Activated T-cell Populations Research Articles

Anti-Inflammatory and T-Cell Immunomodulatory Effects of Banana Peel Extracts and Selected Bioactive Components in LPS-Challenged In Vitro and In Vivo Models

Banana peel (BP) has potent antioxidative properties; however, the anti-inflammatory potential of BP and its related bioactive components remain unclear. This study used solvent extraction and gas chromatography–mass spectrometry (GC–MS) to isolate and identify the active fractions and compounds in BP. BP was extracted with 95% ethanol (BP-95E) and partitioned with an ethyl acetate (EA) and water mixture to obtain the BP-95E-EA and BP-95E-H2O fractions. The BP-95E-EA fractions were further partitioned with n-hexane (Hex) and methanol (MeOH) mixtures to obtain BP-95E-EA-Hex and BP-95E-EA-MeOH subfractions, and the BP-95E-H2O fractions were partitioned with n-butanol (BuOH) to obtain BP-95E-H2O-BuOH subfractions and the H2O residual. The results show that the BP-95E-H2O-BuOH subfractions exhibited the most potent inhibition of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) secretion while down-regulating inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein expression in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. In this active subfraction, five non-polyphenol compounds were identified, namely, 5-hydroxyethyl furfural (5-HMF), guaiol, oleic acid, linoleic acid, and oleamide. 5-HMF, guaiol, and oleamide were the most effective at suppressing IL-6 and TNF-α secretion. The in vivo immunomodulatory action of BP was evaluated in an LPS-induced endotoxemia model of BALB/c mice. Oral administration of BP-95E-H2O-BuOH extracts (42 and 166 mg/kg b.w.) for two weeks lowered the serum levels of IL-6 and TNF-α and normalized the activated T-cell population, as evidenced by an increase in CD3CD69 and decrease in IFN-γ/IL-4 (Th1/Th2) in mice with systemic inflammation. Our findings reveal that BP exhibits anti-inflammatory and T-cell immunomodulatory effects that may contribute to delaying endotoxemia-associated disorders.

Effects of the combination of a monoclonal agonistic mouse anti-OX40 antibody and toll-like receptor agonists: Unmethylated CpG and LPS on an MB49 bladder cancer cell line in a mouse model

PurposeThe basis of the antitumor immunotherapy, of which the purpose is the stimulation of the immune system. We have used two of the Pathogen Associated Molecular Patterns: unmethylated CpG oligonucleotide, a ligand of Toll-like receptor 9 (TLR9), and lipopolysaccharide (LPS) which is recognized by TLR4, combined with an agonistic OX40 receptor-specific monoclonal antibody (anti-OX40), which is expressed by activated regulatory T-cells (and by other activated T-cell populations as well). The objective of this study was to prove the effectiveness of the aforementioned compounds in an animal model, on a bladder cancer cell line.MethodsWe have instilled MB49 cells subcutaneously, to the left musculus biceps femoris. We have created three observation groups, each containing ten mice. After eleven days, all treated mice bearing the size of 5–8 mm (in diameter) tumor were administered CpG + anti-OX40 or LPS + anti-OX40 three times with a three-day lap between each treatment. Mice in the control group did not receive any treatment.ResultsAll the specimens from the control and LPS + anti-OX40 groups have died by the sixtieth day of the observation period, however, five mice from the CpG + anti-OX40 group were still alive. The experiment lasted until the last surviving mouse died, which occurred on the 357th day after tumor implantation.DiscussionThe treatment with LPS did not make anti-OX40 more potent and did not increase the survival times. However, CpG + anti-OX40 has shown increased antitumor activity compared to the other two groups.

CD137+ T-Cells: Protagonists of the Immunotherapy Revolution.

Simple SummaryThe CD137 receptor is expressed by activated antigen-specific T-cells. CD137+ T-cells were identified inside TILs and PBMCs of different tumor types and have proven to be the naturally occurring antitumor effector cells, capable of expressing a wide variability in terms of TCR specificity against both shared and neoantigenic tumor-derived peptides. The aim of this review is thus summarizing and highlighting their role as drivers of patients’ immune responses in anticancer therapies as well as their potential role in future and current strategies of immunotherapy.The CD137 receptor (4-1BB, TNF RSF9) is an activation induced molecule expressed by antigen-specific T-cells. The engagement with its ligand, CD137L, is capable of increasing T-cell survival, proliferation, and cytokine production. This allowed to identify the CD137+ T-cells as the real tumor-specific activated T-cell population. In fact, these cells express various TCRs that are specific for a wide range of tumor-derived peptides, both shared and neoantigenic ones. Moreover, their prevalence in sites close to the tumor and their unicity in killing cancer cells both in vitro and in vivo, raised particular interest in studying their potential role in different strategies of immunotherapy. They indeed showed to be a reliable marker able to predict patient’s outcome to immune-based therapies as well as monitor their response. In addition, the possibility of isolating and expanding this population, turned promising in order to generate effector antitumor T-cells in the context of adoptive T-cell therapies. CD137-targeting monoclonal antibodies have already shown their antitumor efficacy in cancer patients and a number of clinical trials are thus ongoing to test their possible introduction in different combination approaches of immunotherapy. Finally, the intracellular domain of the CD137 receptor was introduced in the anti-CD19 CAR-T cells that were approved by FDA for the treatment of pediatric B-cell leukemia and refractory B-cell lymphoma.

The thioredoxin-1 system is essential for fueling DNA synthesis during T-cell metabolic reprogramming and proliferation

The thioredoxin-1 (Trx1) system is an important contributor to cellular redox balance and is a sensor of energy and glucose metabolism. Here we show critical c-Myc-dependent activation of the Trx1 system during thymocyte and peripheral T-cell proliferation, but repression during T-cell quiescence. Deletion of thioredoxin reductase-1 (Txnrd1) prevents expansion the CD4−CD8− thymocyte population, whereas Txnrd1 deletion in CD4+CD8+ thymocytes does not affect further maturation and peripheral homeostasis of αβT cells. However, Txnrd1 is critical for expansion of the activated T-cell population during viral and parasite infection. Metabolomics show that TrxR1 is essential for the last step of nucleotide biosynthesis by donating reducing equivalents to ribonucleotide reductase. Impaired availability of 2′-deoxyribonucleotides induces the DNA damage response and cell cycle arrest of Txnrd1-deficient T cells. These results uncover a pivotal function of the Trx1 system in metabolic reprogramming of thymic and peripheral T cells and provide a rationale for targeting Txnrd1 in T-cell leukemia.

Phase II study of Vigil® DNA engineered immunotherapy as maintenance in advanced stage ovarian cancer

ObjectivesThe majority of women with Stage III/IV ovarian cancer who achieve clinical complete response with frontline standard of care will relapse within 2years. Vigil immunotherapy, a GMCSF/bi-shRNA furin DNA engineered autologous tumor cell (EATC) product, demonstrated safety and induction of circulating activated T-cells against autologous tumor in Phase I trial Senzer et al. (2012, 2013) . Our objectives for this study include evaluation of safety, immune response and recurrence free survival (RFS). MethodsThis is a Phase II crossover trial of Vigil (1.0×107 cells/intradermal injection/month for 4 to 12 doses) in Stage III/IV ovarian cancer patients achieving cCR (normal imaging, CA-125≤35units/ml, physical exam, and no symptoms suggestive of the presence of active disease) following primary surgical debulking and carboplatin/paclitaxel adjuvant or neoadjuvant chemotherapy. Patients received Vigil or standard of care during the maintenance period. ResultsForty-two patients were entered into trial, 31 received Vigil and 11 received standard of care. No≥Grade 3 toxicity related to product was observed. A marked induction of circulating activated T-cell population was observed against individual, pre-processed autologous tumor in the Vigil arm as compared to pre-Vigil baseline using IFNγ ELISPOT response (30/31 negative ELISPOT pre Vigil to 31/31 positive ELISPOT post Vigil, median 134 spots). Moreover, in correlation with ELISPOT response, RFS from time of procurement was improved (mean 826days/median 604days in the Vigil arm from mean 481days/median 377days in the control arm, p=0.033). ConclusionIn conjunction with the demonstrated safety, the high rate of induction of T-cell activation and correlation with improvement in RFS justify further Phase II/III assessment of Vigil.

Role of CD8(+) T cells in protection against Leishmania donovani infection in healed Visceral Leishmaniasis individuals.

BackgroundMajority of individuals with history of visceral leishmaniasis (VL) exhibit strong immunity to re-infection, however, the mechanism of resistance is poorly understood. It is unclear whether CD8+ T cells contribute to protection against Leishmania donovani infection through cytotoxic activity. The present study aims to evaluate immunological mechanism associated with resistance to the disease in healed VL (HVL) individuals and further, the contribution of CD8+ T cells in the protective immunity.MethodsPeripheral blood mononuclear cells (PBMCs) from VL, HVL and naive groups were exposed in vitro to total soluble Leishmania antigen (TSLA) from L. donovani. The proliferation index was determined by ELISA based lymphoproliferative assay. Cytokines and granzyme B levels were measured by CBA. Activated T-cell populations were estimated using flow cytometry.ResultsWe observed significantly higher lymphoproliferation, cytokines and granzyme B levels in HVL group compared to naive or VL group. More strikingly, we found a strong association (rs = 0.895, P < 0.0001) between proliferation index (PI) and granzyme B level, with a significant proportion of activated CD8+ T cells in HVL group.ConclusionsLeishmania immune group (HVL) exhibited durable and strong cellular immune response to TSLA in terms of lymphoproliferation as well as production of Th1 cytokines and granzyme B. Additionally, the elevated level of activated CD8+ T cells and stimulation of cytotoxic activity through granzyme B production, indicated a possible role of CD8+ T cells in resistance to L. donovani infection in the HVL group.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-014-0653-6) contains supplementary material, which is available to authorized users.

Extrathymic induction of Foxp3+ regulatory T cells declines with age in a T‐cell intrinsic manner

Extrathymically induced Foxp3⁺ regulatory T (Treg) cells contribute to the pool of Treg cells and are implicated in the maintenance of immune tolerance at environmental interfaces. The impact of T-cell senescence on their generation and function is, however, poorly characterized. We report here that steady-state induction of Foxp3 is impaired in aged T cells in vivo. In vitro assays further revealed that this defective generation of Treg cells was independent from the strength of TCR stimulation and arose before T-cell proliferation. Importantly, they also revealed that this impairment of Foxp3 induction is unrelated to known age-related T-cell defects, such as IL-2 secretion impairment, accumulation of activated T-cell populations, or narrowing of the T-cell repertoire. Finally, a loss of extrathymic induction of Foxp3 and tolerance to minor-mismatched skin graft were observed in aged mice treated by nondepleting anti-CD4 antibody. The T-cell intrinsic impairment of Treg-cell generation revealed here highlights age as a key factor to be considered in immune tolerance induction.

Activation of OX40 Prolongs and Exacerbates Autoimmune Experimental Uveitis

T cells are essential for the development of autoimmune uveitis. Although the costimulatory molecule OX40 promotes T-cell function and expansion, it is unclear whether OX40 is implicated in ocular inflammation. The purpose of this study was to examine the role of OX40 in uveitis. Experimental autoimmune uveitis (EAU) was induced in B10.RIII mice by subcutaneous injection of interphotoreceptor retinoid-binding protein peptide 161-180 (IRBP(161-180)). Some mice received an intravenous administration of OX40-activating antibody on days 0 and 4 after IRBP(161-180) sensitization or on days 10 and 14 of uveitis onset. The severity of EAU was evaluated by histology at different time points. In addition, ocular inflammatory cytokine expression was determined by real time-PCR, and peripheral activated CD4(+)CD44(+)CD62L(-) T cells and IL-7Rα expression were analyzed by flow cytometry. The activated CD4(+)CD44(+) lymphocytes were rechallenged with IRBP(161-180) in vitro to assess their antigen recall response. The authors demonstrated a marked OX40 expression by infiltrating lymphocytes in enucleated human eyes with end-stage inflammation. In addition, the administration of OX40-activating antibody prolonged and exacerbated the disease course of EAU. Moreover, activation of OX40 not only increased CD4(+)CD44(+)CD62L(-) lymphocyte number, it upregulated IL-7Rα expression in the activated T-cell population. Lastly, these cells exhibited a stronger interferon-γ response to IRBP(161-180) restimulation in vitro. The results reveal a pathogenic role of OX40 in uveitis. Furthermore, the upregulation of IL-7R in CD4(+)CD44(+) lymphocytes suggests that the activation of OX40 promotes the generation or expansion of uveitogenic memory T cells.

Differentiation of Malignant B-Lymphoma Cells from Normal and Activated T-Cell Populations by Their Intrinsic Autofluorescence

Patients with active posterior and intermediate uveitis have inflammatory cells in their vitreous; those with primary intraocular lymphoma have malignant B-lymphoma cells concomitantly. These cell types cannot be distinguished clinically. The goal of this study was to investigate intrinsic autofluorescence as a noninvasive way of differentiating immune and lymphomatous cell populations. Human primary T cells were stimulated with or without anti-CD3 plus anti-CD28 stimulation. B-lymphoma cells (CA46) were cultured separately. Five experimental groups were prepared: unstimulated T cells, stimulated T cells, CA46 cells, and stimulated T cells mixed with CA46 cells at a ratio of 1:3 or mixed at a ratio of 3:1. Samples were excited with three wavelengths and imaged with a confocal microscope. For each condition, the autofluorescent emissions from the sample were measured. In separate experiments, T cells or CA46 cells were injected into the anterior chamber of a BALB/c mouse eye and autofluorescence was measured. Pure T-cell and lymphoma populations were clearly distinguishable based on autofluorescence intensity spectra. CA46 cells were the least fluorescent when excited with 351-nm light, but most fluorescent when excited with longer wavelengths like 488 nm. Mixed populations of T cells and CA46 cells had emission intensities that fell predictably in between those of the pure populations. An ex vivo study showed that CA46 cells could be detected based on their intrinsic autofluorescence. Our studies showed that normal activated and malignant lymphocyte populations can be distinguished based on their intrinsic autofluorescent properties. Future work with in vivo models may prove useful in facilitating the diagnosis of uveitis and other ocular diseases.

Bone Marrow-Derived Mesenchymal Stem Cells Ameliorate Autoimmune Enteropathy Independently of Regulatory T Cells

Cell-based tolerogenic therapy is a relatively new approach for the treatment of autoimmune diseases. Mesenchymal stem cells (MSCs) have been shown to be potent immunomodulatory agents in a number of experimental and clinical scenarios; however, their use in various autoimmune diseases is undefined. Herein, we report the efficacy of MSC transplantation in a multiorgan autoimmunity model. Mice with defective peripheral tolerance caused by a deficiency in regulatory T cells were used as a testbed for therapy. After screening multiple target tissues of autoimmune attack, we observed an MSC-specific improvement in the histopathology of the distal ileum of treated mice. We then showed that MSCs can reduce mesenteric lymph node (MLN) cellularity in autoimmune mice during active disease and decrease activated T-cell populations in the MLN. Trafficking studies using enhanced green fluorescent protein (eGFP)-reporter MSCs revealed no appreciable engraftment in the intestine, but it did reveal the presence of eGFP+ cells organized in clusters within the MLN, as well as ancillary nodes. Semiquantitative analysis showed no difference in the number of clusters; however, eGFP+ cells in MLNs compared with ancillary nodes had distinct fibroblastoid morphology and formed a network with neighboring eGFP+ cells. Finally, we show evidence that transplantation of MSCs caused global immunosuppression, as measured by increased CD4+ CD8+ thymocyte production and serum interleukin-10 and decreased serum interferon-gamma. These data implicate the intestine as a new site of MSC tolerance induction and should motivate additional studies evaluating the use of MSCs as a treatment for autoimmune enteropathies.

Tacrolimus-FK506 induced immunosuppression in gnotobiotic piglets

Tacrolimus (FK506), an inhibitor of calcineurin, is an immunosuppressive agent used in clinical trials of transplant patients. Although FK506 targets Ca 2+-mediated T-cell signaling, phenotype(s) of the specific target cells and the corresponding cytokine pathways are not well known. In this study, the impact of FK506 on number and characteristic of T-cells in selected lymphoid tissues of gnotobiotic (GB) piglets was determined. FK506-treated GB piglets were compared with untreated GB and conventional piglets. The T-helper, cytotoxic, natural killer, double-positive, and activated T-cell populations were analyzed in suspensions of mononuclear cells isolated from thymus, mesenteric lymph nodes and peripheral blood. In vitro secretion of interleukin-8 and interferon-γ in concanavalin A-stimulated lymphoid cell-cultures was measured by ELISA. Daily intramuscular treatment of GB piglets with 1 mg/kg of FK506 from birth for 4 weeks resulted in lowered ( P<0.05) in vitro secretion of interferon-γ and interleukin-8. Moreover, depletions of MNC in systemic and mucosa-associated lymphoid tissues were observed in piglets treated with FK506. The depletions of mononuclear cells and low levels of interferon-γ and interleukin-8 in piglets treated with FK506 were accompanied by lower proportion of CD3+, CD2+CD4+ and CD2+CD8+ T-cell phenotypes in peripheral blood but not in thymus and mesenteric lymph nodes. These results indicate that FK506-treatment causes immunosuppression in GB piglet, and this effect could be exploited further to study opportunistic pathogens in pig model.

Constraints on CD4 Recovery Postchemotherapy in Adults: Thymic Insufficiency and Apoptotic Decline of Expanded Peripheral CD4 Cells

AbstractTo examine the mechanisms of CD4 reconstitution in an adult population, lymphocyte repopulation was assessed following dose-intense chemotherapy in 25 breast cancer patients, ages 33 to 69 years. Chemotherapy resulted in a greater than 60% reduction in total CD4 T cells and, in particular, a greater than 90% loss of the CD45RA+ CD4 cells. CD4 recovery was protracted, achieving less than 50% of pretreatment levels after 12 to 14 months. Two facets of the CD4 recovery were notable. First, generation of CD45RA+ CD4 cells played only a minor role in the first year, suggesting that thymic production was not the main route of CD4 regeneration. Indeed, recovery of CD45RA+ CD4 cell levels remained limited in half of the patients even after 2 years. Second, expansion of the mature peripheral CD4 cells (CD45RO+) remaining after chemotherapy was the main source of early CD4 repopulation, peaking at 3 to 6 months postchemotherapy. This expansion was limited in duration, however, and was followed by a secondary decline, such that the total CD45RO+ CD4 levels at 9 to 12 months were lower than at 6 months. When stimulated by mitogens, an increased susceptibility to apoptosis was observed in postchemotherapy CD4 cells as compared with those from normal donors. The elevated expression of markers such as HLA-DR during chemotherapy and for several months postchemotherapy is consistent with the presence of an activated T-cell population. CD4 apoptotic frequency correlated with the frequency of HLA-DR expression on T cells. Thus, CD4 recovery is constrained in adults by a limited thymic regenerative capacity and by an increased susceptibility to apoptosis within the expanding peripheral CD4 population.

Gut intraepithelial lymphocytes induce immunity against Cryptosporidium infection through a mechanism involving gamma interferon production.

Immunological control of infection with cryptosporidia in mice is dependent on CD4+ T cells and the production of gamma interferon (IFN-gamma), but to date, the mucosal T cells which produce IFN-gamma local to the infection have not been characterized. We previously showed that immunity against the gastric parasite Cryptosporidium muris could be adoptively transferred to adult SCID (severe combined immunodeficiency) mice with small intestinal intraepithelial lymphocytes (IEL) from previously infected immunocompetent mice, but only if the donor CD4+ T cells were intact. The present investigation examined whether IFN-gamma was important in the effector mechanisms mediated by immune IEL in SCID mice. The development of resistance against C. muris infection in SCID mice given immune IEL was prevented by treatment with a hamster anti-mouse IFN-gamma-neutralizing monoclonal antibody, but following cessation of antibody treatment, the mice recovered from infection. In further experiments, an enzyme-linked immunospot (ELISPOT) technique was used to compare frequencies of IFN-gamma-producing cells in activated T-cell populations from C. muris-immune and naive donor mice. Stimulation with concanavalin A or a rat anti-mouse CD3 monoclonal antibody resulted in detection of greater numbers of cells producing IFN-gamma from immune than naive IEL populations. Small numbers of IEL from C. muris-immune mice, but not from naive mice, also produced IFN-gamma when cultured with soluble oocyst antigen, but this occurred only if gamma-irradiated spleen cells were cocultured with the immune IEL. These results suggested that IEL were important in the generation of immunity to Cryptosporidium and that one of their crucial functions was to produce IFN-gamma at the site of infection.

HLA antigens and lymphocytes in proliferative vitreoretinopathy

An immunohistopathological study was performed on 33 epiretinal membrane specimens obtained during vitreoretinal surgery from patients with rhegmatogenous retinal detachment complicated with proliferative vitreoretinopathy (PVR). Immunofluorescence and immunoperoxidase methods were used to detect major histocompatibility complex or HLA antigens and immunocompetent cells, and to identify the cellular and the extracellular component of the proliferative tissue. The following antigens were detected in epiretinal membranes: cytokeratin in 18 (of 18 cases studied for this antigen), glial fibrillary acidic protein in 20 (of 20), vimentin in 20 (of 20), actin in 16 (of 18), fibronectin in 20 (of 20), macrophage CD68 in 16 (of 18), leukocyte common antigen in 12 (of 18), T-cell CD45R in 13 (of 22), HLA-ABC in 27 (of 33), HLA-DR in all the 33 membranes and HLA-DR alpha chain in 32 of 33 membranes. We observed the presence of macrophages and of an activated T-cell population in PVR membranes. HLA-DR antigen expression was found on pigmented and nonpigmented epithelial cells and on mononuclear cells in all epiretinal membranes. The HLA-DR expression on retinal pigmented epithelial cells could play a role in triggering a local immune response in PVR. These findings suggest the involvement of immunological phenomena and probable interactions between the immune system and peptide growth factors.

The V-region disease hypothesis: new evidence suggests it is probably wrong

Repertoire analyses of activated T-cell populations specific for myelin basic protein, peptides of which cause experimental allergic encephalomyelitis in rats and mice, indicate a very limited utilization of homologous V α and V ß genes in both species. However, the encephalitogenic peptide fragments of myelin basic protein represent different domains of the antigen molecule and the MHC restricting elements are different. This finding has lead to an interpretation, the ‘ V-region disease hypothesis’, which suggests that some TCR molecules may have special effector functions in addition to peptide-MHC recognition. On the basis of recent findings with the rat experimental allergic encephalomyelitis model and preliminary studies in human multiple sclerosis, we present a more conservative and conventional interpretation of the association of certain TCR V-region elements with encephalitogenicity.

Human T-cell recognition of Epstein-Barr virus-induced replication antigen complexes.

Cellular immune responses to Epstein-Barr Virus (EBV)-associated antigens play an important role in the control of EBV-immortalized B lymphocytes. The nature of the antigens that serve as targets for these responses remains largely unknown. The purpose of the experiments reported here was to determine if virus-replication-associated antigens might function as targets for T-cell immunity with the emphasis on EBV-induced early antigen (EA) complex. Activated T-cell populations directed against this group of antigens would theoretically be effective in controlling the production of new virus progeny. Our results demonstrate that polypeptides associated with the EA complex do, in fact, induce the proliferation of memory T-cells from EBV-infected individuals irrespective of their serological status to the EA complex. The major polypeptide associated with the diffuse component of EA (EA-D) was notably effective in inducing a strong proliferative T-cell response. Cell lines established from EBV-infected individuals following continuous exposure to either p17 or p50 components of the EA complex over a 10- to 12-week period were composed primarily of CD4-positive T-cells, although CD8-positive cells also persisted for up to 9 weeks in culture. The data suggest that components of the EA complex might function as important target antigens in the immunosurveillance of EBV-infected cells.

Direct T-cell effects of minoxidii

Minoxidil has been shown to induce hair regrowth in alopecia areata1–4 by mechanisms that remain largely unknown. Alopecia areata is histologically characterized by miniaturized follicles with varying degrees of degeneration5 and by a dense perifollicular infiltration of T lymphocytes (helper, suppressor, and activated), Langerhans cells, and monocytes.6,7 T lymphocytes appear to be the predominant cell type in the perifollicular infiltrates and, by implication, may be of pathogenic significance in the hair loss process. Changes in perifollicular T-cell and activated T-cell populations have been found after treatment with minoxidil.7 Responders to topical 5% minoxidil treatment (ie, those patients who had terminal hair regrowth) have shown decreases in tissue T cells and simultaneous increases in peripheral blood T cells.7

Interleukin-2 production in response to phytohemagglutinin is not necessarily dependent upon the T3-mediated pathway of T-cell activation

The present study was designed to investigate whether heterogeneity exists in the requirement for T3 molecules in the mechanism of T-cell activation and interleukin-2 (IL-2) release by IL-2-producing T-cell clones. Clones were derived from peripheral blood by a culture system which allows clonal expansion of essentially all T lymphocytes or from mixed lymphocyte culture (MLC) activated T-cell population. IL-2-producing clones were selected and cell aliquots treated with anti-T3 monoclonal antibodies (mAb) to induce modulation of T3 surface molecules. Although stimulation of modulated clones with different anti-T3 mAb did not lead to IL-2 production, 4 39 of these clones produced IL-2 after stimulation with phytohemagglutinin (PHA). The ability of these clones to be activated by PHA could not be explained by incomplete T3 modulation. In addition, two alloreactive clones were isolated from MLC population in which modulation of T3 antigens abrogated the IL-2 production induced by either anti-T3 mAb or allogeneic stimulation but had no effect on PHA-induced IL-2 release. These data further support the concept that PHA may trigger some T cells via surface molecules that are independent from the T3-Ti cell receptor molecular complex.

Qa gene expression: biosynthesis and secretion of Qa-2 molecules in activated T cells.

The biosynthesis and expression of the tissue-specific class I molecule Qa-2 have been studied in resting and activated T-cell populations. Polyclonal activation of T lymphocytes induces a 3- to 4-fold increase in the biosynthesis of Qa-2 molecules but no increase in cell-surface levels. Analysis of the biosynthetic pathway of the Qa-2 molecule in activated lymphocytes reveals that approximately equal to 70% of the newly synthesized Qa-2 molecules are secreted as soluble molecules. In resting-cell populations, Qa-2 remains entirely cell-associated. This process is unique to the Qa-2 molecule, since other class I molecules (e.g., H-2Kb and H-2Db) synthesized by activated cells remain cell-associated. The possibility that the secreted Qa-2 molecule is the product of a new Qa gene or an alternatively spliced mRNA is considered. These results indicate that the Qa-2 molecules may not just function as a cell-surface recognition structure but also may serve a role as a soluble factor synthesized by activated lymphoid cell populations.

Monoclonal antibodies specific for H-2K and H-2D antigens on cytotoxic T cells can inhibit their function.

Antibodies specific for murine major histocompatibility gene complex (MHC) class I H-2K and H-2D molecules present on cytotoxic T (Tc) cells have been shown to inhibit their function of target cell lysis. This could only be demonstrated by using a more sensitive assay for T-cell-mediated lysis, and many monoclonal antibodies of different Ig class, origin, and specificity can be shown to inhibit alloreactive as well as MHC-restricted Tc cells. These antibodies inhibit different activated T-cell populations to varying extents, and anti-H-2K but not anti-H-2D antibodies show a synergistic effect with anti-Lyt-2 antibodies. Data here suggest that MHC molecules may be located in or near the T-cell receptor complex on these cells.