Über die strukturabhängige hämolytische Aktivität einiger Cholin-Phosphatide

Eine Anzahl synthetischer Cholinphosphatide wurde hinsichtlich ihrer hämolytischen Wirksamkeit untersucht. Die Lyse der Erythrocyten wurde dabei sowohl in ihrem zeitlichen Verlauf verfolgt, wie auch durch Endpunktsbestimmung bei verschiedenen Konzentrationen quantitativ erfaßt.

Ein direkter Zusammenhang zwischen der Grenzflächenaktivität und der hämolytischen Wirksamkeit der Substanzen besteht nicht. Innerhalb homologer Verbindungsreihen wird dagegen durch die Kettenlänge des apolaren Teils im Molekül eine scharfe Grenze zwischen lytischen und nicht-lytischen Verbindungen gezogen. So zeigt beispielsweise das sehr stark grenzflächenaktive Dipelargonoyl-α-lecithin gegenüber Humanerythrocyten keinerlei hämolytische Wirksamkeit, während Dicaprinoyl-α-lecithin bei gleicher Grenzflächenaktivität eine deutliche Hämolyse verursacht.

Bei einigen der untersuchten Phosphatide wurde überdies ein diskontinuierlicher, zweistufiger Verlauf der Zellzerstörung beobachtet.

Clonal anergy induced in a CD8+ hapten-specific cytotoxic T-cell clone by an altered hapten-peptide ligand

Clonal T-cell anergy has been proposed as a mechanism to ensure peripheral tolerance in vivo. Anergy has been reported to result from T cell activation with inappropriate antigen-presenting cells (APC) or, in the case of CD4+ T cells, also by altered peptide ligands. This study reveals that altered hapten ligands can also induce anergy in CD8+ T cells. The Kb-restricted, trinitrophenyl (TNP) specific cytotoxic T lymphocyte (CTL) clone E6 was found to lyse target cells presenting the TNP-modified peptides M4L-TNP (derived from mouse serum albumin) or O4TNP (derived from chicken ovalbumin), but not the corresponding dinitrophenol (DNP)-modified peptides. However, whereas M4L-DNP was found totally unreactive, O4DNP antagonistically inhibited M4L-TNP-mediated kill if expressed on the same target cell. Moreover, when presented alone on APC, O4DNP, but not M4L-DNP, induced anergy in clone E6 by preventing its subsequent proliferative response to M4L-TNP. The anergic state did not affect agonist-specific cytolysis or T-cell receptor (TCR) down-modulation by the anergized CTL, and proliferative responses were regained upon addition of interleukin (IL)-2 or IL-12 plus IL-18. These findings substantiate the similarity between hapten-and peptide-recognition by T cells. The induction as well as the reversal of anergy in CD8+ CTL may thus be of relevance not only in autoimmunity or tumour rejection, but also in contact hypersensitivity reactions to haptens.

Antigen contacts by Ni-reactive TCR: typical alphass chain cooperation versus alpha chain-dominated specificity

VB17(+) TCR dominate in Ni-driven T cell cultures from highly Ni-sensitized patients. Using transfection of TCR from three CD4(+), VB17(+), Ni-specific human T cell clones, we studied their Ni-MHC contacts by site-directed TCR mutation and combination of alpha and ss chains between different TCR. All three TCR exhibited N-nucleotide-determined Arg-Asp motifs in their CDR3-ss sequences. Two of them were specifically restricted to HLA-DR13, while the third one accepted a variety of HLA-DR alleles. The highly similar alpha or ss chains of the DR13-restricted TCR were interchangable without loss of specificity, but alpha or ss chains of other TCR were not tolerated. Mutations of their Arg-Asp motif revealed loss of reactivity upon exchanging Asp for Glu or Ala and of Arg for Ala but not of Arg for Lys or the Ni binding His. Reactivity was also destroyed by mutation of alpha chain position 51, proposed as a general contact site for MHC. Hence, in these two TCR the Arg-Asp motif is clearly involved in contacting Ni-MHC complexes, and close cooperation between alpha and ss chain is required. In contrast, the third TCR retained Ni reactivity upon mutation of alpha chain position 51 or of its ss chain Arg-Asp motif, which rather affected the pattern of DR cross-restriction. Moreover, its alpha chain paired with various ss chains from other, even mouse TCR, irrespective of their specificity, retaining Ni reactivity as well as promiscuous HLA-DR restriction. This preponderance of an alpha chain in defining specificity indicates fundamental differences in Ni interactions of individual TCR and implies that ss chain similarities may not necessarily result from antigen selection.

Kinetics of CXCR4 and CCR5 up-regulation and human immunodeficiency virus expansion after antigenic stimulation of primary CD4(+) T lymphocytes

The chemokine receptors CCR5 and CXCR4 are coreceptors for the human immunodeficiency virus (HIV) and determine the cell tropism of different HIV strains. Previous studies on their regulation were performed under conditions of unspecific T-lymphocyte stimulation and provided conflicting results. To mimic physiologic conditions, highly purified primary Staphylococcus enterotoxin B (SEB)-reactive CD4 T lymphocytes were stimulated in the presence of autologous antigen-presenting cells and the kinetics of CCR5 and CXCR4 surface expression and HIV replication were studied. Both chemokine receptors were transiently up-regulated with maximal expression at day 3 after stimulation. The stimulated T cells were equally susceptible to productive infection with R5-and X4-tropic virus strains. Thus, antigenic stimulation of T cells promotes efficient replication of both, T cell-tropic and macrophage-tropic HIV. (Blood. 2000;96:1853-1856)

Peptide immunization indicates that CD8+ T cells are the dominant effector cells in trinitrophenyl-specific contact hypersensitivity

The identity of the effector T cell population involved in contact hypersensitivity is still questionable with evidence promoting both CD4+ or CD8+ T cells. Previous experimental studies have relied on the in vivo depletion of T cell subsets using antibody, or the use of knock-out mice with deficiencies in either CD4+ or CD8+ T cell-mediated immunity. To address the role of the class I- and class II-mediated pathways of T cell activation in contact hypersensitivity responses in mice with an intact immune system, we utilized various trinitrophenyl-derivatized peptides, which bind specifically with H-2Kb (major histocompatibility complex class I) or H-2I-Ab (major histocompatibility complex class II). The subcutaneous injection of major histocompatibility complex class II-specific, but not of class I-binding, hapten-derivatized peptides in incomplete Freund's adjuvant induced specific, albeit low, contact hypersensitivity responsiveness to trinitrochlorobenzene. When bone-marrow-derived dendritic cells, however, were pulsed with the same peptides and administered intradermally, the opposite result was observed, namely that the class I binding peptides induced contact hypersensitivity responses similar to that observed after epicutaneous trinitrochlorobenzene application. In contrast, dendritic cells pulsed with major histocompatibility complex class II binding peptides did not reproducibly sensitize for contact hypersensitivity responses. Surprisingly, both immunization protocols efficiently induced CD8+ effector T cells. These results support the notion that CD8+ T cells are the dominant effector population mediating contact hypersensitivity responsiveness and that the CD4+ T cell subset only contributes little if at all.

TCR reactivity in human nickel allergy indicates contacts with complementarity-determining region 3 but excludes superantigen-like recognition

Nickel is the most common inducer of contact sensitivity in humans. We previously found that overrepresentation of the TCRBV17 element in Ni-induced CD4+ T cell lines of Ni-allergic patients relates to the severity of the disease. Amino acid sequences of these beta-chains suggested hypothetical contact points for Ni2+ ions in complementarity-determining region (CDR) 1 and CDR3. To specifically address the molecular requirements for Ni recognition by TCR, human TCR alpha- and beta-chains of VB17+ Ni-reactive T cell clones were functionally expressed together with the human CD4 coreceptor in a mouse T cell hybridoma. Loss of CD4 revealed complete CD4 independence for one of the TCR studied. Putative TCR/Ni contact points were tested by pairing of TCR chains from different clones, also with different specificity. TCRBV17 chains with different J regions, but similar CDR3 regions, could be functionally exchanged. Larger differences in the CDR3 region were not tolerated. Specific combinations of alpha- and beta-chains were required, excluding a superantigen-like activation by Ni. Mutation of amino acids in CDR1 of TCRBV17 did not affect Ag recognition, superantigen activation, or HLA restriction. In contrast, mutation of Arg95 or Asp96, conserved in many CDR3B sequences of Ni-specific, VB17+ TCR, abrogated Ni recognition. These results define specific amino acids in the CDR3B region of a VB17+ TCR to be crucial for human nickel recognition. CD4 independence implies a high affinity of such receptor types for the Ni/MHC complex. This may point to a dominant role of T cells bearing such receptors in the pathology of contact dermatitis.

Functional expression and analysis of a human HLA-DQ restricted, nickel-reactive T cell receptor in mouse hybridoma cells

Nickel-induced contact dermatitis represents a T cell mediated delayed type hyperreactivity. The elucidation of the molecular basis of T cell activation by Ni2+ ions may serve as a model for the understanding of other metal allergies. We describe here the expression of hybrid T cell antigen receptor (TCR) alpha- and beta-genes, containing rearranged human Ni-reactive variable and mouse constant regions, together with human CD4 in a mouse T cell hybridoma. The resulting hybridoma specifically responds to IL-2 secretion to Ni, but not to other metal ions in the presence of HLA-matched antigen-presenting cells. Loss of CD4 decreases, but does not completely abrogate this reactivity. The restricting HLA-DQ element is identified as consisting of DQA1*0101 and DQB1*0501; however, only some of the B cell lines homozygous for these molecules effectively present Ni to the hybridoma. We interpret these data to show that (i) Ni-reactivity is definitely mediated by alpha beta TCR variable regions; (ii) as for peptide-specific TCR, the CD4 co-receptor enhances Ni-reactivity, but is not absolutely essential; (iii) Ni2+ ions like nominal peptide antigens require HLA (here class II) molecules of the APC for presentation; (iv) the restricting molecule may require a special conformation or the association with a particular type of peptide or an as yet unidentified other surface structure on the antigen-presenting cell for effective Ni-presentation.

Antigen-dependent and -independent IFN-gamma modulation by penicillins

The activation of CD4+ T lymphocytes upon Ag stimulation plays a critical role in adverse immune responses including drug-specific hypersensitivity reactions. We examined the modulation of T cell phenotype induced by hapten-specific stimulation using the model of beta-lactam antibiotics such as penicillin G (Pen G), Pen V, and ampicillin (Amp). When PBMC of donors suffering from hypersensitivity reactions against beta-lactams were stimulated in vitro with different doses of Pen G, a preferential expansion of IL-4-producing TCR alphabeta+ cells was detected. A panel of T cell clones was then prepared from Pen G-specific lines after two cycles of restimulation with the hapten. For the majority of these clones, we found that high doses of Pen G induced optimal IL-4 secretion, whereas the amount of IFN-gamma secreted was inversely correlated with the dose of Pen G, thus leading to a hapten-inducible shift of the functional phenotypes for some of the clones. Finally, Pen V and Amp were used to modulate different Ag-induced immune responses. We found that Amp had no influence on the cytokine pattern induced by specific Ag or mitogens. In contrast, Pen V inhibited the secretion of IFN-gamma, but not IL-4, most likely by Ag-independent mechanisms. This last finding may open new applications for immune intervention in those diseases in which polarized Th1 responses are involved in the development of the pathology.

Partial agonism and independent modulation of T cell receptor and CD8 in hapten-specific cytotoxic T cells

We recently demonstrated antagonism for hapten-reactive T cells by altered hapten ligands. Here we investigated partial peptide- or hapten-agonism and effects of antigen stimulation on the expression of TCR and the CD8 coreceptor using a set of DNP- or TNP-peptide-induced, H-2Kb-restricted mouse CTL clones. Various Kb-binding TNP- and DNP-peptides acted as partial agonists, cross-reactively stimulating individual clones for cytotoxicity and IFN-gamma secretion, but failing to induce proliferation or TNF-alpha production. Full agonism, i.e. activation of all possible functions, was usually restricted to those hapten-peptide combinations used for the induction of the respective clones. Our data imply distinctive kinetic optima for TCR antigen contacts in the induction of the various T cell effector functions. Down-regulation of TCR was efficiently induced by full, but with one exception not by partial, agonists, indicating the independence of cytotoxicity or IFN-gamma secretion from TCR modulation. On the other hand, a reduction of TCR expression induced by full agonists was usually not accompanied by synchronous down-modulation of CD8 as reported by others for human T cells. In fact, three of four full agonists and all partial agonists markedly enhanced rather than reduced the expression of CD8. Increased CD8 surface levels enhanced cytolytic potential and increased cross-reactivity patterns of individual clones. Brefeldin A blocked this CD8 induction by partial agonists, and in the case of full agonists resulted in a parallel reduction of both, TCR and CD8. Thus, antigenic stimulation of mouse T cells initially down-modulates CD8 together with TCR, but the loss of coreceptor is over-compensated by a signal for increased CD8 export.

MHC-dependent and -independent activation of human nickel-specific CD8+ cytotoxic T cells from allergic donors

T lymphocytes are critical effectors in the pathogenesis of contact hypersensitivity. Nickel is the most common contact sensitizer in humans and nickel-specific CD4+ T helper cells have been extensively characterized. Because recent observations have suggested the activation of CD8+ T cells in murine models of contact hypersensitivity, we investigated the existence of CD8+ hapten-specific T lymphocytes in patients with allergy to nickel. Nickel-specific T cell lines were generated from the peripheral blood of three allergic donors. The T cell lines were composed of a majority of CD4+ T cells, but CD8+ T cells were also present and their percentage increased with repeated in vitro stimulations. In addition to nickel-reactive helper T cell-0-type or helper T cell-2-type CD4+ T cell clones, CD8+ T cell clones could be derived from these cell lines and a total of 15 clones were further studied. Cytokine production was evaluated for 11 CD8+ T cell clones that were either cytotoxic T cell-0- or cytotoxic T cell-1-type clones. Additional effector functions were investigated on the complete panel of T cell clones. These CD8+ T cells did not only display hapten-specific proliferation, but also specific cytotoxic activities towards autologous EBV-B cells in the presence of nickel. Two different types of CD8+ T cells were characterized. Most of the clones lysed only autologous targets in the constant presence of nickel; however, one clone was able to lyse numerous targets in the presence of NiSO4, irrespective of the expression of either major histocompatibility complex class I or class II molecules. The characterization of nickel-specific cytotoxic CD8+ T cells with different requirements for nickel-specific target lysis, may have important implications in the development or in the control of human contact hypersensitivity reactions to nickel in vivo.

Further characterization of UVB radiation effects on Langerhans cells: altered expression of the costimulatory molecules B7-1 and B7-2

We have reported previously that low-dose UVB radiation (UVBR, 50-200 J/m2) perturbs the antigen-presenting cell (APC) function of murine Langerhans cells (LC) by interfering with yet undefined costimulatory signals. In this study, we investigated (1) the effects of UVBR on the expression of the costimulatory molecules B7-1 and B7-2 on murine LC, (2) the functional consequences of defective B7-1 and B7-2 signalling on primary and secondary T-cell responses induced by LC and (3) the mechanism by which UVBR interferes with B7-1 and B7-2 expression. Ultraviolet-B radiation dose-dependently inhibited the culture-induced upregulation of B7-1 and B7-2 on LC from both UVB-susceptible (UVBs, C57BL/6) and UVB-resistant (UVBR, Balb/c) mice and abrogated their capacity to stimulate proliferation of naive alloreactive T cells and of the KLH (keyhole limpet hemocyanin)-specific T helper (Th)1 clone HDK-1. The UVBR-induced suppression of B7-1 and B7-2 on LC and their perturbed APC function were related, because exogenous triggering of the B7/CD28 pathway with a stimulatory monoclonal antibody (mAb) for CD28 to UVB-irradiated LC partially restored T-cell proliferation. Such reconstitution was not observed when the mAb was added to killed LC, indicating that the UVBR-induced suppression of APC function was not due to lethal effects on LC. Conditioned supernatants from UVB-irradiated epidermal cells did not inhibit the functional upregulation of B7-1 and B7-2, suggesting that UVBR inhibits B7-1 and B7-2 upregulation by acting directly on LC and not by altering LC costimulatory function via release of soluble immunosuppressive factors. In conclusion, UVBR distorts the functional expression of B7-1 and B7-2 on LC from both UVBS and UVBR mice, thereby contributing to the failure of UVB-irradiated LC to stimulate resting alloreactive T cells or KLH-specific Th1 cells.

Molecular features of penicillin allergy

Haptens, such as drugs and other low molecular weight chemicals, become immunogenic only upon binding to proteins. Among antibiotics, penicillins are most commonly used for the treatment of bacterial infections and constitute a typical example of allergy inducing drugs in humans. Previous work on their immunologic properties focused mainly on the examination of IgE-mediated hypersensitivity reactions; however, drug-specific T cell reactions are also involved in causing a serious allergic inflammatory response. This review will focus on the interaction between antibiotic molecules and penicillin-specific T lymphocytes in humans. Experimental data accumulated so far on the reactivity of T cells with penicillin G point to penicilloyl-modified, major histocompatibility complex-associated peptides as T cell epitopes. The recognition specificity of the respective T cell receptors appears to be directed at both the backbone and the specific side chain of penicillin. In contrast, the sequence of the carrier peptides appears to contribute little to the antigenic specificity, mainly as a holder for the haptenic determinant. Finally, recent results demonstrating the capacity of penicillins to modulate, in vitro, the Th0/Th2 phenotype of established T cell clones will be presented and discussed in relation to possible therapeutic applications.

Dominance of the BV17 element in nickel-specific human T cell receptors relates to severity of contact sensitivity

Hypersensitivity to nickel (Ni) represents the most common manifestation of contact allergy in humans. The role of metal-specific T cells in this disease is well established, but the molecular interactions involved in their activation are poorly understood. We examined the T cell receptor (TCR) repertoire in T cells activated with either NiSO4 or NiSO4-treated human serum albumin from six allergic patients. For the three most hyperreactive donors, we found a strong over-representation of the TCR BV17 element. TCR sequencing for one of these donors revealed an additional skewing for AV1 as well as a selection for an N region encoded argine at position 95 of the BV17 complementarity determining region (CDR)3. Since Arg is not known to participate in Ni complexing, we suppose that this selection is driven by contacts with peptide rather than nickel. However, the CDR1 of BV17 contains a unique combination of amino acids (HDA) that bears similarities to known motifs in Ni-binding proteins or peptides. We therefore propose that the severe hypersensitivity reactions found in BV17 over-expressors may be the result of Ni2+ ions bridging the germ-line-encoded BV17 CDR1 loop to corresponding sites in the major histocompatibility complex/peptide complex and thereby creating a superantigen-like enhancement of weak TCR-peptide contacts.

Penicilloyl peptides are recognized as T cell antigenic determinants in penicillin allergy

Although hapten immune responses have been intensively studied in the mouse, very little is known about hapten determinants involved in human allergic reactions. Penicillins, as chemically reactive compounds of low molecular weight, constitute typical examples of hapten allergens for humans. Penicillins become immunogenic only after covalent binding to carrier proteins and in this form frequently induced IgE-mediated allergic reactions in patients subjected to antibiotic treatment. However, our previous data strongly indicated that penicillins also form part of the epitopes contacting the antigen receptors of beta lactam-specific T cells in allergic individuals. We have therefore investigated the molecular constraints involved in the T cell immune response to penicillin G (Pen G). Designer peptides containing a DRB1*0401-binding motif and covalently modified with Pen G via a lysine epsilon-amino group were found to induce proliferation of Pen G-specific T cell clones. A precise positioning of the hapten molecule on the peptide backbone was required for optimal T cell recognition. Furthermore, we extended these observations from our designer peptides to show that a peptide sequence derived from a natural DRB1*1101-binding peptide modified in vitro with Pen G, also acquired antigenic properties. Our data for the first time provide insight into the manner in which allergenic haptens are recognized by human T cells involved in allergic reactions to drugs and suggest possible mechanisms leading to the onset of these adverse immune responses.

Altered hapten ligands antagonize trinitrophenyl-specific cytotoxic T cells and block internalization of hapten-specific receptors

Low molecular chemicals (haptens) frequently cause T cell-mediated adverse immune reactions. Our previous work provided evidence that hapten-specific T cells, in analogy to those specific for nominal peptide antigens, direct their TCR towards hapten-modified, MHC-associated peptides. We now demonstrate that trinitrophenyl (TNP)-specific, class I MHC-restricted CTL from mice may exhibit exquisite specificity for subtle structural details of these hapten determinants, surpassing even the specificity of immunoglobulins. More importantly, these CTL could be antagonized by ligands altered either in their peptide sequence or in their hapten structure. The system was employed to examine the molecular basis of T cell antagonism. Whereas agonists resulted in a dose-dependent downregulation of TCR in different mouse T cell clones, antagonistic peptides totally failed to do so despite engaging the specific TCR. Moreover, simultaneous presentation of antagonist and agonist on the same antigen presenting cell prevented TCR internalization. No signs of anergy or functional receptor inactivation were observed in CTL treated with antagonist-loaded target cells. Based on a serial triggering model of T cell activation, our data favor a model in which antagonists block T cell functions by competitively engaging the specific TCR in unproductive interactions.

Carrier-independent hapten recognition and promiscuous MHC restriction by CD4 T cells induced by trinitrophenylated peptides

The elucidation of mechanisms underlying the recognition of haptens by class II MHC-restricted T cells is instrumental for the understanding of chemical- and drug-induced allergies. We have previously demonstrated that trinitrophenyl (TNP) peptides represent dominant antigenic epitopes for CD8+ and CD4+ mouse T cells triggered by chemically TNP-modified APC. Here, we report the characterization of TNP-specific, CD4+ mouse T cell lines and hybridomas that were induced in vivo and in vitro by defined hapten-conjugated peptides. These peptides, which we had previously shown to induce contact sensitivity to picryl chloride in vivo regardless of sequence homologies to mouse proteins, were found to activate carrier-independent TNP-specific T cells in vitro. We interpret these findings to support our view that carrier-independent T cells, reactive to particularly repetitive hapten epitopes, may play a crucial role in allergies to chemicals and drugs. In addition to carrier independence, one of our hybridomas (IT-H6/A11) exhibited a striking promiscuity of MHC restriction. Although absolutely dependent in its TNP reactivity on the presence of MHC class II molecules, the IT H6/A11 hybridoma completely ignored class II polymorphism and even reacted to TNP peptides presented on human DR molecules. Regarding hapten allergies in humans with a heterozygous situation for three types of class II molecules (DR, DP, and DQ), such promiscuous MHC restriction should lead to the presentation of even higher epitope densities to the respective T cell clones. Hybridoma IT-H6/A11, reacting to TNP independent of carrier peptide and of MHC haplotype, also allowed for an unusually systematic study of the minimal requirements for TNP recognition. Despite an almost complete ignorance of amino acid side chains on the carrier peptide, our data indicate a clearly position-specific interaction of hapten and TCR.

Carrier-independent hapten recognition and promiscuous MHC restriction by CD4 T cells induced by trinitrophenylated peptides

The elucidation of mechanisms underlying the recognition of haptens by class II MHC-restricted T cells is instrumental for the understanding of chemical- and drug-induced allergies. We have previously demonstrated that trinitrophenyl (TNP) peptides represent dominant antigenic epitopes for CD8+ and CD4+ mouse T cells triggered by chemically TNP-modified APC. Here, we report the characterization of TNP-specific, CD4+ mouse T cell lines and hybridomas that were induced in vivo and in vitro by defined hapten-conjugated peptides. These peptides, which we had previously shown to induce contact sensitivity to picryl chloride in vivo regardless of sequence homologies to mouse proteins, were found to activate carrier-independent TNP-specific T cells in vitro. We interpret these findings to support our view that carrier-independent T cells, reactive to particularly repetitive hapten epitopes, may play a crucial role in allergies to chemicals and drugs. In addition to carrier independence, one of our hybridomas (IT-H6/A11) exhibited a striking promiscuity of MHC restriction. Although absolutely dependent in its TNP reactivity on the presence of MHC class II molecules, the IT H6/A11 hybridoma completely ignored class II polymorphism and even reacted to TNP peptides presented on human DR molecules. Regarding hapten allergies in humans with a heterozygous situation for three types of class II molecules (DR, DP, and DQ), such promiscuous MHC restriction should lead to the presentation of even higher epitope densities to the respective T cell clones. Hybridoma IT-H6/A11, reacting to TNP independent of carrier peptide and of MHC haplotype, also allowed for an unusually systematic study of the minimal requirements for TNP recognition. Despite an almost complete ignorance of amino acid side chains on the carrier peptide, our data indicate a clearly position-specific interaction of hapten and TCR.

Selective activation of CD8 T cell effector functions by epitope variants of lymphocytic choriomeningitis virus glycoprotein

We provide evidence for selective activation of different effector functions of CD8+ T lymphocytes by altered peptide ligands. A T cell epitope from the glycoprotein of lymphocytic choriomeningitis virus (p33-41) and single amino acid variants thereof were used for primary in vitro induction of CTL clones. When the CTL were analyzed for cytotoxicity, proliferation, IFN-gamma production, and Ca2+ mobilization, we found that some of the clones showed activation of only their cytotoxic effector function when stimulated with variants of their inducing peptides. For one clone, cytotoxic reactivity was readily detected to the inducing peptide and three of four variants, but only the former was also able to trigger proliferation, IFN-gamma production, and Ca2+ mobilization. Another clone also revealed this dichotomy, but in this case some of the altered peptide ligands in addition to the inducing peptide were able to stimulate the full spectrum of effector functions, whereas others only stimulated cytotoxicity. A third clone revealed inefficient triggering of some effector functions by the peptide variants. Our data suggest that, as described for CD4 T cells, altered peptide ligands may lead to partial activation of effector functions of CD8 T cells. In addition, ligands with glycine substitutions in potential TCR contact positions induced CTL, which were able to recognize peptides with a variety of amino acids in the former glycine position.

Selective activation of CD8 T cell effector functions by epitope variants of lymphocytic choriomeningitis virus glycoprotein

We provide evidence for selective activation of different effector functions of CD8+ T lymphocytes by altered peptide ligands. A T cell epitope from the glycoprotein of lymphocytic choriomeningitis virus (p33-41) and single amino acid variants thereof were used for primary in vitro induction of CTL clones. When the CTL were analyzed for cytotoxicity, proliferation, IFN-gamma production, and Ca2+ mobilization, we found that some of the clones showed activation of only their cytotoxic effector function when stimulated with variants of their inducing peptides. For one clone, cytotoxic reactivity was readily detected to the inducing peptide and three of four variants, but only the former was also able to trigger proliferation, IFN-gamma production, and Ca2+ mobilization. Another clone also revealed this dichotomy, but in this case some of the altered peptide ligands in addition to the inducing peptide were able to stimulate the full spectrum of effector functions, whereas others only stimulated cytotoxicity. A third clone revealed inefficient triggering of some effector functions by the peptide variants. Our data suggest that, as described for CD4 T cells, altered peptide ligands may lead to partial activation of effector functions of CD8 T cells. In addition, ligands with glycine substitutions in potential TCR contact positions induced CTL, which were able to recognize peptides with a variety of amino acids in the former glycine position.

Cross-reactivity of T cell lines and clones to beta-lactam antibiotics

To clarify on a molecular level the specific T cell response to haptens like penicillin G, we generated T cell lines and clones from penicillin-allergic patients. Two types of beta-lactam reactivity of T cells could be delineated: one group of patients showed a rather restricted specificity, as the penicillin-elicited T cell lines generated from such donors proliferated only to the stimulating penicillin, but not to other beta-lactam antibiotics nor to cephalosporines, even if the side chain was identical. This indicates that the penicilloyl structure together with the side chain was recognized by these T cells. The second group comprised patients with more broadly reactive T cells, as they were restimulated by penicillin G as well as by related penicillins like amoxicillin or ampicillin, but not cephalosporines. This indicates that the penicilloyl structure, a common motif of penicillins, was important for T cell recognition. Clones generated from a broadly reactive patient confirmed this heterogeneity, as either monospecific or broadly specific T cell clones could be identified. This broad or very restricted pattern of T cell reactivity was reflected in the use of TCR Vbeta-chains: while the broadly reactive T cell lines showed a heterogenous TCR usage, the highly restricted T cell lines showed an up-regulation of one TCR Vbeta-chain. Thus, our data suggest that the outgrowth of T cells bearing a certain TCR Vbeta may be a sign of a limited cross-reactivity.

Cross-reactivity of T cell lines and clones to beta-lactam antibiotics

To clarify on a molecular level the specific T cell response to haptens like penicillin G, we generated T cell lines and clones from penicillin-allergic patients. Two types of beta-lactam reactivity of T cells could be delineated: one group of patients showed a rather restricted specificity, as the penicillin-elicited T cell lines generated from such donors proliferated only to the stimulating penicillin, but not to other beta-lactam antibiotics nor to cephalosporines, even if the side chain was identical. This indicates that the penicilloyl structure together with the side chain was recognized by these T cells. The second group comprised patients with more broadly reactive T cells, as they were restimulated by penicillin G as well as by related penicillins like amoxicillin or ampicillin, but not cephalosporines. This indicates that the penicilloyl structure, a common motif of penicillins, was important for T cell recognition. Clones generated from a broadly reactive patient confirmed this heterogeneity, as either monospecific or broadly specific T cell clones could be identified. This broad or very restricted pattern of T cell reactivity was reflected in the use of TCR Vbeta-chains: while the broadly reactive T cell lines showed a heterogenous TCR usage, the highly restricted T cell lines showed an up-regulation of one TCR Vbeta-chain. Thus, our data suggest that the outgrowth of T cells bearing a certain TCR Vbeta may be a sign of a limited cross-reactivity.

T cell immune responses to haptens. Structural models for allergic and autoimmune reactions

Protein-reactive chemicals, metal salts and drugs, commonly classified as immunological haptens, are major environmental noxes targeted at the immune system of vertebrates. They may not only interfere with this defense system by toxicity alone, but more often by evoking hapten-specific immune responses resulting in allergic and eventually autoimmune responses. Here, we review recent developments in the analysis of the structural basis of hapten recognition, particularly by T lymphocytes, which represent central elements in cell-mediated, as well as in IgE dependent, allergies. A break-through in this field was the finding that T cells detect haptens as structural entities, attached covalently or by complexation to self-peptides anchored in binding grooves of major histocompatibility antigens (MHC-proteins). Synthetic hapten-peptide conjugates were shown to induce hapten-specific contact sensitivity in mice, opening new routes for studying hapten-induced immune disorders.

T cell recognition of penicillin G: structural features determining antigenic specificity

Penicillin G (Pen G) and other beta-lactam antibiotics frequently induce allergic reactions constituting typical examples of human immune responses to haptens. In fact, penicillins represent a unique set of haptens with outstanding structural variability on the basis of an identical protein-reactive beta-lactam containing backbone. Although both cellular and humoral responses are involved in drug-induced allergies, little is known about the T cell reactivity to penicillins. To understand which structural features determine antigenic specificity, we isolated a panel of MHC-restricted, Pen G-reactive T cell clones from different penicillin-allergic patients and tested them for their capacity to proliferate in the presence of other penicillin derivatives. We found that the antigenic epitope consists of both the amide-linked side chain, which is different in every member of the penicillin family, as well as the thiazolidine ring common to all penicillin derivatives. We also demonstrated the presence of two different types of penicillin-specific T cells, one dependent, and the other independent of antigen processing by autologous antigen-presenting cells. Our data strongly suggest that penicillins form part of the epitopes contacting the antigen receptors of T cells.

Analysis of major histocompatibility complex class I-restricted hapten recognition by mutation of the V-J joining of T cell receptor alpha chains

Hapten-specific T cell responses are responsible for chemically induced immune disorders. However, the molecular details of hapten interactions with T cell receptors (TCR) are poorly understood. Recent studies of trinitrophenyl (TNP)-specific responses revealed major histocompatibility complex-associated TNP-peptides as dominant epitopes for CD8+ and CD4+ T cells. The present study is based on the observation that two H-2Kb/TNP-specific CTL clones (II/7 and III/1), differing exclusively in two amino acids of their TCR alpha chains, also differed in their carrier specificities for various TNP-peptides. The genes of the two alpha chains and the common beta chain were cloned into expression vectors. Transfection of the TCR alpha chain of clone III/1 into a hybridoma of clone II/7 also transferred the fine specificity of clone III/1, indicating that the small alpha chain variations were indeed responsible for the different carrier specificities. Point mutations bridging the difference between the alpha chains of clones II/7 and III/1 and functional studies of the respective TCR alpha beta transfectants into a TCR-negative hybridoma revealed an unexpected result: the two receptors did not represent examples of structural complementarity for different sets of hapten-peptide conjugates; rather, they resembled two structures of principally similar specificity but of significantly different overall affinity. This was demonstrated more directly by comparing the fine specificities of III/1 transfectants expressing or not expressing the co-receptor CD8: the CD8-negative III/1 transfectant assumed a specificity pattern indistinguishable from that of a CD8-expressing, II/7-derived transfectant. Hence, comparable alterations of antigen recognition may be induced either by subtle TCR alterations or by removal of CD8, i.e. by the presence or absence of a non-polymorphic adhesion molecule.

Characterization of processing requirements and metal cross-reactivities in T cell clones from patients with allergic contact dermatitis to nickel

Metal ions such as nickel, cobalt, copper and palladium are known to be potent sensitizers in humans, but the antigenic determinants created by these metals as well as the mechanisms of recognition by specific T cell clones are still not elucidated. In this paper, nickel-specific T lymphocyte clones were isolated from four patients exhibiting contact dermatitis to this metal. A panel of 42 independent T cell clones was studied. They were shown to recognize nickel in the context of major histocompatibility complex (MHC) class II molecules and to belong to the CD4 subset. Using fixed autologous Epstein-Barr virus-transformed B cells as antigen-presenting cells (APC), we could distinguish two distinct groups of T cell clones on the basis of processing requirements: 40% of the T cell clones were strictly processing dependent, whereas the remaining 60% could proliferate in response to nickel even in the presence of glutaraldehyde-fixed APC. Furthermore, we present arguments indicating that individual Ni-specific T cell clones cross-react with some transition metals (e.g. Cu or Pd), but not with others (e.g. Co, Cr and Pt), presented by identical MHC class II molecules. These results thus provide an explanation for the multiple metal-reactivities observed in vivo in human patients: they indicate that for Cu and Pd, these co-reactivities in vivo might be due to cross-reactivity at the clonal level. Our findings also suggest that this is not the case for cobalt allergy, which might result from cosensitization of the patient to cobalt in addition to nickel.

Carrier-reactive hapten-specific cytotoxic T lymphocyte clones originate from a highly preselected T cell repertoire: implications for chemical-induced self-reactivity

We have recently described trinitrophenyl (TNP)-specific cytotoxic T lymphocyte (CTL) clones from C57BL/6 mice specific for hapten-modified peptides bearing a TNP-lysine in a peripheral position, i.e. in position 7 of H-2Kb-bound octapeptides. CTL recognition of such determinants is always sequence-dependent due to co-recognition of TNP as well as amino acid side chains of the carrier peptide. By the use of glycine-based designer peptides for primary induction of CTL in vitro, we have identified two sub-epitopes on individual position 7-haptenated peptides that form two TcR contact points and which can be independently recognized by cloned CTL. One of these sub-epitopes is represented by the hapten itself, the other by the amino acids tyrosine and lysine in positions 3 and 4 of the carrier peptide, respectively. Immunization with such TNP-modified peptides frequently results in the specific induction of CTL also reacting with the unmodified carrier peptides. DNA sequence analyses of the TcR revealed an extraordinary similarity of several independent TcR of CTL from individual mice and induced with different TNP-peptides. These receptor similarities clearly correlate with structural elements common to the immunizing peptides and suggest their origin from positive thymic selection of TcR on Kb-associated associated self-peptides bearing Tyr in position 3. Our data provide additional information concerning the topology of TcR binding to peptide/MHC complexes with, but also without, TNP. They also indicate a mechanism which might explain the potential of chemicals or drugs to induce autoimmune phenomena.

Cross-reactive trinitrophenylated peptides as antigens for class II major histocompatibility complex-restricted T cells and inducers of contact sensitivity in mice. Limited T cell receptor repertoire

The induction of contact sensitivity in mice by hapten reagents such as trinitrochlorobenzene (TNCB) involves the activation of class II major histocompatibility complex (MHC)-restricted, hapten-specific, CD4+ T cells. Reports from different laboratories have indicated that the relevant antigenic epitopes in such reactions might include hapten-conjugated, MHC class II-associated peptides. This study for the first time directly demonstrates that hapten-peptides account for the majority of determinants recognized by trinitrophenyl (TNP)-specific CD4+ T lymphocytes. The sequences of those TNP carrier peptides do not have to be related to mouse proteins. Thus, we show that TNP-modified peptides derived from mouse IgG, pigeon cytochrome c or staphylococcal nuclease known to bind to I-Ab or from lambda repressor with specificity to I-Ad as well as TNP-proteins such as bovine serum albumin, ovalbumin or keyhole limpet hemocyanin all create class II-restricted hapten determinants for a number of TNP-specific T cell clones and hybridomas. All of these cells were induced with cells modified by trinitrobenzene sulfonic acid (TNBS). In addition, we present arguments indicating that individual TNP-specific helper T cells may cross-react with different TNP-peptides bound to identical class II molecules. Chemical treatment of antigen-presenting cells with TNCB or TNBS may thus result in a limited number of particularly repetitive immunodominant hapten epitopes. Immunodominant epitopes were also indicated by an overrepresentation of the TCR elements V beta 2 and V alpha 10 in I-Ab/TNP-specific T cells. Most importantly, however, we demonstrate that TNP attached to lysine 97 in the staphylococcal nuclease peptide 93-105 (i.e. a clearly "non-self" sequence) is able to prime mice for subsequent elicitation of contact sensitivity by TNCB in the absence of foreign protein. We take this to indicate that those TNP-peptide determinants defined by us as immuno-dominant are responsible for the induction of contact sensitivity to haptens.

T cell recognition of haptens, a molecular view

Our review attempts to summarize the present knowledge on how T lymphocytes recognize chemically modified autologous cells. Concerning the broad spectrum of chemically and drug-induced allergic and autoimmune diseases, the molecular mechanisms of hapten recognition by T cells are clearly of more than academic interest. The past few years revealed that in contrast to the expectations of many researchers, major histocompatibility complex (MHC)-restricted hapten-specific T cell receptors in their majority do not react to covalently modified MHC molecules, but to haptenized peptides associated with the MHC peptide-binding groove. This finding allowed the introduction of synthetic hapten-peptide conjugates, the MHC specificity of which may be predetermined by allele-specific peptide sequence motifs. Thus, it has now become feasible to selectively hapten-modify defined sets of MHC molecules on living cells, and to study their immunological properties. In that way two major types of hapten-specific T cell receptors were identified: one reacting to hapten without caring for the chemical composition of the carrier peptide, and the other contacting hapten and peptide by two apparently independent contact sites. The consequences of these findings for hapten-specific allergies and autoimmunities, but also for our molecular understanding of antigen recognition by T cells are discussed.

Intracellular processing of hapten-modified protein for MHC class I presentation: cytoplasmic delivery by pH-sensitive liposomes

Phagocytic or endocytic uptake of pH-sensitive liposomes has been shown to result in the release of entrapped material into the cytosol. This system can therefore be applied to the targeted delivery of protein antigens into the MHC class I presentation pathway of antigen-processing cells. We have used trinitrophenyl (TNP)-modified chicken ovalbumin encapsulated in liposomes to examine the intracellular processing of haptenated proteins and the presentation of TNP-modified peptides to MHC class I-restricted hapten-specific CTL. Here, we demonstrate for the first time that hapten-modified proteins can undergo intracellular processing by macrophages, that similar peptides are produced in the form of unmodified or haptenated derivatives, and that TNP-peptides are transported to the cell surface and presented to class I-restricted CTL via the ER/Golgi pathway. This system can now be used to study T-cell responses to naturally processed hapten-conjugated peptides in vitro and in vivo.

Molecular analysis of the T-cell receptor V beta 5 and V beta 8 repertoire in pancreatic lesions of autoimmune diabetic NOD mice

The repertoire of V beta 5 and V beta 8 T-cell receptors in pancreatic lesions of autoimmune diabetic NOD mice was analysed by sequencing the CDR3 and adjacent regions. T-cell receptor mRNA isolated from four different cell populations (i.e. spleen, lymph node, infiltrated islets from male and female NOD mice) was amplified by PCR and cloned; out of these, 339 clones were sequenced. Of 170 beta chains sequenced from intra-islet T cells, nearly 90% were unique and six other sequences were found 2 to 4 times. These data argue against any oligoclonality of the islet infiltrate. Despite the lack of clonal restriction, we observed a bias in TcR usage which indicates the existence of some selective pressure with regard to TcR structure. Of the V beta 5 positive cells, 30% to 40% showed a rearrangement of V beta 5 to J beta 2.6 and a complete lack of V beta 5-J beta 1.6 combination. The selective J beta usage was not restricted to islets but was found in all tissues analysed. V beta 8 positive cells did not show such an overrepresentation of V beta-J beta combinations with the exception of clones of infiltrated islets of partially diabetes-resistant male NOD mice. There the rearrangement of V beta 8-J beta 1.1 was markedly over-expressed. Analysis of the CDR3 region did not show selection of specific TcR with regard to region length. However, we found a restricted use of amino acids in the second position of the CDR3 region. V beta 8 chains had conserved an aspartic acid from the germline configuration in about half of the cases in all tissues analysed. V beta 5 chains also showed diversity of position 2 but not islet specificity of rearrangements. Mutated chains had a clear bias towards proline indicating selective pressure in favour of this amino acid. In conclusion, sequence analysis of V beta 5 and V beta 8 TcRs excludes oligoclonality of T-cell receptors in pancreatic lesions. The bias found for J beta usage and CDR3 structure was seen also in extra-pancreatic tissues and thus probably is due to selective pressure during T-cell maturation in thymus or periphery.

Structural complexity of antigenic determinants for class I MHC-restricted, hapten-specific T cells. Two qualitatively differing types of H-2Kb-restricted TNP epitopes

The understanding of chemically induced allergic or autoimmune disorders requires a detailed structural analysis of the antigenic determinants produced by chemical modification of cells. Using H-2Kb-restricted, TNP-specific cytotoxic mouse T cells and synthetic, Kb-associating TNP-peptides, we define at least two types of functionally distinguishable TNP epitopes. The first one contains TNP in position 4 of different Kb-binding octapeptides and is detected by the majority of in vitro-induced TNP/Kb-specific CTL. This immunodominant structure could be imitated by oligo-glycine based "designer peptides," containing only the Kb "anchor-residues" and TNP-Lys in position 4. A second, qualitatively different determinant is created by TNP-Lys in position 7. T cells of such specificity are rare and recognize TNP only in context of unique peptide sequences. In this case, designer peptides revealed a complex antigenic determinant comprised of TNP-7 and unmodified amino acids in positions 3 and 4. Chances to form a particular determinant of this type by chemical modification are small and, thus, each clone will detect only few epitopes per cell. In contrast, the dominant TNP-4 epitope on differing peptides results in highly repetitive determinants. TCR specific for the rare TNP-7 structure were found to simultaneously contact TNP in position 7 and unmodified amino acids in positions 3 and 4. However, they may also react individually with either the peptide or the hapten part of these complex determinants. This implies a potentially important role of such structures in the induction of autoimmunities: resting T cells, bearing low affinity receptors to self peptides may be activated by peptide/hapten complexes and allow recall responses to the isolated peptide epitope of the unmodified self peptide.

Structural complexity of antigenic determinants for class I MHC-restricted, hapten-specific T cells. Two qualitatively differing types of H-2Kb-restricted TNP epitopes

The understanding of chemically induced allergic or autoimmune disorders requires a detailed structural analysis of the antigenic determinants produced by chemical modification of cells. Using H-2Kb-restricted, TNP-specific cytotoxic mouse T cells and synthetic, Kb-associating TNP-peptides, we define at least two types of functionally distinguishable TNP epitopes. The first one contains TNP in position 4 of different Kb-binding octapeptides and is detected by the majority of in vitro-induced TNP/Kb-specific CTL. This immunodominant structure could be imitated by oligo-glycine based "designer peptides," containing only the Kb "anchor-residues" and TNP-Lys in position 4. A second, qualitatively different determinant is created by TNP-Lys in position 7. T cells of such specificity are rare and recognize TNP only in context of unique peptide sequences. In this case, designer peptides revealed a complex antigenic determinant comprised of TNP-7 and unmodified amino acids in positions 3 and 4. Chances to form a particular determinant of this type by chemical modification are small and, thus, each clone will detect only few epitopes per cell. In contrast, the dominant TNP-4 epitope on differing peptides results in highly repetitive determinants. TCR specific for the rare TNP-7 structure were found to simultaneously contact TNP in position 7 and unmodified amino acids in positions 3 and 4. However, they may also react individually with either the peptide or the hapten part of these complex determinants. This implies a potentially important role of such structures in the induction of autoimmunities: resting T cells, bearing low affinity receptors to self peptides may be activated by peptide/hapten complexes and allow recall responses to the isolated peptide epitope of the unmodified self peptide.

Purified MHC class I molecules present hapten-conjugated peptides to TNP/H-2Kb-specific T cell hybridomas

Several trinitrophenyl (TNP)-specific mouse cytotoxic T cell (CTL) clones recognize TNP-conjugated peptides in association with class I MHC Kb-molecules. Here we show that CD8+ T cell hybridomas derived from these CTL exhibit the same pattern of antigen-specificity as their parent CTL-clones. These T cell hybridomas reacted with TNBS- or TNP-peptide modified syngeneic target cells, and also with affinity purified, immobilized Kb-molecules preloaded with TNP-peptides. These findings demonstrate most directly that MHC-associated, haptenated peptides create functional antigenic epitopes for TNP-specific CTL. Furthermore, using purified Kb-molecules and a panel of Kb-binding TNP-conjugated peptides, we demonstrated that the epitope density is a critical factor in triggering these T cell hybridomas. Chemical modification of immobilized Kb-layers resulted in poor antigenicity, implying low epitope density and therefore arguing against covalent MHC-haptenization as a major source of T cell antigenic determinants.

Role of hapten-anchoring peptides in defining hapten-epitopes for MHC-restricted cytotoxic T cells. Cross-reactive TNP-determinants on different peptides

Synthetic hapten-peptide conjugates selectively modify cell-bound MHC class I molecules in a haplotype-specific way. We investigated the contribution of the carrier peptides to the structural specificity of T cell-antigenic TNP epitopes, using different H-2Kb-binding TNP-peptides and a collection of TNP/Kb-specific CTL clones. Adjustment of peptide sequences to the proposed Kb-specific "motif" (octamers with F or Y and L in positions 5 and 8, respectively) enhanced Kb-binding and antigenicity by many orders of magnitude. Moreover, several clones reacted to peptides, containing the "motif" and TNP-lysine in position 4 but were otherwise unrelated by sequence. TNP in other positions was not recognized by these cells, but other CTL reacted to TNP in position 7. This points to the positioning of hapten determinants within the MHC binding groove as a major role of the anchoring peptide. However, determination of the limiting amounts of TNP peptides that elicit antigenicity or inhibit other Kb-restricted CTL reactions revealed that TCR also recognize variations in the sequences of carrier peptides. This contribution is low for TNP in position 4 but high in position 7, indicating lysine in position 4 as a particularly dominant and cross-reactive hapten-anchoring site in Kb-associated peptides. This implies that cell modification with lysine-reactive TNP reagents results in immunodominant, highly repetitive TNP epitopes, which may explain the strong antigenicity and the allergenic properties of TNP, as well as the restricted TCR repertoire directed against this hapten. Our data further recommend hapten peptides for general studies of TCR-Ag interactions because in contrast to pure protein Ag, hapten epitopes tolerate substantial structural variations in the MHC-anchoring peptide, and can be located by hapten-specific antibodies.

Role of hapten-anchoring peptides in defining hapten-epitopes for MHC-restricted cytotoxic T cells. Cross-reactive TNP-determinants on different peptides

Synthetic hapten-peptide conjugates selectively modify cell-bound MHC class I molecules in a haplotype-specific way. We investigated the contribution of the carrier peptides to the structural specificity of T cell-antigenic TNP epitopes, using different H-2Kb-binding TNP-peptides and a collection of TNP/Kb-specific CTL clones. Adjustment of peptide sequences to the proposed Kb-specific "motif" (octamers with F or Y and L in positions 5 and 8, respectively) enhanced Kb-binding and antigenicity by many orders of magnitude. Moreover, several clones reacted to peptides, containing the "motif" and TNP-lysine in position 4 but were otherwise unrelated by sequence. TNP in other positions was not recognized by these cells, but other CTL reacted to TNP in position 7. This points to the positioning of hapten determinants within the MHC binding groove as a major role of the anchoring peptide. However, determination of the limiting amounts of TNP peptides that elicit antigenicity or inhibit other Kb-restricted CTL reactions revealed that TCR also recognize variations in the sequences of carrier peptides. This contribution is low for TNP in position 4 but high in position 7, indicating lysine in position 4 as a particularly dominant and cross-reactive hapten-anchoring site in Kb-associated peptides. This implies that cell modification with lysine-reactive TNP reagents results in immunodominant, highly repetitive TNP epitopes, which may explain the strong antigenicity and the allergenic properties of TNP, as well as the restricted TCR repertoire directed against this hapten. Our data further recommend hapten peptides for general studies of TCR-Ag interactions because in contrast to pure protein Ag, hapten epitopes tolerate substantial structural variations in the MHC-anchoring peptide, and can be located by hapten-specific antibodies.

Peptide-conjugated hapten groups are the major antigenic determinants for trinitrophenyl-specific cytotoxic T cells

Several trinitrophenyl (TNP)-specific mouse cytotoxic T cell (CTL) clones recognize TNP-conjugated peptides in association with class I MHC molecules ('hapten-peptide determinants'). However, cell modification with trinitrobenzene sulfonic acid (TNBS) also leads to the formation of TNP determinants covalently attached to MHC molecules ('altered self'). To determine the importance of 'peptide' versus 'altered self' determinants, we used the mutant cell line RMA-S which expresses peptide-free ('empty') Kb and Db molecules at 26 degrees C. Additionally, we stabilized Kb molecules on RMA-S cells at 37 degrees C using the Kb binding heptapeptide N53-59 derived from the vesicular stomatitis virus nucleoprotein. Lacking lysine, this peptide remains unmodified by TNBS and, therefore, only allows the formation of 'altered self' TNP determinants on occupied Kb molecules. RMA-S targets, pretreated or untreated with N53-59, upon TNBS modification were only lysed poorly or not at all by four different TNP-specific CTL. In contrast, all of these clones efficiently lysed TNBS-treated, unmutated RMA cells, and three of them strongly reacted with RMA or RMA-S cells in the presence of tryptic TNP-BSA peptides. Moreover, the clone unreactive for TNP-BSA peptides also recognized TNP self-peptides extracted from TNBS-treated syngeneic spleen cells. Taken together, these data clearly show that TNP residues linked to MHC via associated peptides but not by covalent bondage represent the dominant antigenic epitopes for class I MHC-restricted, hapten-specific T cells.

Synthetic peptides anchor T cell-specific TNP epitopes to MHC antigens

Several TNP-specific, H-2Kb-restricted mouse CTL clones were identified which specifically lysed target cells in the presence of tryptic digests of TNP-modified BSA. Glutaraldehyde fixation of cells revealed that the tryptic fragments did not require further cellular processing. Chromatographic fractionation of digested TNP-BSA identified the peptide TNP-BSA222-231, containing a TNP-modified lysine at BSA position 227, as the antigenic entity. The corresponding synthetic peptide was immunologically cross-reactive with the digest. All clones reactive with TNP-BSA222-231 cross-reacted with a similar peptide from mouse serum albumin (TNP-MSA126-135), favoring the assumption that TNP-BSA222-231 represents an artificial determinant, cross-reacting with some as yet unidentified, TNP-modified, Kb-associated self-peptides. Some of our clones also cross-reacted with tryptic digests of TNP-OVA or TNP-keyhole limpet hemocyanin. We interpret these findings to indicate that 1) a significant proportion of hapten (TNP) determinants for T cells are anchored to MHC via peptides; and 2) the amino acid sequence of these peptides may only partly define the specificity of the T cell-relevant hapten epitope, implying a particularly repetitive nature of these determinants. The production of T cell-antigenic hapten-peptide conjugates will hopefully open new roads to study immune responses to environmental allergens.

Antigen contact sites in class I major histocompatibility complex-restricted, trinitrophenyl-specific T cell receptors

Cloned trinitrophenyl (TNP)-specific cytotoxic T cells (CTL) were obtained from mice transgenic for the beta chain of the antigen-specific receptor (TcR) of a Kb-restricted, TNP-specific CTL clone (BT7.4.1). The transgene-expressing CTL, specific for TNP/Kb were found to select for TcR alpha chains highly similar to that of the transgene donor clone BT7.4.1. In that way, two clones (II/7 and III/1) were identified whose TcR differed from the BT7.4.1 receptor only in their N alpha- and J alpha-sequences, i.e. within the third complementarity-determining regions of their alpha chains (CDR3 alpha). Moreover, the TcR of clones II/7 and III/1 had both rearranged the same J alpha element, thus differing from each other by only two amino acids in their V alpha/J alpha junctional regions. Functionally, however, clone III/1 exhibited unique cytolytic specificities for synthetic, Kb-binding TNP-peptides as well as for chemically TNP-modified allogeneic (H-2k) target cells. These findings demonstrate that (a) similar to "conventional" peptide antigens, synthetic hapten-peptide determinants are contacted by CDR3 alpha-determined amino acids of the TcR and (b) in contrast to current models, CDR alpha also appears to influence the major histocompatibility complex restriction specificity of a given TcR.

Synthetic peptides anchor T cell-specific TNP epitopes to MHC antigens

Several TNP-specific, H-2Kb-restricted mouse CTL clones were identified which specifically lysed target cells in the presence of tryptic digests of TNP-modified BSA. Glutaraldehyde fixation of cells revealed that the tryptic fragments did not require further cellular processing. Chromatographic fractionation of digested TNP-BSA identified the peptide TNP-BSA222-231, containing a TNP-modified lysine at BSA position 227, as the antigenic entity. The corresponding synthetic peptide was immunologically cross-reactive with the digest. All clones reactive with TNP-BSA222-231 cross-reacted with a similar peptide from mouse serum albumin (TNP-MSA126-135), favoring the assumption that TNP-BSA222-231 represents an artificial determinant, cross-reacting with some as yet unidentified, TNP-modified, Kb-associated self-peptides. Some of our clones also cross-reacted with tryptic digests of TNP-OVA or TNP-keyhole limpet hemocyanin. We interpret these findings to indicate that 1) a significant proportion of hapten (TNP) determinants for T cells are anchored to MHC via peptides; and 2) the amino acid sequence of these peptides may only partly define the specificity of the T cell-relevant hapten epitope, implying a particularly repetitive nature of these determinants. The production of T cell-antigenic hapten-peptide conjugates will hopefully open new roads to study immune responses to environmental allergens.

Increased frequency of 2,4,6-trinitrophenyl (TNP)-specific, H-2b-restricted cytotoxic T lymphocyte precursors in transgenic mice expressing a T cell receptor beta chain gene from an H-2b-restricted, TNP-specific cytolytic T cell clone

T cell antigen receptors (TcR) expressing V alpha 10/J alpha BBM142 genes in association with beta chains containing J beta 2.6 elements were found to be predominant among 2,4,6-trinitrophenyl (TNP)-specific, H-2b-restricted cytolytic T cell lines (CTL). To assess the relative contribution of the TcR beta chain to the TNP specificity as well as to the selection of the respective TcR alpha chain elements we generated transgenic mice expressing the TcR beta chain of the H-2b/TNP-specific CTL clone BT7.4.1. The TcR of this clone does not belong to the type predominant among H-2b/TNP-specific CTL, as it consists of an alpha chain encoded by a V alpha 8/J alpha DO gene rearrangement and a V beta 2/J beta 1.1-containing beta chain. In the transgenic mice almost all T cells exclusively express the transgenic V beta 2 gene, as a result of allelic exclusion. TNP-specific, H-2b-restricted precursors were found at 7- to 8-fold higher frequency in these mice as compared with non-transgenic littermates. In H-2b/d heterozygous transgenic mice, an increased frequency of TNP-specific precursors was found only in H-2b, but not in H-2d-restricted CTL. Analysis of H-2b/TNP-specific CTL lines derived from V beta 2-transgenic mice indicated a preferential association of the transgenic TcR beta chain with endogenous alpha chains encoded by V alpha 8 and J alpha BBM142 genes. This suggests that the hapten TNP is recognized like typical peptide antigens by combinatorial TcR alpha and beta contact sites.

Predominant T cell receptor gene elements in TNP-specific cytotoxic T cells

H-2b class I-restricted, TNP-specific CTL clones were obtained by limiting dilution cloning of either short term polyclonal CTL lines or spleen cells of TNP-immunized mice directly ex vivo. Sequence analyses of mRNA coding for TCR alpha- and beta-chains of 11 clones derived from CTL lines from individual C57BL/6 mice revealed that all of them expressed unique but clearly nonrandom receptor structures. Five alpha-chains (45%) employed V alpha 10 gene elements, and four of those (36%) were associated with J beta 2.6-expressing beta-chains. The alpha-chains from these four TCR, moreover, contained an acidic amino acid in position 93 of their N or J region-determined sequences. Clones isolated directly from spleen cells carried these types of receptors at lower frequency, 27% V alpha 10 and 19% J beta 2.6, indicating that bulk in vitro cultivation on Ag leads to selection for these particular receptors. However, even in TNP-specific CTL cloned directly ex vivo, V alpha 10 usage was increased about fivefold over that in Ag-independently activated T cells in H-2b mice (4 to 5%). The selection for V alpha 10/J beta 2.6-expressing cells was obtained repeatedly in other TNP-specific CTL lines from C57BL/6 mice but not in FITC-specific CTL from the same strain or in TNP-specific CTL lines from B10.BR (H-2k) or B10.D2 (H-2d) mice. We conclude from this (a) that the selection for V alpha 10/J beta 2.6+ T cells is driven by the complementarity of these receptors to a combination of TNP and MHC epitopes and (b) that predominant receptor structures reflect the existence of a surprisingly limited number of "T cell-relevant" hapten determinants on the surface of covalently TNP-modified cells.

Predominant T cell receptor gene elements in TNP-specific cytotoxic T cells

H-2b class I-restricted, TNP-specific CTL clones were obtained by limiting dilution cloning of either short term polyclonal CTL lines or spleen cells of TNP-immunized mice directly ex vivo. Sequence analyses of mRNA coding for TCR alpha- and beta-chains of 11 clones derived from CTL lines from individual C57BL/6 mice revealed that all of them expressed unique but clearly nonrandom receptor structures. Five alpha-chains (45%) employed V alpha 10 gene elements, and four of those (36%) were associated with J beta 2.6-expressing beta-chains. The alpha-chains from these four TCR, moreover, contained an acidic amino acid in position 93 of their N or J region-determined sequences. Clones isolated directly from spleen cells carried these types of receptors at lower frequency, 27% V alpha 10 and 19% J beta 2.6, indicating that bulk in vitro cultivation on Ag leads to selection for these particular receptors. However, even in TNP-specific CTL cloned directly ex vivo, V alpha 10 usage was increased about fivefold over that in Ag-independently activated T cells in H-2b mice (4 to 5%). The selection for V alpha 10/J beta 2.6-expressing cells was obtained repeatedly in other TNP-specific CTL lines from C57BL/6 mice but not in FITC-specific CTL from the same strain or in TNP-specific CTL lines from B10.BR (H-2k) or B10.D2 (H-2d) mice. We conclude from this (a) that the selection for V alpha 10/J beta 2.6+ T cells is driven by the complementarity of these receptors to a combination of TNP and MHC epitopes and (b) that predominant receptor structures reflect the existence of a surprisingly limited number of "T cell-relevant" hapten determinants on the surface of covalently TNP-modified cells.

Reactivity of V beta 17a+ CD8+ T cell hybrids. Analysis using a new CD8+ T cell fusion partner

Tolerance to IE molecules leads to deletion of V beta 17a-bearing T cells. Both, the CD4+ as well as the CD8+ T cell subsets are affected. A large percentage of CD4+ V beta 17a+ T cell hybrids recognize IE molecules. We now have investigated the reactivity for IE antigens of CD8+ V beta 17a+ T cell hybrids. Using a transfection approach, we have introduced the murine CD8 molecule into different V beta 17a+ T cell hybrids. Furthermore, the CD8 cDNA was transfected into the BW5147 alpha-beta- fusion partner. This allowed us to generate a large number of V beta 17a+ T cell hybrids by fusion with the appropriate T cells. Only 6% of T cell hybrids were stimulated to produce IL-2 upon incubation with IE+ cells. However, in those, the CD8 molecule seemed not to contribute to the IE reactivity of the hybrid, since mAbs against the CD8 molecule failed to inhibit their reactivity. This low percentage of V beta 17a+ CD8+ IE-reactive T cell hybrids contrasts with the strong reduction of CD8+ V beta 17a+ T cells in IE+ mice, strongly suggesting that elimination of such cells in the thymus occurs when they are coexpressing CD4 and CD8. This view was confirmed by the occasional expression of CD4 in some hybrids in which case IE reactivity was detected. Furthermore, we demonstrated the functional integrity of the introduced CD8 molecule by: (a) reconstitution of the IL-2 response in a class I-restricted TNP-specific T cell hybrid; and (b) by generation of alloreactive class I-restricted T cell hybrids using the new CD8+ fusion cell line. This CD8+ fusion partner, BWLyt2-4, should prove useful to study antigen processing and antigen presentation requirements of class I-restricted T cells.

Stabilization of detergent-solubilized Ca2+-ATPase by poly(ethylene glycol)

The (Ca2+ + Mg2+)-ATPase from sarcoplasmic reticulum (SR) has been solubilized with 1-alkanoyl propanediol-3-phosphorylcholines with chainlengths ranging between 8 and 12 C atoms. A marked dependence of the ATPase activity upon the chainlength was found, indicating that alkyl chainlengths with 12 C atoms are necessary for retention of activity. Addition of poly(ethylene glycol) to the eluting buffers used for gel filtration of the ATPase-detergent micelles was found to increase the activity and the long-term stability significantly. In the presence of Ca2+, the elution volume indicated an ATPase dimer, whereas in the absence of Ca2+ the elution volume indicated a monomeric solution. The purity of the preparations after gel filtration was improved by subsequent chromatography with a hydroxyapatite column.

Growth-dependent variation of major histocompatibility complex (MHC) restriction and expression of Ly-2 and CD3/alpha/beta T cell receptor in cloned cytotoxic T cells

The specificity of major histocompatibility complex (MHC)-restricted antigen recognition by cytotoxic T cells (CTL) has been clearly correlated to the alpha/beta T cell receptor (TcR) complex on the T cell surface. Occasional changes in the specificity of in vitro cultivated CTL clones, therefore, have been suspected to result from alterations of the genes coding for the TcR alpha and/or beta chain. Here we demonstrate that pronounced variations in the stringency of MHC restriction, previously reported to occur during long-term culture of 2,4,6-trinitrophenyl (TNP)-specific CTL clones, may occur rapidly in a growth-dependent, reversible manner, i.e. without structural TcR variation. Several H-2b TNP-specific CTL clones were shown to possess strong cross-reactivity for H-2k TNP target cells when seeded at low cell numbers, but exhibit reduced or undetectable cross-reaction to H-2k TNP in high-density cultures. Another clone revealed "heteroclitic" properties with significantly stronger cytotoxic activity towards allogeneic (H-2k) than syngeneic (H-2b) TNP-modified target cells. In this case dilute cultures appeared as exclusively allo-MHC restricted, whereas dense cultures were allo/self cross-restricted. In all instances these phenomena were accompanied by cell density-dependent quantitative changes in the expression of Ly-2 and T cell antigen receptor. CTL from dilute cultures had at least 2-fold higher surface concentrations of Ly-2 and CD3 antigens than cells from dense cultures while other surface markers such as Thy-1 or LFA-1 were completely identical. No such effects were observed for CTL clones exhibiting cell density-independent specificity patterns. We conclude from these findings that (a) the stringency of MHC restriction specificity may be significantly affected by the amount of expressed TcR and/or Ly-2 molecules, (b) CTL possess mechanisms to regulate Ly-2 and TcR expression and, hence, their MHC-restricted antigen recognition, and (c) the ability to regulate Ly-2 and TcR expression may be altered during prolonged culture of a CTL clone.

Dominance of one T-cell receptor in the H-2Kb/TNP response

T-cell receptors (TCRs) recognize foreign antigens in the context of major histocompatibility complex (MHC)-encoded cell surface proteins. These receptors are heterogeneous, dimeric glycoproteins composed of disulphide linked alpha- and beta-chains. We analysed the diversity of TCRs in a collection of H-2Kb-restricted, 2,4,6-trinitrophenyl (TNP)-specific (H-2Kb/TNP) cytotoxic T-cell (Tc) clones from C57BL/6 mice. Investigation of the beta-chain messenger RNAs revealed that nearly half of these independent clones expressed an identical beta-chain gene. We show here that almost all the Tc clones expressing the predominant beta-chain gene also express an identical alpha-chain gene. These results show that a strong selective pressure acted on the Tc population, resulting in a skewing of the TCR repertoire for H-2Kb/TNP and in the dominant expression of one TCR with this specificity. Possible explanations for this skewing include antigen-driven clonal expansion and network interactions.

Loss of antigen recognition and impaired cytolytic function in most hybrids between cytotoxic T cells and BW5147

In this paper we demonstrate that the generation of cytotoxic T-cell hybridomas (CTH) that retain classically H-2 restricted and antigen-specific lytic activity is not generally feasible by fusion of cytotoxic T cells (CTL) with the AKR thymoma BW5147. However, CTH that express a nonspecific lytic activity are readily generated, as revealed by lectin-dependent assays. We analyse several such hybridomas for the nature of their lytic activity and for the expression of various function-associated T-cell molecules. We show that the lytic activity retained by CTH is atypical in that only P815 mastocytoma cells, and no other tumour targets, are lysed in the presence of phytohaemagglutinin (PHA). However, in other respects this lytic activity resembles that of normal CTL: it requires cellular contact, results in a reduction of the viability of the target cells, and is sensitive to both EDTA and low temperature. Lytic CTH express low amounts of T-cell antigen receptor (TCR), whereas non-lytic CTH have no detectable TCR on their surface. Most CTH, lytic or non-lytic, fail to express Lyt 2. We conclude that the loss of antigen specificity in CTH is due to reduced expression of T-cell antigen receptor as well as of other functionally relevant molecules. We further conclude from this work that a search for a better fusion partner may be indicated to facilitate the reliable production of cytotoxic T-cell hybridomas.

Preferential expression of a defined T-cell receptor beta-chain gene in hapten-specific cytotoxic T-cell clones

A multitude of different antigens can be recognized by T cells through specific receptors. Both the alpha- and beta-chains of the T-cell receptor contribute to the antigen recognition portion. The repertoire of beta-chain variable region (V beta) gene segments is limited to some 20 elements which seem to be used randomly in different T cells. Diversity at the beta-chain level can be created in several ways: a multiplicity of germline gene segments; combinatorial diversity by rearranging different V, diversity (D), joining (J) and constant (C) region elements; junctional diversity by joining gene segments at different sites; N-region diversity, that is, insertion of random nucleotides at junctional sites; and somatic mutation. However, the major sources and the extent of diversity of the T-cell receptor are unclear. To address this issue, 42 H-2Kb-restricted, 2,4,6-trinitrophenyl (TNP)-specific cytotoxic T-cell (Tc) clones from C57BL/6 mice were characterized with respect to expression of different beta-chain gene segments in messenger RNA using specific oligonucleotide probes. We report here that nearly half of the Tc clones use identical elements for productive beta-chain gene rearrangement. Thus, there is a restriction in the use of beta-chain gene segments in this panel of Tc clones which favours a particular V beta--D beta--J beta--C beta combination with a defined D beta element.

Hapten-specific cytotoxic T cell clones undergo somatic variation of their antigen recognition specificity

Two experimental systems have demonstrated somatic variation of antigen recognition specificity of long-term cytotoxic T cell (CTL) clones. System 1 used CTL clone BT7.4.1 with strict specificity for Kb/TNP, which had been continuously cultured for 15 months in the presence of H-2b/TNP stimulator cells and interleukin 2. Upon removal of the TNP antigen from the cultures, 99% of the clone cells within about 10 cell divisions lost their ability to grow in the presence of antigen and interleukin 2 (lethal variants). Of the surviving 1%, about 60% retained the ability to lyse target cells in the presence of lectins but only 12% could be considered as "wild type" BT7.4.1 cells, i.e. they still specifically lysed H-2b/TNP-bearing target cells. The majority of the growing cells, thus, had to be considered as specificity loss variants. Several specificity loss variants were established in culture and were shown to express membrane-bound T cell "receptor" heterodimer similar to their TNP-specific ancestor, BT7.4.1. Principally the same types of variants were generated in cultures growing in the presence of TNP antigen, although in quantitatively reduced numbers. Under these conditions the specific stimulator cells appeared to impose a significant selective advantage for "wild type" CTL since even after 15 months the cultures fully retained their specificity for the nominal antigen. In system 2, the development of cytolytic fine specificity of a panel of 42 individual Kb/TNP-specific CTL clones was followed over a period of 8 months of in vitro culture. At the beginning of the test, 37 of these clones exhibited significant cross-reactivity for lysis of H-2k/TNP target cells. This number of cross-reactive clones continuously diminished with time and dropped to only 4 clones after 8 months in culture. All 42 clones retained their original Kb/TNP specificity and after losing their reactivity for H-2k/TNP usually showed no decrease but rather an increase in their cytotoxic activity towards Kb/TNP target cells. Loss of H-2k/TNP cross-reactivity was not accompanied by loss of Lyt-2 or of LFA-1 surface antigens or by loss of sensitivity of the cytotoxicity to inhibition by anti-Lyt-2 or by anti-LFA-1 antibody. We conclude from these observations that in vitro cultivated CTL clones, at least those of C57BL/6 anti-TNP-C57BL/6 specificity, are not stable in terms of their antigen recognition specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Involvement of the T cell antigen receptor and of Lyt-2 in the cytotoxic function of aged killer (AK) T cells

Aged killer (AK) T cells are antigen-independent, IL-2-requiring variants of antigen-dependent CTL clones that have lost their original antigen specificity and have acquired, instead, specific cytotoxicity for P815 target cells. In this report we study whether AK cells use a similar or a different target cell recognition system than that of bona fide CTL. To this end, we selected from a cloned AK line variants that are partially or completely deficient in specific target recognition and/or in cytotoxic function, and analyzed these variants for expression of the T cell antigen receptor and of Lyt-2. Variants were selected from the prototype AK line (Cl 96) with specific, as well as lectin-facilitated, cytotoxicity for P815 tumor cells. Variants could be grouped into four types with increasing degrees of functional deficiency, which correlated with loss of T cell receptor and/or loss of Lyt-2. In short, loss of Lyt-2 was reflected in loss of specific target recognition, and loss of the T cell antigen receptor was reflected in loss of all cytotoxic activity. We conclude from these results that both Lyt-2 and the T cell antigen receptor are required for specific target cell recognition and the T cell antigen receptor is, in addition, required for cytotoxic function. Moreover, since AK cells express a somatically acquired specificity that differs from that of their clonal precursors, it appears that cytotoxic T cells may change their antigen receptor from one specificity to another during tissue culture.