bearing monocytic cell lines U937 and HL-60 were efficient feeder cells whereas T cell lines (Jurkat, Molt-4, Ke37) did not support clonal CLP activation. These data indicate that clonal activation of CLP and differentiation into cytotoxic effector cells under LD culture conditions are critically influenced by the type and number of feeder cells used.

The interleukin-2 receptor, its physiology and a new approach to a selective immunosuppressive therapy by anti-interleukin-2 receptor monoclonal antibodies

In this report we have summarized our findings on the IL-2 receptor and our attempts to find an IL-2 receptor targeted immunosuppressive therapy. IL-2 receptors are detectable in two different forms: as monomeric, surface expressed, and as dimeric, presumably non-surface expressed molecules. The dimeric form seems to be non-covalently bound to an as yet undefined 110 KD molecule. The functions of the monomeric versus the dimeric form, as well as that of the noncovalently bound molecule, and their relationship to high and low affinity IL-2 receptors are not yet clear and remain to be elucidated. Upon antigenic or mitogenic stimulation, IL-2 receptors became expressed at the surface of T-lymphocytes. Receptor expression is accompanied by the capacity of the cells to proliferate in response to IL-2. Resting T-cells do not proliferate in response to IL-2. IL-2 dependent proliferation of cells without external stimulation is either due to the presence of a small number of IL-2 receptor bearing cells in the respective population or due to a small number of IL-2 receptors present on the surface of cells. IL-2 itself does not induce IL-2 receptor expression on resting cells but has been shown to up-regulate its own receptor once expressed. In contrast to resting lymphocytes, some leukemic cells and early embryonic thymocytes in the species tested constitutively express IL-2 receptors. The role of such constitutively expressed receptors is not yet clear. As demonstrated in mice, the requirement(s) for induction of IL-2 receptor expression for the helper/inducer subset (Lyt-2+) are different from those of the cytotoxic/suppressor subset (L3T4+). In contrast to Lyt-2+ cells, the accessory cell requirement for L3T4+ cells could not be replaced by cytokines. Whether Lyt-2+ cells require an additional, not yet defined receptor inducing factor (RIF) besides IL-2 in order to become IL-2 receptor positive and to consequently proliferate in response to IL-2, is a matter of controversy. There is evidence that interleukin-1 and some functionally related factors produced by leukemic cells enhance expression and/or function of the IL-2 receptors. IL-2 receptors of the high and low affinity type expressed upon antigenic stimulation are cleared from the cell surface. As demonstrated in this report, the vast majority of them, probably those of low affinity type, are released from the cells continuously. The mechanism of their release and the possible immunoregulatory role of circulating receptors found in the serum of animals is not yet clear.(ABSTRACT TRUNCATED AT 400 WORDS)

Interferon: a cytotoxic T lymphocyte differentiation signal

Human T cell clones which were able to proliferate in response to specific stimuli but could not kill even in the presence of lectins were found to acquire the specific lytic function when interferon alpha or gamma was added on day 1 of the 7-day restimulation culture. These results demonstrate that interferon may act as a cytotoxic T lymphocyte differentiation signal. This signal can be blocked by the monoclonal antibody LeoA1 which recognizes a 70-kDa cell surface structure, involved in cytotoxic T lymphocyte differentiation.

Interleukin 2 induces both, growth and maturation of lectin reactive Lyt-2+ but not Lyt-2-precursor cells and regulates the cytolytic potential of effector cells

This study investigated the requirements for lymphokines derived by recombinant (rec.) DNA technology for the induction of growth and maturation in highly purified lectin reactive T cell subsets. Nylon purified C57BL/6 lymph node T cells were treated with monoclonal anti-Lyt-2.2 or anti-L3T4 antibodies and fluorescence labeled (FITC) anti-immunoglobulin antibodies and were positively selected into Lyt-2+ (L3T4-) and Lyt-2- (L3T4+) lymphocyte subsets using a fluorescence-activated cell sorter. Sorted T lymphocytes, which were devoid of accessory cells were incubated either in bulk culture (2 X 10(2) - 3 X 10(4) cells/microculture) or under limiting dilution conditions (2.5-1,000 cells/well) with lectin (Concanavalin A, Leukoagglutinin) and rec. human Interleukin 2 (rec. hIL-2) and/or rec. mouse Interferon gamma (rec. mIFN-gamma). The data show that Lyt-2+ lymphocytes respond to lectin and rec. hIL-2 with growth and development of cytolytic activity in the absence of other exogenous factor(s) or accessory cells. The presence of monoclonal antibodies to the Interleukin 2 receptor during the sensitization phase ablated the induction of Con A reactive precursor cells of cytolytic lymphocytes (CTL-P) by either rec. hIL-2 or conventional IL-2 containing lymphokine sources, indicating the essential role of IL-2 during activation of Lyt-2+ T lymphocytes. In contrast, Lyt-2- lymphocytes could not be induced by lectin and rec. hIL-2 alone for proliferation and always required the presence of accessory cells for significant growth. Exogenous rec. m IFN gamma was unable to induce growth and cytolytic activity in Con A reactive Lyt-2+ cells and did not significantly effect their response to rec. hIL-2. Limiting dilution experiments revealed that 10-16% of the Lyt-2+ lymphocytes responded to Con A and rec. hIL-2 with growth (GTL-P). The frequencies of CTL-P, determined under similar conditions, were always lower compared to GTL-P. However the results suggest that the differences observed between both precursor populations is due to differential sensitivity of the detection system rather than to the recruitment of distinct T cell subsets. Furthermore, it was shown that at least 50% of lectin reactive CTL-P were induced by rec. hIL-2 to secrete IFN-gamma under optimal conditions. The finding that some of the conventional lymphokine sources were superior to rec. hIL-2 in the induction of growth and cytolytic activity suggests the existence of mediators distinct from IL-2 that regulate the expansion of CTL-P.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of resting T lymphocytes by a monoclonal antibody directed against an allotypic determinant on the T cell receptor

The murine monoclonal antibody F23.1 reacts with an allotypic determinant on the beta chain of the T cell receptor expressed by approximately 20% of T helper and cytotoxic T lymphocytes of most common mouse strains. This IgG2a antibody, either in soluble form or covalently coupled to Sepharose beads, can activate resting T cells from naive animals to proliferate. Interestingly, under all conditions of activation, the antibody can only induce proliferation if exogenous lymphokines in the form of Con A supernatant are provided. Thus, it is unlike most lectins and anti-T3 antibodies in this regard. Furthermore, under all conditions of culture, F23.1 activates preferentially the Lyt-2+ subset of T cells. This is the case even in the presence of accessory cells. Further evidence is provided that two soluble lymphokines, different from IL2, are required to initiate IL2-dependent growth and to allow the expression of lytic activity.