T-T-cell interactions during the vitro cytotoxic allograft responses. I. Soluble products from activated Lyl+ T cells trigger autonomously antigen-primed Ly23+ T cells to cell proliferation and cytolytic activity

Physical optimization of cell proliferation and differentiation using spinner flask and microcarriers

Abstract

The traditional breeding industry has been increasingly saturated and caused environmental pollution, disease transmission, excessive resource use, and methane emission; however, it still cannot meet the needs of the growing population. To explore other alternatives, researchers focused on cell agriculture and cell-based meat, especially large-scale cell culture. As a prerequisite for production, large-scale culture technology has become an important bottleneck restricting cell-based meat industrialization. In this study, the single-factor variable method was adopted to examine the influence of Cytodex1 microcarrier pretreatment, spinner flask reaction vessel, cell culture medium, serum and cell incubation, and other influencing factors on large-scale cell cultures to identify the optimization parameters suitable for 3D culture environment. Collagen and 3D culture were also prospectively explored to promote myogenesis and cultivate tissue-like muscle fibers that contract spontaneously. This research lays a theoretical foundation and an exploratory practice for large-scale cell cultures and provides a study reference for the microenvironment of myoblast culture in vitro, a feasible direction for the cell therapy of muscular dystrophy, and prerequisites for the industrialized manufacturing of cell-based meat.

Graphical Abstract

Unlike CD4+ T-cell help, CD28 costimulation is necessary for effective primary CD8+ T-cell influenza-specific immunity

The importance of costimulation on CD4(+) T cells has been well documented. However, primary CTLs against many infections including influenza can be generated in the absence of CD4(+) T-cell help. The role of costimulation under such "helpless" circumstances is not fully elucidated. Here, we investigated such a role for CD28 using CTLA4Ig transgenic (Tg) mice. To ensure valid comparison across the genotypes, we showed that all mice had similar naïve precursor frequencies and similar peak viral loads. In the absence of help, viral clearance was significantly reduced in CTLA4Ig Tg mice compared with WT mice. CD44(+) BrdU(+) influenza-specific CD8(+) T cells were diminished in CTLA4Ig Tg mice at days 5 and 8 postinfection. Adoptive transfer of ovalbumin-specific transgenic CD8(+) T cells (OT-I)-I cells into WT or CTLA4Ig Tg mice revealed that loss of CD28 costimulation resulted in impairment in OT-I cell division. As shown previously, neither viral clearance nor the generation of influenza-specific CD8(+) T cells was affected by the absence of CD4(+) T cells alone. In contrast, both were markedly impaired by CD28 blockade of "helpless" CD8(+) T cells. We suggest that direct CD28 costimulation of CD8(+) T cells is more critical in their priming during primary influenza infection than previously appreciated.

Anti H-2Dd alloreactivity mediated by herpes-simplex-virus specific cytotoxic H-2k T lymphocytes is associated with H-2Dk

Herpes-simplex-virus (HSV) specific, H-2k-restricted, immune cytotoxic T lymphocytes also lyse noninfected H-2d target cells. Genetic mapping studies revealed that HSV-specific Dk-restricted CTL cross-react with allogeneic targets expressing Dd alloantigens. Cold target inhibition experiments indicate that only a minority of HSV-specific CTL mediate cross-reactive cytolysis. The data give an example of where the phenomenon of H-2-restricted versus nonrestricted responsiveness is not due to distinct subsets of T cells but solely depends on the antigenic determinants recognized.

CD4 help-independent induction of cytotoxic CD8 cells to allogeneic P815 tumor cells is absolutely dependent on costimulation

Mice made transgenic (Tg) for a rat anti-mouse CD4 Ab (GK mice) represent a novel CD4-deficient model. They not only lack canonical CD4 cells in the periphery, but also lack the residual aberrant Th cells that are found in CD4-/- mice and MHC class II-/- mice. To analyze the role of CD4 help and costimulation for CTL induction against alloantigens, we have assessed the surface and functional phenotype of CD8 cells in vivo (e.g., clearance of allogeneic P815 cells) and in vitro. In our CD4-deficient GK mice, CTL responses to allogeneic P815 cells were induced, albeit delayed, and were sufficient to eliminate P815 cells. Induction of CTL and elimination of allogeneic P815 cells were inhibited both in the presence and absence of CD4 cells by temporary CD40 ligand blockade. This indicated that direct interaction of CD40/CD40L between APCs and CD8 cells may be an accessory signal in CTL induction (as well as the indirect pathway via APC/CD4 interaction). Furthermore, whereas in CTLA4Ig single Tg mice P815 cells were rejected promptly, in the double Tg GK/CTLA4Ig mice CTL were not induced and allogeneic P815 cells were not rejected. These findings suggest that CD40/CD40L is involved in both CD4-dependent and CD4-independent pathways, and that B7/CD28 is pivotal in the CD4-independent pathway of CTL induction against allogeneic P815 cells.

Enhancement of anti-tumor activity of natural killer cells by BALL-1, a B cell lymphoma line

The anti-tumor activity of human peripheral blood mononuclear cells (PBMC) against various tumor cell line cells (K562, Daudi, KMG-2, and KATOIII) was enhanced by coculture with irradiated BALL-1, but not with other irradiated B cell line cells (NALM-1, Namalwa, and Daudi). PBMC cocultured with BALL-1, however, failed to exhibit evident cytotoxicity against autologous concanavalin A-induced lymphoblasts. The enhancement of the anti-tumor activity seemed not to be correlated with EBNA and HLA-DR expression on B cell line cells. Monoclonal antibodies (mAbs) against interleukin (IL)-2, interferon-gamma, IL-12, IL-15, tumor necrosis factor-alpha and lymphotoxin showed little or no suppression of the anti-tumor activity of PBMC treated with irradiated BALL-1. Furthermore, the culture supernatants of BALL-1 failed to enhance the anti-tumor activity of PBMC, suggesting no involvement of soluble factors in the induction of the anti-tumor activity. The anti-tumor activity of PBMC treated with BALL-1 was synergistically enhanced by an additional IL-2 stimulation. Periodate-lysine-paraformaldehyde-fixed, but not ethanol- or acetone-fixed, BALL-1 could significantly enhance the anti-tumor activity. Furthermore, BALL-1-derived membrane fraction, but not that of Daudi, enhances the anti-tumor activity. It was thus suggested that some membrane glycoproteins on the cell surface of BALL-1 play a crucial role in the induction of the anti-tumor activity. By analysis using mAbs against human leukocytes, we found that depletion of CD11b, CD16, and CD56-positive cells resulted in decreased anti-tumor activity, suggesting that the main effector cells in the BALL-1-induced anti-tumor activity were natural killer (NK) cells. The present results thus raise the possibility that BALL-1, probably via membrane glycoproteins, modulates NK cell-mediated anti-tumor activity.

Rapamycin inhibits proteasome activator expression and proteasome activity

Rapamycin (RAPA) is a potent immunosuppressive drug, and certain of its direct or indirect targets might be of vital importance to the regulation of an immune response. In this study, we used differential hybridization to search for human genes whose expression was sensitive to RAPA. Seven RAPA-sensitive genes were found and one of them encoded a protein with high homology to the alpha subunit of a proteasome activator (PA28 alpha). This gene was later found to code for the beta subunit of the proteasome activator (PA28 beta). Activated T and B cells had up-regulated PA28 beta expression at the mRNA level. Such up-regulation could be suppressed by RAPA, FK506, and cyclosporin A. RAPA and FK506 also repressed the up-regulated PA28 alpha messages in phytohemagglutinin (PHA)-stimulated T cells. At the protein level, RAPA inhibited PA28 alpha and PA28 beta in the activated T cells according to immunoblotting and confocal microscopy. Probably as a consequence, there was a fourfold increase of proteasome activities in the peripheral blood mononuclear cell lysate after the PHA activation. RAPA could inhibit the enhanced part of the proteasome activity. Considering the critical role played by the proteasome in degrading regulatory proteins, our data suggest that the proteasome activator is a relevant and important downstream target of rapamycin, and that the immune response could be modulated through the activity of the proteasome.

Cytokine modulatable signalling through macrophage HLA class II. 1. IFN-gamma upregulates the efficiency of Ca2+ mobilization in response to ligation of macrophage HLA-DP

The human macrophage line 2MAC, established recently from peripheral blood, expresses a number of lineage-specific markers as well as a broad array of intercellular adhesion molecules, including high levels of HLA class I and class II. We have presented evidence elsewhere that 2MAC can be productively applied to the study of signal transduction through macrophage HLA class II. Namely, we showed that ligation of 2MAC HLA class II, but not HLA class I, by monoclonal antibody (mAb) elicits an increase in free cytoplasmic Ca2+ concentration [Ca2+]i. Moreover, this Ca2+ flux appears to be functionally relevant: ligation of HLA-DR, but not HLA class I, by mAb results in the Ca2+ mobilization-dependent induction of tissue factor, the high-affinity cellular receptor for factor VII/VIIa. Here we show that 2MAC is uniquely valuable for addressing the efficiency of signal transduction through HLA class II. Namely, we show here that prior culture of 2MAC cells with interferon-gamma (IFN-gamma) profoundly upregulates subsequent Ca2+ mobilization in response to ligation of HLA-DP in the absence of increased cell surface HLA-DP expression. Because IFN-gamma has no effect on 2MAC HLA-DP expression, IFN-gamma must upregulate Ca2+ mobilization by increasing the efficiency of signal transduction through HLA class II (HLA-DP), by targeting some other component of the macrophage HLA class II signalling pathway.

Perforin and Fas killing by CD8+ T cells limits their cytokine synthesis and proliferation

During an immune response, effector CD8+ T cells can kill infected cells by the perforin-dependent pathway. In comparison to CD4+ T cells, which are major sources of cytokines, normal CD8+ T cells produced less interleukin 2 and interferon gamma, and proliferated less vigorously after antigenic stimulation. Killing of target cells was a major cause of these reduced responses, since perforin-deficient CD8+ T cells showed substantially increased cytokine synthesis and proliferation. Cytotoxicity by the alternate Fas pathway also resulted in self-limitation of CD8+ T cell cytokine synthesis. This relationship between cytotoxicity and cytokine synthesis may regulate CD8+ T function in different phases of an immune response.

Expression of human mitochondrial NADP-dependent isocitrate dehydrogenase during lymphocyte activation

In the process of identifying genes involved in optimization of lymphocyte activation, we have cloned the human mitochondrial NADP-dependent isocitrate dehydrogenase (mNADP-IDH) cDNA. The cDNA and its deduced amino acid (AA) sequence had a high degree of homology with those of the porcine and bovine. The heart and muscle had the highest constitutive expression of the gene. The expression of steady-state mRNA in the resting T and B lymphocytes was low but was induced after mitogen stimulation. The mRNA levels peaked around 48 h and remained elevated at 72 h. At the protein level, the mitochondrial but not cytosolic NADP-IDH activity was augmented after the mitogen stimulation. There was no cell cycle-dependent fluctuation of mNADP-IDH expression in synchronized Jurkat cells. In T and B cells, rapamycin (RAPA) could repress the mitogen-stimulated mNADP-IDH expression, although most of the early or late phase activation-related genes including a G-protein beta subunit-related gene H12.3 were not affected by the drug. The restricted expression of the gene in certain tissues and the activation-related expression in lymphocytes suggest that this gene might be necessary for optimal functions in heart, muscle, and the activated lymphocytes.

Cytokine gene expression in human cardiac allograft recipients

The long-term success of heart transplantation for end-stage heart disease has been hindered by the problems associated with acute and chronic graft rejection, opportunistic infections and potentially fatal complications of intensive immunosuppression. A more complete understanding of the biology of transplant rejection should provide the basis for the development of improved methods for controlling and monitoring rejection. Cytokines, the soluble factors which regulate the immune response, are central to the rejection process. The objective of this study was to analyse cytokine mRNA transcripts in 99 biopsy samples and 89 blood samples from 65 and 35 Stanford Medical Center cardiac transplant recipients, respectively, gathered between January 1990 and January 1992. Following RNA extraction and conversion to cDNA, samples were amplified with cytokine-specific primers for interleukins (IL) 1 to 8, TNF-beta (tumour necrosis factor-beta) and IFN-gamma (interferon-gamma) and were analysed by gel electrophoresis and Southern blot hybridization. Our results demonstrate that despite chronic immunosuppressive therapy, the peripheral blood of transplant recipients expressed a higher combined percentage of different cytokine transcripts than did peripheral blood obtained from normal volunteers. In transplant patients, detection of cytokine transcripts for IL-1 alpha, IL-1 beta and IL-2 increased with time after transplantation. Intragraft IL-7 gene expression was significantly increased in biopsies diagnosed with mild (grade 1) rejection when compared to those with no evidence of rejection or with moderate to severe rejection. Implications of these results in light of possible mechanisms of rejection and of new approaches to immunotherapy are discussed.

T-helper- and accessory-cell-independent cytotoxic responses to human tumor cells transfected with a B7 retroviral vector

As a means to increase the immunogenicity of tumor cells, we have developed a retroviral vector to transfect human B7, a molecule capable of delivering co-stimulatory signals to T cells. Three different tumors, a melanoma, an ovarian carcinoma and a myelomonocytic leukemia, were transfected with high efficiency. When compared for their capacity to stimulate allogeneic T cells, B7+ but not B7- tumor cells were able to stimulate strong proliferative and cytotoxic responses. The effector CTL generated recognised B7+ and B7- cells as well as untransfected tumor cells, indicating that B7 is required in the inductive but not the effector phase of the response. Remarkably, B7+ tumor cells were able to induce cytotoxic responses both by CD4-depleted and by CD8-purified T cells, demonstrating that expression of B7 is at the same time necessary and sufficient to induce a cytotoxic response in the absence of T-helper cells and accessory cells.

Immune responses in interleukin-2-deficient mice

The role of costimulatory signals in T cell induction was evaluated in mice lacking the interleukin-2 (IL-2) gene. In vitro secondary antiviral T cell responses were absent unless IL-2 was added, confirming the crucial role of IL-2 in vitro. In vivo, primary and secondary cytotoxic T cell responses against vaccinia and lymphocytic choriomeningitis virus were within normal ranges. B cell reactivity to vesicular stomatitis virus was not impaired. T helper cell responses were delayed but biologically functional. Natural killer cell activity was markedly reduced but inducible. These normal in vivo immune responses in IL-2-deficient mice question the importance of IL-2 as defined by in vitro studies.

T-cell-T-cell collaboration in allograft responses

T-cell-T-cell collaboration in allogeneic responses traditionally has been viewed as the requirement for CD4+ T helper cells in the activation of CD8+ cytotoxic T cells. In this regard, the role of the CD4+ T cell is primarily to provide growth factors, such as interleukin-2, on which the CD8+ T cell is dependent. However, expanding information concerning the function of T-cell subsets, and the roles of antigen-presenting cells and cytokines in regulating immune responses, requires that the basic tenets of T-cell interactions be re-evaluated.

Tumor rejection after direct costimulation of CD8+ T cells by B7-transfected melanoma cells

A variety of tumors are potentially immunogenic but do not stimulate an effective anti-tumor immune response in vivo. Tumors may be capable of delivering antigen-specific signals to T cells, but may not deliver the costimulatory signals necessary for full activation of T cells. Expression of the costimulatory ligand B7 on melanoma cells was found to induce the rejection of a murine melanoma in vivo. This rejection was mediated by CD8+ T cells; CD4+ T cells were not required. These results suggest that B7 expression renders tumor cells capable of effective antigen presentation, leading to their eradication in vivo.

Immunosuppression of triptolide and its effect on skin allograft survival

In this study the immunosuppressive properties of triptolide were evaluated. Triptolide was found to inhibit skin allograft rejection in a dose-dependent manner. This inhibitory effect was time dependent. Triptolide at 0.1 mg/kg/day significantly prolonged the graft survival when triptolide was given for 9 days after transplantation, but not before transplantation. In vitro studies showed that triptolide markedly suppressed cytotoxic T-lymphocyte (CTL) induction and mixed lymphocyte reaction (MLR) at concentrations ranging from 0.08 to 10 ng/ml. The inhibition on MLR was also significant when triptolide was added to the cultures at 36 h after initial incubation. Furthermore, exogenous IL-2 did not reverse this inhibitory effect of triptolide. Our results suggest that triptolide inhibits lymphocyte activation at a relatively late stage, and its effect on immune response is not exerted through altering IL-2 production.

Interleukin-2 receptor positive cells in human decidua during the first trimester of pregnancy and their association with macrophages

Maternal immune rejection of the fetus could sometimes be the cause of unexplained recurrent spontaneous abortion. Components of the T cell-mediated immunity were investigated in the first trimester of pregnancy in women having spontaneous abortion and compared to those with normal pregnancy having a termination on social grounds. Interleukin 2 (IL-2) had no proliferative effect on the trophoblasts of chorionic villi and there were also no IL-2 receptors in these cells. However IL-2 receptor positive cells were found in the decidua in 7 out of 24 women with normal pregnancy and in 12 out of 18 with spontaneous abortion. A high density of macrophages showed an association with IL-2 receptors in both groups. There were no differences with respect to T-cytotoxic cells and T-helper cells in cases of normal pregnancy (with and without IL-2 receptor positive cells), whereas in women having spontaneous abortion we found lower densities of T-helper and T-cytotoxic cells in those without IL-2 receptors than in those with IL-2 receptors.

Prethymic nylon wool-passed bone marrow cells, substituting for helper T cells, can augment the generation of cytotoxic T lymphocytes from their precursors

Nylon wool-passed bone marrow (NW-BM) cells treated with anti-Thy.1 monoclonal antibody and complement were added to a mixed lymphocyte culture which contained a limiting number of lymph node cells, as responder cells, and a sufficient number of mitomycin-c-treated allogeneic spleen cells as stimulator cells. NW-BM cells of the same MHC haplotype as responder cells enhanced the generation of allo-specific cytotoxic T lymphocytes (CTL) not only at a relatively high dose (3 x 10(3) cells/well) of responder cells, but also at an extremely dilute dose (1 x 10(3) cells/well). NW-BM cells which had a third-party MHC haplotype, a haplotype different from both responder and stimulator cells, also enhanced the generation of CTL at relatively high doses, but not at low doses, of responder cells. NW-BM cells which had MHC haplotypes identical with those of responder cells induced CTL from helper T cell-depleted responder cells, but NW-BM cells which had the third-party haplotype did not. These results showed that the enhancing effects of NW-BM cells of the same MHC haplotype as responder cells might be due to a specific helper effect and the enhancing effect of NW-BM cells of the third-party haplotype might be due to a nonspecific filler effect, which only conditioned the cultured cells. It was also found that, to exhibit the helper effect, NW-BM cells had to possess MHC class II, but not MHC class I, molecules in common with CTL precursors. This study showed that in the induction of CTL, prethymic NW-BM cells had a capability comparable to that of mature helper T cells.

Regulation of human interleukin-2 and interferon-gamma gene expression by suppressor T lymphocytes

Concomitant with induction of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) gene expression in human tonsil cells, mitogenic stimulation induces a transient activation of cells able to effectively suppress expression of these genes. Induction of IL-2 and IFN-gamma genes largely precedes appearance of suppressor cell activity, allowing expression of both genes to occur before strong down-regulation is exerted by activated suppressor cells. Suppressive activity induced in one cell population can inhibit IL-2 and IFN-gamma gene expression in another population from the same donor. The distinct nature of suppressor cells is supported by the absence of down-regulation of IL-2 gene expression in a helper cell line, MLA-144; yet, in these cells, negative control can be expressed when active suppressor cells are introduced. Our findings support the concept that actual levels of IL-2 and IFN-gamma gene activity are regulated to a large extent by the differential kinetics of activation of suppressor cells on one hand and of cells expressing the IL-2 and IFN-gamma genes on the other.

IL-4-supported induction of cytolytic T lymphocytes requires IL-2 and IL-6

Previous work indicated that a CTL response can be generated by the combination of IL-2 plus IL-6 or IL-4 alone. Because of the ubiquitous production of IL-6 and its apparent ability to induce IL-2, we explored the interdependence of these lymphokines in supporting a CTL response from murine thymocytes. For thymocytes cultured in IL-4, further addition of IL-6 enhanced thymocyte proliferation. In addition, a role for IL-6 in thymocyte activation was indicated by the ability of anti-IL-6 mAb to block both IL-4-directed proliferation and the cytotoxic response found in the presence of IL-4. The addition of IL-2 to limiting doses of IL-4 augmented the CTL response; however, the response to high levels of IL-4 was not augmented by addition of IL-2. Consistent with this apparent involvement of IL-2 in the IL-4-mediated response we found: (a) that mAb to IL-2 significantly reduced the CTL response generated in the presence of IL-4; (b) that IL-2 activity was present in culture supernatant following incubation of thymocytes with high levels of IL-4; and (c) that enhanced IL-2 receptor expression found in the presence of IL-4 was blocked with the addition of anti-IL-2 antibody to the thymocyte culture. In contrast to the data for proliferation, anti-IL-4 mAb had no effect on the generation of CTL in the presence of IL-2 + IL-6 but readily blocked the CTL response to IL-4. These results indicate that, for thymocyte responders, the CD8+ CTL generated in the presence of IL-4 require both IL-2 and IL-6.

Association of interleukin-2 therapy with staphylococcal bacteremia

The authors prospectively monitored patients undergoing leukapheresis for peripheral stem cell harvesting (PSCH) or lymphokine activated killer (LAK) cell generation for 3 weeks after catheter placement for evidence of local or systemic infections. Over a 1-year period, 16 patients underwent leukapheresis for PSCH in preparation for autologous bone marrow transplantation (ABMT). The original catheters remained in place an average of 20 days without any documented infections. Seventeen patients underwent leukapheresis as part of a low-dose interleukin-2 (IL-2) treatment for LAK cell generation, and their catheters remained in place an average of 20.2 days with three documented episodes of bacteremia (18%). Eight patients treated with high-dose IL-2 also underwent leukapheresis for LAK cell generation and their catheters remained in place an average of 12 days with three documented episodes of bacteremia (38%). In all cases of bacteremia, Staphylococcus species were isolated from the blood. The IL-2 exposure level was associated with the risk of bacteremia (P = 0.01). Other potential risk factors (e.g., number of pheresis procedures, complement level, serum immunoglobulin levels, absolute neutrophil count) were not related to this risk.

Aberrant regulation of interleukin-2 but not of interferon-gamma gene expression in Down syndrome (trisomy 21)

The regulated expression of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) genes was analyzed in peripheral blood mononuclear cells derived from 29 noninstitutionalized Down syndrome individuals and compared to that of 32 normal donors. Culture conditions were chosen that measure the transient, phytohemagglutinin-induced expression of IL-2 and IFN-gamma mRNA, as well as the intactness of post-transcriptional and suppressor T cell-dependent mechanisms that control this expression. The latter was achieved by analyzing, respectively, the superinduction of IL-2 and IFN-gamma mRNA occurring upon culture with cycloheximide or after low-dose gamma-irradiation. A convenient, sensitive, and quantitative assay for specific mRNA was devised, suitable for measuring mRNA levels expressed in cells from 1 ml of peripheral blood. Analysis of individuals with Down syndrome revealed a pronounced decrease in inducibility of the IL-2 gene. By contrast, induction of IFN-gamma mRNA was as vigorous as that observed for normal donors. In cells from trisomic subjects, superinduction of IFN-gamma mRNA by cycloheximide was at least as extensive as for normal donors, while in the case of IL-2 mRNA, it was weaker. These abnormal patterns of IL-2 gene expression were seen irrespective of age. Our findings demonstrate a selective impairment of IL-2 gene expression in Down syndrome, rather than a general deficiency in helper T cells.

Role of major and minor histocompatibility antigens in the suppression of alloreactive cytotoxic responses induced by alloantigen pretreatment

We have recently shown that priming mice with allogeneic strain A spleen cells before immunization with (A x B)F1 spleen cells strongly suppresses the cytotoxic T-lymphocyte (CTL) response directed against linked strain B alloantigens. This specific decrease in the CTL responses against the second immunizing alloantigen is associated with a high CTL response against the first priming alloantigen. The suppression of CTL responses against the strain B alloantigens is, however, not due to killing of F1 spleen cells by anti-A CTL, since it was observed after immunization of primed mice with a mixture of (A x B)F1 and B cells. In the present study, attempts were made to determine the relative contribution of H-2 and minor histocompatibility background antigens towards induction of suppression. Our results demonstrate that priming and immunizing spleen cells have only to share H-2 antigens in order to induce a downregulation of CTL responses directed against the linked alloantigens. This indicates that immunity against H-2 antigens is sufficient to induce suppression. However, priming against minor histocompatibility antigens also induces suppression, but only if spleen cells used for priming and immunization share H-2 antigens with the recipient strain. Therefore, the suppression can be induced by priming with non-H-2 antigens but is H-2-restricted. This study has also demonstrated that suppression can be induced by intraperitoneal or subcutaneous administration of allogeneic cells.

Dendritic cells stimulate primary human cytolytic lymphocyte responses in the absence of CD4+ helper T cells

Cytotoxic lymphocytes are typically generated from unfractionated suspensions of human lymphocytes by stimulating with heterogeneous APCs and exogeneous growth factors. We have found that human blood dendritic cells can directly stimulate allogeneic human CD8+ T cells to proliferate and express antigen-specific cytotoxic activity. These primary responses, which are accompanied by the release of T cell growth factor(s), are induced in the absence of CD4+ helper T cells and are not inhibited by anti-CD4 mAb. Both antigen-specific CTL as well as nonspecific NK cells can be elicited by dendritic cells. The NK cell response can be depleted at the precursor level by panning with an anti-CD11b mAb, which removes a CD11b+/CD28-, CD16+ subset from the starting CD4- responders. Allogeneic blood monocytes are neither stimulatory nor inhibitory of these primary CD4- MLRs, even though monocytes present alloantigen in such a way as to be recognized as specific targets for CTL that have been sensitized by dendritic cells. The number of CD8+ cells that are blast transformed and express an activated phenotype (i.e., HLA DR/DQ+, CD25/IL-2R+, CD45R-) reaches 30-40% of the culture at day 4-5, the peak of the helper-independent response. We conclude that antigen-presentation by dendritic cells is sufficient in itself to prime cytolytic precursors. We speculate that using dendritic cell stimulators and CD4- responders in MLRs may be more efficient than standard tissue typing approaches for the detection of subtle, but important class I MHC-restricted histoincompatibilities in human transplantation.

Activation of CD8+ T cells by allogeneic class II-deficient B-cell lines derived from patients with bare lymphocyte syndrome

The major histocompatibility complex (MHC) class II antigens (Ags) are known to carry the major stimulating determinants of the primary mixed lymphocyte reactions (MLR). We investigated the mechanism of generating HLA class I-directed alloreactive T-cells in primary MLR. With the use of class II-deficient EBV-transformed B-lymphoblastoid cell lines (B-LCLs) derived from patients with bare lymphocyte syndrome (BLS), we have demonstrated in the present study that class I disparity alone can trigger primary MLR in the absence of exogenous IL-2. The CD8+ T cells were primary MLR-responsive cells, and the CD4+ T cells seem to play no role in primary MLR when class II alloantigens are not involved in stimulation. Addition of autologous macrophages did not influence the primary MLR response. The primary MLR was completely blocked by anti-class I or anti-CD8 antibodies but not by anti-class II or anti-CD4 antibodies. The MLC-generated CD8+ T cells exhibited cytolytic activity as well as proliferative responses. The proliferative response of the CD8+ T cells was specifically directed against class I antigens, demonstrated by proliferative assays; and the helper-independent CD8+ T cells were generated only when the activation of CD4+ T cells did not occur. This observation suggests that functional recruitment of T-cell receptor (TCR) repertoire is under active regulation, and the suppression of CD8+ T-cell helper recruitment appears to be dictated by the CD4+ T-cell subset. Further analysis of the primed T-cell specificities showed that alloreactivity of the CD8+ T cells was mostly accounted for by the HLA-B Ags.(ABSTRACT TRUNCATED AT 250 WORDS)

Antitumor effects of a new interleukin-2 slow delivery system on methylcholanthrene-induced fibrosarcoma in mice

The interleukin-2 (IL-2) mini-pellet, the carrier material of which is a biocompatible and biodegradable atelocollagen refined from bovine skin, contains 1 x 10(6) units of IL-2 and can release IL-2 slowly in vivo by diffusion and dissolution. We have evaluated the antitumor effects of the IL-2 mini-pellet on an established solid murine tumor, methylcholanthrene-induced fibrosarcoma (Meth A). The subcutaneous administration of the IL-2 mini-pellet alone on days 8 and 11 after tumor inoculation significantly inhibited tumor growth. A significant inhibition was also seen when it was combined with the intravenous injection of 5 x 10(7) lymphokine-activated killer (LAK) cells, in comparison to the untreated controls. Moreover, therapy with the IL-2 mini-pellet alone or in combination with LAK cells also prolonged the survival of mice bearing Meth A fibrosarcoma. In order to determine the precise mechanism of action of these antitumor effects, we tested splenocytes of treated mice for cytotoxic activity in vitro and investigated tumor tissues by an immunohistochemical method. On day 2 after the administration of the IL-2 mini-pellet, the lytic activity of splenocytes against both YAC-1 and JTC-11 cells (i.e. NK and LAK activity) was significantly augmented, and on day 7 a massive accumulation of lymphocytes, which were mainly like Thy1+ and/or asialo-GM1+ LAK cells, was seen in the tumor. These findings indicate that the IL-2 mini-pellet is an appropriate system for local administration of IL-2 and can induce LAK-like effector cells at the target site.

Low molecular weight human T-cell response immunopotentiator: alpha-2'-deoxy-3-deazaguanosine

We have examined the immunological activity of a unique alpha-nucleoside analog of 2'-deoxyguanosine in which the pyrimidine ring nitrogen in the 3 position is replaced by CH [6-amino-1, 5-dihydro-1-(2-deoxy-alpha-D-erythro-pentofuranosyl)imidazo[4,4-c] pyridin-4-one, alpha-d3DGuo, 1] and its structural analogs. The alpha-d3DGuo is not mitogenic to human PBL. It displayed consistently, however, a potent immunoenhancing activity on PHA-induced human lymphocyte proliferation at concentrations ranging from 0.0125 mM to 0.4 mM in a dose dependent manner. These findings thus suggest that mitogenicity is not a pre-requisite for the immunoenhancing effect. The maximal potentiating effect of alpha-d3DGuo is usually exerted at the bottom range of the dose response to PHA. The magnitude of increase is about the same as that mediated by rIL-2. Similarly, Con A mediated lymphocyte proliferation is markedly enhanced by alpha-d3DGuo. When added during allogeneic MLR, alpha-d3DGuo also augmented the proliferation of alloreactive T-cells and the magnitude of response was similar to that induced by rIL-2. The alpha-d3DGuo induced increase in allogeneic response was dependent on concentrations of both alpha-3dDGuo and alloantigens as noted with T-mitogen induced proliferative responses. The cytotoxic activity of lymphocytes induced in allogeneic mixed cultures was also augmented by alpha-d3DGuo. It showed, however, no potentiating effect on B-lymphocytes proliferation stimulated either with SAC or PWM. The alpha-d3DGuo is also able to restore, at least partially, the depressed proliferative responses of T-cells to both PHA and Con A.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-random migration of CD4 and CD8 T cells: changes in the CD4: CD8 ratio and interleukin 2 responsiveness of efferent lymph cells following in vivo antigen challenge

In this investigation we have examined some of the cellular and molecular changes in efferent lymph that drains from an antigen-stimulated peripheral lymph node. Resting efferent lymph is characterized by a higher percentage of CD4+ cells and consequently, a higher CD4/CD8 ratio than peripheral blood. Following antigen stimulation of a cannulated peripheral lymph node in antigen-primed sheep, the percentage of CD4+ cells in efferent lymph increases above the resting level during days 1, 2 and 3 post antigen stimulation. This is followed on days, 3, 4, and 5 after antigen stimulation by an increase in the percentage of CD8+ cells above the resting level which occurs as the percentage of CD4+ cells returns to the resting level. These changes cause the CD4/CD8 ratio to first increase above the resting value during the CD4 phase and then decrease below the resting value during the CD8 phase. During the CD4 phase a lymphokine activity is present in cell-free lymph fluid. Lymph fluid collected at this time supports the proliferation of activated T cells. Supernatants generated from efferent cells collected at a similar time and cultured in vivo for 24 h without any further stimulation are capable of releasing this material. During the CD8 phase cells expressing functional interleukin(IL)2 receptors appear in lymph fluid. The data suggests a sequential exit of T cell subsets from an antigen-stimulated lymph node and that the appearance of IL2-like activity and IL2-responsive cells in efferent lymph fluid are temporally distinct events.

Modulation of both interleukin 2 receptor expression and interleukin 2 production during experimental murine Trypanosoma cruzi infection

A massive activation of T cells takes place during the early stages of a Trypanosoma cruzi infection in mice. We present data indicating that substantial amounts of interleukin 2 (IL-2) are secreted and IL-2 receptors are expressed during the period of increased proliferation (4-7 days post infection). Both concanavalin A-induced proliferation and IL-2 production are markedly decreased later in the acute infection (around 3 weeks post infection). This proliferation cannot be restored by externally added IL-2. Simultaneously, there is a drastic reduction in the number of both high- and low-affinity IL-2 receptors. The reduction is not attributable to the elimination of a particular T-cell population. In vivo administration of recombinant IL-2 failed to improve resistance to T. cruzi parasites as measured by parasitaemia and mortality.

Therapeutic uses of interleukin-2 and lymphokine-activated killer (LAK) cells

Interleukin-2 (IL-2) is the first of a growing list of lymphokines to be cloned and available for preclinical and clinical evaluation. A product of T-helper lymphocytes, IL-2 augments the cytolytic activity of T-lymphocytes and natural killer (NK) cells, stimulates the proliferation of these cells, and induces the formation of lymphokine-activated killer (LAK) cells. LAK cells exhibit cytolytic activity against a broad range of both freshly isolated and cultured tumor cells, while exhibiting limited cytolytic activity against normal cells. The apparently large therapeutic index suggested by in vitro studies is strongly supported by the antitumor responses seen in preclinical studies. Initial clinical studies reported encouraging response rates, but the actual role of IL-2 and/or LAK cell infusion in cancer therapy has yet to be determined, and may only represent the first step in managing the tumoricidal potential of the immune system.

Suppression of T-lymphocyte blastogenesis by ovine trophoblast protein-1 and human interferon-alpha may be independent of interleukin-2 production

Cells derived from the trophoblast tissue of a day 15 sheep conceptus released substances that inhibit incorporation of [3H]thymidine into phytohemagglutinin (PHA)-stimulated ovine lymphocytes. This effect was partially reversed by addition of antiserum to ovine trophoblast protein-1 (oTP-1), a major secretory product of day 13-21 sheep conceptuses and a protein structurally and functionally related to alpha-interferons (IFN-alpha). Human IFN-alpha, unlike dexamethasone, inhibits phytohemagglutinin-induced lymphocyte blastogenesis without reducing interleukin-2 (IL-2) production by the cultures, and conditioned medium containing IL-2 does not promote [3H]thymidine incorporation into ovine lymphocytes when oTP-1 is present. Thus, oTP-1, by virtue of being an IFN, may have a local immunomodulatory role by selectively inhibiting the proliferative responses of certain maternal immune cells to IL-2.

Interleukin-2 release from lymphocytes of patients with head and neck cancer

Interleukin-2 (IL-2) plays a central role in cellular immune regulation. In vitro this cytokine is secreted after mitogenic stimulation with phorbolester (PMA), phytohemagglutinin A (PHA), or the monoclonal T cell antibody OKT3. In our experiments the IL-2 concentration was measured in a biologic system using an IL-2-dependent murine cytotoxic T cell line. Control subjects who were age-matched to patients with head and neck cancers did not show an altered IL-2 production in vitro, irrespective of whether they were accustomed to high alcohol consumption or cigarette smoking. Patients with cancer of the larynx did not differ significantly from control subjects. Most prominent was the significant reduction in IL-2 release of patients with cancer of the oropharynx and in patients with positive lymph nodes in the neck. Impaired IL-2 secretion in head and neck cancer patients may therefore be an additional prognostic indicator worthy of further investigation.

Side effects of antibiotics on immune response parameters and their possible implications in antimicrobial chemotherapy

Antibiotics may influence immune response by quite different ways. By screening the multitude of publications on this subject, the aim of this overview was to arrive at a basic generalizing statement on the relationship between chemical structure or mode of action of antibiotics and the effect on immune response and to get an indication on whether certain in vitro and/or ex vivo parameters could represent comparable effects under clinical conditions. - The influence of antibiotics on immune response may arise by direct effects on immunocompetent cells, i.e. in the absence of microorganisms, or indirectly by changes in structure or metabolic products of germs induced by subminimal inhibitory concentrations (subMIC's). In the former case, stimulatory and inhibitory effects have been observed on phagocytosis and intracellular killing activity, on antibody production including IgE, on different parameters of cellular immunity (e.g. foodpad swelling reaction, MIF-production, mitogen/antigen induced lymphocyte proliferation and delayed type hypersensitivity skin reaction), on mediator production as interleukins or prostaglandins and the expression of corresponding receptors on immunocompetent cells as well as on the course of experimental infections with primary resistant microorganisms. - Indirect effects are related to the influence of subMIC's of antibiotics on the morphology and structure of microorganisms, on their antigenicity/immunogenicity or on their serosensitivity and enzyme and toxin production. - This overview shows that - according to the actual knowledge - antibiotics may exhibit immunological side effects which, however, can not strictly be attributed to certain chemical structures or to a certain mode of action. - It has to be considered that a literary study comparing the results of different authors is rendered difficult by the often nonhomogeneity of experimental procedures and the fact that little is known yet about immunological side effects of antibiotics in man, i.e. under clinical conditions.

Dual-label immunocytochemistry of the active multiple sclerosis lesion: major histocompatibility complex and activation antigens

Fresh-frozen autopsy material containing active inflammatory lesions from 9 different patients with multiple sclerosis (MS) was analyzed by immunocytochemistry using a panel of monoclonal antibodies, and a dual-label immunocytochemical method was developed which permitted the simultaneous detection of two different surface markers on a single cell. We now report the following. (1) The predominant T-cell phenotype within MS lesions is CD2,3,8. This phenotype marks the suppressor-cytotoxic subset. (2) These cells do not express the natural killer cell marker NKH-1, which is present on a subset of CD8-positive cells in peripheral blood. (3) The infiltrating cell expresses class I (HLA A, B, C), but not class II (DR and DQ), major histocompatibility complex (MHC) molecules. (4) Other T-cell surface molecules, including the activation antigens interleukin-2 receptor, Ta1, and T11-3, as well as the marker 2H4, are largely not expressed. (5) Endothelial cells express both class I and class II MHC molecules and the 4B4 molecule in both MS and control tissue. (6) Astrocytes within the vicinity of MS lesions are predominantly class II MHC-negative. These results demonstrate that the T-cell infiltrate present in MS tissue on autopsy has a restricted phenotypic profile, but they also raise the possibility that, within this population, few activated effector cells are present.

Con A-stimulated thymocytes produce interleukin 2 after removal of Lyt-1 positive cells

Mouse lymphocytes produce several lymphokines, including interleukin 2 (IL-2) and colony-stimulating factors (CSFs) following stimulation with T-cell mitogens. However, very little IL-2 is produced by thymocytes upon concanavalin A (Con A) stimulation. Strong selective inhibition of IL-2 production was observed when fresh spleen cells were mixed with Con A-activated thymocytes. Sorting of populations on the basis of antigenic phenotype showed that the cell mediating the blockage in IL-2 secretion is a large T cell expressing markers for both Lyt-1 and Lyt-2. This specific inhibition of IL-2 accumulation was not mediated by a soluble product, or by absorption on expressed IL-2 receptors on the activated thymocytes. Removal of the Lyt-1 positive cells from a thymocyte population renders it capable to produce IL-2 upon Con A stimulation, indicating a functional role of these cells.

Modulation of cellular anti-tumour responses by tumour-specific T suppressor lymphocytes

Tumour-specific Ts cells, induced by a protocol which simulates early stages of tumourigenesis in BALB/c mice by the syngeneic plasmacytoma ADJ-PC-5, suppress the generation of specific cytotoxic T lymphocytes (CTL) in a primary in vitro mixed lymphocyte tumour culture (MLTC) of BALB/c spleen cells against ADJ-PC-5. The influence of these Ts cells on the generation of non-specific killer cell activity has now been analysed. The data show that non-specific killer cells generated during in vitro MLTC lyse both ADJ-PC-5 and YAC-1 cells. They are different from tumour-specific CTL as shown by cold target inhibition experiments and on the basis of their different phenotype. The generation of non-specific killer activity during MLTC can be completely suppressed by ADJ-PC-5 specific Ts cells. Activation of non-specific killer cells by recombinant interleukin-2 (r IL2) alone is not influenced by these Ts cells. The in vitro data are best explained by assuming that the target for suppression are ADJ-PC-5 specific T helper cells. Their inactivation will result in depletion of IL2 in the culture, which is required to activate non-specific killer cells. Prevention of activation of specific and non-specific killer cells in vitro by activated tumour-specific Ts cells in the presence of the tumour, suggests that similar mechanisms might operate in vivo and that inactivation of tumour-specific T helper cells might be of central relevance.

The autonomy of CD8+ T cells in vitro and in vivo

Experiments have been carried out in vitro and in vivo to determine to what extent CD8+ T cells in the rat can function independently of any helper activity from CD4+ cells. We have identified the culture conditions required for the autonomous proliferation of CD8+ T cells in the rat mixed leucocyte culture (MLC) and in particular have studied both the kinetics of the response and the effect of replacing the homologous serum, used in our previous MLC experiments, with fetal calf serum (FCS). The results obtained using FCS show that, early in the MLC, CD8+ T-cells proliferate at a comparable rate to the CD4+ subset but that, within 48-72 hr, the proliferation rate of the CD8+ cells ceases to increase with time. In contrast, the proliferation of the CD4+ T cells appears to be limited only by the exhaustion of the culture medium. The results also show that the proliferative responses of both CD4+ and CD8+ T cells are inhibited in homologous serum but that it is the CD8+ subset that is more affected. When CD8+ T cells, in homologous serum, are co-cultured with irradiated CD4+ T cells the proliferative activity is increased, indicating that the helper activity of the CD4+ T cells can over-ride the inhibitory effect of the serum. In vivo we have compared the abilities of injected CD4+ and CD8+ T cells to mediate rejection of skin allografts on nude rats. Grafts were rejected more rapidly on recipients of low doses of CD4+ T cells than on rats given 200 times as many CD8+ T cells. Thoracic duct lymphocytes (TDL) obtained 5 weeks after CD8+ T-cell injection always contained a population of CD4+ T cells, even when the injected CD8+ T-cell inoculum contained less than 0.1% CD4+ cells as contaminants. Evidence was obtained that these CD4+ T cells found in TDL displayed alloreactivity in MLC. Further, the intentional injection of very low doses of CD4+ cells led, after 5 weeks, to frequencies of CD4+ T cells, in thoracic duct lymph, equal to that obtained by the injection of 200 times as many cells of the same phenotype. It appears that, in T-cell-deficient rats, CD4+ cells can expand over 2000 times in a few weeks. Such expansion may explain the relatively slow rejection of skin allografts observed in these experiments when nude rats were injected with putatively pure populations of CD8+ T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effects of cimetidine on interleukin-2 production by peripheral blood lymphocytes in advanced ovarian carcinoma

The present study was designed to elucidate the effect of cimetidine on CD4 and CD8 positive cells, interleukin-2 (IL-2) production and IL-2 receptor expression in peripheral blood lymphocytes (PBL) from patients with advanced ovarian carcinoma during the course of combination chemotherapy. The absolute number of CD8 (but not CD4) positive cells in PBL from patients with advanced ovarian carcinoma before surgery was significantly higher than that with benign ovarian tumor, while the IL-2 productivity was significantly lower. However, the IL-2 receptor expression was comparable to that with benign ovarian tumor. When a combination chemotherapy consisting of cisplatin, adriamycin and cyclophosphamide was given to these ovarian cancer patients, the IL-2 production was markedly depressed. If cimetidine was given with the combination chemotherapy, the inhibition of IL-2 production by chemotherapy was significantly diminished with a significant increase of CD4 positive cells. On the other hand, the IL-2 receptor expression was not affected by this treatment. When treatment with cimetidine was initiated after completion of chemotherapy, the depressed IL-2 production was restored to the level of control patients with benign ovarian tumor. The restoration seemed to result from an increase in proportion of CD4 positive cells. However, the expression of IL-2 receptor remained unchanged even if cimetidine was given.

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.

T4+ T helper cell function in vivo: differential requirement for induction of antiviral cytotoxic T-cell and antibody responses

This study documents the differential requirements of T4+ T helper cells in the induction of virus-specific cytotoxic T-lymphocyte (CTL) and antibody responses during acute lymphocytic choriomeningitis virus infection. Two monoclonal antibodies (GK1.5 and RL172.4) directed against the L3T4 (T4) molecule were used for depleting T helper cells from mice. Depletion of T4+ cells caused a pronounced suppression of antiviral antibody response (20-fold decrease) but had minimal effect on virus-specific CTL response (less than 2-fold reduction). Despite the elimination of greater than 90% of T helper cells, anti-L3T4-treated mice were able to generate a CTL response of sufficient magnitude to control the viral infection. In contrast, depletion of Lyt2+ T cells abrogated the CTL response and the ability to eliminate virus. Thus, our results underscore the importance of the Lyt2+ T-cell subset in controlling infection with this virus and show that a deficiency of T4+ T cells is likely to have a more severe effect on antibody production than on CTL responses.

Antigen-independent activation of cytotoxic T cells by lymphokines

Supernatants from phorbol myristate acetate (PMA)-stimulated EL4.IL2 cells (EL4.PMA), but not recombinant IL-2 (rIL-2), induced the production of cytotoxic T lymphocytes (CTL) in low density murine spleen cell cultures. CTL induction in these cultures was completely abrogated by treatment with anti-Thy-1 or anti-Lyt-2 antibody plus complement but not by anti-L3T4 antibody plus complement. Fractionation of EL4.PMA on a Sephadex G-150 column demonstrated that the CTL-inducing activity in EL4.PMA eluted with an apparent molecular weight of about 44,000 and was partially separated from IL-2. This 44,000 MW material was shown to contain insignificant amounts of PMA. Following a 3-day culture period with the partially purified factor, C57BL/6J thymocytes could proliferate and differentiate into cytotoxic cells in response to rIL-2, whereas there was no proliferation or generation of cytotoxic cells when the thymocytes were cultured in rIL-2 alone. The number of IL-2 receptor-positive cells in C57BL/6J thymocytes also increased from 1.1% to 22.8% after 3 days of culture in the partially purified factor. Recombinant IL-4 (BSF-1) and IL-5 (TRF), when used alone or in combination with rIL-2, were unable to induce a cytotoxic response under similar culture conditions. These findings are consistent with the interpretation that EL4.PMA contains a novel lymphokine that directly, or indirectly, induces the expression of IL-2 receptors on resting CTL precursors without intentional stimulation by specific antigen. In the presence of IL-2, these precursors may then differentiate into effector CTL.

Reactivity of Ly-2+ T cells against 2,4,6-trinitrophenyl (TNP)-modified syngeneic stimulator cells: specificity, frequency of interleukin 2-producing Ly-2+ helper T cells and clonal segregation from Ly-2+ cytotoxic T lymphocytes

The in vitro reactivity of purified murine Ly-2+ and L3T4+ T cells towards 2,4,6-trinitrophenyl (TNP)-modified syngeneic stimulator cells was analyzed. Both T cell subpopulations autonomously proliferated and produced interleukin 2. In either the Ly-2+ or L3T4+ T cell subset the frequencies of TNP-specific interleukin 2 (IL 2)-producing T lymphocyte precursors (IL 2 TL-p) were equally high (f = 1/400-1/1000). Clonally developing IL 2 TL of either T cell subset showed an exquisite antigen (TNP) specificity as shown by the split culture approach. TNP-specific Ly-2+ IL-2 TL used class I MHC (H-2Kk) gene products as major histocompatibility complex (MHC) restriction elements, while L3T4+ IL 2 TL proved to be class II MHC (H-2I-AkI-Ek) restricted. Clonal segregation analyses revealed that the majority of clonally developing TNP-reactive Ly-2+ TL segregated into either IL 2 TL-p or cytotoxic T lymphocyte presursors, i.e. both functions appear to be mutually exclusive. Less than 10% of the responding Ly-2+ T cells seemed to be bifunctional. These findings provide compelling evidence for the L3T4+ T cell-independent, autonomous reactivity of Ly-2+ T cells in MHC-restricted antigen-specific responses and suggest T-T cell interactions within the functional heterogenous Ly-2+ T cell population.

Responsiveness of T cells to mutant major histocompatibility complex class I antigen. I. Obligatory dependence of proliferative response on the presence of stimulator type accessory cells

Proliferative response of splenic T cells of C57BL/6 mice to mutant major histocompatibility complex (MHC) class I antigen (H-2Kbm1) was examined with regard to the role of accessory cells. T cell proliferation in mixed lymphocyte culture (MLC) was not induced when accessory cells were removed from stimulator spleen cells by passage through Sephadex G-10 or nylon-wool column. Anti-Iab antibodies did not inhibit the proliferative response to class I antigen, whereas the same antibodies completely blocked the response to class II antigen (Iabm12). Accessory cells may not be mere presenters of MHC class I antigen because stimulator cells fixed with 0.05% paraformaldehyde lost the stimulating function. The proliferative response was partially recovered by the addition of recombinant interleukin 1 (IL-1) and/or IL-2 to MLC devoid of stimulator type accessory cells. It is concluded that stimulatory type accessory cells were obligatorily involved in the T cell proliferation, and the production of IL-1 by accessory cells is thought to play a critical role in this process.