Nonspecific inhibitor released by T acceptor cells reduces the production of interleukin-2

Immunostimulation by retinoic acid

Retinoids have been shown to inhibit tumour growth in several model systems. In this paper evidence that immune effectors are important for this effect is discussed. Injection of retinoic acid (RA) into mice before challenge with allogeneic or syngeneic tumour cells results in a strong increase in cell-mediated cytotoxicity specific for the respective tumour. This stimulation appears to be due to effects taking place before or during the induction phase rather than the effector phase of cell-mediated cytolysis. The effector cells responsible for cytotoxicity express the Thy 1 antigen, are H-2 specific and are therefore T killer cells. The induction of T cell-mediated cytotoxicity requires the participation of the lymphokine interleukin 2 (IL-2). The possibility was tested that RA directly or indirectly influences the production of IL-2 and thereby stimulates the induction of T killer cells. Results indeed show that RA-injected mice display an increased capacity to produce IL-2 upon stimulation of their splenocytes in a mixed lymphocyte reaction. It appears therefore that RA has an effect on T cells that are destined to produce IL-2 upon antigenic challenge. Since IL-2 plays a role not only in the induction of specific cytotoxic T cells but also in the induction of natural killer (NK) cells, RA was also tested in a model system in which NK cells appear to play an important protective role. Results showed that split-dose irradiated mice that lose their NK activity and subsequently develop leukaemia can be protected from leukaemogenesis either by reconstitution with NK cells or by injection with RA. The question of whether this effect is due to stimulation of immune effectors or is a direct effect on the preleukaemic cells is discussed.

Effects of Brazilin on induction of immunological tolerance by sheep red blood cells in C57BL/6 female mice

Brazilin was examined for its effects on the induction of immunological tolerance. Brazilin was administered to C57BL/6 female mice for 2 consecutive days before the immunization with high dose SRBC (10(9) cells) which can produce immunological tolerance. Delayed type hypersensitivity, IgM plaque forming cells, ConA induced IL-2 production and mitogen- or antigen-induced proliferation of lymphocytes were measured as evaluation parameters. Administration of brazilin prior to immunization could keep the DTH and IL-2 production almost optimally immunized levels. Brazilin also inhibited the elevation of non-specific suppressor cell activity. ConA induced proliferation of splenocytes in high dose SRBC immunized mice was significantly decreased by pretreatment of brazilin. And this might be one of the reason for augmentation of DTH by brazilin. However, IgM plaque forming cells were not affected by the treatment of brazilin. These results indicate that brazilin prevents the induction of immunological tolerance caused by high dose SRBC by suppressing the elevation of suppressor cell activity and by inhibiting the decrease in IL-2 production in C57BL/6 female mice.

Inhibition of human immunodeficiency virus replication by nonimmunosuppressive analogs of cyclosporin A

Analogs of the immunosuppressive cyclic undecapeptide cyclosporin A (CsA) with substitutions in positions 1, 4, 6, and/or 11 were rationally designed to possess substantially diminished or no immunosuppressive activity. When these compounds were assayed for their capacity to interfere with the replication of human immunodeficiency virus, some displayed a potent antiviral activity in newly infected cells. However, only CsA could interfere with virus replication in persistently infected cells. One CsA analog with antiviral activity costimulated the phytohemagglutinin-induced production of interleukin 2 by human lymphocytes. Human immunodeficiency virus particles from drug-exposed cells showed lower infectivity than virions from untreated cells. Thus, these nonimmunosuppressive analogs of CsA constitute a promising class of lead compounds to develop drugs for effective treatment of the acquired immunodeficiency syndrome.

Ultraviolet-induced suppressor T cells and factor(s) in murine contact photosensitivity. III. Mode of action of T-cell-suppressor factor(s) and interaction with cytokines

The mode of action of T-cell-suppressor factor (TsF) induced by ultraviolet B (UVB) preirradiation in terms of interaction with several cytokines was studied. Suppression of murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) by preirradiation of the sensitizing site to low doses of UVB was caused by antigen-specific suppressor T cells (Ts) and was not associated with the generation of efferent limb-acting suppressor cells. TsF released by Ts inhibited the proliferation of immune lymph node (LN) cells in vitro and reduced interleukin (IL)-2 production of these cells in an antigen-specific fashion without affecting the IL-2 receptor (IL-2R) expression. Both rIL-2 and rGM-CSF have the ability to restore CPS responses in the UVB-preirradiated mice when administered after but not before photosensitization. However, rIL-2 but not rGM-CSF counteracted the in vivo inhibitory effect of TsF. rGM-CSF did not affect the density of I-A+ epidermal Langerhans cells (LCs). It was suggested that TsF inhibited IL-2-mediated immune T-cell proliferation, while rGM-CSF reconstituted the CPS by enhancing the function of photodamaged LCs. These results indicate multiple steps of the UVB-induced immunosuppression circuit, each of which seems to be controlled by different immunomodulators.

A contra-IL-2 cytokine derived from mice suppressed for collagen-induced arthritis

The present study identifies and characterizes a cytokine derived from a T cell hybridoma which inhibits interleukin-2 (IL-2) function. The T cell hybridoma, T101N, was derived from somatic cell hybridization of lymphoid cells from mice suppressed for collagen-induced arthritis. Serial dilution of T101N cell culture medium reveals a concentration-dependent inhibition of recombinant IL-2 induced proliferation. Physiochemical properties of the inhibitor indicate that the contra-IL-2 activity is optimally resolved at 37 degrees C and neutral pH. Analysis of the molecular characteristics of the contra-IL-2 activity indicate that the cytokine activity is most biologically active as a pentimeric molecule of high molecular weight. Apparent molecular weight of monomeric contra-IL-2 is approximately 30,000-35,000 Da.

In vivo administration of histoincompatible lymphocytes leads to rapid functional deletion of cytotoxic T lymphocyte precursors

It is well established that a single intravenous injection of F1 lymphocytes can rapidly and specifically reduce the ability of a parental recipient to generate CTL against donor alloantigens in a subsequent MLR. By fluorescently labeling the injected cells, we have been able to identify, and if desired, remove them in cell suspensions prepared from recipient spleen and lymph node. The injected cells, whether F1 or syngeneic, appeared to form part of the normal recirculating pool. Removal of injected F1 cells from responder lymph node or spleen cell suspensions had no effect on the response reduction observed in the 5-d in vitro MLR (typically 80% reduction for responder cells taken 2 d after injection of F1 cells). When the frequency of CTL precursors (CTLp) was measured by limiting dilution, it was reduced to the same degree as the MLR response, implying that response reduction is due to a reduction in the number of activatable CTL in the responder cell suspension. An equal mixture of responder cells from treated (i.e., F1 injected) and control mice gave a measured CTLp frequency equivalent to the average of the separate frequencies, implying the absence of suppressor cells active in vitro. Labeled F1 cells recovered from a first recipient could be used to induce response reduction in a second recipient. The results are discussed in terms of APCs that functionally delete rather than stimulate CTLp that recognize them (i.e., a "veto mechanism"). These experiments appear to rule out a role for in vivo-induced suppressor cells up to 8 d after injection of semiallogeneic cells but do not address the question of whether they are induced at later times.

Infection of B lymphocytes by the human immunodeficiency virus and their susceptibility to cytotoxic cells

The T4 molecule (CD4) is an important component of the human immunodeficiency virus (HIV) receptor. As yet, no other component has been demonstrated. We report here that two cell lines, a B lymphoblastoid cell line (Gupta) and a glial cell line (HEB) derived from human embryonal brain tissue, are productively infectable with two distinct isolates of HIV as judged by electron microscopy and immunological and virological studies. These two cell lines do not display detectable surface CD4 glycoprotein. However, using S1 nuclease analysis, we have found that both cell lines do express low levels of CD4 mRNA. Neither of them produced syncytia formation upon HIV infection, a recognized feature of HIV-infected cells strongly expressing the CD4 glycoprotein. It is conceivable that the CD4 mRNA is translated, resulting in meager surface expression of CD4 molecules undetectable by conventional techniques. Therefore, infection with HIV may be one of the most sensitive methods of demonstrating low levels of CD4 expression by human cells. Furthermore, HIV-infected Gupta cells have here been shown to be more susceptible to the lytic activity of natural killer (NK) cells than their uninfected counterparts. These phenomena may be important for pathogenesis of HIV-associated disorders.

Antigen specific down regulation of murine collagen induced arthritis: T suppressor cell circuits in arthritis immunotherapy

The present article summarizes a series of experiments which have been performed to describe an antigen-specific suppressor cell pathway for the suppression of the erythema and edema associated with an animal model of rheumatoid arthritis, collagen induced arthritis (CIA). Initial studies utilized the adoptive transfer of splenic cell subpopulations to establish the presence of suppressor cells in lymphoid tissues of mice which were suppressed for collagen induced arthritis. Subsequent studies generated T cell hybridomas from animals which had been suppressed for collagen induced arthritis by a single injection of a large quantity of Type II collagen. The T cell hybridomas varied in their self surface expression of glycoproteins which are associated with genetically determined functions. The suppressor T cells generated, described a regulatory suppressor cell pathway comprised of at least afferent suppressor T cells and effector suppressor T cells. The cells act in an antigen-specific fashion with regard to the suppression of collagen induced arthritis but appear to be polymorphic in their recognition of the interstitial collagens. The studies, taken together, indicate that the use of antigen specific T suppressor cells in the form of T cell hybridomas can be utilized as a form of immunotherapy in experimental arthritis.

Immediate and long-term effects of radiation on the immune system of specific-pathogen-free mice

Studies on the immediate and long-term effects of radiation on the immune system of specific-pathogen-free mice are summarized in this paper. There was a striking difference in the radiation response of lymphocyte subsets; B cells consist of a fairly radiosensitive homogeneous population, whereas T cells consist of a large percentage (greater than 90 per cent) of radiosensitive and a small percentage (less than 10 per cent) of extremely radioresistant subpopulations. Ly 1+ and Ly 2+ lymphocytes appear equally radiosensitive, although the percentage of radioresistant cells was slightly larger for the former (approximately 5.5 per cent) than the latter (approximately 2.5 per cent). There was a significant strain difference in the radiosensitivity of immune-response potential in mice; immunocompetent cells of C3H mice were more radioresistant than those of BALB/c, C57BL/6, and B10.BR mice. Studies on the long-term effect of radiation on immune system in mice indicated no evidence for accelerated ageing of the immunologic functions when radiation exposure was given to young adults. Preliminary results on the enhancing effect of low dose radiation on cytotoxic T cell response in vitro are also discussed.

Interleukin 2 and its receptor: structure, function and therapeutic potential

In this review, salient molecular, biochemical and functional features of human interleukin 2 (IL-2), its membrane receptor, and its clinical relevance are outlined. We also describe experimental systems, where observed biological or pharmacological effects of IL-2 could be applied to corresponding clinical situations. In particular, IL-2 has been intensively studied in the context of cancer therapy. We discuss the rationale for the use of IL-2 in cancer treatment and our experience in this area. A better understanding of the IL-2 system and, specifically, the nature of signals transduced through it will allow us to manipulate the immune response in a variety of different ways, resulting in new approaches to investigation of immune responsiveness in general. This may have a profound impact on clinical medicine.

Biological properties of suppressive E-receptor factor on lymphokine function

A potent immunosuppressive factor isolated from malignant ascites fluids showed serological cross-reactivity with the E-receptor of human peripheral blood T lymphocytes. Thus, this factor was named suppressive E-receptor (SER) factor. In this study, we examined the effect of this immunosuppressor, SER, on lymphokine functions of human mononuclear cells participating in polyclonal T cell activation. SER is active at nanomolar concentrations in vitro and the inhibitory effect of SER was most pronounced when added at the initiation of stimulation with phytohemagglutinin or anti-T3 antibody. Concomitant with the inhibition on PHA-induced DNA synthesis, lymphocytes that were treated with SER failed to progress beyond G1 phase of cell cycle. These growth-arrested cells did expire after 7 days of culture in vitro. This anti-proliferative effect of SER was more easily demonstrated with normal lymphoid cells in culture than transformed cells or fibroblast cells. SER effectively interfered with the lympho-proliferative properties of interleukin 2 (IL 2) on human peripheral blood mononuclear cells and an IL 2-dependent murine cytotoxic T cell line. However, excess quantities of exogenous IL 2, especially when added in conjunction with IL 1, were able to partially overcome the ability of SER to inhibit T cell proliferation. In contrast to the inhibition on DNA synthesis of human lymphoblasts, expression of IL 2 receptor was only minimally inhibited by SER during the first 24 h of culture (24% inhibition at 12 h and 34% inhibition at 24 h) but it was followed by full expression of IL 2 receptor by 48 h. Thus, SER merely reduced the rate of expression of IL 2 receptor and was not able to inhibit the transcription of new message from activated T lymphocytes. Taken together, these studies indicate that SER acts as a noncytolytic anti-proliferative factor on immune responses that are mediated by T cells. SER appears to act on a relatively late event during T cell activation, perhaps on some portion of the DNA replication pathway.

Functional analysis of antigen-nonspecific T-cell suppression. I. Effect of mitogen-induced T suppressor cells on helper-T-cell clones

The effect of mitogen-induced nonspecific suppressor T cells (Ts)2 on T-helper-cell activity was investigated using isolated clones of murine T-helper cells as targets. TNP-self-reactive Thy1+, Ly1+ T-cell clones were isolated after continuous culture of T cells derived from picryl chloride-sensitized mice and were characterized by their ability to proliferate in an antigen-specific and MHC-restricted manner. In addition, selected T-cell clones were found to produce both interleukin-2 (Il-2) and T-cell replacing factor (TRF), lymphokines characteristic of helper T cells. Concanavalin A (Con A)-induced Ts cells inhibited the antigen-specific proliferation of these helper-T cell clones in a noncytotoxic manner even in the presence of exogenous Il-2. This implied that failure to proliferate was not merely due to an inability of these clones to produce Il-2. The kinetics of suppression also suggested that early T-cell activation signals were not affected. Furthermore, coculture experiments indicated that while proliferation could be severely inhibited, the actual secretion of lymphokines such as Il-2 and TRF by the T-helper clones was not. Our data suggest that nonspecific Ts modulation of proliferation versus helper factor production are under separate control in cloned T-cell populations, with lymphokine secretion remaining intact in the presence of Con A-induced Ts cells.

Soluble factors secreted by naturally occurring suppressor cells that interfere with in vivo graft-vs.-host disease and with T cell responsiveness in vitro

A potent immunosuppressive factor (SUF) is found in the supernatant of short-term cultures of unstimulated thymocytes or spleen cells of neonatal mice and rats and in culture medium of hybridoma cell lines established by fusing neonatal mouse spleen cells with T lymphoma cells (the BW 5147 line). In vitro incubation of spleen cells with SUF suppresses the acute in vivo graft-vs.-host disease, normally induced by allogeneic spleen cells in lethally irradiated mice. Incubation of bone marrow cells with SUF does not affect the hemopoietic stem cells. The addition of SUF to mixed lymphocyte reaction cultures strongly suppresses lymphocyte proliferation. The non-species-restricted inhibition of cell proliferation induced by SUF is shown not to be due to toxicity or nonspecific interference with DNA synthesis. Molecular size fractionation of crude SUF revealed two active moieties: a large moiety of molecular mass greater than 100 kDa and a small moiety of less than 3 kDa. The high kDa moiety mediates T cell unresponsiveness both in vivo and in vitro. In vitro studies revealed that this moiety primarily affects an early event in the proliferative response to alloantigen and mitogen, that prevents interleukin 2 (IL 2) receptor expression and, consequently, blastogenesis and DNA duplication. It does not affect, however, the synthesis of IL 2. The suppressive activity of the low kDa moiety can be demonstrated only in in vitro systems. Pre-treatment of donor lymphocytes with this fraction cannot prevent graft-vs.-host disease mortality. The inhibition of cell proliferation induced by this fraction in vitro is most likely due to interference with the utilization of IL 2, as suggested by its suppressive effect on the proliferation of CTLL-2 cells (an IL 2-dependent cell line).

Recombinant interleukin-2 directly augments the cytotoxicity of human monocytes

Interleukin-2 (IL-2), originally described as a growth factor required for sustained proliferation of T cells in vitro is a glycoprotein hormone of known structure which appears to be important for the generation of immune responses in vivo. As well as T lymphocytes, B lymphocytes and large granular lymphocytes with natural killer activity (NK cells) can also respond to IL-2. The action of IL-2 seemed to be limited specifically to lymphocytes, however, and the term 'T-lymphocytotrophic hormone' was used. Here we provide evidence that human monocytes display a substantially increased cytotoxic activity as a direct and rapid response to human recombinant IL-2 but not to human recombinant glycosylated interferon-gamma (IFN-gamma) or lipopolysaccharide. Our results reveal a previously unknown function of IL-2 and suggest its possible involvement in monocyte-T cell interactions.

T-cell depletion of allogeneic bone marrow prevents acceleration of graft-versus-host disease induced by exogenous interleukin 2

Highly purified human recombinant interleukin 2 (IL-2) markedly accelerated lethal GVHD in the H-2-identical B10.BR----CBA combination, but had no effect when the donor cells were depleted of mature (Thy-1.2-positive) T lymphocytes, indicating a strong immunopotentiating effect of IL-2 on mature T cells causing GVHD. In the same donor-host combination, IL-2 did not influence the recovery from the post-transplantation bone marrow aplasia. The results suggest that IL-2 could be considered for adjuvant hormonal therapy to enhance immune recovery in recipients of T-cell-depleted allogeneic marrow.

Suppression of interleukin-2 production by macrophages in genetically susceptible mice infected with Leishmania major

Spleen cells from BALB/c mice infected with 2 X 10(7) L. major promastigotes and developing progressive disease produced significantly lower levels of interleukin-2 (IL-2) in response to concanavalin A stimulation than did spleen cells from uninfected mice. In contrast, spleen cells from sublethally irradiated and infected mice, which were able to contain lesion development, produced significantly higher levels of IL-2. The increase in IL-2 production closely paralleled lesion regression. Mice protectively immunized by four intravenous injections with lethally irradiated promastigotes also produced enhanced levels of IL-2, which were sustained after challenge infection. In contrast, spleen cells from BALB/c mice given four s.c. injections of irradiated promastigotes produced high levels of IL-2 before but not after infection. These mice eventually produced levels of IL-2 indistinguishable from those of unimmunized mice with progressive disease. There is thus an inverse relation between disease progression and the ability of spleen cells to produce IL-2. Spleen cells from mice with uncontrolled disease not only produced lower levels of IL-2 but also impaired IL-2 production by normal spleen cells. The ability to inhibit IL-2 was abrogated by passing the cells through a Sephadex G-10 column, removal of plastic adherent cells, and removal of carbonyl iron-ingesting cells. Furthermore, Sephadex G-10 column-treated and plastic adherent, nonspecific esterase-positive spleen cells from mice with progressive disease were able to suppress IL-2 production by normal splenic T cells. The suppressive activity of the adherent cells was not affected by treatment with anti-Thy-1.2 antibody and complement. In contrast, adherent spleen cells from uninfected mice were devoid of such suppressor activity. The depressed IL-2 production by spleen cells from progressively infected mice could be restored to that of normal spleen cells by the addition of indomethacin to the culture. There was however, no correlation between IL-2 production and IL-1 activity in infected or immunized BALB/c mice. Thus, it appears that the suppression of IL-2 production is mediated by prostaglandins elaborated by macrophages from chronically infected mice.

Interaction of idiotype-specific T suppressor factor with the hapten-specific third-order T suppressor subset results in antigen-nonspecific suppression

The interaction between the third-order T suppressor (Ts3) cell and the idiotype (Id)-specific second-order Ts factor (TsF2) was studied in the phenyltrimethylamino (TMA) hapten system. The experimental system which we used allowed the independent analysis of induction and activation requirements of Ts3. The procedure consisted of inducing the Ts3 in vivo and activating the enriched T-cell populations containing Ts3 in vitro with TsF2. The suppressive potential was then tested in mice previously primed for delayed-type hypersensitivity responses which were also treated with cyclophosphamide to deplete Ts3 and other drug-sensitive Ts cell types. Using this experimental system, it was found that the Id-specific TsF2 was required for the in vitro activation of Ts3. Furthermore, the TsF2 activated only the homologous and not heterologous antigen-primed Ts3-containing T cells and moreover, the target of TsF2 was found to be the Ts cells bearing hapten-specific receptors. Once the TMA hapten-specific Ts3 was activated with TsF2, the ensuing suppression was antigen nonspecific. The data demonstrate that the Ts3 represents a final effector Ts cell type in the TMA system.

Advances in understanding cell interactions in tissue resorption. Relevance to the pathogenesis of periodontal diseases and a new hypothesis

Much of the connective tissue degradation that takes place in periodontal diseases is mediated by proteolytic enzymes. Previous studies have focused on the action of proteinases released by invading polymorphonuclear neutrophils and macrophages, and bacterial enzymes. In view of recent work establishing that resident connective tissue cells can be induced by cytokines to bring about the destruction of their own matrix, we propose a new hypothesis. In this we envisage that a critical step is the interaction of bacterial antigens with inflammatory cells, resulting in the production of a cytokine, interleukin-1. Our interpretation of in vitro evidence is that the loss of connective tissue attachment and bone matrix resorption in periodontal diseases is mediated by metalloproteinases such as collagenase and stromelysin released by cells of the periodontium. Such proteolytic destruction can be induced by interleukin-1, whose production may not be dependent on a specific microbial flora but may be triggered by a number of organisms. It is now clear that interleukin-1 has multiple actions on both immune and non-immune cells; these include the induction of lymphocyte differentiation and proliferation and the stimulation of bone and cartilage resorption, and prostaglandin and metalloproteinase synthesis by connective tissues. It seems likely that further knowledge about the production and function of this cytokine will have an increasing impact in many diseases that involve resorption, particularly since interleukin-1-like molecules can be produced by cell types other than monocytes/macrophages, including keratinocytes and fibroblasts.

Nonspecific inhibitor of DNA synthesis elaborated by T-acceptor cells. II. Requirements for its production and action

The production of a nonspecific inhibitor of DNA synthesis (nsINH) appears to be one of the final events in the T-suppressor cell circuit in mice exposed to contact sensitizers. We report here that: The nsINH suppresses the proliferative response to a polyclonal T-cell mitogen, concanavalin A (Con A), regardless of the dose of Con A used. It also suppresses DNA synthesis in lymphoid cells stimulated with alloantigens. This suppression can be completely eliminated by adding exogenous interleukin 2 (IL-2). DNA synthesis in lymphoid cells exposed to nsINH before the proliferative stimulus is uninfluenced so that activation of the lymphoid cells at the same time as exposure to nsINH seems to be a requirement for its action. Since the activity of nsINH can be absorbed by activated Lyt-1+ or Lyt-2+ lymphocytes, the early activated T cell appears to be a target of the action of nsINH. The production of nsINH is abolished or severely reduced by adult thymectomy. Natural killer (NK) cells are resistant to nsINH action and no interferon (IFN)-like activity can be demonstrated in nsINH preparation using a conventional assay for IFN.

Acquired immunodeficiency with disseminated cryptococcosis

A 9 year old Portuguese boy presented with severe wasting and a disseminated cryptococcal infection that resolved after massive doses of intrathecal and parenteral antifungal agents. Clinical and laboratory findings were consistent with AIDS. Apart from neonatal blood transfusions, there were no identified risk factors for HTLV III infection.

Regulation of human cytotoxic T-lymphocyte responses by a soluble suppressor factor

We describe some aspects of the biology of a suppressor factor (SF) secreted by actively metabolizing and dividing alloantigen-primed T cells which functions by regulating human cytotoxic T-lymphocyte (CTL) activation. The SF functions most effectively during the first 24 hr of CTL activation, while it does not function at the CTL effector stage. Both T cells and adherent cells are capable of absorbing out the biological activity from suppressor factor supernatants. Experiments demonstrated that either fresh adherent cells or the addition of interleukin 2 (IL-2) into the test system could reverse the effects of the SF on CTL activation. These data suggest that the SF could be acting by either indirectly restricting IL-2 availability to proliferating CTLs by limiting adherent cell interleukin 1 (IL-1) secretion or, alternatively, SF acting directly on the IL-2-producing T cells.

The role of dendritic cells in the initiation of immune responses to contact sensitizers. I. In vivo exposure to antigen

Twenty-four hours after skin painting mice with picryl chloride (PIC) there was a four- to fivefold increase in the numbers of dendritic cells (DC) isolated from the lymph nodes. These DC initiated primary proliferative and cytotoxic responses when added to cultures of normal syngeneic lymph node cells. The proliferative response was enhanced when the donors of the responding lymph node cells were sensitized with the same antigen. Contact sensitivity developed in syngeneic mice injected into the footpads with 30,000-50,000 DC from lymph nodes of mice painted with picryl chloride 1 day previously. Thus, 1 day after skin painting mice, there were dendritic cells in the draining lymph nodes which were able both to initiate primary stimulation of lymphocytes in vitro and to sensitize recipient mice to give specific delayed hypersensitivity reactions.

Activation of suppressor T cells by low-molecular-weight factors secreted by spleen cells from tumor-bearing mice

The spleens of mice bearing large M-1 fibrosarcomas have been shown to contain several populations of cells which nonspecifically suppress antibody synthesis by cocultured normal spleen cells. It has now been shown that the spleens of tumor-bearing mice also contain inducer cells which secrete soluble factors capable of activating suppressor T cells from unprimed precursor cells. The activated suppressor cells are Thy 1+, Lyt 1+2+ and secrete a soluble suppressive factor. They inhibit the in vitro generation of antibody-forming cells by cocultured normal spleen cells stimulated by T-cell-dependent antigens. They do not, however, suppress the antibody response to T-cell-independent antigens and do not inhibit antibody synthesis by cocultured nude mouse spleen cells cultured with T-cell-dependent antigens and exogenous helper factors. In addition, suppression is blocked if conditioned medium containing T-cell growth factors is added to the suppressor cell assays. These data suggest that cells in the spleens of tumor-bearing mice secrete inducing factors which activate suppressor cells. These activated suppressor cells in turn secrete soluble suppressor factors which inhibit antibody synthesis, possibly by interfering with the synthesis or release of T-cell growth factors.

Augmentation of interleukin-2 production and delayed hypersensitivity in mice infected with Mycobacterium bovis and fed a diet supplemented with vitamin A acetate

High-dose Mycobacterium bovis-infected mice fed a vitamin A acetate-supplemented diet developed a positive skin reaction to purified protein derivative of mycobacteria, and their spleen cells showed an increased IL-2 production in vitro.

Correction of interleukin-2 production in patients with systemic lupus erythematosus by removal of spontaneously activated suppressor cells

Interleukin-2 (IL-2) production in vitro is depressed in systemic lupus erythematosus (SLE) patients. It is not known whether this abnormality is caused by a defect in the producer lymphocytes or by excessive suppression. We report that removal of OKT8 (Leu 2a)+ cells increased the IL-2 production by in vitro-stimulated lymphocytes to normal or above normal levels in 19 of 21 SLE patients. This increase was more apparent in those patients with clinically inactive disease and/or receiving less than 7.5 mg of prednisone. Removal of OKT8+ cells from normals did not significantly increase IL-2 activity. SLE, but not normal, OKT8+ cells decreased IL-2 production when added back to autologous OKT8-depleted cells. In some experiments, OKT8+ cells from normal donors also suppressed IL-2 production in SLE. This result suggests that the defect in IL-2 production is complex and may involve multiple cell interactions. Three lines of evidence suggest that the SLE OKT8+ cells actively inhibit the production of IL-2 rather than passively absorb this lymphokine: (a) only 3.2% of SLE lymphocytes expressed IL-2 receptors as detected with anti-Tac; (b) freshly prepared SLE lymphocytes did not absorb IL-2; and (c) cell-free supernatants from SLE OKT8+ cells inhibited IL-2 production, but not IL-2 activity. Double-labeling studies by flow cytometry revealed that 19.3% of SLE OKT8+ cells were also Ia-positive, and approximately 33% co-expressed the natural killer cell marker, HNK-1 (Leu 7). Removal of Leu 7+ cells also significantly elevated IL-2 production in SLE. These studies suggest that one or more circulating mononuclear cell subsets in SLE patients can suppress IL-2 production and that one subset may possibly belong to a non-T, non-B "third mononuclear population."

Acquired immunological tolerance of foreign cells is impaired by recombinant interleukin 2 or vitamin A acetate

The susceptibility of newborn mice to the inception of tolerance after exposure to antigen is associated with their deficiency in the production of endogenous interleukin 2 (IL-2). As further evidence of the complicity of IL-2 in the inception and maintenance of tolerance, it is shown here that a solid and long-lasting state of tolerance induced by the intravenous injection into newborn CBA mice of lymphoid cells from (CBA X C57BL/10ScSn)F1 hybrids can be brought to an end by the administration of exogenous IL-2 or by supplementing an otherwise normal diet with vitamin A acetate, the effect of which is to increase the proportion of the moiety of the T-cell population that produces IL-2. These results indicate that certain nonspecific stimuli can influence whether immunological tolerance is maintained.

Characterization of two suppressor cells that together prevent in vivo development of cytolytic T cells to hapten-altered self

Two suppressor cell populations that interact to down-regulate in vivo development of the cytolytic T-cell (CTL) response to trinitrophenyl-modified syngeneic spleen cells (TNP-SC) have been further characterized. Suppressor cells induced by the iv injection of trinitrophenyl-modified syngeneic spleen cells possess Thy 1.2 antigen. Their precursors are insensitive to pretreatment of host animals with cyclophosphamide (CY). Suppressor cells that arise after dermal sensitization with trinitrochlorobenzene are also Thy 1.2 antigen positive but their precursors are sensitive to pretreatment with CY. These characteristics of the two suppressor T cells (Ts) are identical to those of the two Ts that are generated by similar methodologies and that together suppress contact sensitivity (CS) to picryl chloride. Neither the CS nor CTL response was suppressed when host animals possessed only one set of Ts. In contrast to suppression of CS at the efferent phase, development of CTL was suppressed only when the two Ts were present early during sensitization (afferent phase). Since the results point to several similarities between the two sets of Ts that are active in the down-regulation of the CS and CTL responses, it is suggested that the two dissimilar immune responses directed to the same hapten, namely CS and CTL, may be controlled by the same suppressor cells. Since it appears that the two sets of Ts interact to affect different phases of the CS and CTL responses, down-regulation of each must be accomplished through different mechanisms.

Immunological unresponsiveness in leprosy

The various forms of leprosy form a clinical and immunological spectrum which offers extraordinary possibilities for insight into immunoregulatory mechanisms in man. At one pole, tuberculoid leprosy, patients develop high levels of cell-mediated immunity which ultimately results in killing of bacilli in the tissues, albeit often with damage to nerves. At the lepromatous pole, patients exhibit selective immunological unresponsiveness to antigens of M. leprae. Even though all currently known protein species of M. leprae and BCG are cross-reactive, lepromatous patients unreactive to M. leprae antigens frequently respond strongly to tuberculin. In vitro experiments suggest the existence of lepromin-induced suppressor activity, mediated by both monocytes and T cells. The T suppressor cells have the T8 phenotype of which 50% express the activation markers, Ia and FcR. The one unique species of antigen of the leprosy bacillus is a phenolic glycolipid, and it appears that the TS cells largely recognize the terminal trisaccharide of this unique antigen. Depletion of the TS cells restores in vitro reactivity of lymphocytes to lepromin in a portion of lepromatous patients, and addition of IL-2-containing supernatants partially restores responsiveness to M. leprae antigens. Vaccination of lepromatous patients with a mixture of M. leprae and live BCG restores cell-mediated immunity in the majority of lepromatous patients, and concomitantly reduces the in vitro suppressor activity and number of activated T8 cells. These experiments suggest the existence of stage-of-disease related suppressor cells in leprosy which appear to block the responsiveness of TH capable of responding to either specific or cross-reactive mycobacterial antigens. The mode of action of these TS appears to be the inhibition of production of IL-2 and other lymphokines. Successful immunotherapeutic vaccination appears to overcome this block in the majority of patients.

T suppressor factor activity is due to two separate molecules. The Lyt-1(-)2+I-J+ cells of mice primed with antigen make an antigen binding molecule which is only active when complemented by cofactor made by Lyt-1+2(-)I-J+ cells

Mice primed with picrylsulfonic acid (PSA) and then painted on the skin with picryl chloride produce antigen-specific T suppressor factor (TsF). In contrast unpainted primed mice fail to produce active TsF. This is not due to the absence of the antigen binding part of TsF but to the absence of a cofactor. This cofactor is (a) antigen nonspecific and occurs in potassium chloride extract of normal spleen cells. It also occurs in the 24 hr supernatant of normal cells modified by haptenisation with picryl or the unrelated NP antigen (4-hydroxy-3-nitrophenylacetyl), and in preparations of conventional TsF (PSA/PCl) from painted PSA-primed mice; (b) bears I-J determinants; and (c) is produced by Lyt-1+2(-)I-J+ cells. The antigen binding molecule occurs alone in the supernatant of PSA-primed mice. It lacks I-J determinants and has a molecular weight around 35,000 and 75,000. It is produced by Lyt-1(-)2+I-J+ cells and is only active when complemented by cofactor. However, the complementation is genetically restricted and the restriction maps to the I-J subregion of the MHC.

In vivo and in vitro administration of interleukin 2-containing preparation reverses T-cell unresponsiveness in Mycobacterium bovis BCG-infected mice

Mice infected with high doses of Mycobacterium bovis BCG (3 X 10(7)) showed a marked impairment of delayed-type hypersensitivity to PPD in vivo, and their splenic T cells failed to proliferate when cultured in vitro with concanavalin A or PPD. However, this state of unresponsiveness could be reversed both in vitro and in vivo by the administration of an interleukin 2 (IL-2)-containing preparation. IL-2 produced spontaneously by the gibbon lymphosarcoma T-cell line MLA-144 and T-cell-conditioned medium from a mixed lymphocyte reaction were able to increase DNA synthesis of splenic T lymphocytes from BCG-immunosuppressed mice cultured with concanavalin A or PPD. Furthermore, BCG-infected mice treated in vivo with at least 100 U of IL-2 showed a positive skin reaction to PPD, and their spleen cells were fully responsive in vitro. The reversal of BCG-induced immunosuppression was not observed when infected mice were injected with IL-2 preparations previously incubated with blast cells, a procedure known to remove IL-2 activity. These results indicate that the basis of BCG-induced unresponsiveness is a deficiency in the production of IL-2 rather than a lack of reactive T cells.

A diet enriched in vitamin A acetate or in vivo administration of interleukin-2 can counteract a tolerogenic stimulus

A conventional diet enriched in retinyl acetate (vitamin A acetate; VAA) or in vivo administration of exogenous interleukin-2 (IL-2) can effectively annul the otherwise tolerogenic stimulus represented by (CBA X C57BL/10ScSn) F1 cells injected intraperitoneally into newborn CBA mice. On the basis of these data and results of others, we postulate that an antigenic stimulus associated with a relative lack of IL-2 (or generally the lack of a 'secondary stimulus') can be tolerogenic rather than immunogenic. However, the tolerogenicity of the antigenic stimulus can be substantially reduced or even converted to sensitization (R. P. Cleveland & H. N. Claman, J. Immun. 124, 474-480, 1980), when the antigenic signal is appropriately associated with a concomitant or additional stimulus possibly mediated through IL-2.

Nonspecific inhibitor of contact sensitivity made by T-acceptor cells: triggering of T cells armed with antigen-specific T-suppressor factor (TsF) requires both occupancy of the major histocompatibility complex recognition site by soluble I-J product and cross-linking of the antigen recognition sites of the TsF

The phenomenon of associative recognition, i.e., the recognition of antigen together with major histocompatibility complex products (MHC) was studied in a model system. T-acceptor cells armed with antigen-specific T-suppressor factor (TsF) released a nonspecific inhibitor of the transfer of contact sensitivity when exposed to antigen together with MHC. The MHC product occurred in a KCl extract of cells and behaved genetically and serologically as I-J. Cells armed with anti-picryl or anti-"oxazolone" TsF could be triggered by the corresponding "bis-picryl-L-lysine" and "bis-oxazolone-L-lysine" together with MHC. This suggested that cross-linking of antigen recognition sites on separate molecules of TsF might be required. To investigate this possibility the bifunctional "mixed" hapten "N alpha-picryl-N epsilon-oxazolone-L-lysine," which is univalent with respect to the picryl and oxazolone haptenic groups, was synthesized. This triggered cells armed with a mixture of anti-picryl and anti-oxazolone TsF but not cells armed with either TsF alone. It was concluded that both occupancy of the I-J recognition site and the cross-linking of separate molecules of TsF was required for triggering. Moreover the hapten and the KCl extract could be given sequentially and in either order. This finding suggested that the triggering of the release of nonspecific inhibitor was due to the separate recognition of I-J and antigen and not to new antigenic determinants produced by their interaction.

Suppressive mechanisms in alloantigen-induced T cell responses

In this report we examined the possibility that suppression of the mixed lymphocyte response by MLR-TsF results from interference with IL-2 regulation of T cell proliferation. Two distinct processes of inhibition involving both a direct effect on IL-2-driven proliferation of responder T cells, and induction of a second-order suppressor cell (Ts2) were described. Exogenous IL-2 did not abrogate MLR-TsF-induced suppression, and activated responder cells from suppressed cultures expressed functional IL-2 receptors by IL-2 adsorption analysis. Thus, suppression is not due to lack of available IL-2 or to abnormal acquisition of receptors for IL-2 during T cell activation. In contrast, a profound MLR-TsF effect on IL-2-induced proliferation of HT2 cells as well as MLR-activated cells was observed even after presaturation of receptors with excess IL-2. These results differentiated the direct responder cell effect of MLR-TsF from its Ts2 inductive capacity, and localized the defect in responder cell proliferation to events occurring subsequent to IL-2 binding. When analyzed in terms of proposed models for hormone-receptor interactions, characteristic dose-response curves similarly predict a postreceptor defect. Examination of the Ts2 pathway of suppression revealed a late-acting inhibitory effect peaking 72 h after MLR initiation. A minor part of Ts2 activity was susceptible to exogenous IL-2, and may reflect a requirement for IL-2 during Ts2 expansion. However, the most significant component of Ts2-mediated suppression was resistant to excess IL-2, and IL-2 production was normal in Ts2-regulated cultures, thus ruling out limitation of IL-2 for responder cell use as the major mechanism of Ts2 suppression. The complete pathway of Ts2 suppression and its functional relationship to other MLR-TsF inhibitory activities is not yet fully understood. However, these results suggest that the ultimate mechanisms of alloantigen-induced suppression involve late events of the IL-2-dependent lymphokine cascade.

Enhancement of specific antitumor immunity in mice fed a diet enriched in vitamin A acetate

Age-matched male CBA mice on a conventional or a vitamin A acetate (VAOAc)-rich diet were immunized with irradiated cloned 3-methylcholanthrene- or Harvey sarcoma virus-induced (McSa-1 or HT3-2.1) sarcoma cells and then challenged with viable corresponding or unrelated (non-crossreacting) syngeneic sarcoma cells. The survival of the specifically immunized mice on the VAOAc diet was significantly prolonged in comparison with all control groups of mice as assessed by using logrank tests. Moreover, the specific immunization markedly decreased the incidence of tumors after the McSa-1 (but not HT3-2.1) challenge in a group of mice on the VAOAc diet (5% tumor incidence) compared with the equivalent group on the control diet (50% tumor incidence). Neither the VAOAc diet nor in vivo immunization alone or combined influenced natural killer cell activity. Specific T-cell-mediated cytotoxicity after in vivo priming and in vitro boosting with sarcoma cells was increased in VAOAc-fed mice. However, the marginal increase in cytotoxicity does not in itself explain the strikingly increased resistance to tumor transplants in preimmunized mice on the VAOAc diet in comparison with preimmunized mice on the control diet. The results indicate that a diet enriched in VAOAc can modify the ability of the immune system of a mouse to respond effectively to tumor antigens and can influence whether a tumor grows or regresses.

T-cell-mediated enhancement of host-versus-graft reactivity in mice fed a diet enriched in vitamin A acetate

Retinol (vitamin A) and some of its derivatives have an important role in: (1) regulating growth, proliferation and differentiation of various tissues and (2) maintaining reproduction and visual function in man and higher animals. Vitamin A and retinoids are also known as potent immunoregulatory and antineoplastic agents. Their ability to increase reactivity to histoincompatible tissues is well documented but the mechanism of this action is unclear. Here we report that mice fed on an otherwise conventional diet supplemented with vitamin A acetate (VAA) respond to 10(5) semiallogeneic cells (a suboptimal dose) in a host-versus-graft (HvG) reaction, whereas mice on a conventional diet do not. It is possible to transfer this enhanced immune reactivity by injecting lymphoid cells from VAA-fed animals into those syngeneic mice maintained on the conventional diet. Using a positive selection technique, we demonstrate that the phenotype of the cell probably responsible for this phenomenon is Lyt 1+ 2-.