Immunoregulation by Vbeta specific antibodies in myasthenia gravis: mining physiological T cell homeostasis for TCR specific therapy.

Besides regulatory T cells, also comprising T cell receptor (CR)-specific T cells, it is increasingly evident that natural autoantibodies, among which anti-TCR antibodies represent additional immunomodulators in the immune system. We took advantage of myasthenia gravis (MG), a well-characterized antibody-mediated autoimmune disease, to demonstrate that without prior vaccination against TCR determinants, patients with MG present increased circulating anti-TCR antibodies directed to the dominant TCR used by pathogenic T cells. These findings, pointing to a regulatory protective role of anti-TCR antibodies, are discussed in the context of the mechanisms of action and the physiological role of anti-TCR antibodies in T cell homeostasis, and of the puzzling world of regulatory T cells. Natural anti-TCR antibodies are found in the serum of all individuals, with prevalence in physiological and pathological situations such as ageing, pregnancy, allograft transplantation, retroviral infection, and autoimmune diseases, including MG. The common link is the mounting of immune responses against alloantigens, pathogens or autoantigens, conferring on anti-TCR antibodies a broader role in controlling responses to any antigen (self or non-self) and more generally in T cell homeostasis. This homeostasis mechanism may well be exploited in therapeutic strategies based on TCR peptide vaccination in autoimmune diseases.     

Recruitment and activation of macrophages by pathogenic CD4 T cells in type 1 diabetes: evidence for involvement of CCR8 and CCL1

Adoptive transfer of diabetogenic CD4 Th1 T cell clones into young NOD or NOD.scid recipients rapidly induces onset of diabetes and also provides a system for analysis of the pancreatic infiltrate. Although many reports have suggested a role for macrophages in the inflammatory response, there has been little direct characterization of macrophage activity in the pancreas. We showed previously that after migration to the pancreas, diabetogenic CD4 T cell clones produce a variety of inflammatory cytokines and chemokines, resulting in the recruitment of macrophages. In this study, we investigated mechanisms by which macrophages are recruited and activated by T cells. Analysis of infiltrating cells after adoptive transfer by the diabetogenic T cell clone BDC-2.5 indicates that large numbers of cells staining for both F4/80 and CD11b are recruited into the pancreas where they are activated to make IL-1beta, TNF-alpha, and NO, and express the chemokine receptors CCR5, CXCR3, and CCR8. Diabetogenic CD4 T cell clones produce several inflammatory chemokines in vitro, but after adoptive transfer we found that the only chemokine that could be detected ex vivo was CCL1. These results provide the first evidence that CCR8/CCL1 interaction may play a role in type 1 diabetes through macrophage recruitment and activation.     

TCR reserve: a novel principle of CD4 T cell activation by weak ligands

Some ligand-receptor systems have a receptor reserve where a maximal response can be achieved by occupation of a fraction of available receptors. An implication of a receptor reserve is the expansion of the number of ligands for response. To determine whether T cells follow receptor reserve, we have characterized the effect of reducing TCR levels on CD4 T cell responses elicited by altered peptide ligands that vary in potency. Agonist peptide is unaffected by a 90% reduction in TCR level while proliferation to weak agonists is significantly inhibited when TCR expression is reduced by 40%. Thymocyte-negative selection similarly demonstrates a differential requirement of TCR for response to agonist, weak agonist, and partial agonist. Therefore, our data demonstrate receptor reserve as a novel principle of T cell activation in which excess TCRs expand the antigenic repertoire to include less potent ligands.     

Viruses and cytokines: evidence for multiple roles in pancreatic beta cell destruction in type 1 insulin-dependent diabetes mellitus

Insulin-dependent (type 1) diabetes mellitus (IDDM) is due to the selective autoimmune-mediated destruction of pancreatic beta cells possibly initiated by viruses. To elucidate the possible role of viruses and cytokines in the pathogenesis of IDDM, we have examined the effect of reovirus infection on beta cell major histocompatibility complex (MHC) expression and the effect of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) on beta cell function in vitro. Infection of RIN-m5F (rat insulinoma) cells with reovirus-1 or reovirus-3 was associated with a tenfold increase in class 1 MHC protein and mRNA expression. Reovirus infection did not induced the expression of class 11 MHC by RIN-m5F cells. Exposure of reovirus to ultraviolet light almost completely abolished its ability to induce class 1 MHC protein expression on infected cells. Murine islets cultured for 3 days with IFN-gamma and/or TNF-alpha had a significantly reduced insulin response to glucose, which was more marked with a combination of the cytokines. During 6 days of culture in IFN-gamma plus TNF-alpha islets underwent noticeable degeneration associated with an 80% reduction in insulin content. These findings together with previous data suggest viruses and cytokines may have multiple roles in beta cell destruction, indirectly through enhanced MHC protein expression and directly through functional impairment and loss of viability.     

Role of regulatory T cells for the treatment of type 1 diabetes mellitus.

Beta-cell specific autoreactive T cells can be found in patients with type I diabetes (T1D) and in healthy controls. They are usually controlled by a network of regulatory mechanisms including CD4+CD25+Foxp3+ regulatory T cells (Tregs). It was suspected that defects in Treg number and activity are causally related to the development of T1D. Although there are hints that this concept might be true, it is neither proven in animal models nor in patients with T1D. However, increasing the number of Tregs by adoptive transfer can be used to prevent and treat even established T1D. It was demonstrated that Tregs recognizing beta-cell antigens are far more efficient in treating the disease than polyspecific Tregs. The use of beta-cell specific Tregs is also leading to a tissue specific immunotolerance without perturbing the general immunocompetence. Two sources for beta-cell specific Tregs are currently employed: First natural Tregs specific for beta-cells are expanded IN VITRO and reinfused into diabetic animals. Second na?ve or activated T cells specific for beta-cell antigens are IN VITRO converted to Tregs by genetic manipulation or by specific cytokine combinations. Both approaches were successful in treating even established diabetes in animal models. Before such therapies can be used in patients safety measures regarding the fate and the effects of the transferred Tregs have to be studied. Besides this ethical considerations are important in regard to what risks we should take to treat a disease in young patients which can otherwise be treated medically. In the meantime the concept of Tregs for therapy of T1D is supported by successful clinical attempts to induce these cells IN VIVO by administration of monoclonal antibodies against CD3. If subsequent studies show that Tregs represent a safe and efficient source for therapy, they could become an important weapon in the fight against immune mediated pathology.     

Thyroid volume as measured by ultrasonography in patients With type 1 diabetes mellitus without thyroid dysfunction.

The aim of this cross-sectional study was to assess and compare thyroid volume and its derminants in a cohort of type 1 diabetes mellitus (DM1) and compare the results to a healthy control group. We studied 65 DM1 patients treated with an intensive insulin regimen and 65 matched controls. In all participants we evaluated weight, height, BMI, waist-hip ratio, body surface area and body composition variables determined by using a bioelectrical impedance analyser. Thyroid size was estimated by ultrasonography. We determined basal TSH, anti-thyroid antibodies and urinary iodine excretion. Body weight, height, BMI and body surface area were similar in DM1 patients and in controls. Fat-free mass was higher in both male and female DM1 patients than in controls (64.4 +/- 6.9 vs. 60.4 +/- 8.2 kg, p=0.03 and 48.3 +/- 5.7 vs. 45.4 +/- 6, p=0.04, respectively), and fat mass was lower in male DM1 patients than in controls (9.7 +/- 7 vs. 14.2 +/- 8.1 kg, p=0.01). Thyroid volume was greater in both male and female DM1 patients than in controls (11.12 +/- 2.87 vs. 9.63 +/- 2.27 ml, p=0.0001 and 9.5 +/- 2.3 vs. 7.7 +/- 2 ml, p=0.002, respectively). Urinary iodine excretion was similar in the two groups. In both DM1 patients and controls, thyroid volume correlated with weight, height, BMI, waist-hip ratio, body surface area, fat-free mass and the multivariate linear regression analysis with thyroid volume as the dependent variable showed that fat-free mass in either group was the only significant determinant of thyroid volume. We conclude that DM1 patients had larger thyroid volume compared with healthy controls with similar anthropometry; body composition is different in DM1 patients and that the anthropometric and body composition variables, especially fat-free mass and body surface area, predict thyroid volume either in DM1 patients or in healthy controls.     

Stimulator cell-dependent requirement for CD2- and LFA-1-mediated adhesions in T lymphocyte activation by superantigenic toxins.

The staphylococcal enterotoxins and related microbial T cell mitogens stimulate T cells by cross-linking variable parts of the T cell receptor (TCR) with MHC class II molecules on accessory or target cells. We have used cloned human T cells and defined tumor cells as accessory cells (AC) to study the requirements for T cell activation by these toxins. On AC expressing high levels of CD54 (intercellular adhesion molecule-1, ICAM-1) and CD58 (lymphocyte function-associated antigen-3, LFA-3), mAb to CD2 were relatively ineffective in inhibiting the response to the toxins and antibodies to the lymphocyte function-associated antigen-1 (LFA-1) did not inhibit at all. If added together, however, these mAb inhibited the response completely. Similar results were obtained using antibodies to the target structures of CD2 and LFA-1. In contrast, on cells expressing low levels of LFA-3, mAb to LFA-1 but not to CD2 were strongly inhibitory. The same pattern of inhibition was found when these same cells were used as presenters of specific antigen to the T cells. These data show that adhesions via CD2 or LFA-1 are alternatively required for the stimulation of the T cells by superantigenic toxins and demonstrate another similarity between T cell stimulation by superantigens and by specific antigen recognition.     

Incomplete activation of CD4 T cells by antigen-presenting transitional immature B cells: implications for peripheral B and T cell responsiveness

B cells leave the bone marrow as transitional B cells. Transitional B cells represent a target of negative selection and peripheral tolerance, both of which are abrogated in vitro by mediators of T cell help. In vitro, transitional and mature B cells differ in their responses to B cell receptor ligation. Whereas mature B cells up-regulate the T cell costimulatory molecule CD86 (B7.2) and are activated, transitional B cells do not and undergo apoptosis. The ability of transitional B cells to process and present Ag to CD4 T cells and to elicit protective signals in the absence of CD86 up-regulation was investigated. We report that transitional B cells can process and present Ag as peptide:MHC class II complexes. However, their ability to activate T cells and elicit help signals from CD4-expressing Th cells was compromised compared with mature B cells, unless exogenous T cell costimulation was provided. A stringent requirement for CD28 costimulation was not evident in interactions between transitional B cells and preactivated CD4-expressing T cells, indicating that T cells involved in vivo in an ongoing immune response might rescue Ag-specific transitional B cells from negative selection. These data suggest that during an immune response, immature B cells may be able to sustain the responses of preactivated CD4(+) T cells, while being unable to initiate activation of naive T cells. Furthermore, the ability of preactivated, but not naive T cells to provide survival signals to B cell receptor-engaged transitional immature B cells argues that these B cells may be directed toward activation rather than negative selection when encountering Ag in the context of a pre-existing immune response.     

Induction of peripheral tolerance in dual TCR T cells: an evidence for non-dominant signaling by one TCR

Recently, the existence of T cells with dual T cell receptor (TCR) in the immune system is generally accepted, while it has been controversial whether signals through one TCR would affect the functions of the other. In this study T cells expressing two different TCR were obtained from cross-hybrids of LCMV and AND TCR transgenic mice specific for the gp33 and peptide fragment of PCC (fPCC), respectively. Peptide stimulation demonstrated that the dual TCR T cells functioned independently in an antigen-specific manner. To examine whether the tolerance targeted for the one TCR affects the responsiveness of the other, the cross-hybrids were treated with gp33. Although T cells from F1 mice were rendered anergenic to gp33, no functional changes to fPCC were observed in terms of cellular proliferation and IL-2 secretion, suggesting that the dual TCR T cells remained reactive to fPCC. We therefore propose that signaling through the TCR is receptor-specific and 'negative dominance' of one TCR by tolerance induction is not applicable in this dual TCR system.     

Inhibition by salbutamol of GHRH-induced GH release in type 1 diabetes mellitus.

Patients with type 1 diabetes mellitus (IDDM) show augmented GH secretion, which is implicated in the pathogenesis of microvascular complications. On the other hand, it is well known that beta-adrenergic receptors have inhibitory influence on GH secretion, likely via stimulation of hypothalamic somatostatin. Since the possibility of pharmacological suppression of GH secretion would be of value in IDDM, we investigated the effect of salbutamol (SAL, 4 mg orally at -60 min) on the GH response to GHRH (1 micrograms/kg iv at 0 min) in 6 well-controlled (mean HbA1c +/- SEM: 7.3 +/- 0.5%) patients with IDDM. Salbutamol was able to inhibit basal GH levels (p < 0.05) as well as to abolish the GHRH-induced GH rise. After SAL administration, a significant (p < 0.05) reduction of glucagon levels was also found. Our data show that the enhancement of beta 2 adrenergic activity by oral therapeutical doses of SAL inhibits basal and GHRH-stimulated GH secretion in patients with IDDM.     

Vgamma4(+) T cells promote autoimmune CD8(+) cytolytic T-lymphocyte activation in coxsackievirus B3-induced myocarditis in mice: role for CD4(+) Th1 cells

T cells expressing the Vgamma4 T-cell receptor (TCR) promote myocarditis in coxsackievirus B3 (CVB3)-infected BALB/c mice. CD1, a major histocompatibility complex (MHC) class I-like molecule, is required for activation of Vgamma4(+) cells. Once activated, Vgamma4(+) cells initiate myocarditis through gamma interferon (IFN-gamma)-mediated induction of CD4(+) T helper type 1 (Th1) cells in the infected animal. These CD4(+) Th1 cells are required for activation of an autoimmune CD8(+) alphabeta TCR(+) effector, which is the predominant pathogenic agent in this model of CVB3-induced myocarditis. Activated Vgamma4(+) cells can adoptively transfer myocarditis into BALB/c mice infected with a nonmyocarditic variant of CVB3 (H310A1) but cannot transfer myocarditis into either uninfected or CD1(-/-) recipients, demonstrating the need for both infection and CD1 expression for Vgamma4(+) cell function. In contrast, CD8(+) alphabeta TCR(+) cells transfer myocarditis into either infected CD1(-/-) or uninfected recipients, showing that once activated, the CD8(+) alphabeta TCR(+) effectors function independently of both virus and CD1. Vgamma4(+) cells given to mice lacking CD4(+) T cells minimally activate the CD8(+) alphabeta TCR(+) cells. These studies show that Vgamma4(+) cells determine CVB3 pathogenicity by their ability to influence both the CD4(+) and CD8(+) adaptive immune response. Vgamma4(+) cells enhance CD4(+) Th1 (IFN-gamma(+)) cell activation through IFN-gamma- and CD1-dependent mechanisms. CD4(+) Th1 cells promote activation of the autoimmune CD8(+) alphabeta TCR(+) effectors.     

Modulation of the B cell response to T-independent antigens by prostaglandins: evidence for effector system cross-talk.

The extracellular environment is a major factor in determining the responsiveness of a cell to particular stimuli. For example, E series prostaglandins suppress B cell responses to T-independent antigens, mitogen stimulation of DNA synthesis and proliferation, and the primary immune response. We investigated the effects of prostaglandins on the intracellular signals generated by receptor-coupled effector systems in B lymphocytes. Pretreating splenocytes from athymic nude mice with forskolin, PGE1, or PGE2 decreased the magnitude of anti-IgM-induced changes in cytosolic free [Ca2+]. Addition of 8-Br-cAMP, forskolin, PGE1, or PGE2 following stimulation with anti-IgM resulted in a decrease in the intracellular calcium signal measured by fluorescence-activated cell sorting using Indo-1 as a Ca2+ indicator. This decrease was not a result of an inhibition of influx across the plasma membrane. Thus activation of adenylate cyclase by prostaglandins modifies the generation of signals by phosphoinositidase C. This effector system cross-talk between adenylate cyclase and phosphoinositidase C is consistent with and may account for the inhibitory effects of prostaglandins in B cell responses.     

Differential recruitment of B and T cells in coxsackievirus B4-induced pancreatitis is influenced by a capsid protein.

Two genetically similar variants of coxsackievirus B4, CB4-P and CB4-V, cause distinct disease syndromes in mice. A multidisciplinary approach was used to examine the events occurring in situ. The CB4-P variant induced acute pancreatitis, followed by repair of the exocrine tissues, while the CB4-V variant induced chronic pancreatitis, characterized by extensive destruction of the exocrine tissues. Since CB4-V replicated more efficiently than CB4-P in vivo, the more extensive tissue injury associated with CB4-V infection could be explained as the result of a higher level of viral replication. However, the fact that CB4-V replicated more efficiently in a mouse strain that survives infection than in a strain that succumbs to infection suggests that immune-mediated mechanisms as well as viral cytolysis may contribute to pancreatic tissue injury. To address the role of the immune system in virus-induced pancreatitis, the cell types within the inflammatory infiltrate were analyzed by flow cytometry. B cells (34 to 75%) were the most abundant, followed by T cells (10 to 30%), natural killer cells (4 to 8%), and macrophages (0 to 6%). Recruitment (and perhaps proliferation) of B and T cells to the pancreatic tissues was influenced by viral strain. Differential recruitment of T and B cells may reflect altered antigenic sites between CB4-P and CB4-V. The viral sequence that affected T- and B-cell recruitment was identified as a threonine residue at position 129 of the VP1 capsid protein.     

B cell activation: role of dendritic and T cell factors in the response to thymic-independent and -dependent antigens

We described a cloned dendritic cell, clone Den-1, that is a potent accessory cell for some B cell responses. Clone Den-1 produces a novel lymphokine that is distinct from previously described factors produced by T cells. In the present study, we compare the role of nonspecific helper factors produced by Den-1 (Den-1 SN) or the T cell thymoma EL4 (EL4-SN) in promotion of B cell plaque-forming cell (PFC) responses to a variety of antigens. We find that the antigen in culture determines the B cell requirement for dendritic and/or T cell factors. B cell PFC responses to TNP-Brucella abortus (BA) and TNP-lipopolysaccharide (LPS) are greatly increased by EL4-SN but show little, if any, enhancement with Den-1 SN. Responses to TNP-polyacrylamide are reconstituted by either Den-1 SN or EL4-SN, whereas responses to TNP-Ficoll, TNP-dextran and TNP-levan are reconstituted by Den-1 SN and are much less sensitive to factors present in EL4-SN. Responses to SRBC require the presence of both Den-1 SN and EL4-SN. We also show that the time at which Den-1 SN must be provided to the B cell is dependent on the antigen in culture. Our findings are discussed in terms of present classification of antigens based on their ability to stimulate various B cell subpopulations.     

Broad TCR usage in functional HIV-1-specific CD8+ T cell expansions driven by vaccination during highly active antiretroviral therapy

During chronic HIV-1 infection, continuing viral replication is associated with impaired proliferative capacity of virus-specific CD8+ T cells and with the expansion and persistence of oligoclonal T cell populations. TCR usage may significantly influence CD8+ T cell-mediated control of AIDS viruses; however, the potential to modulate the repertoire of functional virus-specific T cells by immunotherapy has not been explored. To investigate this, we analyzed the TCR Vbeta usage of CD8+ T cells populations which were expanded following vaccination with modified vaccinia virus Ankara expressing a HIV-1 gag/multiepitope immunogen (MVA.HIVA) in HIV-1-infected patients receiving highly active antiretroviral therapy. Vaccinations induced the re-expansion of HIV-1-specific CD8+ T cells and these showed broad TCR Vbeta usage which was maintained for at least 1 year in some individuals. By contrast, virus-specific CD8+ T cell populations in the same donors which failed to expand after vaccination and in unvaccinated controls were oligoclonal. Simultaneously, we observed that CD8+ T cells recognizing vaccine-derived HIV-1 epitopes displayed enhanced capacity to proliferate and to inhibit HIV-1 replication in vitro, following MVA.HIVA immunizations. Taken together, these data indicate that an attenuated viral-vectored vaccine can modulate adaptive CD8+ T cell responses to HIV-1 and improve their antiviral functional capacity. The potential therapeutic benefit of this vaccination approach warrants further investigation.     

Analysis of two distinct B cell activation pathways mediated by a monoclonal T helper cell. II. T helper cell secretion of interleukin 4 selectively inhibits antigen-specific B cell activation by cognate, but not noncognate, interactions with T cells

A single monoclonal T helper (Th) clone can activate B cells in two distinct pathways; a cognate pathway requiring a major histocompatibility complex (MHC)-restricted T-B cell interaction, and a noncognate pathway not requiring an MHC-restricted T-B cell interaction. The present study was undertaken to investigate whether Th cells mediating a given immune response provide further regulatory function to B cells other than helper function. It was demonstrated that conditions of high antigen concentration which activate a noncognate B cell activation pathway simultaneously inhibit IgG responses. The inhibition is shown to be mediated by the T cell factor interleukin 4, produced by activated cloned Th cells. The inhibitory effect of this factor is directed to B cells and is MHC-unrestricted, antigen-nonspecific, and IgG class-specific. In addition to being susceptible to the effects of augmenting cells and suppressor cells, cloned Th cell populations can therefore themselves function as regulatory cells to inhibit IgG responses when stimulated with high dose of specific antigen. These results indicate that Th cells function to regulate B cells both positively and negatively, depending upon the activation conditions.     

Disulfiram reactivates latent HIV-1 in a Bcl-2-transduced primary CD4+ T cell model without inducing global T cell activation

Highly active antiretroviral therapy (HAART) can reduce plasma HIV-1 levels to below the detection limit. However, due to the latent reservoir in resting CD4(+) cells, HAART is not curative. Elimination of this reservoir is critical to curing HIV-1 infection. Agents that reactivate latent HIV-1 through nonspecific T cell activation are toxic. Here we demonstrate in a primary CD4(+) T cell model that the FDA-approved drug disulfiram reactivates latent HIV-1 without global T cell activation. The extent to which disulfiram reactivates latent HIV-1 in patient cells is unclear, but the drug alone or in combination may be useful in future eradication strategies.     

The role of immunoglobulin receptors and T cell mediators in B lymphocyte activation. I. B cell activation by anti-immunoglobulin and anti-idiotype reagents

The possibility that the failure of anti-mouse immunoglobulin (Ig) antibody to induce antibody synthesis by B cells might be due to reversible receptor blockade was investigated. Murine spleen cells were cultured for 3 days in the presence of minute quantities of intact of (Fab') fragments of rabbit anti-mouse Ig antibody. Thereafter, the cells were washed and either trypsin treated or not before reculturing for 18 hr. Only cells that had been trypsinized after culturing with either intact or fragments of anti-Ig gave a vigorous polyclonal antibody response. This response was extremely T dependent, since T cells or culture supernatants from Con A-activated T cells were required for the B cell response. Moreover, anti-delta was much more effective than anti-mu in inducing antibody synthesis. Finally, the use of three different anti-idiotypic antisera rather than anti-Ig reagents selectively activated the specific idiotype in each instance. The findings demonstrate that anti-Ig reagents can potentiate the response of B cells to signals delivered by T cells.