IL-2 receptor expression in autoimmune MRL-lpr/lpr mice. The expanded L3T4-, Lyt-2- population does not express p75 and cannot generate functional high-affinity IL-2 receptors

Autoimmune MRL-lpr/lpr mice develop an SLE-like disease characterized by a profound lymphadenopathy within an L3T4-, Lyt-2- (DN), B220+ T-cell population. Despite its immature phenotype this subset expresses mature alpha beta TCR belonging predominantly to the V beta 8 gene family and appears to be identical to an activated form of a minor T cell population present in both the thymus and periphery of normal mice. However, the mechanisms underlying the greatly increased cellularity in lpr/lpr-bearing mice are not understood. In this study, the IL-2R expression of lpr/lpr T cells was examined to assess the contribution of IL-2-mediated division to their expansion. The lpr/lpr DN T cells lacked high-affinity IL-2R, even after stimulation, suggesting that IL-2-dependent proliferation plays no role in the expansion of these cells and demonstrating the existence of this unusual T cell phenotype in vivo.     

Autoimmune CD4+ T cells interfere with immune tolerance to a thymic-independent antigen

The ability of autoimmune T cell subsets to interfere with tolerization of B cells can be studied by using thymic-independent Ag. We have defined an abnormality within the CD4+ T cell compartment in young NZB and MRL-lpr/lpr mice by studying tolerance of spleen and B cells to the thymic independent Ag, fluorescein-Brucella abortus. Tolerization of spleen cells is defective in MRL-lpr/lpr mice, but not MRL-+/+ or C3H.lpr mice, suggesting that the defect requires both the autosomal MRL background and the lpr gene to be present. T enriched cells from NZB mice and from MRL-lpr/lpr mice (but not MRL-+/+ or C3H.lpr mice) reverse tolerance in spleen cells from [NZB X DBA/2]F1 and C3H/HeJ mice, respectively. This interference is removed by treatment with anti-CD4 antibody and C. Supernatants from cultured T cells of NZB and MRL-lpr/lpr mice also prevent tolerance in spleen cells of [NZB X DBA/2]F1 and MRL-+/+ mice, respectively, unless CD4+ cells are removed prior to T cell culture. Removal of T cells from NZB and MRL-lpr/lpr spleen cells allows normal tolerization of B cells, which is abrogated by the addition of syngeneic T cells or cultured T cell supernatants. This effect also depends on the presence of CD4+ T cells. These studies show that in MRL-lpr/lpr mice, through interaction of the lpr and MRL background genes in a T cell subset, and in NZB mice, CD4+ T cells interfere with B cell tolerance to a thymic-independent Ag.     

High level expression of the plasma cell antigen PC.1 on the T-cell subset expanding in MRL/MpJ-lpr/lpr mice: detection with a xenogeneic monoclonal antibody and alloantisera

MRL/MpJ-lpr/lpr (MRL-lpr/lpr) mice spontaneously develop a systemic lupus erythematosus-like syndrome associated with the expansion of a T-cell subset exerting helper activity for autoantibody production. Several studies have demonstrated that these T cells have unusual phenotypic characteristics including the expression of the B220 B-cell marker. To further characterize the antigenic profiles of these T cells, we have generated monoclonal antibodies (MAb) by immunizing rats with MRL-lpr/lpr T cells. Using flow cytofluorometry analysis, one of these MAb (4G6), described here, was found to react strongly with T cells of MRL-lpr/lpr mice but weakly with T cells of congenic mice lacking the lpr mutation (MRL/MpJ-+/+ mice). This MAb also stained brightly T cells from C3H/Hej-lpr/lpr mice and dimly those from normal C3H/Hej mice. However, it failed to react with T cells from C57Bl/6-lpr/lpr mice or normal C57Bl/6 (B6) mice. Analysis of 4G6 reactivity (weak vs negative) of T cells in a series of inbred strains demonstrated a correlation with the Pca-1a genotype known to result in expression of the PC.1 antigen on plasma cells. Immunoprecipitation studies revealed that the 4G6 antigen has a mean apparent molecular weight of 115,000, under reducing conditions, similar to that of PC.1. Moreover, high expression of 4G6 was found on plasmacytoma lines and B blasts but not on T blasts. Identity of the 4G6 antigen with PC.1 was confirmed by the finding that conventional anti-PC.1 alloantisera could block the cell surface binding of the 4G6 MAb. Therefore, T cells from MRL-lpr/lpr (and C3H-lpr/lpr) mice aberrantly carry high levels of a plasma cell antigen, detected by the 4G6 MAb, which substantiates further that these T cells represent a unique subset with some surface properties of the B-cell lineage.     

Induction of allograft tolerance in the absence of Fas-mediated apoptosis.

Using certain immunosuppressive regimens, IL-2 knockout (KO) mice, in contrast to wild-type (wt) controls, are resistant to the induction of allograft tolerance. The mechanism by which IL-2 regulates allograft tolerance is uncertain. As IL-2 KO mice have a profound defect in Fas-mediated apoptosis, we hypothesized that Fas-mediated apoptosis of alloreactive T cells may be critical in the acquisition of allograft tolerance. To definitively study the role of Fas in the induction of transplantation tolerance, we used Fas mutant B6.MRL-lpr mice as allograft recipients of islet and vascularized cardiac transplants. Alloantigen-stimulated proliferation and apoptosis of Fas-deficient cells were also studied in vivo. Fas mutant B6.MRL-lpr (H-2b) mice rapidly rejected fully MHC-mismatched DBA/2 (H-2d) islet allografts and vascularized cardiac allografts with a tempo that is comparable to wt control mice. Both wt and B6.MRL-lpr mice transplanted with fully MHC-mismatched islet allografts or cardiac allografts can be readily tolerized by either rapamycin or combined costimulation blockade (CTLA-4Ig plus anti-CD40L mAb). Despite the profound defect of Fas-mediated apoptosis, Fas-deficient T cells can still undergo apoptotic cell death in vivo in response to alloantigen stimulation. Our study suggests that: 1) Fas is not necessarily essential for allograft tolerance, and 2) Fas-mediated apoptosis is not central to the IL-2-dependent mechanism governing the acquisition of allograft tolerance.     

Purified Protein from Salmonella typhimurium Inhibits the Interleukin-2 Response of Murine Splenic T-Lymphocytes Activated with Anti-CD3 Antibody

Previously, we demonstrated that the immunosuppression induced by a purified preparation of Salmonella typhimurium-derived inhibitor of T-cell proliferation (STI) can be observed in terms of suppression of the proliferation of murine spleen cells stimulated with a mitogenic lectin. In the present study, I observed that STI inhibited the interleukin-2 (IL-2) response of purified murine splenic T lymphocytes stimulated with anti-CD3 antibody. The flow cytometric analysis of IL-2 receptor (IL-2R) expression on T cells showed that STI specifically suppressed the expression of IL-2Rβ and IL-2Rγ. Furthermore, when the IL-2-dependent T-cell line CTLL-2 was incubated with STI, the growth of CTLL-2 cells was significantly inhibited. These results suggest that the target cells for STI are T cells themselves, and that the suppression of T-cell proliferation induced by STI might involve a defect in the IL-2 receptor (IL-2R) function of T cells.     

Ontogeny and function of B220+ L3T4+ T-cell subset of MRL/Mp-lpr/lpr mice

T-cell-enriched populations obtained from lymph nodes (LNs) of 4-month-old MRL/Mp-lpr/lpr (MRL-lpr), C3H/HeJ-lpr/lpr (C3H-lpr), and C3H/HeJ-gld/gld (C3H-gld) mice were studied for the expression of B220, L3T4, and Lyt 2 antigens. A new B220+ L3T4+ phenotype was demonstrated in T-cell populations of these mice by two-color flow cytometry with phycoerythrin-conjugated monoclonal antibodies (MoAb) to L3T4 and FITC-anti-B220 MoAb. The generation of the T subset was apparently under the influence of the lpr or gld gene, since it could not be demonstrated in T-cell-enriched populations of MRL/Mp- +/+ and normal C3H mice. The expression level of L3T4 antigen on the T subset was lower than that on B220- L3T4+ cells, while the level of B220 antigen was similar to that of B220+ L3T4- or B220+ Lyt 2- cells. The B220+ L3T4+ phenotype appeared in LNs and spleens, but not in thymuses, of MRL-lpr mice as early as 2 months of age. Its proportion to whole LN T cells at this age was equivalent to that observed in 4-month-old mice. Functional studies on FACS-sorted cell populations revealed that the T subset similar to B220+ L3T4- cells possessed deficiencies in the IL-2-IL-2 receptor system. The appearance of the T subset with an intermediate phenotype and its functional defects suggests that lpr and gld genes in these autoimmune mice exert their influences on the ontogeny and function of L3T4+ T cells and contribute to the induction of early lupus.     

Myeloid suppressor lines inhibit T cell responses by an NO-dependent mechanism.

CD11b(+)Gr-1(+) myeloid suppressor cells (MSC) accumulate in lymphoid organs under conditions of intense immune stress where they inhibit T and B cell function. We recently described the generation of immortalized MSC lines that provide a homogeneous source of suppressor cells for dissecting the mechanism of suppression. In this study we show that the MSC lines potently block in vitro proliferation of T cells stimulated with either mitogen or antigenic peptide, with as few as 3% of MSC cells causing complete suppression. Inhibition of mitogenic and peptide-specific responses is not associated with a loss in IL-2 production or inability to up-modulate the early activation markers, CD69 and CD25, but results in direct impairment of the three IL-2R signaling pathways, as demonstrated by the lack of Janus kinase 3, STAT5, extracellular signal-regulated kinase, and Akt phosphorylation in response to IL-2. Suppression is mediated by and requires NO, which is secreted by MSC in response to signals from activated T cells, including IFN-gamma and a contact-dependent stimulus. Experiments with inducible NO synthase knockout mice demonstrated that the inhibition of T cell proliferation by CD11b(+)Gr-1(+) cells in the spleens of immunosuppressed mice is also dependent upon NO, indicating that the MSC lines accurately represent their normal counterparts. The distinctive capacity of MSC to generate suppressive signals when encountering activated T cells defines a specialized subset of myeloid cells that most likely serve a regulatory function during times of heightened immune activity.     

Strain-dependence and cellular aspects of the acceleration of age-dependent shift in class-specific helper and suppressor activity in the thymus of MRL/Mp mice by the LPR gene

Previous studies of the immunoregulatory activity of thymocytes from SJL/J mice have shown loss of suppressor activity for the antibody response by 24 weeks of age with appearance of helper activity. At the same time, suppressor cells developed which inhibit the generation of cytotoxic T lymphocytes (CTL). We now show a similar pattern of helper and suppressor activity in MRL/Mp mice. Presence of the lpr/lpr genotype significantly accelerated the onset of these changes in thymocyte activity. A similar pattern of thymocyte activity was not detected in C57B1/6 mice. In aged MRL-lpr mice, evidence of increased suppressor cell activity for the CTL response could be demonstrated in spleen, and the suppressor was sensitive to treatment with anti-thy 1.2 + complement. The magnitude of the deficiency in the CTL response in MRL-lpr mice was greater than could be accounted for by suppressor cell activity alone. Measurement of the frequency of CTL precursors (CTLP), the yield of CTL per CTLP, and the ability to produce and to respond to interleukin 2 (IL-2) indicated that a drop in CTLP frequency, subnormal generation of IL-2, and probably an intrinsic defect in the responsiveness of MRL-lpr CTLP to IL-2 was contributing to the defective CTL response. We were not able to link suppressor T cells with reduced responsiveness to IL-2. Ageing involves different patterns of change in immunoregulatory T-cell subsets in different strains of mice, depending on their genetic constitution. The general implications of this conclusion for prediction of immune dysfunction with age in genetically distinct members of an outbred population are discussed.     

Constitutive expression of a chimeric receptor that delivers IL-2/IL-15 signals allows antigen-independent proliferation of CD8+CD44high but not other T cells

We have prepared transgenic mice whose T cells constitutively express a chimeric receptor combining extracellular human IL-4R and intracellular IL-2Rbeta segments. This receptor can transmit IL-2/IL-15-like signals in response to human, but not mouse, IL-4. We used these animals to explore to what extent functional IL-2R/IL-15R expression controls the capacity of T cells to proliferate in response to IL-2/IL-15-like signals. After activation with Con A, naive transgenic CD8+ and CD4+ T cells respond to human IL-4 as well as to IL-2. Without prior activation, they failed to proliferate in response to human IL-4, although human IL-4 did prolong their survival. Thus, IL-2-induced proliferation of activated T cells requires at least one other Ag-induced change apart from the induction of a functional IL-2R. However, a fraction of CD8+CD44high T cells proliferate in human IL-4 without antigenic stimulation or syngeneic feeder cells. In contrast, CD4+CD44high T cells are not constitutively responsive to human IL-4. We conclude that although all transgenic T cells express a functional chimeric receptor, only some CD8+CD44high T cells contain all molecules required for entry into the cell cycle in response to human IL-4 or IL-15.     

Accessory cell-derived helper signals in human T-cell activation with phytohemagglutinin: induction of interleukin 2-responsiveness by interleukin 6, and production of interleukin 2 by interleukin 1 [corrected

Interleukins (IL-) 1 and 6 have been shown to represent accessory signals for T-cell activation. In the present study, we further examined the effects of both cytokines on accessory cell-depleted human T cells stimulated with phytohemagglutinin (PHA). The addition of IL-6 to the cultures resulted in T-cell proliferation; however, IL-1 was unable to support PHA-induced T-cell growth. The addition of IL-1 consistently induced a low level of IL-2 production and strongly enhanced T-cell proliferation in the presence of IL-6. Thus, the effect of IL-1 on T-cell growth becomes apparent only in the presence of IL-6. Blocking the IL-2-receptor (IL-2R) with the monoclonal antibodies anti-Tac and MikBêta 1 (directed to the alpha and bêta chains of the IL-2R, respectively) had no effect on PHA/IL-6-supported proliferation, but completely eliminated the growth-enhancing effect of IL-1. On the other hand, a neutralizing anti-IL-4-antiserum did not affect PHA/IL-6- or PHA/IL-6/IL-1-induced proliferation. Further experiments showed that IL-6 enhances T-cell responsiveness to IL-2, as evidenced by enhanced IL-2-induced proliferation. However, we could not find an effect of IL-6 on the expression of IL-2R as measured by staining with anti-Tac and with MikBêta 1 or by binding of (125I)-IL-2 to T cells. It can be concluded from these studies that IL-1 and IL-6 have different helper effects on PHA-induced T-cell activation. In the presence of PHA, IL-6 induces limited IL-2/IL-4-independent growth, and more importantly it renders T cells responsive to IL-2. IL-1 provides a signal leading to IL-2 production. The combination of IL-1 and IL-6 represents a synergistic helper signal, leading to an IL-2-dependent pathway of proliferation.     

T cells from autoimmune "IL 2-defective" MRL-lpr/lpr mice continue to grow in vitro and produce IL 2 constitutively

MRL-lpr/lpr mice and other autoimmune strains that bear the lpr gene develop a profound lymphadenopathy characterized by an expansion of a unique dull Lyt-1+2- T cell population. Because fresh splenic and lymph node T cells from such mice stimulated Con A in vitro are extremely defective in IL 2 production and proliferation, T cell lines derived from MRL-lpr/lpr spleens were established and maintained for several months, and were analyzed for their factor production to define their growth requirements. The results indicate that cultivation in vitro leads to constitutive production of IL 2 and the capacity to respond to growth factors, thereby facilitating the continuous proliferation of T cells bearing the dull Lyt-1+2- phenotype in vitro in the absence of exogenous antigen or mitogen. These studies indicate that MRL-lpr/lpr T cells have the ability to produce IL 2 and to respond to IL 2 with long-term proliferation. In addition, the impaired responsiveness to Con A of fresh MRL-lpr/lpr lymph node T cells was found to be quite transitory, because even short-term culture allowed MRL lpr/lpr T cells to respond normally.     

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.     

Relative roles of T-cell receptor ligands and interleukin-2 in driving T-cell proliferation

Stimulation of T cells by the T-cell receptor (TCR)/CD3 complex results in interleukin-2 (IL-2) synthesis and surface expression of the IL-2 receptor (IL-2R), which in turn drive T-cell proliferation. However, the significance of the requirement of IL-2 in driving T-cell proliferation, when TCR stimulation itself delivers potential mitogenic signals, is unclear. We show that blocking of IL-2 synthesis by Cyclosporin A (CsA) suppressed both the Concanavalin A (Con A)- and phorbol myristate acetate (PMA)/ionomycin-induced proliferation of T cells. The latter is also inhibited by anti-IL-2R. Kinetic studies showed that T-cell proliferation begins to become resistant to CsA inhibition by about 12 h and became largely resistant by 18 h of stimulation. PMA, the protein kinase C activator, enhanced Con A-induced T-cell proliferation if added only within first 12 h of stimulation, and not after that. Given the fact that, in the present study, TCR is downregulated within 2 h of Con A stimulation and T cells entered the S phase of cell cycle by about 18 h of stimulation, the above results suggest that TCR stimulation provides the initial trigger to the resting T cells, which allows the cells to traverse the first two third portions of G1 phase of cell cycle and become proliferation competent. IL-2 action begins afterward, delivering the actual proliferation signal(s), allowing the cells to traverse the rest of G1 phase and enter the S phase of the cell cycle.     

E2F1 and E2F2 are differentially required for homeostasis-driven and antigen-induced T cell proliferation in vivo

Homeostasis-driven T cell proliferation occurs in response to a lymphopenic environment and is mediated by TCR and IL-7 signaling. In this report, we demonstrate a defect in the proliferation of murine naive and memory T cells lacking both E2F1 and E2F2 in response to lymphopenic conditions, suggesting that E2F1 and E2F2 function redundantly downstream of TCR and/or IL-7 signaling during homeostasis-driven proliferation. In contrast, T cell proliferation in response to antigenic stimulation is either unaffected (in vivo) or potentiated (ex vivo) by loss of E2F1 and E2F2, indicating divergent requirements for these E2F factors in T cell proliferation mediated by distinct stimuli. E2F1/E2F2 double knockout (DKO) T cells enter S phase in response to homeostatic signaling, but fail to divide, suggesting that S phase progression is either incomplete or defective. In addition, E2F1/E2F2 DKO mice do not recover normal T cell numbers following exposure to a sublethal dose of radiation, indicating that this defect in homeostasis-driven proliferation is physiologically relevant. Consistent with their failure in cell cycle progression, the differentiation of DKO T cells into memory T cells in response to homeostatic signals is significantly reduced. These observations support the idea that proliferation is required for memory T cell formation and also have implications for the development of clinical strategies to minimize the occurrence of lymphopenia-induced autoimmunity.     

Signaling thresholds govern heterogeneity in IL-7-receptor-mediated responses of naïve CD8(+) T cells

Variable sensitivity to T-cell-receptor (TCR)- and IL-7-receptor (IL-7R)-mediated homeostatic signals among na?ve T cells has thus far been largely attributed to differences in TCR specificity. We show here that even when withdrawn from self-peptide-induced TCR stimulation, CD8(+) T cells exhibit heterogeneous responses to interleukin-7 (IL-7) that are mechanistically associated with IL-7R expression differences that correlate with relative CD5 expression. Whereas CD5(hi) and CD5(lo) T cells survive equivalently in the presence of saturating IL-7 levels in vitro, CD5(hi) T cells proliferate more robustly. Conversely, CD5(lo) T cells exhibit prolonged survival when withdrawn from homeostatic stimuli. Through quantitative experimental analysis of signaling downstream of IL-7R, we find that the enhanced IL-7 responsiveness of CD5(hi) T cells is directly related to their greater surface IL-7R expression. Further, we identify a quantitative threshold in IL-7R-mediated signaling capacity required for proliferation that lies well above an analogous threshold requirement for survival. These distinct thresholds allow subtle differences in IL-7R expression between CD5(lo) and CD5(hi) T cells to give rise to significant variations in their respective IL-7-induced proliferation, without altering survival. Heterogeneous IL-7 responsiveness is observed similarly in vivo, with CD5(hi) na?ve T cells proliferating preferentially in lymphopenic mice or lymphoreplete mice administered with exogenous IL-7. However, IL-7 in lymphoreplete mice appears to be maintained at an effective level for preserving homeostasis, such that neither CD5(hi) IL-7R(hi) nor CD5(lo) IL-7R(lo) T cells proliferate or survive preferentially. Our findings indicate that IL-7R-mediated signaling not only maintains the size but also impacts the diversity of the na?ve T-cell repertoire.     

Stimulation of murine T cell subsets with anti-CD3 antibody. Age-related defects in the expression of early activation molecules

Splenocytes from young (3 to 4 mo) and aged (24 to 26 mo) C57BL/6 mice were stimulated with anti-CD3 epsilon mAb in vitro. At the time of peak DNA synthesis (day 2), cells from aged mice incorporated congruent to 60% less [3H]TdR than cells from young mice. This age-related defect was not attributable to gross differences in anti-CD3 does optima, response kinetics, accessory cell function, numbers of T cells cultured, CD4+:CD8+ cell ratios or surface levels of CD3 epsilon molecules. In an attempt to analyze pre-S phase events in these responses, we monitored CD4+ and CD8+ cells in splenocyte cultures for the time-dependent expression of three T cell activation markers: RL388 Ag and IL-2R and transferrin R. Parallel analyses of mean T cell size and cell cycle phase distributions were performed. Non-activated T cells from both age groups similarly expressed moderate levels of RL388 Ag, low levels of transferrin R, and undetectable levels of IL-2R. Analysis of stimulated T cells revealed, in both age groups: 1) detectable increases in expression of all three markers by 6 h of culture, and continued increases associated with blastogenesis and G1 phase transit and 2) a preferential stimulation of the CD8+ subset to a state of high level marker expression. Age group comparisons of activation marker expression over time suggested that the age-related defect reflects proportionally smaller fractions of CD4+ and CD8+ cells that respond normally, rather than a general defect in all T cells or a subset-specific defect. Finally, we found that supernatants from aged donor cell cultures stimulated with anti-CD3 contained less Il-2 than those of young controls. Addition of an IL-2 containing supernatant to aged donor cell cultures increased, but did not restore, the S phase response on day 2; however, the response on day 3 was comparable to the peak (day 2) response of young controls. These data suggest that exogenous IL-2 can improve the aged response, perhaps by expanding the fraction of normally reactive T cells.     

A purified protein from Salmonella typhimurium inhibits high-affinity interleukin-2 receptor expression on CTLL-2 cells

Previously, we have demonstrated that the immunosuppression induced by the purified substance Salmonella typhimurium-derived inhibitor of T-cell proliferation (STI) involves T-cell non-responsiveness to interleukin-2 (IL-2). In the present study, it was found that STI inhibited the growth of CTLL-2 cells, which are an IL-2-dependent cytotoxic T-cell line. Analysis of IL-2 receptor (IL-2R) function showed that STI inhibited high-affinity receptor expression and internalization by CTLL-2 cells. Furthermore, FACS analysis demonstrated that STI inhibited both β chain and γ chain expression of IL-2R on the cells. These results suggest that the suppression of T-cell proliferation induced by STI results from a defect in IL-2R function.     

Changing patterns of lymphocyte proliferation, IL-2 production and utilization, and IL-2 receptor expression in mice infected with Schistosoma mansoni

In murine schistosomiasis mansoni the soluble egg Ag (SEA)-induced L3T4+ T cell-mediated circumoval granulomatous response peaks at the acute stage (8w) and undergoes Lyt-1+, Lyt-2+ suppressor cell mediated down-modulation at the chronic stage (20w) of the infection. In the present study lymphoproliferation, IL-2 production, utilization, and IL-2R display were examined in splenic lymphocytes of infected mice. The L3T4+ subset was the major SEA-specific proliferative population at both stages of the infection. Chronic infection spleen cells or the L3T4+ subset proliferated less compared with their acute infection counterparts. Elimination of the Lyt-2+ subset did not improve diminished proliferation. Chronic infection cells and the Lyt-2+ subset stimulated with SEA and exogenous rIL-2 regained their proliferative ability to a level comparable with acute infection cells. Ag-stimulated acute infection T cells produced 40 to 50 chronic infection cells less than 5 U/ml IL-2. Elimination of L3T4+ T cells diminished, and the Lyt-2+ T cells left unchanged IL-2 production in the acute infection cells. Elimination of Lyt-2+ subset from the chronic infection population did not enhance IL-2 production. Exogenously added rIL-2 was equally utilized by acute or chronic infection T cells. Scatchard plots of [125I]IL-2 binding showed similar numbers of high affinity receptors on acute (189) and chronic infection cells (118), but the number of low affinity receptors was higher on the acute (2229) vs the chronic infection lymphocytes (578). Analysis of IL-2R expression by two-color fluorescence and flow cytometry revealed that 30 to 40% of the acute, chronic infection L3T4+ cells displayed receptor. Receptor expression increased by added SEA, or SEA + rIL-2. R display among Lyt-2+ cells was only 12 to 18%. SEA stimulation enhanced receptor display more among the acute, SEA + rIL-2 stimuli raised receptor expression only among chronic infection lymphocytes. These data do not show inherent defect in IL-2R display, or utilization in chronic infection T cells. Diminished IL-2 production appears to be the cause of decreased T cell responsiveness.     

JNK2 is required for efficient T-cell activation and apoptosis but not for normal lymphocyte development

BACKGROUND: The Jun N-terminal kinase (JNK) signaling pathway has been implicated in cell proliferation and apoptosis, but its function seems to depend on the cell type and inducing signal. In T cells, JNK has been implicated in both antigen-induced activation and apoptosis. RESULTS: We generated mice lacking the JNK2 isozymes. The mutant mice were healthy and fertile but defective in peripheral T-cell activation induced by antibody to the CD3 component of the T-cell receptor (TCR) complex - proliferation and production of interleukin-2 (IL-2), IL-4 and interferon-gamma (IFN-gamma) were reduced. The proliferation defect was restored by exogenous IL-2. B-cell activation was normal in the absence of JNK2. Activation-induced peripheral T-cell apoptosis was comparable between mutant and wild-type mice, but immature (CD4(+) CD8(+)) thymocytes lacking JNK2 were resistant to apoptosis induced by administration of anti-CD3 antibody in vivo. The lack of JNK2 also resulted in partial resistance of thymocytes to anti-CD3 antibody in vitro, but had little or no effect on apoptosis induced by anti-Fas antibody, dexamethasone or ultraviolet-C (UVC) radiation. CONCLUSIONS: JNK2 is essential for efficient activation of peripheral T cells but not B cells. Peripheral T-cell activation is probably required indirectly for induction of thymocyte apoptosis resulting from administration of anti-CD3 antibody in vivo. JNK2 functions in a cell-type-specific and stimulus-dependent manner, being required for apoptosis of immature thymocytes induced by anti-CD3 antibody but not for apoptosis induced by anti-Fas antibody, UVC or dexamethasone. JNK2 is not required for activation-induced cell death of mature T cells.