"In vivo" activated splenic T cells are refractory to interleukin 2 growth "in vitro"

Naturally activated CD4+ T cells are highly enriched for cytokine-producing cells

Most T cells in a normal non-immunized individual are in a resting state. However, a small proportion of splenic T cells are large activated cells both in specific pathogen-free and antigen-free mice. To further elucidate the effector functions associated with these "naturally" activated CD4+ T cells, we have characterized the expression of various membrane markers, cytokine production and T helper activity by these cells. We show that naturally activated CD4+ T cells express activation markers and contain tenfold higher proportions of cells producing IL-4, IL-10 and IFN-gamma as compared to small CD4+ T cells. Despite the high proportion of IFN-gamma producers, naturally activated CD4+ T cells still induce B cell proliferation and differentiation. These results are discussed in the context of normal physiological autoreactivity.

A model for developmentally acquired thymus-dependent tolerance to central and peripheral antigens

Current models of tolerance to peripheral, tissue-specific antigens contain some major caveats. First, they consider peripheral tolerance independently from intrathymic T cell selection, a dichotomy that is challenged by observations on TE-induced tolerance. Second, they do not account for the fact that vertebrates are more readily tolerised in development than in adult life. Third, they do not explain the fact that embryonic/neonatal tolerance to foreign tissues can only be induced by HC or TE. A model of thymic selection and peripheral tolerance is developed here that resolves those problems, by assuming two classes of T cell effector functions, one being regulatory and the other aggressive. Three postulates are required: (1) both epithelial and hemopoietic cellular compartments of the thymic stroma can support both positive and negative selection of T cells, but with vastly different avidity requirements and efficiency; (2) positively selected T cells with the highest avidity that escape deletion are activated intrathymically and irreversibly committed for regulatory effector functions; (3) the functional phenotype of all other thymic emigrants is determined in the periphery upon encounter with antigen. Functional commitment in the periphery depends on the maturity stage (RTE or PMR) of the immunocompetent cell, on the nature of the antigen-presenting cells, and on the effector classes of other T lymphocytes interacting on the same presenting cell. This model explains a number of observations on experimental autoimmune disease and transplantation tolerance, and it contains several readily testable predictions.

Regulatory T cells in thymic epithelium-induced tolerance. I. Suppression of mature peripheral non-tolerant T cells

Athymic mice grafted at birth with allogeneic thymic epithelium (TE) display life-long tolerance to tissue grafts of the TE donor strain, in spite of harboring peripheral T cells capable of rejecting those grafts. Tolerance is maintained in these chimeras by TE-specific regulatory CD4 T cells. We presently address the quantification and the mechanisms of this dominant tolerance process. C57BL/6 mice containing variable but defined numbers of peripheral, resident T cells received cell transfers of graded numbers of peripheral T cells from B6(BALB E10) chimeras (C57BL/6 nude mice grafted with TE from 10-day-old BALB/c embryos), resulting in a series of animals containing a wide range of donor (tolerant) versus host (non-tolerant) T cell chimerism. Increasing the relative representation of donor T cells results in a progressive delay in the rejection of BALB/c skin grafts, life-long tolerance being achieved at a ratio of tolerant and non-tolerant T cell populations of 1. In recipients displaying full tolerance, graft-reactive non-tolerant T cells were not deleted, anergized or committed to noninflammatory functions. Thus, sorted host T cells from tolerant recipients readily rejected BALB/c skin grafts upon transfer to immunodeficient animals. Finally, measurements of "helper" and inflammatory activities, as well as interleukin-4 and interferon-gamma production, failed to discriminate between T cell populations from tolerant and non-tolerant animals after specific in vitro stimulation. We conclude that: (a) TE-selected regulatory T cells can suppress, in a quantitative manner, in vivo T cell responses against major and minor histocompatibility antigens expressed by the TE and, (b) this suppressive activity neither inactivates mature non-tolerant T cells, nor does it seem to drive their differentiation along noninflammatory pathways.

Transplantation tolerance is unrelated to superantigen-dependent deletion and anergy

C57BL/6 (B6; I-E-, Mls-2b) nude mice, reconstituted at birth with thymic epithelium (TE) from BALB/c (BA; I-E+, Mls-2a) day 10 embryos (E10), permanently accepted BALB/c skin, when grafted as adults. T-cell receptor repertoire analyses in the periphery of these mice revealed no difference in frequencies of I-E/superantigen-reactive T-cell receptor V beta families, as compared to chimeras constructed with syngeneic B6 E10 TE. T lymphocytes bearing V beta 3, V beta 5, and V beta 11 T-cell receptors, from either allogeneic or syngeneic TE chimeras, responded equally well to in vitro receptor-dependent stimulation. Similar results were obtained with nude mice reconstituted at birth with E14 thymuses, already colonized by hemopoietic cells. These observations indicate that neither TE cells nor the progenies of hemopoietic precursors that colonize the thymus up to E14 express or functionally present the superantigens addressed here; it follows that tolerance to skin grafts and superantigen-related T-cell deletions are unrelated phenomena.

Qualitative Shift of Lymphokine Production in Response to Stimulation, as a Consequence of Preactivation In Vivo or In Vitro

Lymphokine production, analysed at the single cell level, was compared in resting and primed T-cell populations. Cells were preactivated in vitro by repeated mitogen stimulations, or isolated as large, low density cells naturally activated in vivo, from normal spleens of unimmunized animals. A similar qualitative shift in the pattern of lymphokines synthesized after restimulation was found as a result of in vivo and in vitro preactivation of cells. Repeated stimulations in vitro resulted in a qualitative shift in the lymphokines produced in response to activation, from a dominance of IL-2 during the first and second culture, to a dominance of IL-4 and IL-5 in the later stimulations. In vivo activation lead to a similar separation of lymphokine production as primarily IL-2 was made by small resting cells, while large cells preferentially produced IL-4 and IL-5. IFN-gamma was produced by both small and large cells. Preactivation in vitro lead to a more rapid appearance of lymphokines during restimulation. In contrast, the in vivo naturally activated cells responded with a slow onset of lymphokine production when stimulated in vitro.

Expansion and clonal deletion of peripheral T cells induced by bacterial superantigen is independent of the interleukin-2 pathway

Injection of the bacterial superantigen Staphylococcus aureus enterotoxin B (SEB) into mice provokes a rapid expansion and subsequent contraction of the pool of SEB-reactive T cells bearing T cell receptor (TcR) V beta 8 gene products. Given that interleukin 2 (IL-2) stimulates proliferation, abolishes anergy, and counteracts apoptotic cell death in T cells in vitro, we tested whether the IL-2 synthesis inhibitor cyclosporin A (CsA) or a vaccinia virus recombinant releasing high amounts of human IL-2 modulate SEB responses in vivo. Surprisingly, neither IL-2 nor CsA were able to change the in vivo kinetics and magnitude of SEB-induced expansion, unresponsiveness to SEB, and peripheral clonal deletion of T cells expressing products of the SEB-reactive TcR V beta 8 gene family. In accord with these in vivo observations, IL-2 is incapable of reversing "anergy" and apoptotic cell death of V beta 8+ SEB-reactive T cells isolated from SEB-primed mice in vitro. Accordingly, upon SEB injection V beta 8+ T cells expand rapidly, without expressing IL-2 receptor (IL-2R)alpha chains in vivo, although SEB induces IL-2R alpha in vitro. Altogether, these results indicate that the IL-2/IL-2R-mediated pathway is not involved in T cell repertoire modulation by bacterial superantigens. Moreover, the data suggest that unresponsiveness of V beta 8+ T cells from SEB-primed mice is not a reversible process, but involves an unreversible commitment to programmed cell death. Absence or presence of IL-2 responsiveness could be a hallmark to distinguish truly reversible anergy and peripheral clonal deletion.

Clonal expansion precedes anergy and death of V beta 8+ peripheral T cells responding to staphylococcal enterotoxin B in vivo

Staphylococcal enterotoxin B (SEB) selectively stimulates T cells bearing T cell receptor V beta 8 domains and hence provides a useful model to study immunity and tolerance in vivo. We show here that V beta 8+ T cells in both CD4+ and CD8+ subsets expand dramatically (fivefold) in lymphoid tissues of mice 2-4 days following injection with SEB. This initial clonal expansion, which is accompanied by a transient hyper-reactivity to SEB, is followed by a rapid decrease in V beta 8+ cells and a concomitant induction of specific non-responsiveness which persists for at least 30 days. Selective death of V beta 8+ cells occurs during this latter phase. Taken together, our data indicate that clonal expansion, anergy and death can occur as sequential stages of an immune response in vivo.

Impaired clonogenic potential of CD25 positive T cells in lymph nodes involved by B cell non-Hodgkin's lymphomas

In vivo activated T cells (CD25+) present in lymph nodes involved by B-non-Hodgkin's lymphomas (B-NHL) were investigated here for their ability to proliferate in vitro. CD25-/CD25+ T cells were isolated using a rosette method with magnetic beads, then the frequency of proliferating T lymphocyte-precursors (PTL-P) in both populations was assessed by limiting dilution experiments, in the presence of IL2, PHA and allogeneic spleen cells as feeders. In a total of 16 cases studied, growing microcultures were observed in all cases for CD25- T cells (mean value of PTL-P frequency: 1/32; range 1/10 - 1/2899) but in 6 cases only for CD25+ T cells (mean value of PTL-P frequency: 1/441; range 1/119 - 1/3736); the absence of any proliferative cultures in the 10 other cases indicated that the number of PTL-P was inferior to 1/12480. These results suggest that the proliferative potential of CD25+ T cells infiltrating lymph nodes involved by B-NHL is paradoxically decreased.

Effect of zinc on the proliferative response of human lymphocytes: mechanism of its mitogenic action

To study the effect of Zn on the proliferative response of normal human lymphocytes, ZnCl2 at a final concentration of 10(-4) M was added to cultures of peripheral blood mononuclear cells (PBMC) stimulated with concanavalin A (Con A) and to autologous mixed lymphocyte cultures of responder T lymphocytes and irradiated autologous non-T cells. Addition of Zn increased by about 50% the synthesis of DNA in cultures stimulated with either 10 or 20 micrograms/ml of Con A and markedly enhanced the autologous mixed lymphocyte reaction, which increased about 5-fold in the presence of Zn. In a narrow dose range, Zn induced per se the incorporation of [3H]thymidine by PBMC, with maximal effects in cultures stimulated with 10(-4) M ZnCl2. The percentage of cells expressing receptors for IL-2 and transferrin as assessed by immunofluorescence with the monoclonal antibodies (mAb) anti-Tac and OKT9, respectively, significantly increased when PBMC were stimulated with 10(-4) M ZnCl2 alone. Maximal [3H]thymidine incorporation and maximal percentage of cells bearing those activation markers were observed on day 6 of culture. Thus, the increase in the uptake of [3H]thymidine induced by Zn is not artifactual but due to progression in the cell cycle. Incubation with the mAb anti-Tac significantly inhibited the proliferative response to Zn, indicating that this requires binding of IL-2 to its receptor. However, addition of human recombinant IL-2 did not increase [3H]thymidine incorporation by PBMC cultured in the presence of ZnCl2.

Localization of gamma/delta T cells to the intestinal epithelium is independent of normal microbial colonization

Using monoclonal antibodies identifying all gamma/delta and alpha/beta T cell receptors in cytofluorometric analysis, we have compared the composition of intestinal intraepithelial lymphocytes (i-IEL) in euthymic and athymic germ-free (GF) and conventional (SPF) mice. The results show a marked influence of microbial colonization in the numbers of single-positive (CD4+ or CD8+) alpha/beta i-IEL, but little effect in the pool size or characteristics of gamma/delta i-IEL. In young athymic mice, virtually no alpha/beta i-IEL are detected, while considerable numbers of gamma/delta i-IEL remain, though reduced in GF animals.

Homogenous junctional sequence of the V14+ T-cell antigen receptor alpha chain expanded in unprimed mice

Nucleotide sequences of VJ (variable-joining) junctional regions of V14+ alpha-chain T-cell receptor genes show that most V alpha 14+ T cells use one alpha chain (V alpha 14J alpha 281 with a one-nucleotide N region, which is frequently used in keyhole limpet hemocyanin-specific suppressor T-cell hybridomas) in unprimed mice. Moreover, the frequency of this alpha-chain expression was greater than 1.5% of the total alpha chains found in laboratory strains, including B10 congenic mice. This is about 10(4) times higher than was expected. The V14J281 alpha-chain expression was relatively low but was significant in CD4+/CD8+ immature thymocytes and became quite high in mature single-positive T cells, implying that this alpha chain is selected during T-cell maturation. V14J281 expression increased with time after birth and reached a maximum at around 5 weeks of age. The ligand seems to be a self molecule and to be present in laboratory strains but to be absent in a wild mouse, Mus musculus molossinus, because bone marrow chimeras clearly showed that bone marrow cells derived from Mus musculus molossinus negative for this alpha chain raised V14J281-positive T cells in a C57BL/6 environment. The above results suggest that there are some selection mechanisms for this cell type other than those for conventional alpha beta T cells and also that the homogenous VJ junction of the V14J281 alpha chain plays a pivotal role in the selection of the T cell and its ligand reactivity.

Clinical modeling of T cell vaccination against autoimmune diseases in rats. Selection of antigen-specific T cells using a mitogen

Effective T cell vaccination against experimental autoimmune diseases involves treatment with activated, autoimmune T lymphocytes. The present study was undertaken to learn whether antigen-specific T cells present in low frequency could be selected in vitro without using the specific antigen. The rat models of adjuvant arthritis and experimental autoimmune encephalomyelitis were investigated using proliferation assays and limiting dilution techniques to quantify the changes in reactivity of a heterogenous population of lymphocytes to the relevant antigen. Stimulation with concanavalin A for 2 d and then culture in IL-2-containing medium led to a substantial increase in the activity and frequency of the specific autoimmune T cells. Enrichment of antigen-specific T cells could be demonstrated using lymph node, spleen, or peripheral blood lymphocytes, from rats late in the course of disease. The effect was not evident in lymphocytes from the thymus. These results are relevant to the clinical application of T cell vaccination and to investigation of self-antigens in autoimmune disease.

Naturally activated and resting T cells differ in their activation requirements for growth and secretory activities

"Naturally activated" (NA) and "small resting" (SR) T lymphocytes were stimulated with anti-CD3 or anti-thy 1 monoclonal antibodies (mAbs). Both proliferation and secreted IL-2, IL-3/GM-CSF activities were found in NA T cell, but not in SR T cell cultures. SR T cells could be fully activated by anti-CD3 only if PMA or IL-2 was added to the cultures. NA T cell proliferation induced with anti-CD3 was blocked with anti-IL-2 or anti-IL-2R mAbs. The combination of anti-CD3 and rec IL-4 was not effective in promoting SR T cell proliferation. IL-4 plays a minor role in NA T cell activation with anti-CD3, as assayed with neutralizing anti IL-4 mAbs. No differences in the proliferative and secretory activities were found when NA or SR T cells were stimulated with Con A. Both NA and SR T cells responded when stimulated with the calcium ionophone A23187 plus PMA. Only NA T cells responded to A23187 alone. The mechanisms and the possible physiologic relevance of this differential responsiveness behavior are discussed.

Limiting dilution analysis of the T cell response to Plasmodium chabaudi chabaudi in mice

A limiting dilution assay system was developed in order to measure the in-vitro T cell response to antigens of the erythrocytic stages of Plasmodium chabaudi. The conditions of the assay are such that only CD4+ T cells are able to respond. The assay allows the determination of the frequencies of T cells which proliferate and/or which develop into helper cells for antibody production during a primary infection. A specific response from splenic T cells can be measured as early as 7 days after infection, and is still significant 3 months after injection of P. chabaudi. At all times the frequency of proliferating cells was greater than the precursor frequency of T helper cells. This suggests that a proportion of CD4+ T cells in this assay, although they respond to malarial antigen, do not develop into helper cells for antibody production. This limiting dilution assay will be a useful method by which to evaluate the functional heterogeneity of the CD4+ T cell response to malaria antigens.

Interleukin 2 receptor expression and interleukin 2 production in exponentially growing T cells: major differences between in vivo and in vitro proliferating T lymphocytes

In the present study we have assessed the growth requirements for in vivo proliferating mature T cells. For that purpose we have selected experimental approaches which allow the study of exponential growth in vivo of a major fraction of T cells, and make it possible to obtain large numbers of T cells in cycle. Two types of growing T cell populations were used: peripheral T lymphocytes, proliferating exponentially after transfer into syngeneic athymic nude mice, and activated T cells in lymph nodes of normal mice draining the site of oxazolone administration. The results obtained show that mature T cell growth in vivo is not accompanied by expression of high-affinity interleukin 2 (IL2) receptor in the majority of activated cells, is not abrogated by in vivo administration of anti-IL2 receptor antibodies or enhanced by the in vivo injection of recombinant IL2, and that in vivo growing T cells do not produce detectable amounts of IL2, as evaluated functionally by limiting dilution assays or the presence of IL2 mRNA, detected by Northern blots or in situ hybridization. The presented data thus indicate that the rules known to apply to T cell activation and proliferation in vitro differ from those used by in vivo growing T lymphocytes, at least in the two systems studied.

Peripheral T lymphocytes: expansion potential and homeostatic regulation of pool sizes and CD4/CD8 ratios in vivo

Peripheral T lymphocytes are self-renewable cell populations since, when transferred into syngeneic T cell-deficient athymic mice, they expand in the absence of exogenous antigen stimulation. Quantification of the expansion potential of CD4+ cells by transfer of the same population into successive host mice shows that these cells are able to divide up to 56 times in vivo. Therefore, as a population, CD4+ cells can increase in size 8 x 10(5)-fold, an expansion potential of similar magnitude to that previously reported for colony-forming units. Injection of different numbers of T cells at different CD4/CD8 ratios is followed by T cell accumulation to a similar plateau in recipient nude mice. This indicates that peripheral T lymphocytes are tightly regulated by homeostatic mechanisms that control pool sizes and CD4/CD8 ratios, in a manner independent of the cell input into the peripheral compartment. This kinetic behavior of mature T cells permits the maintenance at the periphery of any T cell specificity previously selected in the thymus. The expansion capacity of peripheral T cells may also allow extensive modulation of peripheral T cell specificities, which would confer a major role to post-thymic selection of mature peripheral T cell repertoires.

Mechanism of T cell proliferation in vivo: analysis of IL-2 receptor expression and activation of c-myc and c-myb oncogenes during lymphatic regeneration

The mechanism of T cell proliferation was studied using in vivo lymphatic regeneration as the model. Lymphatic regeneration was induced by injecting a sublethal dose (300 mg/kg) of cyclophosphamide (Cy) into mice. Majority of the regenerating splenic T cells were found to be in the cell cycle, nearly 30% being found in S/G2+M phases resembling the ratio obtained for mitogen activated T cells in vitro. Expression of interleukin-2 receptor (IL-2R) was defined by the monoclonal anti-IL-2R antibody, AMT-13. Only 1-3% of regenerating T cells were IL-2R positive (while about 30% of the in vitro activated T cells were IL-2R positive). Accordingly, these cells did not respond to IL-2 in vitro. However, when the freshly isolated regenerating T cells were cultured in the presence of Con A or PMA + ionophore A 23187, IL-2R was readily induced. The regenerating T cells were further analyzed for the expression of the cellular oncogenes c-myc and c-myb. These cells expressed about three times more c-myb mRNA than Con A-stimulated T cells and the levels were comparable to those seen in thymocytes. By contrast, the amount of c-myc mRNA was similar in the regenerating T cells and in Con A-activated T cells, but weak or barely detectable in splenocytes and thymocytes. Taken together, our results imply that the vigorous T cell proliferation during cyclophosphamide-induced lymphatic regeneration is independent of the IL-2/IL-2R hormone system, like T-cell precursor proliferation in the thymus, and is characterized by both high c-myb expression typical for thymocytes and high c-myc expression typical for in vitro proliferation-activated T cells.

Immunotherapy of experimental autoimmune encephalomyelitis (EAE): differential effect of anti-IL-2 receptor antibody therapy on actively induced and T-line mediated EAE of the Lewis rat

Treatment of Lewis rats with monoclonal anti-interleukin-2 receptor (IL-2 R) antibody ART-18 is highly efficient in protecting the recipients from T-line transferred experimental autoimmune encephalomyelitis (tEAE) in vivo. In contrast, ART-18 did not affect the development of EAE actively induced (aEAE) by immunization with myelin basic protein (MBP) in complete Freund's adjuvant (CFA). ART-18 caused a slight delay in the development of aEAE only in combination with a subtherapeutic dose of cyclosporine A (Cy-A), but failed to influence duration or severity of clinical signs. The discrepancy in therapeutic efficiency of ART-18 in tEAE and aEAE could be due to a different intensity of IL-2 R-expression on in vitro- and in vivo-activated MBP-specific T cells. Our results therefore caution against a general therapeutic application of anti IL-2 R-directed therapy in all manifestations of T-cell-mediated autoimmunity.

Limiting dilution analysis of the frequency of IL2 responsive T cells in lymph nodes involved by B-cell non-Hodgkin's lymphomas

Total T lymphocytes separated from twelve lymph nodes involved by B-NHL were studied in limiting dilution experiments for their ability to proliferate in the presence of both R-IL2 used at a final concentration of 40 U/ml and irradiated autologous malignant B cells as feeders. The number of proliferating T-lymphocyte precursors (PTL-P) thus estimated was low in each case (mean: 1/4503; range, 1/200 to 1/11013). Once expanded, proliferation of the IL2 responsive T cells in the presence of autologous malignant B cells remained strictly dependent on the addition of exogenous IL2. Control cases consisted of T lymphocytes separated from peripheral blood of six healthy subjects and cultured in the presence of both R-IL2 (40 U/ml) and irradiated autologous total mononuclear cells as feeders; the mean frequency of PTL-P thus obtained (1/173; range, 1/49 to 1/457) was significantly higher than in malignant lymph nodes (p less than 0.01). These findings do not support the hypothesis that, in this series of patients, expansion of malignant B cells may lead to the activation and growth of T cells sensitized against the tumour.

IL-2 antibody production in lupus mice

We show here that antibody responses to IL-2 were detected in NZBWF1 and BXSB mice but not in MRL/lpr mice in vivo and in vitro. Lipopolysaccharide (LPS), in the presence or in the absence of T cells, also induced anti-IL-2 antibody production in NZBWF1 and BXSB mouse spleen cells but not in MRL/lpr spleen cells in vitro. Anti-IL-2 antibody production increased progressively with age. Supernatants (SN) obtained from NZBWF1 B cell cultures were able to elicit anti-IL-2 antibody production in LPS-stimulated spleen cells of normal BALB/c mice, whereas SN from NZBWF1 T cells culture had no detectable effect.