Possible targeting of G protein coupled receptors to manipulate inflammation in vivo using synthetic and natural ligands.

Cyclic AMP elevating Gs protein coupled receptors were considered for a long time to be immunosuppressive. One of these receptors, adenosine A(2A) receptor, was implicated in a physiological mechanism that down regulates inflammation and protects tissues from excessive immune mediated damage. Targeting of these receptors by selective agonists may lead to better protocols of anti-inflammatory treatments. At the same time inhibiting the Gs protein coupled mediated signalling with antagonists could be explored in studies of approaches to enhance inflammation and tissue damage. Enhancement of targeted tissue damage is highly desirable when it is cancerous tissue, while enhancement of inflammatory events might be desirable in the development of new vaccine adjuvants.

Differential effects of physiologically relevant hypoxic conditions on T lymphocyte development and effector functions.

Direct measurements revealed low oxygen tensions (0.5-4.5% oxygen) in murine lymphoid organs in vivo. To test whether adaptation to changes in oxygen tension may have an effect on lymphocyte functions, T cell differentiation and functions at varying oxygen tensions were studied. These studies show: 1) differentiated CTL deliver Fas ligand- and perforin-dependent lethal hit equally well at all redox conditions; 2) CTL development is delayed at 2.5% oxygen as compared with 20% oxygen. Remarkably, development of CTL at 2.5% oxygen is more sustained and the CTL much more lytic; and 3) hypoxic exposure and TCR-mediated activation are additive in enhancing levels of hypoxia response element-containing gene products in lymphocyte supernatants. In contrast, hypoxia inhibited the accumulation of nonhypoxia response element-containing gene products (e.g., IL-2 and IFN-gamma) in the same cultures. This suggests that T cell activation in hypoxic conditions in vivo may lead to different patterns of lymphokine secretion and accumulation of cytokines (e.g., vascular endothelial growth factor) affecting endothelial cells and vascular permeabilization. Thus, although higher numbers of cells survive and are activated during 20% oxygen incubation in vitro, the CTL which develop at 2.5% oxygen are more lytic with higher levels of activation markers. It is concluded that the ambient 20% oxygen tension (plus 2-ME) is remarkably well suited for immunologic specificity and cytotoxicity studies, but oxygen dependence should be taken into account during the design and interpretation of results of in vitro T cell development assays and gene expression studies in vivo.

Adenosine deaminase deficiency increases thymic apoptosis and causes defective T cell receptor signaling.

Adenosine deaminase (ADA) deficiency in humans results in a severe combined immunodeficiency (SCID). This immunodeficiency is associated with severe disturbances in purine metabolism that are thought to mediate lymphotoxicity. The recent generation of ADA-deficient (ADA(-/-)) mice has enabled the in vivo examination of mechanisms that may underlie the SCID resulting from ADA deficiency. We demonstrate severe depletion of T and B lymphocytes and defects in T and B cell development in ADA(-/-) mice. T cell apoptosis was abundant in thymi of ADA(-/-) mice, but no increase in apoptosis was detected in the spleen and lymph nodes of these animals, suggesting that the defect is specific to developing thymocytes. Studies of mature T cells recovered from spleens of ADA(-/-) mice revealed that ADA deficiency is accompanied by TCR activation defects of T cells in vivo. Furthermore, ex vivo experiments on ADA(-/-) T cells demonstrated that elevated adenosine is responsible for this abnormal TCR signaling. These findings suggest that the metabolic disturbances seen in ADA(-/-) mice affect various signaling pathways that regulate thymocyte survival and function. Experiments with thymocytes ex vivo confirmed that ADA deficiency reduces tyrosine phosphorylation of TCR-associated signaling molecules and blocks TCR-triggered calcium increases.

Study of A(2A) adenosine receptor gene deficient mice reveals that adenosine analogue CGS 21680 possesses no A(2A) receptor-unrelated lymphotoxicity.

Cell surface A(2A) adenosine receptor (A(2A)R) mediated signalling affects a variety of important processes and adenosine analogues possess promising pharmacological properties. Demonstrating the receptor specificity of potentially lymphotoxic adenosine-based drugs facilitates their development for clinical applications. To distinguish between the receptor-dependent and -independent lymphotoxicity and apoptotic activity of adenosine and its analogues we used lymphocytes from A(2A)R-deficient mice. Comparison of A(2A)R-expressing (+/+) and A(2A)R-deficient (-/-) cells in cyclic AMP accumulation assays confirmed that the A(2A)R agonist CGS 21680 is indeed selective for A(2A) receptors in T-lymphocytes. Incubation of A(2A)R-expressing thymocytes with extracellular adenosine or CGS 21680 in vitro results in the death of about 7-15% of thymocytes. In contrast, no death was induced in parallel assays in cells from A(2A)R-deficient mice, providing genetic evidence that CGS 21680 does not display adenosine receptor-independent intracellular cytotoxicity. The A(2A) receptor-specific lymphotoxicity of CGS 21680 is also demonstrated in a long-term (6-day) in vitro model of thymocyte positive selection where addition of A(2A)R antagonist ZM 241,385 did block the effects of CGS 21680, allowing the survival of T cells. The use of cells from adenosine receptor-deficient animals is proposed as a part of the screening process for potential adenosine-based drugs for their receptor-independent cytotoxicity and lymphotoxicity.

Comparison of Fas- versus perforin-mediated pathways of cytotoxicity in TCR- and Thy-1-activated murine T cells.

T cell-mediated cytotoxicity can be triggered by cross-linking of TCR or Thy-1 surface proteins. While the TCR-triggered signaling initiates both perforin- and Fas ligand (FasL)-Fas-mediated mechanisms of cytotoxicity, it was not clear which mechanism was utilized by Thy-1-triggered signals and which pathway of cytotoxicity was triggered at low levels of antigen expression. It is shown that glycophosphatidylinositol-linked surface glycoprotein Thy-1 preferentially activates FasL-Fas- but not perforin-mediated cytotoxicity. This is explained by the lesser intensity of Thy-1-mediated signaling in T cells. The data suggest that Thy-1-triggered Fas-mediated cytotoxicity is completely dependent on cross-talk between Thy-1 and TCR signals since mutations in TCR-CD3 complex molecules or inhibition of tyrosine kinases or calcineurin abolished or strongly inhibited Thy-1-triggered FasL-Fas-mediated cytotoxicity. Lower concentrations of antigenic peptide or levels of cross-linking with anti-TCR-CD3 mAb are required to trigger Fas-mediated than perforin-mediated cytotoxicity by different cytotoxic T lymphocyte (CTL) lines and clones, and it is shown that cross-linking of Thy-1 is much less efficient in triggering accumulation of second messengers (intracellular Ca(2+)) than cross-linking of TCR on CTL. Taken together, these data reflect the possibility of differential activation of FasL and/or perforin pathways of cytotoxicity depending on the nature of activating stimuli and surface receptor.

Ecto-protein kinases: ecto-domain phosphorylation as a novel target for pharmacological manipulation?

An increasing number of studies document the presence of protein kinases facing outwards at the cell surface of a diverse array of cells. These ecto-protein kinases phosphorylate cell-surface proteins and soluble extracellular substrates, and thus could affect many physiological processes involving cell-cell contacts, cellular differentiation and proliferation, ion fluxes and cellular activation. To date, only limited attention has been paid to exploring ecto-protein kinases as possible pharmacological targets. Here, the identification and physiological role of ecto-protein kinases in different biological systems is described; it is suggested that ecto-protein kinases are attractive and novel candidates for pharmacological manipulation under various (patho)physiological conditions.

The extracellular versus intracellular mechanisms of inhibition of TCR-triggered activation in thymocytes by adenosine under conditions of inhibited adenosine deaminase.

The absence or low levels of adenosine deaminase (ADA) in humans result in severe combined immunodeficiency (SCID), which is characterized by hypoplastic thymus, T lymphocyte depletion and autoimmunity. Deficiency of ADA causes increased levels of both intracellular and extracellular adenosine, although only the intracellular lymphotoxicity of accumulated adenosine is considered in the pathogenesis of ADA SCID. It is shown that extracellular but not intracellular adenosine selectively inhibits TCR-triggered up-regulation of activation markers and apoptotic events in thymocytes under conditions of ADA deficiency. The effects of intracellular adenosine are dissociated from effects of extracellular adenosine in experiments using an adenosine transporter blocker. We found that prevention of toxicity of intracellular adenosine led to survival of TCR-cross-linked thymocytes in long-term (4 days) assays, but it was not sufficient for normal T cell differentiation under conditions of inhibited ADA. Surviving TCR-cross-linked thymocytes had a non-activated phenotype due to extracellular adenosine-mediated, TCR-antagonizing signaling. Taken together the data suggest that both intracellular toxicity and signaling by extracellular adenosine may contribute to pathogenesis of ADA SCID. Accordingly, extracellular adenosine may act on thymocytes, which survived intracellular toxicity of adenosine during ADA deficiency by counteracting TCR signaling. This, in turn, could lead to failure of positive and negative selection of thymocytes, and to additional elimination of thymocytes or autoimmunity of surviving T cells.

Patterns of A2A extracellular adenosine receptor expression in different functional subsets of human peripheral T cells. Flow cytometry studies with anti-A2A receptor monoclonal antibodies.

Signaling through A2A adenosine receptors (A2AR) regulates T lymphocyte expansion and modulates T cell receptor (TCR)-mediated effector functions in vitro. To understand the role of A2ARs in the regulation of immune response, we investigated the expression levels of this receptor in different functional lymphocyte subsets. Monoclonal anti-A2AR antibody was used to develop a flow cytometric assay to quantify the expression A2ARs on lymphocytes. We report that detectable levels of expression of A2ARs are much higher among T cells than B cells. More CD4(+) than CD8(+) T cells express A2ARs, but activation of T cells increases A2AR expression, predominantly in CD8(+) T cells. No significant differences were found in the proportion of A2AR+ cells between CD8(low) and CD8(high) T cells or between TCR/CD3(low) and TCR/CD3(high) T cells. Studies of T helper cell subsets (TH1 and TH2) reveal that lymphokine-producing cells are much more likely to express A2ARs than are cells that do not produce lymphokines. These results suggest that A2ARs are variably expressed on T cell subsets and may regulate cytokine production in activated T lymphocytes.

Extracellular purines and their receptors in immunoregulation. Review of recent advances.

T cells are important effector cells in natural antiviral and anticancer immunity. It is important to reveal the cellular and molecular requirements for T cell differentiation and effector functions. We explored the idea that the final outcome of antigen receptor-driven immune processes is at least partially determined by physiologically abundant small signaling molecules in extracellular environment of lymphocytes in different tissues. Extracellular purines (ATP and adenosine) and their (purinergic) receptors were studied as an example of such molecules. Studies of functional effects of extracellular ATP and adenosine in immunoregulation have evolved in studies of individual molecules of purinergic receptors and of phosphorylation of extracellular domains of functionally important proteins. ATP-gated membrane pore, p2x 7(formerly p2z receptor) and A2a adenosine receptors are found to be predominantly expressed in T cells. The Gs-protein coupled A2a receptors activate cAMP-dependent protein kinase which was shown to have dual role in regulation of T cells functions. The results of our recent studies of adenosine receptors indicate that A2a receptors on T cell surface may play immunosuppressive role in conditions which lead to accumulation of extracellular adenosine. These conditions include pharmacological intervention with widely used anti-inflammatory drugs (methotrexate and sulfasalazine) and extracellular environment near large solid tumors. Hypoxic conditions in such tumors are known to cause accumulation of extracellular adenosine, which, in turn, as we have shown, could inhibit incoming antitumor cytotoxic T-lymphocytes from destroying the tumor. Normal development and functions of immune cells require adenosine deaminase (ADA) activity. Absence or low levels of ADA in humans result in severe combined immunodeficiency (SCID), which is characterized by hypoplastic thymus, T lymphocyte depletion, and autoimmunity. ADA SCID is currently explained only by intracellular lymphotoxicity of accumulated adenosine. We propose that T cell depletion, immunodeficiency, and autoimmunity could also be due to extracellular adenosine-induced signaling, which inhibits the antigen receptor (TCR) signaling and therefore affects the TCR-driven positive and negative selection of thymocytes. This, in turn, may lead to changes in antigen receptor repertoires and to immunodeficiency, Such properties of adenosine receptors suggest an expanded understanding of pathogenesis of ADA SCID as being due to two independent (intracellular and extracellular) mechanisms of adenosine action. It was conclusively demonstrated that functionally important T cell surface proteins including T cell receptor- are constitutively Ser/Thr phosphorylated on their ectodomains. We identified the major ecto-protein kinase activity in T-lymphocytes as casein kinase II-like (CKII-like) protein kinase. Consensus phosphorylation sites for serine and threonine protein kinases were found to be strongly evolutionary conserved in both alfa and beta TCR chains constant region. We have shown that ecto- or releasable by T-cells protein phosphatase has properties of PP1 and PP2a class protein phosphatase. Such covalent modifications of ectodomains may change T cells cognate interactions by e.g. affecting TCR-multimolecular complex formation and antigen binding affinity. It is suggested that TCR ectodomain phosphorylation could serve as a potential mechanism for regulation of TCR-mediated T-lymphocytes response.

Memory of extracellular adenosine A2A purinergic receptor-mediated signaling in murine T cells.

Accumulation of extracellular and intracellular adenosine (Ado) under hypoxic conditions or in the absence of adenosine deaminase results in lymphocyte depletion and in severe combined immunodeficiency, which are currently explained by direct intracellular lymphotoxicity of Ado metabolites. In support of the alternative, "signaling" mechanism, we show that extracellular Ado (extAdo) suppresses all tested T cell receptor (TCR)-triggered effector functions of T lymphocytes including the TCR-triggered FasL mRNA up-regulation in cytotoxic T lymphocytes. Strong evidence against the intracellular lymphotoxicity of Ado (and in support of the signaling model) is provided by abrogation of TCR-triggered growth inhibition in Ado-exposed T cells. The brief exposure to Ado was sufficient to observe inhibition of TCR-triggered effector functions. The "memory" of T cells to exposure to extAdo is best explained by sustained increases in cAMP. Selective agonist (CGS21680) and antagonist (ZM241385) of A2A adenosine receptor were used in functional assays and cDNA probes for different sybtypes of adenosine receptors were used in Northern blot studies. A2A receptors are identified as the predominantly expressed subtype of Gs-coupled Ado receptors in T cells. The demonstration of cross-talk between the A2A receptors and TCR in both directions support the possible role of A2A receptors in mechanisms of extAdo-mediated immunosuppression in vivo under adenosine deaminase deficiency and hypoxic conditions in, e.g., solid tumors.

Phosphorylation of T-lymphocyte plasma membrane-associated proteins by ectoprotein kinases: implications for a possible role for ectophosphorylation in T-cell effector functions.

Extracellular adenosine triphosphate (ATPo) has been suggested to play a role in lymphocyte effector functions. Recently, it has been suggested that MgATP2- may be the molecular species which is involved in modulating the lytic interaction between cytotoxic T-lymphocytes (CTL) and their target cells. In this study, we provide evidence that ATPo mediates the phosphorylation of extracellular proteins on T-lymphocytes through the action of ectoprotein kinases. The ectophosphorylation is temperature-dependent, supported by Mg2+ and Mn2+, and both ATP and GTP, whereas kinase activity and/or substrates were removed by pretreatment of intact lymphocytes with trypsin. We show the presence of extracellular ATP/GTP-binding sites, indicating the presence of ectoenzymes on intact lymphocytes. The major ectoprotein kinase was identified as a casein kinase II-like protein kinase and could be inhibited by heparin, whereas its activity was enhanced by spermine. The ectoprotein kinase showed remarkable substrate specificity, phosphorylating the serum protein vitronectin, but not fibronectin. In experiments with the cell-impermeable protein kinase inhibitor K-252b, we demonstrate the possible functional importance of ectoprotein kinase in CTL-mediated cytotoxicity, i.e., target cell death was completely blocked by K-252b without affecting intracellular phosphorylation. These results suggest that ectoprotein phosphorylation may possibly be an important event in immunologically relevant cell-cell interactions.

Leukocyte function-associated antigen-1-dependent lysis of Fas+ (CD95+/Apo-1+) innocent bystanders by antigen-specific CD8+ CTL.

Exquisite specificity toward Ag-bearing cells (cognate targets) is one of the most important properties of CD8+ CTL-mediated cytotoxicity. Using highly Ag-specific CD8+ CTL lines and clones, which spare noncognate, Ag-free targets, we found that in the presence of Ag-bearing targets the CTL acquire the ability to lyse noncognate target cells (bystanders). It is shown that the unexpectedly rapid and efficient lysis of bystanders by Ag-activated CTL is mediated by a Fas ligand (FasL)/Fas-based mechanism and does not depend on perforin. The CTL lysed Fas-expressing bystanders, but spared the Fas-negative or anti-Fas mAb-resistant bystander cells. Accordingly, the FasL-deficient gld/gld CTL did not kill bystanders, while perforin-deficient CTL did. Unlike anti-Fas mAb-induced cell death, the lysis of bystanders was not only FasL/Fas dependent but also required adhesion molecule LFA-1 on the surface of the activated CTL. Lysis of bystanders is viewed as acceptable "collateral" damage, but the persistent presence of activated CTL could result in immunopathologies involving functional Fas-expressing tissues.

Effects of extracellular ATP and adenosine on different thymocyte subsets: possible role of ATP-gated channels and G protein-coupled purinergic receptor.

To explore the possible role of purinergic receptors in thymocyte development and in pathogenesis of adenosine deaminase SCID, we studied effects of extracellular adenosine triphosphate (ATP(ext)) and adenosine on TCR- and steroid hormone-triggered processes in mouse thymocytes. Reverse transcriptase-PCR analysis confirms the mRNA expression of several types of purinergic receptors, while the functioning of ATP receptors in thymocytes is reflected by ATP(ext)-induced intracellular calcium increases and by thymocyte subset-specific sensitivity to the effects of ATP(ext) and adenosine. Only ATP(ext), but not the ATP catabolites, adenosine, dexamethasone, or TCR cross-linking, was efficient in triggering rapid protein synthesis independent lysis of CD4+8- thymocytes and peripheral CD4+ T cells. In contrast, extracellular adenosine specifically induced the apoptosis of CD4+8+ thymocytes. ATP(ext) also induced a slower process of DNA fragmentation and protein synthesis-dependent apoptosis in all thymocyte subsets. ATP(ext) had an additive effect with TCR cross-linking in the induction of thymocyte death, but, unexpectedly, the effects of ATP(ext) at high concentration were antagonistic to steroid-induced apoptosis. Described here, the properties of ATP(ext) and adenosine are consistent with their involvement in the regulation of T cell development due to differential expression and signaling through purinergic receptors in different thymocyte subsets. The possible role of purinergic receptor signaling in T cell differentiation and adenosine deaminase SCID is discussed.

Transient up-regulation of P2Y2 nucleotide receptor mRNA expression is an immediate early gene response in activated thymocytes.

In studies designed to understand the roles of P2 nucleotide receptors in differentiation of T lymphocytes, we observed a transient and protein synthesis-independent enhancement of mRNA expression for the G protein-coupled P2Y2 receptor in mouse thymocytes after the addition of steroid hormone or T cell receptor (TCR) crosslinking by anti-TCR mAb. Conversely, dexamethasone-induced increases in mRNA expression for the ligand-gated ion channel P2X1 receptor was detected in rat, but not mouse, thymocytes, raising questions about the previously suggested role of P2X1 receptors in thymocyte apoptosis. Flow cytometry analysis of thymocyte subsets excluded the possibility that the observed increases in P2Y2 receptor mRNA expression were due to the enrichment of steroid-treated cells with an P2Y2 mRNA-rich thymocyte subset. Triggering of TCR-mediated intracellular signaling pathways through crosslinking of TCR or by addition of phorbol ester and Ca2+ ionophore also resulted in the up-regulation of P2Y2, but not P2X1, receptor mRNA. It is proposed that the rapid increase of P2Y2 receptor mRNA expression could be a common early event in responses of T cells to different activating stimuli. Taken together with the recently discovered ability of nucleotide receptor-initiated signaling to antagonize or enhance the effects of TCR crosslinking or steroids on thymocytes, the observed rapid up-regulation of P2Y2 receptor mRNA expression may reflect an immediate early gene response where newly expressed cell surface nucleotide receptors provide regulatory feedback signaling from extracellular ATP in the T cell differentiation process.

Perturbation of the expression of the catalytic subunit C alpha of cyclic AMP-dependent protein kinase inhibits TCR-triggered secretion of IL-2 by T helper hybridoma cells.

The role of cAMP-dependent protein kinase (PKA) in the regulation of TCR-triggered IL-2 secretion was studied by transfecting T hybridoma cells with cDNA encoding the inhibitory regulatory subunit (RI alpha) of PKA with mutations in cAMP-binding sites (RI alpha(m)) or by pretreating T cells with catalytic subunit-alpha (C alpha) antisense mRNA oligonucleotides. Transfected RI alpha(m) was expected to compete with endogenous regulatory subunits and to irreversibly inactivate the catalytic subunit in RI alpha(m)-C alpha complexes. It was shown that C alpha and RI alpha are the major PKA subunits in T cells, thereby justifying the choice of RI alpha(m) and C alpha antisense oligos to modulate PKA activity in T lymphocytes. Perturbation of the expression of PKA subunits by RI alpha(m) resulted in transfectants with 1) no changes in basal PKA activity but inhibited cAMP-inducible PKA activity or 2) inhibited basal PKA activity but unaffected cAMP-inducible PKA activity. Transfectants with inhibited basal PKA activity had changed (inhibited) levels of TCR-triggered IL-2 production. The anti-C alpha antisense mRNA oligomers also inhibited basal PKA activity and TCR-triggered production of IL-2. The experiments described here and recently reported studies of the effects of C alpha inactivation on CTL effector functions and IFN-gamma secretion suggest that basal PKA activity could be required for the propagation of TCR-triggered signals needed for lymphokine secretion by T cells.

Phosphorylation of extracellular domains of T-lymphocyte surface proteins. Constitutive serine and threonine phosphorylation of the T cell antigen receptor ectodomains.

The extracellular accumulation of ATP after activation of T-lymphocytes, as well as the presence of ecto-protein kinases in these cells, led us to propose that T cell surface receptors could be regulated through the reversible phosphorylation of their extracellular domains (ectodomains). Here, in a model system, we used T cell transfectants which express T cell antigen receptor chains lacking intracellular and transmembrane protein domains and 32Pi metabolic labeling of cells to definitively demonstrate phosphorylation of ectodomains of T cell surface proteins. We show that alphabetaTCR ectodomains were phosphorylated intracellularly and constitutively on serine and threonine residues and were then expressed on the T cell surface in phosphorylated form. TCR ectodomains also could be phosphorylated at the cell surface when extracellular [gamma-32P]ATP or [gamma-32P]GTP were used as phosphate donors with the same cells. Consensus phosphorylation sites for serine and threonine protein kinases were found to be strongly evolutionary conserved in both alpha and beta TCR chains constant regions. These results are consistent with the hypothesis, where T cell surface proteins which are phosphorylated intracellularly on their ectodomains, could subsequently be expressed at the cell surface and then be reversibly modified by ectoprotein phosphatase(s) and by ectokinase(s). Such modifications may change T cells cognate interactions by, e.g. affecting TCR-multimolecular complex formation and antigen binding affinity. It is suggested that alphabetaTCR ectodomain phosphorylation could serve as a potential mechanism for regulation of alphabetaTCR-mediated T-lymphocytes response.

Cytotoxic lymphocytes. Two ways to kill target cells.

Of the two pathways implicated in target-cell damage by cytotoxic lymphocytes, secretory granule exocytosis seems to dominate in anti-viral immunity whereas the Fas pathway may regulate immune responses.

Development and antigen specificity of CD8+ cytotoxic T lymphocytes in beta 2-microglobulin-negative, MHC class I-deficient mice in response to immunization with tumor cells.

beta 2-Microglobulin knockout mice (beta 2-m-/-) with MHC class I expression deficiency are able to develop functional TCR(+)-alpha beta, CD8+ CTLs in response to tumor cell injection. The i.p. injection of beta 2-m-/- mice with tumor results in the massive accumulation of highly lytic CD8+ CTLs in the peritoneum and causes the local recruitment of CD8+ T cells into lymph nodes and spleens of immune animals. The accumulation of CD8+ CTLs in peritoneum is accompanied by the rejection of tumor cells and the survival of animals. The deficiency in MHC class I expression in beta 2-m/- mice is reflected in the delayed tumor rejection and CD8+ cell accumulation during the primary anti-tumor response in comparison with normal mice. The secondary response, however, is identical in normal and MHC class I-deficient mice. The rejection of tumor cells appears to be MHC class I directed because no rejection of tumors, no accumulation of CD8+ CTLs, and no survival of animals were observed when syngeneic tumor cells were used for injection with the notable exception of anti-minor Ag response. The Ag specificity of CD8+ CTLs in beta 2-m-/- mice is demonstrated using a panel of tumor target cells and class I transfectants. Although no substantial differences were found in the number and specificity of peritoneal CD8+ CTLs in beta 2-m-/- and normal mice using tumor rejection studies, the analysis of TCR-V beta phenotype using the panel of mAbs revealed the reduction in proportion of TCR-V beta 5 and TCR-V beta 6 used by CD8+ cell population from beta 2-m-/- mice. Development of lytic and H-2-directed CD8+ cells in regional lymph nodes was also observed after footpad immunization of beta 2-m-/- mice with TNP-labeled C57BL/6 splenocytes, suggesting anti-minor Ag reaction.

Detection of distinct sets of newly synthesized polypeptides in supernatants of TCR-triggered T cell clones. Implication for the search for new lymphokines.

Using metabolic radiolabelling of proteins, which are newly synthesized during TCR-triggered T cell activation we were able to visualize distinct patterns of secreted polypeptides (with molecular weights ranging from 6 to 44 kDa) in supernatants of different T helper-1, T helper-2 and cytotoxic T cell clones. Most of these detected proteins are secreted in response to TCR-crosslinking (or to combined action of PMA and A231287), in an extracellular Ca(2+)-dependent manner and their appearance in supernatants was completely blocked by the addition of RNA synthesis or protein synthesis inhibitors or EGTA. Cyclosporin A (CsA) blocks secretion of several detected polypeptides, but does not affect TCR-triggered synthesis and secretion of others reflecting the existence of TCR-triggered, CsA-insensitive protein synthesis and secretion pathway. The insensitivity of secretion of several easily detectable polypeptides to inhibition by CsA offers a promising approach to further define the CsA-resistant and calcineurin-independent molecular pathways of TCR-triggered T cell activation. Several lymphokines (e.g., interferon-gamma, tumor necrosis factor, interleukin-4 and interleukin-10) are identified among the visualized set of secreted polypeptides. Since other, yet unidentified, secreted polypeptides in the same set of secreted proteins share important properties with known lymphokines it seems promising to use described approach in search for new lymphokines.