T helper cells recognize an idiotope located on peptide 88-114/117 of the light chain variable domain of an isologous myeloma protein (315)

Isolated variable region light chain 315 (VL-315), the VL domain of a myeloma protein of BALB/c origin, induces T cells of BALB/c (H-2d) mice that help the adoptive secondary anti-4-hydroxy-3-iodo-5- nitrophenylacetyl (NIP) antibody response to NIP-Fab315. The location of the epitope recognized by helper cells was examined with two fragments of VL-315, obtained by cleavage with cyanogen bromide at Met 87. Both N-terminal fragment 1-86 and C-terminal fragment 88-114/117 elicited BALB/c antibodies that bound to the respective fragments and to VL-315. By contrast, only fragment 88-114/117, which consists of the third hypervariable region, J region, and 5-7 amino acids of the C region, induced helper cells that augmented the anti-NIP response to NIP-Fab 315.     

Regulatory idiotopes. Induction of idiotype-recognizing helper T cells by free light and heavy chains

Previously, we have demonstrated the induction of T helper cells that recognize idiotype by antigen (19), idiotype (20), and antiidiotype (12). The T cell population has been characterized and found to recognize both the T15 and M167 myeloma proteins, which share PC binding specificity but differ in idiotypic specificities. In the present work, we used isolated heavy and light chains of T15 and M167 to generate T helper cells, and examined the response to trinitrophenyl (TNP)-T15 and TNP-M167. We found that the heavy chains induced a dose- dependent response to TNP-T15 and TNP-M167, while the light chain priming was ineffective. When isolated chains of a monoclonal anti-T15 antibody (F6-3) were used to induce idiotype-recognizing T cells, only the F6-3 light chains generated T cell help for TNP-T15 and TNP-M167. Evidently, the idiotypic determinant that is recognized by the T cells is not dependent upon the conformation of combined heavy and light chains. These data show that the Th2 helper cells for the T15/M167 idiotopes are induced by free heavy chains of T15 and M167; the Th1 T cells that interact with the Th2 population, of T15 and M167; the Th1 T cells that interact with the Th2 population, however, can be triggered by free light chains of an antiidiotypic hybridoma antibody. These provocative findings suggest a new model for the T helper cell network.     

Antigen-binding T cells as helper cells. Separation of helper cells by immune rosette formation

The spleen T cells from mice immunized 6 days earlier with either chicken gamma globulin (CGG) or with donkey erythrocytes (DRC) were rosetted with CGG-coated sheep erythrocytes or with DRC. The immune rosettes (RFC) (antigen-binding cells) were separated from the bulk of nonrosette-forming cells (non-RFC) by 1-g velocity sedimentation and the RFC and non-RFC tested for helper activity in cooperative antihapten responses in vitro. RFC or non-RFC were mixed with normal or hapten-primed spleen cells, challenged with the appropriate hapten-carrier conjugate and cultured for 4 days in Marbrook tissue cultures. The helping activity was quantitated from the numbers of antihapten antibody-producing cells generated per culture. The results show that specific helper cell activity could be selectively recovered in the immune rosette-forming cell population whereas the non-RFC population was depleted of help. These findings indicate that the helper T cells express specific antigen binding receptors.     

Antiidiotypes against anti-H-2 monoclonal antibodies. V. In vivo antiidiotype treatment induces idiotype-specific helper T cells

Mice have been treated in vivo with xenogeneic antiidiotypes prepared against a murine monoclonal anti-H-2Kk antibody, 11-4.1. B cell immune responses have been found to be altered by such treatment as evidenced by a modification in the idiotypic repertoire of the humoral response to H-2 antigens. Transfer of purified T cells into nude mice before anti-idiotype treatment showed that T cells are involved in the induction of idiotope-bearing antibodies by xenogeneic antiidiotype. Studies using bone marrow chimeras indicate that the environment in which either T or B cells mature does not appear to alter VH region genetic control of induction of antiidiotype-induced molecules. By adoptive transfer studies, T cells from antiidiotype-treated mice were found capable of modifying the idiotypic repertoire of B cells subsequently exposed to antigen even when the T cells were obtained from antiidiotype-primed mice of inappropriate allotype. Although it still must be determined whether idiotypic or antiidiotypic T cells are involved in such B cell idiotype regulation, these results indicate that some T cell functions are altered by xenogeneic antiidiotypes prepared against B cell products and suggest that T cell immunity to major histocompatibility complex antigens may also be affected by such reagents.     

Idiotype-anti-idiotype network. II. Activation of silent clones by treatment at birth with idiotypes is associated with the expansion of idiotype-specific helper T cells

BALB/c mice immunized with bacterial levan (BL) produce a vigorous antibody response that fails to include antibodies expressing the idiotype of the beta 2 leads to 6 fructosan-binding myeloma protein ABPC48 (A48). Treatment of newborn BALB/c mice at 1 d of age with 0.1- 10 microgram of either the A48 myeloma protein or monoclonal proteins that share idiotopes with the A48 family, followed by immunization with BL 2-4 wk later, produces an anti-BL response that is dominated by the A48Id. Various degrees of activation of the A48Id BL response were observed by injecting mice with A48 monoclonal protein only up until 3 wk of age. Activation of the A48Id clones by treating with A48 monoclonal protein was ineffective in mice who were older than 4 wk. Elicitation of an A48Id BL response required specific antigenic stimulation with either beta 2 leads to 6 or beta 2 leads to 1 fructosan epitopes, because it does not occur after injection with TNP- Ficoll in spite of the A48 treatment. The expansion of A48Id clones in mice treated at birth with A48 monoclonal protein is associated with an increase in A48Id-specific helper T cells. The binding specificity of these cells was demonstrated by infusing them into nu/nu BALB/c mice and observing that they rendered help that enalbed the animal to mount an anti-TNP response after immunization only with A48-TNP, but not with MOPC384-TNP conjugates. The helper activity of these cells is sensitive to the effects of treatment with anti-Lyt-1.2 antibodies plus complement. A predominantly A48Id BL-specific response can be transferred into lethally irradiated mice by infusing them with purified T and B cells from A48-treated mice. The transfer of this response can be ablated by treating the T cells with anti-Lyt-1.2 antibodies plus complement. These results indicate that A48Id-specific helper cells possess the ability to select the A48Id-bearing B cell precursors for expression, thus exerting a fine-tuning effect on the idiotypic expression of the anti-BL repertoire. We propose that this idiotype-induced idiotype response, which can be, in principal, induced by idiotypes provided by the mother, plays an important role in the expansion of precursors of antibody-forming cells during embryonic as well as postnatal life.     

Molecular characterization of a cross-reactive idiotope on human immunoglobulins utilizing the VH4-21 gene segment

The anti-idiotypic (anti-Id) antibody (Ab) 9G4 binds a cross-reactive idiotope (CRI) present in a select group of human autoantibodies. This Id has been localized to the portion of immunoglobulin (Ig) heavy (H) chains encoded by the VH4-21 gene segment, a member of the human VH4 family. This gene segment is utilized by essentially all cold agglutinin (CA) Abs with I/i specificity isolated from patients with CA disease stemming from chronic lymphoproliferative disorders. In this study, mutational analysis of a CA has been used to determine the structural basis for 9G4 binding to Abs utilizing the VH4-21 gene segment. Recombinant CA H chain mutants were produced and their 9G4 reactivity determined. Mutants were generated by exchanging VH4-21 sequences in the FR1, CDR1, and CDR2 with corresponding sequences from a closely related gene segment V71-2, a VH4 family member that is associated neither with Abs having CA activity nor with Abs that react with 9G4. The results indicate that the motif AVY at amino acid positions 23-25 in FR1 defines the 9G4 idiotope. Reaction of these recombinant Abs with a polyclonal rabbit anti-CA antiserum absorbed to render it specific for a CA CRI also maps predominantly to FR1. These findings indicate that the solvent-exposed FR1 plays an important role in eliciting an immune response to Igs.     

T helper 1 and T helper 2 cells are pathogenic in an antigen-specific model of colitis.

Dysregulated T cell responses to enteric bacteria have been implicated as a common mechanism underlying pathogenesis in rodent models of colitis. However, the bacterial species and T cell specificities that induce disease have been poorly defined. We have developed a model system in which target antigen, bacterial host, and corresponding T cell specificity are defined. OVA-specific T cells from DO11.RAG-2(-/-) TCR transgenic mice were transferred into RAG-2(-/-) recipients whose intestinal tracts were colonized with OVA-expressing or control Escherichia coli. Transfer of antigen-naive DO11.RAG-2(-/-) T cells into recipients colonized with OVA-E. coli resulted in enhanced intestinal recruitment and cell cycling of OVA-specific T cells; however, there was no development of disease. In contrast, transfer of polarized T helper (Th) 1 and Th2 populations resulted in severe wasting and colitis in recipients colonized with OVA-expressing but not control E. coli. The histopathologic features of disease induced by Th1 and Th2 transfers were distinct, but disease severity was comparable. Induction of disease by both Th1 and Th2 transfers was dependent on bacterially associated OVA. These results establish that a single bacterially associated antigen can drive the progression of colitis mediated by both Th1 and Th2 cells and provide a new model for understanding the immunoregulatory interactions between T cells responsive to gut floral antigens.     

T cells recognize minor histocompatibility antigens on H-2 allogeneic cells

B10.A animals were rendered tolerant to B10.M spleen cells by injection of (B10.A X B10.M)F1 cells into neonates. Adult animals accepted B10.M skin grafts and failed to generate cytotoxic effector cells in vitro against B10.M H-2 antigens. In vivo inoculation of tolerant animals with A.CA spleen cells, followed by in vitro challenge with similar cells, resulted in the generation of cytotoxic effector cells that had specificity for the A strain minor histocompatibility (H)-antigens in the context of the H-2f haplotype. If these animals were boosted in vitro with A strain spleen cells, cross-priming could be demonstrated, whereby the cytotoxic effect was restricted by the H-2a haplotype. These data indicate that at least two sets of T cells co-exist in tolerant animals, one capable of recognizing antigens in the context of the host H-2 haplotype, and the other able to recognize antigens in the context of the tolerated H-2-allogeneic haplotype. Because tolerant animals inoculated with A-strain spleen cells in vivo and boosted in vitro with A.CA spleen cells failed to generate a cytotoxic effect against A.CA, it is unlikely that minor H-antigens need to be processed by host lymphoreticular cells.     

Epitopes associated with MHC restriction site of T cells. III. I-J epitope on MHC-restricted T helper cells

I-J epitopes were found to be associated with the functional site of the class II MHC-restricted helper T (Th) cells: Virtually all of the H-2k-restricted Th cell function of H-2kxbF1 T cells was inhibited by the anti-I-Jk mAb, leaving the H-2b-restricted function unaffected. The I-Jk epitope was inducible in Th cells of different genotype origin according to the environmental class II antigens present in the early ontogeny of T cells. Although above results suggested that I-J is the structure reflecting the inducible MHC restriction specificity, further studies revealed some interesting controversies: First, the I-J phenotype did not always correlate with the class II restriction specificity, e.g., I-Ab-restricted Th from 5R was I-Jk-positive, whereas I-Ak-restricted Th of 4R was not. Second, there was no trans expression of parental I-J phenotypes and restriction specificities in F1 Th, e.g., the I-J phenotype was detected only on I-Ab-restricted Th of (4R X 5R)F1, whereas it was absent on I-Ak-restricted Th. This strict linkage between the restriction specificity and I-J phenotype was also found on Th cells developed in bone marrow chimera constructed with intra-H-2-recombinant mice. The expression of I-Jk was always associated with the restriction specificity of the relevant host. Thus, the restriction specificity of Th cells followed the host type, and the I-J expression on Th was exactly the same as that expressed by the host haplotype. These results indicate that I-J is an isomorphic structure adaptively expressed on Th cells that is involved in the unidirectional regulatory cell interactions, and that the polymorphism cannot be explained merely by the restriction specificity of the conventional T cell receptor heterodimer.     

Sendai virus-specific T cell clones. V. Induction of a virus-specific response by antiidiotypic antibodies directed against a T helper cell clone

We used an antiidiotypic antibody directed against a Sendai virus-specific T helper cell clone to stimulate an immune response in vivo. In addition, the antiidiotypic antibody induced T cells that mediated a delayed-type hypersensitivity (DTH) response in several different mouse strains. Induction of the DTH response by the antiidiotypic antibody, in contrast to the DTH responses induced by virus, demonstrated a remarkable lack of H-2 restriction.     

Cytotoxic T cells recognize a peptide from the circumsporozoite protein on malaria-infected hepatocytes

Irradiated malaria sporozoites can induce CD8+ T cells that are required for protection against infection. However, the parasite antigens targeted by this immune response are unknown. We have discovered a 16-amino acid epitope from the Plasmodium yoelii circumsporozoite (CS) protein that is recognized by cytotoxic T cells from immune mice. Lymphocytes stimulated with this peptide can kill P. yoelii liver stage parasites in vitro in an MHC-restricted, antigen-specific manner. Thus, epitopes from the CS protein are presented on the surface of infected hepatocytes and can be targets for T cells, even though intact CS protein has not been detected on the surface of the infected hepatocyte. A vaccine that induced CTL to parasite antigens might protect humans against malaria by eliminating liver stage parasites.     

T cell receptor-independent immunosuppression induced by dexamethasone in murine T helper cells.

The immune and inflammatory responses are largely inhibited by glucocorticosteroids. In thymocytes, for example, glucocorticosteroids cause apoptosis, whereas they suppress the activity of phospholipase A2 and the production of eicosanoids in tissues actively engaged in inflammation. The immunosuppressive action of dexamethasone (DEX) was studied in vitro by employing a model cell system, namely the murine Th2 clone D10.G4.1 (D10) and its clonotypic anti-T cell receptor (TCR) mAb 3D3. Although the proliferative response of D10 cells to 3D3 stimulation was not affected by DEX, the costimulation provided by IL-1 was dramatically inhibited. Substitution of 3D3 by exogenous IL-4 (as the IL-1 costimulant) failed to prevent the inhibition of proliferation caused by DEX. Yet, when 3D3-mediated stimulation of TCR was supplemented with IL-2, D10 cells were capable of proliferating, even in the presence of DEX. Thus, TCR stimulation on D10 cells remained intact and their resulting propagation was not compromised by DEX treatment. These results provide evidence that immunosuppression caused by DEX is TCR independent and involves an early cytokine-signalling event.     

HIV and T follicular helper cells: a dangerous relationship

HIV infection leads to progressive destruction of infected CD4 T cells, hypergammaglobulinemia, and loss of memory B cells. Germinal centers, which are key to memory B cell formation and protective antibody responses, are major HIV reservoirs in which the virus replicates within T follicular helper (TFH) cells. In this issue of the JCI, the Koup and Streeck groups report that chronic SIV/HIV infection promotes TFH cell accumulation, which may drive B cell dysregulation. Their discoveries suggest that HIV harnesses TFH cells to evade the antibody response.     

Idiotypic markers of polyclonal B cell activation. Public idiotypes shared by monoclonal antibodies derived from patients with systemic lupus erythematosus or leprosy.

We investigated idiotypic markers of monoclonal antibodies derived from patients with polyclonal B-cell activation. Four monoclonal antibodies with different ligand binding specificities derived from a patient with lepromatous leprosy and three monoclonal anti-DNA antibodies from two patients with SLE were studied. Three new public idiotopes, which were common to monoclonal antibodies from all three patients, were defined by five polyclonal rabbit antiidiotypes, two monoclonal mouse antiidiotopes, and a monoclonal mouse antibody against a synthetic peptide that contains residues of the heavy chain CDR-1 of a monoclonal lupus anti-DNA antibody. The antibody against the synthetic idiotype was found to react with native immunoglobulins in solution. One idiotope was found to be consistently immunogenic in all animals tested. Since the three patients are of different ethnic origins, these shared idiotypes are probably encoded by germline V genes. These genes may be recurrently expressed in states of polyclonal B-cell activation, regardless of etiology. The results suggest that some autoantibodies arise by expansion of a pool of precursors in the normal antibody repertoire.     

Induction of cytotoxic T cell precursors in vivo. Role of T helper cells

Strain AS rats respond with two populations of cytotoxic T lymphocytes to stimulation in vitro by the major histocompatibility complex (MHC)-incompatible strain HL rat tumor (HL-A2T2). One is specific for MHC alloantigens present on both HL-A2T2 and normal HL targets, the other is tumor specific. The activation of these killer cells requires helper T lymphocytes. The tumor-specific helper cells depend on syngeneic radioresistant accessory cells to present the tumor antigens in an immunogenic form. The appropriate helper-accessory cell interaction results in the production of soluble factors which then induce the maturation of precursor cells into effective killer cells. Studies with a procedure for inducing negative selection of T cells in vivo showed that short-term exposure to HL-A2T2 tumor induced selection only for TH but not cytotoxic T lymphocyte precursors (CTLp). Simultaneous injection of supernatants from concanavalin A-activated spleen cell cultures, however, did produce selection of CTLp. These and other findings suggest that under normal circumstances in vivo, both signals (recognition of antigen and acceptance of maturation factors) are provided in the vicinity of an antigen presenting macrophage-like accessory cell.     

Type 1 T helper and type 2 T helper cells: functions, regulation and role in protection and disease.

Two very distinct cytokine secretion patterns have been defined among murine CD4+ T cells. Type 1 helper (TH1), but not type 2 helper (TH2), cells produce interleukin (IL)-2, gamma-interferon (IFN-gamma) and tumour necrosis factor-beta, whereas TH2, but not TH1, cells express IL-4, IL-5, IL-6 and IL-10. The different cytokine patterns lead to different functions of the two types of T cell. In general, TH2 cells are excellent helpers for B-cell antibody secretion, particularly IgE responses. On the other hand TH1 cells induce delayed-type hypersensitivity reactions. There is general agreement that the different functional subsets of TH cells arise post-thymically from a common pool of precursors and as a consequence of activation of antigen. However, the factors affecting differentiation of TH precursors into the TH1 or TH2 subsets are still unclear. Mutual cross-regulation between TH1 (via IFN-gamma) and TH2 (via IL-10) has also been reported. Recently, human T cell clones similar to murine TH1 and TH2 cells have been demonstrated. Most allergen- or helminthic antigen-specific CD4+ human T cell clones have a TH2 phenotype, whereas the majority of T-cell clones specific for mycobacterial antigens or antigens responsible for type IV hypersensitivity exhibit a TH1 phenotype. Human TH2 clones provide B-cell help for IgE synthesis, whereas most TH1 clones are cytolytic for antigen-presenting cells, including B lymphocytes. It is highly probable that the selective or preferential activation of CD4+ T-cell subsets secreting defined patterns of cytokines is of major importance in determining the class of immune effector function, thus influencing both protection and immunopathology.     

Structure-function relationships among highly diverse T cells that recognize a determinant from influenza virus hemagglutinin.

We have analyzed the structural and genetic basis for T cell recognition of the complex formed between antigen and class II products of the major histocompatibility complex by performing sequence analysis of T cell receptors (TCRs) induced in response to the helper T cell site 1 of the influenza virus hemagglutinin. The results demonstrate, first, that structurally highly diverse TCRs can be utilized in recognition of the same antigen/I-Ed complex: 12 of 13 TCRs utilize unique V alpha/V beta gene segment combinations, suggesting that approximately 70 different V alpha/V beta combinations are available to BALB/c mice in response to this determinant. Second, comparison of these sequences with the ability of each hybridoma to recognize a panel of peptide analogues suggests that alpha and beta chains of these TCRs frequently determine specificity for the NH2-terminal and the COOH terminal portions, respectively, of the site 1 determinant.     

Clonal analysis of F1 hybrid helper T cells. I-A subregion-encoded hybrid determinants restrict the activity of keyhole limpet hemocyanin- specific helper T cells

Clonal expansion of isolated precursors to helper T cells was induced in limiting dilution cultures of keyhole limpet hemocyanin (KLH)-primed F1 hybrid lymph node cells. Progeny of each isolated precursor was tested for helper activity by transfer to independent cultures with hapten-primed B cells of either parental or F1 hybrid origin. The major histocompatibility complex (MHC) restriction specificity of each F1 hybrid helper T clone was determined. To assess the contribution of I-A and I-E subregion-encoded genes to the expression of these restriction elements, helper T cell cultures derived from F1 hybrids between strains with recombinant H-2 haplotypes were analyzed. Parental and unique F1 hybrid MHC determinants that are encoded entirely within the I-A subregion were found to restrict the activity of KLH-specific helper T cells.     

Regulatory functions of hapten-reactive helper and suppressor T lymphocytes. II. Selective inactivation of hapten-reactive suppressor T cells by hapten-nonimmunogenic copolymers of D-amino acids, and its application to the study of suppressor T-cell effect on helper T-cell development

An experimental condition was established in vivo for selectively eliminating hapten-reactive suppressor T-cell activity generated in mice primed with a para-azobenzoate (PAB)-mouse gamma globulin (MGG)-conjugate and treated with PAB-nonimmunogenic copolymer of D-amino acids (D- glutamic acid and D-lysine; D-GL). The elimination of suppressor T-cell activity with PAB-D-GL treatment from the mixed populations of hapten- reactive suppressor and helper T cells substantially increased apparent helper T-cell activity. Moreover, the inhibition of PAB-reactive suppressor T-cell generation by the pretreatment with PAB-D-GL before the PAB-MGG-priming increased the development of PAB-reactive helper T-cell activity. The analysis of hapten-specificity of helper T cells revealed that the reactivity of helper cells developed in the absence of suppressor T cells was more specific for primed PAB-determinants and their cross-reactivities to structurally related determinants such as meta-azobenzoate (MAB) significantly decreased, as compared with the helper T-cell population developed in the presence of suppressor T lymphocytes. In addition, those helper T cells generated in the absence of suppressor T cells were highly susceptible to tolerogenesis by PAB-D- GL. Similarly, the elimination of suppressor T lymphocytes also enhanced helper T-cell activity in a polyclonal fashion in the T-T cell interactions between benzylpenicilloyl (BPO)-reactive T cells and PAB- reactive T cells after immunization of mice with BPO-MGG-PAB. Thus inhibition of BPO-reactive suppressor T-cell development by the BPO-v-GL- pretreatment resulted in augmented generation of PAB-reactive helper T cells with higher susceptibility of tolerogenesis to PAB-D-GL. Thus, these results support the notion that suppressor T cells eventually suppress helper T-cell activity and indicate that the function of suppressor T cells related to helper T-cell development is to inhibit the increase in the specificity and apparent affinity of helper T cells in the primary immune response. The hapten-reactive suppressor and helper T lymphocytes are considered as a model system of T cells that regulate the immune response, and the potential applicability of this system to manipulating various T cell-mediated immune responses is discussed in this context.