Alteration at a single amino acid residue in the T cell receptor alpha chain complementarity determining region 2 changes the differentiation of naive CD4 T cells in response to antigen from T helper cell type 1 (Th1) to Th2

Regulation of T Helper Cell Fate by TCR Signal Strength

T cells are critical in orchestrating protective immune responses to cancer and an array of pathogens. The interaction between a peptide MHC (pMHC) complex on antigen presenting cells (APCs) and T cell receptors (TCRs) on T cells initiates T cell activation, division, and clonal expansion in secondary lymphoid organs. T cells must also integrate multiple T cell-intrinsic and extrinsic signals to acquire the effector functions essential for the defense against invading microbes. In the case of T helper cell differentiation, while innate cytokines have been demonstrated to shape effector CD4⁺ T lymphocyte function, the contribution of TCR signaling strength to T helper cell differentiation is less understood. In this review, we summarize the signaling cascades regulated by the strength of TCR stimulation. Various mechanisms in which TCR signal strength controls T helper cell expansion and differentiation are also discussed.

Analysis of lymphocytes in patients with Plasmodium vivax malaria and its relation to the annexin-A1 and IL-10

BACKGROUND

Malaria is the most prevalent parasitic disease in the world. In Brazil, the largest number of malaria cases (98%) is within the Legal Amazon region, where Plasmodium vivax is responsible for over 80% of diagnosed cases. The aim of this study was to investigate the annexin-A1 expression in CD4+, CD8+ T cells, regulatory T cells (Treg) and cytokine IL-10 quantification in plasma from patients with malaria caused by P. vivax.

METHODS

The quantification of the cytokine IL-10 of patients infected with P. vivax and healthy controls were evaluated by enzyme-linked immunosorbent assay (ELISA). The determination of the expression of annexin-A1 in lymphocytes from patients and healthy controls was determined by immunofluorescence staining. All results were correlated with the parasitaemia and the number of previous episodes of malaria.

RESULTS

The cytokine IL-10 plasma levels showed a significant increase in both patients with low (650.4 ± 59.3 pg/mL) and high (2870 ± 185.3 pg/mL) parasitaemia compared to the control (326.1 ± 40.1 pg/mL). In addition, there was an increase of this cytokine in an episode dependent manner (individuals with no previous episodes of malaria--primoinfected: 363.9 ± 31.1 pg/mL; individuals with prior exposure: 659.9 ± 49.4 pg/mL). The quantification of annexin-A1 expression indicated a decrease in CD4+ and CD8+ T cells and an increase in Treg in comparison with the control group. When annexin-A1 expression was compared according to the number of previous episodes of malaria, patients who have been exposed more than once to the parasite was found to have higher levels of CD4+ T cells (96.0 ± 2.5 A.U) compared to primoinfected (50.3 ± 1.7). However, this endogenous protein had higher levels in CD8+ (108.5 ± 3.1) and Treg (87.5 ± 2.5) from patients primoinfected.

CONCLUSION

This study demonstrates that in the patients infected with P. vivax the release of immunoregulatory molecules can be influenced by the parasitaemia level and the number of previous episodes of malaria. annexin-A1 is expressed differently in lymphocyte sub-populations and may have a role in cell proliferation. Furthermore, annexin-A1 may be contributing to IL-10 release in plasma of patients with vivax malaria.

Dose-dependent induction of murine Th1/Th2 responses to sheep red blood cells occurs in two steps: antigen presentation during second encounter is decisive

The differentiation of CD4 T cells into Th1 and Th2 cells in vivo is difficult to analyze since it is influenced by many factors such as genetic background of the mice, nature of antigen, and adjuvant. In this study, we used a well-established model, which allows inducing Th1 or Th2 cells simply by low (LD, 10(5)) or high dose (HD, 10(9)) injection of sheep red blood cells (SRBC) into C57BL/6 mice. Signature cytokine mRNA expression was determined in specific splenic compartments after isolation by laser-microdissection. LD immunization with SRBC induced T cell proliferation in the splenic T cell zone but no Th1 differentiation. A second administration of SRBC into the skin rapidly generated Th1 cells. In contrast, HD immunization with SRBC induced both T cell proliferation and immediate Th2 differentiation. In addition, splenic marginal zone and B cell zone were activated indicating B cells as antigen presenting cells. Interestingly, disruption of the splenic architecture, in particular of the marginal zone, abolished Th2 differentiation and led to the generation of Th1 cells, confirming that antigen presentation by B cells directs Th2 polarization. Only in its absence Th1 cells develop. Therefore, B cells might be promising targets in order to therapeutically modulate the T cell response.

Increased ribonuclease expression reduces inflammation and prolongs survival in TLR7 transgenic mice

TLR7 activation is implicated in the pathogenesis of systemic lupus erythematosus. Mice that overexpress TLR7 develop a lupus-like disease with autoantibodies and glomerulonephritis and early death. To determine whether degradation of the TLR7 ligand RNA would alter the course of disease, we created RNase A transgenic (Tg) mice. We then crossed the RNase Tg to TLR7 Tg mice to create TLR7 × RNase double Tg (DTg) mice. DTg mice had a significantly increased survival associated with reduced activation of T and B lymphocytes and reduced kidney deposition of IgG and C3. We observed massive hepatic inflammation and cell death in TLR7 Tg mice. In contrast, hepatic inflammation and necrosis were strikingly reduced in DTg mice. These findings indicate that high concentrations of serum RNase protect against immune activation and inflammation associated with TLR7 stimulation and that RNase may be a useful therapeutic strategy in the prevention or treatment of inflammation in systemic lupus erythematosus and, possibly, liver diseases.

Lipopolysaccharide-activated dendritic cells: "exhausted" or alert and waiting?

LPS-activated dendritic cells (DCs) are thought to follow a set program in which they secrete inflammatory cytokines (such as IL-12) and then become refractory to further stimulation (i.e., "exhausted"). In this study, we show that mouse DCs do indeed lose their responsiveness to LPS, but nevertheless remain perfectly capable of making inflammatory cytokines in response to signals from activated T cells and to CD40-ligand and soluble T cell-derived signals. Furthermore, far from being rigidly programmed by the original activating stimulus, the DCs retained sufficient plasticity to respond differentially to interactions with Th0, Th1, Th2, and Th17 T cells. These data suggest that LPS activation does not exhaust DCs but rather primes them for subsequent signals from T cells.

Human antitumor CD8+ T cells producing Th1 polycytokines show superior antigen sensitivity and tumor recognition

Adoptive transfer of T cells expressing transgenic TCR with antitumor specificity provides a hopeful new therapy for patients with advanced cancer. To fulfill a large need for TCR with high affinity and specificity for various tumor entities, we sought to identify parameters for rapid selection of CTL clones with suitable characteristics. Twelve CTL clones displaying different Ag sensitivities for the same peptide-MHC epitope of the melanoma-associated Ag tyrosinase were analyzed in detail. Better MHC-multimer binding and slower multimer release are thought to reflect stronger TCR-peptide-MHC interactions; thus, these parameters would seem well suited to identify higher avidity CTL. However, large disparities were found comparing CTL multimer binding with peptide sensitivity. In contrast, CD8(+) CTL with superior Ag sensitivity mediated good tumor cytotoxicity and also secreted the triple combination of IFN-γ, IL-2, and TNF-α, representing a Th1 pattern often missing in lower avidity CTL. Furthermore, recipient lymphocytes were imbued with high Ag sensitivity, superior tumor recognition, as well as capacity for Th1 polycytokine secretion after transduction with the TCR of a high-avidity CTL. Thus, Th1 polycytokine secretion served as a suitable parameter to rapidly demark cytotoxic CD8(+) T cell clones for further TCR evaluation.

Differential expression of Ly6C and T-bet distinguish effector and memory Th1 CD4(+) cell properties during viral infection

CD4(+) T cells differentiate into multiple effector types, but it is unclear how they form memory T cells during infection in vivo. Profiling virus-specific CD4(+) T cells revealed that effector cells with T helper 1 (Th1) or T follicular helper (Tfh) cell characteristics differentiated into memory cells, although expression of Tfh cell markers declined over time. In contrast to virus-specific effector CD8(+) T cells, increased IL-7R expression was not a reliable marker of CD4(+) memory precursor cells. However, decreased Ly6C and T-bet (Tbx21) expression distinguished a subset of Th1 cells that displayed greater longevity and proliferative responses to secondary infection. Moreover, the gene expression profile of Ly6C(lo)T-bet(int) Th1 effector cells was virtually identical to mature memory CD4(+) T cells, indicating early maturation of memory CD4(+) T cell features in this subset during acute viral infection. This study provides a framework for memory CD4(+) T cell development after acute viral infection.

Characterization of antigenic variants of hepatitis C virus in immune evasion

BACKGROUND

Antigenic variation is an effective way by which viruses evade host immune defense leading to viral persistence. Little is known about the inhibitory mechanisms of viral variants on CD4 T cell functions.

RESULTS

Using sythetic peptides of a HLA-DRB1*15-restricted CD4 epitope derived from the non-structural (NS) 3 protein of hepatitis C virus (HCV) and its antigenic variants and the peripheral blood mononuclear cells (PBMC) from six HLA-DRB1*15-positive patients chronically infected with HCV and 3 healthy subjects, the in vitro immune responses and the phenotypes of CD4+CD25+ cells of chronic HCV infection were investigated. The variants resulting from single or double amino acid substitutions at the center of the core region of the Th1 peptide not only induce failed T cell activation but also simultaneously up-regulate inhibitory IL-10, CD25-TGF-β+ Th3 and CD4+IL-10+ Tr1 cells. In contrast, other variants promote differentiation of CD25+TGF-β+ Th3 suppressors that attenuate T cell proliferation.

CONCLUSIONS

Naturally occuring HCV antigenic mutants of a CD4 epitope can shift a protective peripheral Th1 immune response into an inhibitory Th3 and/or Tr1 response. The modulation of antigenic variants on CD4 response is efficient and extensive, and is likely critical in viral persistence in HCV infection.

TCR affinity for self-ligands influences the development and function of encephalitogenic T cells

The specificity and affinity of self-reactive T cells is likely to impact the development of autoimmune-disease causing T cells in the thymus as well as their function in the periphery. We identified a naturally occurring, low affinity variant of an MBP Ac1-11/I-A^u specific TCR that is known to induce EAE. Thymocytes in mice carrying the transgenes for this low affinity TCR were poorly positively selected, as compared to their high affinity TCR expressing counterparts. Nonetheless, CD4 T cells bearing the low affinity TCR accumulated in the periphery of the mice. Unlike mice expressing the high affinity TCR, these mice very rarely developed disease. However, if endogenous TCR expression was eliminated by breeding to RAG1 deficient mice, 100% of the mice carrying either the high or the low affinity versions of the TCR developed EAE. Intriguingly, while the incidence of EAE increased, the age of onset of disease in both mice was identical. These data suggest disease onset occurs during a short window of mouse development.

T helper cell differentiation more than just cytokines

CD4(+) T helper (T(H)) cells play a critical role in orchestrating a pleiotropy of immune activities against a large variety of pathogens. It is generally thought that this is achieved through the acquisition of highly specialized functions after activation followed by the differentiation into various functional subsets. The differentiation process of naive precursor T(H) cells into defined effector subsets is controlled by cells of the innate immune system and their complex array of effector molecules such as secreted cytokines and membrane bound costimulatory molecules. These provide a unique quantitative or qualitative signal initiating T(H) development, which is subsequently reinforced via T cell-mediated feedback signals and selective survival and proliferative cues, ultimately resulting in the predominance of a particular T cell subset. In recent years, the number of defined T(H)cell subsets has expanded and the once rigid division of labor among them has been blurred with reports of plasticity among the subsets. In this chapter, we summarize and speculate on the current knowledge of the differentiation requirements of T(H) cell lineages, with particular focus on the T(H)17 subset.

Surface expression of MPT64 as a fusion with the PE domain of PE_PGRS33 enhances Mycobacterium bovis BCG protective activity against Mycobacterium tuberculosis in mice

To improve the current vaccine against tuberculosis, a recombinant strain of Mycobacterium bovis bacillus Calmette-Guérin (rBCG) expressing a Mycobacterium tuberculosis vaccine candidate antigen (MPT64) in strong association with the mycobacterial cell wall was developed. To deliver the candidate antigen on the surface, we fused the mpt64 gene to the sequence encoding the PE domain of the PE_PGRS33 protein of M. tuberculosis (to create strain (H)PE-ΔMPT64-BCG), which we have previously shown to transport proteins to the bacterial surface. In a series of protection experiments in the mouse model of tuberculosis, we showed that (i) immunization of mice with (H)PE-ΔMPT64-BCG provides levels of protection significantly higher than those afforded by the parental BCG strain, as assessed by bacterial colonization in lungs and spleens and by lung involvement (at both 28 and 70 days postchallenge), (ii) rBCG strains expressing MPT64 provide better protection than the parental BCG strain only when this antigen is surface expressed, and (iii) the (H)PE-ΔMPT64-BCG-induced MPT64-specific T cell repertoire when characterized by β chain variable region-β chain joining region (BV-BJ) spectratyping indicates that protection is correlated with the ability to recruit gamma interferon (IFN-γ)-secreting T cells carrying the BV8.3-BJ1.5 (172 bp) shared rearrangement. These results demonstrate that (H)PE-ΔMPT64-BCG is one of the most effective new vaccines tested so far in the mouse model of tuberculosis and underscore the impact of antigen cellular localization on the induction of the specific immune response induced by rBCG.

The Goldilocks model for TCR-too much attraction might not be best for vaccine design

Recent research on T cell-antigen interactions suggests that tighter binding is not always better at eliciting an effective immune response.

The function of follicular helper T cells is regulated by the strength of T cell antigen receptor binding

How follicular helper T cells (T(FH) cells) differentiate to regulate B cell immunity is critical for effective protein vaccination. Here we define three transcription factor T-bet-expressing antigen-specific effector helper T cell subsets with distinguishable function, migratory properties and developmental programming in vivo. Expression of the transcriptional repressor Blimp-1 distinguished T zone 'lymphoid' effector helper T cells (CD62L(hi)CCR7(hi)) from CXCR5(lo) 'emigrant' effector helper T cells and CXCR5(hi) 'resident' T(FH) cells expressing the transcriptional repressor Bcl-6 (CD62L(lo)CCR7(lo)). We then show by adoptive transfer and intact polyclonal responses that helper T cells with the highest specific binding of peptide-major histocompatibility complex class II and the most restricted T cell antigen receptor junctional diversity 'preferentially' developed into the antigen-specific effector T(FH) compartment. Our studies demonstrate a central function for differences in the binding strength of the T cell antigen receptor in the antigen-specific mechanisms that 'program' specialized effector T(FH) function in vivo.

Annexin-A1: a pivotal regulator of the innate and adaptive immune systems

The glucocorticoids are the most potent anti-inflammatory drugs that we possess and are effective in a wide variety of diseases. Although their action is known to involve receptor mediated changes in gene transcription, the exact mechanisms whereby these bring about their pleiotropic action in inflammation are yet to be totally understood. Whilst many different genes are regulated by the glucocorticoids, we have identified one particular protein-annexin A1 (Anx-A1)-whose synthesis and release is strongly regulated by the glucocorticoids in many cell types. The biology of this protein, as revealed by studies using transgenic animals, peptide mimetics and neutralizing antibodies, speaks to its role as a key modulator of both of the innate and adaptive immune systems. The mechanism whereby this protein exerts its effects is likely to be through the FPR receptor family-a hitherto rather enigmatic family of G protein coupled receptors, which are increasingly implicated in the regulation of many inflammatory processes. Here we review some of the key findings that have led up to the elucidation of this key pathway in inflammatory resolution.

Alterations in T cell signal transduction by M. leprae antigens is associated with downregulation of second messengers PKC, calcium, calcineurin, MAPK and various transcription factors in leprosy patients

Mycobacterium leprae, the causative agent of leprosy, challenges host defense mechanism by impairing the signal transduction of T cells which leads to downregulation of T cell proliferation, mainly as a consequence of interference with IL-2 production. In this study we sought to identify how soluble forms of M. leprae antigen(s) or particulate (liposome) delivery of the same antigens with two immunomodulators Murabutide and T cell peptide of Trat protein influence the transcription of IL-2 gene in anergic T cells of lepromatous patients. It was demonstrated that MLCwA/ManLAM stimulated cells of BL/LL patients showed defects in both jun-NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) activities there by resulting in decreased AP-1 activity. Additionally these cells showed reduced calcium levels, PKC activity and calcineurin (CN) activity. This led to impaired nuclear translocation of NFkappaB and NFAT in these patients. In contrast, when same M. leprae antigen(s) were incorporated with the two immunomodulators in liposomal form, increased transcription of IL-2 gene was observed especially in BL/LL patients which appears to be due to, at least in part, to increased expression of AP-1 Fos and Jun family members, NFkappaB and NFAT1 proteins. The increased expression of these transcription factors correlated with increased ERK/JNK, PKC and CN activities in these patients. Since activation of ERK/JNK/PKC kinases and CN phosphatase are required for stimulation of IL-2 transcription, these data provide a molecular explanation for the block in IL-2 production by M. leprae antigens. Thus the above study revealed suppression of all the three distinct biochemical pathways, viz. Ca-CN-NFAT pathway, PKC-NF-kappaB pathway, and MAPK-AP-1 pathway by M. leprae antigen(s) in anergized T cells of lepromatous patients which were activated by liposomal delivery of M. leprae antigens containing the two immunomodulators leading to optimal induction of IL-2 gene expression, which was required for the activation, and proliferation of T cells in lepromatous patients.

Influence of leflunomide on gastrointestinal Candida albicans infection induced in naive and arthritic newborn mice

Mucosal Candida albicans infection in immunocompromised individuals being treated with recently advanced drugs can progress to systemic disease. One such medication applied in patients with rheumatoid arthritis is leflunomide. The object of the present study was to investigate the effect of leflunomide on a model of gastrointestinal (g.i.) C. albicans infection induced in naïve or arthritic mice and on the host resistance to systemic re-infection. Newborn mice were orally inoculated with 1 x 10(5) colony forming units (CFU) of C. albicans and at age of 5 weeks they were treated with 5 mg/kg or 20 mg/kg of leflunomide for 10 consecutive days. Both doses elevated the yeast colonization of the stomach, without the dissemination into the internal organs. This was in parallel with the enhanced delayed type hypersensitivity (DTH) reaction to the yeast. Contrary to that, leflunomide caused a shift to Th2 reactivity by prevalence of IL-4 to IFN-gamma and a suppression of anti-Candida antibody synthesis by a higher dose. It might be supposed that infection increased autoimmune response in arthritic mice, according to stimulated DTH reaction to collagen. The administration of leflunomide during the simultaneous development of infection and arthritis diminished anti-Candida and anti-collagen antibody synthesis compared to untreated infected arthritic mice. The improved survival of arthritic infected animals against severe systemic re-infection was not changed after administration of leflunomide to re-infected arthritic mice. We can conclude that although leflunomide influenced cytokine secretion and suppressed anti-Candida antibody production it neither provokes a progression from gastrointestinal to systemic C. albicans infection nor increases the susceptibility to severe C. albicans re-infection of arthritic mice.

Comparative assessment of Th1 and Th2 cytokines of swamp type buffalo and other bubaline breeds by molecular cloning, sequencing and phylogenetics

Comparative assessment of Th1 and Th2 cytokines of three bubaline breeds namely swamp buffalo, its crossbreed with riverine buffalo (CB), and the improved breed of Bulgarian Murrah buffalo (BMB), was done by molecular cloning, sequencing and phylogenetic analysis. The Th1 cytokines analyzed included IL-2, IL-12p35, IL-12p40, and IFN-gamma while Th2 cytokines included IL-4 and IL-10. Both groups showed strict conservation in the putative secondary structures and amino acid residues within the tribe Bovini, which indicated functional cross-reactivity. Nucleotide sequence homology ranged from 98.6 to 100.0% and was lowest for IL-12p35. With regard to amino acid sequence, the lowest homology was observed in IL-4 with 97.8%. This substitution was mainly due to differences in mRNA splicing. The phylogenetic relationship of the buffalo breeds was analyzed and showed them as a cluster comprised mainly of species belonging to the order Artiodactyla, including cattle and pigs. A deeper knowledge of these cytokine structures will favor understanding of water buffalo immunology and how much it differs from its closest subspecies and other animals.

Directed evolution of human T cell receptor CDR2 residues by phage display dramatically enhances affinity for cognate peptide-MHC without increasing apparent cross-reactivity

The mammalian alpha/beta T cell receptor (TCR) repertoire plays a pivotal role in adaptive immunity by recognizing short, processed, peptide antigens bound in the context of a highly diverse family of cell-surface major histocompatibility complexes (pMHCs). Despite the extensive TCR-MHC interaction surface, peptide-independent cross-reactivity of native TCRs is generally avoided through cell-mediated selection of molecules with low inherent affinity for MHC. Here we show that, contrary to expectations, the germ line-encoded complementarity determining regions (CDRs) of human TCRs, namely the CDR2s, which appear to contact only the MHC surface and not the bound peptide, can be engineered to yield soluble low nanomolar affinity ligands that retain a surprisingly high degree of specificity for the cognate pMHC target. Structural investigation of one such CDR2 mutant implicates shape complementarity of the mutant CDR2 contact interfaces as being a key determinant of the increased affinity. Our results suggest that manipulation of germ line CDR2 loops may provide a useful route to the production of high-affinity TCRs with therapeutic and diagnostic potential.

Mycobacterium tuberculosis in the adjuvant modulates the balance of Th immune response to self-antigen of the CNS without influencing a “core” repertoire of specific T cells

In the present study, we use modified CDR3 beta-chain spectratyping (immunoscope) to dissect the effect of Mycobacterium tuberculosis (MT)-derived proteins on individual PLP139-151-specific cells in the SJL mouse strain. In this model, the immunoscope technique allows the characterization of a public TCR that involves rearrangement of Vbeta10 and Jbeta1.1 and a semi-private TCR characterized by rearrangement of Vbeta4 and Jbeta1.6. Both rearrangements are specific for PLP139-151 and sequences of the CDR3 region of the two beta-chains show a conserved motif for the public rearrangement and related but more variable sequences for the semi-private rearrangement. MT-derived proteins promote increase of IFN-gamma-secreting cells. However, we observe that the presence and amount of MT used during immunization have no effect on the frequency of usage, polarization and in vivo expansion of cells carrying the studied rearrangements. Rather, the strong Th1-promoting effect of adjuvant is possibly due to recruitment toward Th1 of a wider spectrum of TCR repertoires. Therefore, instead of having a comprehensive effect on the entire repertoire, MT modulates the immune response by affecting a subset of antigen-specific T cells whose polarization can be adapted to the environment. This step establishes the final balance between Th1 and Th2 and may be essential for the enhancement or protection of disease.

Different Competitive Capacities of Stat4- and Stat6-Deficient CD4+ T Cells during Lymphophenia-Driven Proliferation

The outcome of an immune response relies on the competitive capacities acquired through differentiation of CD4(+) T cells into Th1 or Th2 effector cells. Because Stat4 and Stat6 proteins are implicated in the Th1 vs Th2 generation and maintenance, respectively, we compare in this study the kinetics of Stat4(-/-) and Stat6(-/-) CD4(+) T cells during competitive bone marrow reconstitution and lymphopenia-driven proliferation. After bone marrow transplantation, both populations reconstitute the peripheral T cell pools equally well. After transfer into lymphopenic hosts, wild-type and Stat6(-/-) CD4(+) T cells show a proliferation advantage, which is early associated with the expression of an active phospho-Stat4 and the down-regulation of Stat6. Despite these differences, Stat4- and Stat6-deficient T cells reach similar steady state numbers. However, when both Stat4(-/-) and Stat6(-/-) CD4(+) T cells are coinjected into the same hosts, the Stat6(-/-) cells become dominant and out-compete Stat4(-/-) cells. These findings suggest that cell activation, through the Stat4 pathway and the down-regulation of Stat6, confers to pro-Th1 T cells a slight proliferation advantage that in a competitive situation has major late repercussions, because it modifies the final homeostatic equilibrium of the populations and favors the establishment of Th1 CD4(+) T cell dominance.

Chronic heart allograft rejection in rats demonstrates a dynamic interplay between IFN-γ and IL-10 producing T cells

The relative roles of different types of T cells and their modes of alloantigen recognition and cytokine production in chronic rejection have been controversial. This may be due to the use of models involving various immune interventions. We recently reported a rat heart allograft model (PVG.1U-to-PVG.R8) that consistently develops chronic rejection without any immune manipulations. Using this model, we investigated the frequency of indirectly activated alloreactive CD4+ T cells and directly/indirectly induced CD8+ T cells and characterized their cytokine profiles at various times posttransplantation. In vitro quantitative-proliferative and intracellular cytokine assays were performed using recipient lymphocytes as responders against donor and third party stimulator cells. Intragraft transcript levels for IFN-gamma were measured using competitive RT-PCR. We observed a steady increase in the frequency of donor reactive CD4+ T cells, peaking on day 18-22 posttransplantation, followed by a decline to background levels on day 60. These cells produced high levels of IL-10 that steadily increased throughout the 100-day experimental period. In contrast, the frequency of donor reactive CD8+ T cells was similar to that of naïve cells and remained unchanged throughout the study. CD8+ T cells produced high amounts of IFN-gamma only on days 39-45 posttransplantation when chronic rejection was apparent. There was a sharp increase in intragraft IFN-gamma transcripts on days 8-12 that peaked on days 39-45 followed by a steady decrease thereafter. Our results demonstrate that chronic rejection in this model involves a dynamic interplay between alloreactive CD8+IFN-gamma+ and CD4+IL-10+ T cells, both of which may have differential effects on the pathogenesis of the disease.

Skin scratching switches immune responses from Th2 to Th1 type in epicutaneously immunized mice

BACKGROUND

The balance between Th1 and Th2 subsets is important with respects to susceptibility and resistance to particular infection or autoimmune diseases. However, the mechanism controlling Th1/Th2 balance remains unclear, although several factors have been reported to induce Th1/Th2 differentiation. Atopic Dermatitis (AD) that is a chronic skin disorder has been known as Th2 biased nature characterized by high expression of IgE in the serum. In contrast, the chronic skin lesions express IFNgamma and some patients don't show IgE in the serum. Thus, the pathology is also complicated now.

OBJECTIVE

We focused on skin scratching that is common feature in the patients. In this study, we investigated in order to determine whether skin scratching regulates immune responses in murine epicutaneous sensitization model.

METHODS

The scratched mice on abdominal skin using wire brush were applied with keyhole limpet hemocyanin (KLH) on the skin using occlusive patch. We examined the immune responses including delayed type hypersensitivity (DTH) reaction, antigen-specific serum immunoglobulin formation, and cytokine expressions on the local skin in comparison with mice without scratching.

RESULTS

We found that the epicutaneously sensitized mice with KLH on abdominal skin showed Th2 biased immune response including expression of antigen-specific IgE in the serum and IL-13 in the local skin. Surprisingly, scratching on local abdominal skin using wire brush exchanged the immune response from Th2 dominance to Th1, because the mice displayed DTH reaction and significant level of antigen-specific IgG2a and IgG2b but not IgE in the serum. Furthermore, the abdominal skin showed significant level of IFNgamma but not IL-13.

CONCLUSION

These data demonstrate that skin scratching switches immune response from Th2 biased response to Th1. This suggests that skin scratching play critical roles as one of exogenous immune modulator. This murine sensitization model may help to understand natures of several allergic disorders including AD.

Induction of FucT-VII by the Ras/MAP kinase cascade in Jurkat T cells

Induction of the alpha1,3-fucosyltransferase FucT-VII in T lymphocytes is crucial for selectin ligand formation, but the signaling and transcriptional pathways that govern FucT-VII expression are unknown. Here, using a novel, highly phorbol myristate acetate (PMA)-responsive variant of the Jurkat T-cell line, we identify Ras and downstream mitogen-activated protein (MAP) kinase pathways as essential mediators of FucT-VII gene expression. PMA induced FucT-VII in only a subset of treated cells, similar to expression of FucT-VII in normal activated CD4 T cells. Introduction of constitutively active Ras or Raf by recombinant retroviruses induced FucT-VII expression only in that subset of cells expressing the highest levels of Ras, suggesting that induction of FucT-VII required a critical threshhold of Ras signaling. Both PMA treatment and introduction of active Ras led to rolling on E-selectin. Pharmacologic inhibition studies confirmed the involvement of the classic Ras-Raf-MEK-extracellular signal-regulated kinase (Ras-Raf-MEK-ERK) pathway in FucT-VII induction by PMA, Ras, and Raf. These studies also revealed a second, Ras-induced, Raf-1-independent pathway that participated in induction of FucT-VII. Strong activation of Ras represents a major pathway for induction of FucT-VII gene expression in T cells.

T cell recognition of distinct peptide:I-Au conformers in murine experimental autoimmune encephalomyelitis

We have used T cells bearing TCRs that are closely related in sequence as probes to detect conformational variants of peptide-MHC complexes in murine experimental autoimmune encephalomyelitis in H-2(u) mice. The N-terminal epitope of myelin basic protein (MBP) is immunodominant in this model. Our studies have primarily focused on T cell recognition of a position 4 analog of this peptide (MBP1-9[4Y]) complexed with I-A(u). Using site-directed mutagenesis, we have mapped the functionally important complementarity determining region residues of the 1934.4 TCR Valpha domain. One of the resulting mutants (Tyr(95) to alanine in CDR3alpha, Y95A) has interesting properties: relative to the parent wild-type TCR, this mutant poorly recognizes Ag complexes generated by pulsing professional APCs (PL-8 cells) with MBP1-9[4Y] while retaining recognition of MBP1-9[4Y]-pulsed unconventional APCs or insect cell-expressed complexes of I-A(u) containing tethered MBP1-9[4Y]. Insect cell expression of recombinant I-A(u) with covalently tethered class II-associated invariant chain peptide or other peptides which bind relatively weakly, followed by proteolytic cleavage of the peptide linker and replacement by MBP1-9[4Y] in vitro, results in complexes that resemble peptide-pulsed PL-8 cells. Therefore, the distinct conformers can be produced in recombinant form. T cells that can distinguish these two conformers can also be generated by the immunization of H-2(u) mice, indicating that differential recognition of the conformers is observed for responding T cells in vivo. These studies have relevance to understanding the molecular details of T cell recognition in murine experimental autoimmune encephalomyelitis. They are also of particular importance for the effective use of multimeric peptide-MHC complexes to characterize the properties of Ag-specific T cells.

A pool of central memory-like CD4 T cells contains effector memory precursors

The L51S mutation in the D10.G4.1 TCR alpha-chain reduces the affinity of the TCR to its ligand by affecting the interactions among the TCR, the beta-chain of I-A(k), and the bound peptide. We show that this mutation drives the generation of a pool of memory CD44(high)CD62L(neg)CD45RB(neg) CD4 TCR transgenic T cells. Their activation threshold is low, such that they proliferate in response to lower concentrations of agonist peptides than naive L51S CD4 T cells. Unlike effector memory CD4 T cells, however, they lack immediate effector function in response to TCR stimulation. These cells express IL-2R alpha only after culture with specific peptide. Although they can be recovered from lymph nodes, the majority lack the expression of the lymph node homing receptor CCR7. When these cells receive a second TCR stimulation in vitro, they differentiate into potent Th2-like effector cells, producing high levels of IL-4 at doses of agonist peptide too low to stimulate cytokine release from similarly differentiated naive L51S CD4 T cells. Having these properties, the L51S TCR transgenic memory CD4 T cells cannot be classified as either strict central memory or effector memory, but, rather, as a pool of memory T cells containing effector memory precursors.

SWAP-70-like adapter of T cells, an adapter protein that regulates early TCR-initiated signaling in Th2 lineage cells

We describe the isolation of a protein, SWAP-70-like adapter of T cells (SLAT), which is expressed at high levels in thymocytes and differentiated Th2 cells. SLAT expression was upregulated in differentiating Th2 cells and downregulated in Th1 cells. Ectopic SLAT expression exerted positive or negative effects on IL-4 versus IFNgamma induction, respectively. TCR signaling induced translocation of SLAT to the immunological synapse and its association with ZAP-70 kinase. SLAT reduced the association of ZAP-70 with TCR-zeta and interfered with ZAP-70 but not Lck signaling. Consistent with these results, pharmacological inhibition of ZAP-70 also induced Th2 skewing. Thus, SLAT is a protein which plays a role in Th2 development and/or activation, perhaps by interfering with ZAP-70 signaling.

Identification of immunodominant epitopes derived from the respiratory syncytial virus fusion protein that are recognized by human CD4 T cells

Memory CD4 T-cell responses against respiratory syncytial virus (RSV) were evaluated in peripheral blood mononuclear cells of healthy blood donors with gamma interferon enzyme-linked immunospot (Elispot) assays. RSV-specific responses were detected in every donor at levels varying between 0.05 and 0.3% of CD4 T cells. For all donors tested, a considerable component of the CD4 T-cell response was directed against the fusion (F) protein of RSV. We characterized a set of 31 immunodominant antigenic peptides targeted by CD4 T cells in the context of the most prevalent HLA class II molecules within the Caucasian population. Most antigenic peptides were HLA-DR restricted, whereas two dominant DQ peptides were also identified. The antigenic peptides identified were located across the entire sequence of the F protein. Several peptides were presented by more than one major histocompatibility complex class II molecule. Furthermore, most donors recognized several F peptides. Detailed knowledge about immunodominant antigenic peptides will facilitate the ability to monitor CD4 T-cell responses in patients and the measurement of correlates of protection in vaccinated subjects.

Recognition of a specific self-peptide: self-MHC class II complex is critical for positive selection of thymocytes expressing the D10 TCR

We examined the specificity of positive and negative selection by using transgenic mice carrying a variant of the D10 TCR. We demonstrate that a point mutation at position 51 within the CDR2alpha segment significantly reduces the avidity of this TCR for its cognate ligand, but does not impact recognition of nonself MHC class II molecules. Although structural studies have suggested that this TCR site interacts with the MHC class II beta-chain, the avidity of this TCR for its ligand and the function of the T cell can be reconstituted by a point mutation in the bound antigenic peptide. These data demonstrate that the bound peptide can indirectly alter TCR interactions by influencing MHC structure. Remarkably, reducing the avidity of this TCR for a specific antigenic peptide-MHC ligand has a dramatic impact on thymic selection. Positive selection of thymocytes expressing this TCR is nearly completely blocked, whereas negative selection on allogenic MHC class II molecules remains intact. Therefore, the recognition of self that promotes positive selection of the D10 TCR is highly peptide-specific.

Restriction of de novo pyrimidine biosynthesis inhibits Th1 cell activation and promotes Th2 cell differentiation

Leflunomide, an inhibitor of de novo pyrimidine biosynthesis, has recently been introduced as a treatment for rheumatoid arthritis in an attempt to ameliorate inflammation by inhibiting lymphocyte activation. Although the immunosuppressive ability of leflunomide has been well described in several experimental animal models, the precise effects of a limited pyrimidine supply on T cell differentiation and effector functions have not been elucidated. We investigated the impact of restricted pyrimidine biosynthesis on the activation and differentiation of CD4 T cells in vivo and in vitro. Decreased activation of memory CD4 T cells in the presence of leflunomide resulted in impaired generation and outgrowth of Th1 effectors without an alteration of Th2 cell activation. Moreover, priming of naive T cells in the presence of leflunomide promoted Th2 differentiation from uncommitted precursors in vitro and enhanced Th2 effector functions in vivo, as indicated by an increase in Ag-specific Th2 cells and in the Th2-dependent Ag-specific Ig responses (IgG1) in immunized mice. The effects of leflunomide on T cell proliferation and differentiation could be antagonized by exogenous UTP, suggesting that they were related to a profound inhibition of de novo pyrimidine biosynthesis. These results indicate that leflunomide might exert its anti-inflammatory activities in the treatment of autoimmune diseases by preventing the generation of proinflammatory Th1 effectors and promoting Th2 cell differentiation. Moreover, the results further suggest that differentiation of CD4 T cells can be regulated at the level of nucleotide biosynthesis.

Functional plasticity of an antigen-specific memory CD4 T cell population

The protective nature of memory immune responses is attributed largely to terminally differentiated memory T cells that retain memory of the antigen via the antigen receptor and memory of the effector functions that initially cleared the pathogen. It is not known whether a given population of antigen-specific memory T cells is endowed with functional flexibility to provide protective responses against antigens reencountered in different immunological contexts. Here, we examine functional properties of influenza hemagglutinin (HA)-specific memory CD4 T cells recovered from adoptive hosts that received in vitro-activated HA-specific T cell receptor-transgenic CD4 T cells 2 months to 1 year previously. We demonstrate that this HA-specific memory CD4 T cell population bearing a clonal T cell receptor can produce predominantly T helper 1 or T helper 2 effector cytokines depending on the nature of the recall stimulus. Our findings reveal remarkable functional plasticity within an antigen-specific memory T cell population and have direct implications for modulating memory T cell function in vaccine design and treatments for autoimmune diseases.

The Th1/Th2 cytokine balance changes with the progress of the immunopathological lesion of Sjogren's syndrome

Expression of type-1 and type-2 cytokines at the mRNA level in labial salivary glands (LSG) of patients with Sjogren's syndrome (SS), as reported by several groups, have generated conflicting results. In the present study we have directly examined the production of IL-4, IL-13 and IFN-gamma by lymphocytes infiltrating the LSG of 44 consecutive patients referred for SS evaluation. Cytokines production was evaluated following in vitro culture of LSG in the presence of IL-2. IFN-gamma and IL-13 were detected in the majority of SN (24/44 and 26/44, respectively) while IL-4 was present in 5/44 SN. The presence of IFN-gamma was significantly higher in SS patients, as opposed to patients who did not fulfil the criteria for SS (P < 0.01). In addition, almost all cultured lymphocytes expressed mRNA for IFN-gamma (17/19 cultures) and IL-13 (18/19) while IL-4 mRNA was also expressed at high frequency (14/19 cultures). Interestingly, the IFN-gamma mRNA copies in cultured lymphocytes correlated significantly with the intensity of lymphocytic infiltration as evaluated by Chisholm's score (P < 0.01). Furthermore, RT-PCR of RNA extracted from whole LSG from 14 SS patients also demonstrated the presence of all cytokines in the majority of the cases and the prevalence of IFN-gamma in LSG with high-grade infiltration. Because IL-13 was produced by the majority of the cultured LSG, IgE production was also evaluated. Interestingly, IgE was detected in 21/44 LSG culture SN and mainly in those biopsies that had Chisholm's score less than 0.5 (P < 0.05). We conclude that lymphocytes infiltrating the LSG are capable of producing both Th1 and Th2 cytokines and that the balance between them shifts in favour of Th1 in LSG with high infiltration score and in patients with SS.

Sustained NFAT signaling promotes a Th1-like pattern of gene expression in primary murine CD4+ T cells

T cell activation is known to be critically regulated by the extent and duration of TCR-induced signaling pathways. The NFAT family of transcription factors is believed to play an important role in coupling these quantitative differences in TCR-induced signaling events into changes in gene expression. In this study we have specifically investigated the effects of sustained NFAT signaling on T cell activation by introducing a constitutively active mutant version of NFATc1 (caNFATc1) into primary murine CD4(+) T cells and examining its effects on gene expression. We now report that ectopic expression of caNFATc1 partially mimics TCR signaling, resulting in enhanced expression of CD25 and CD40 ligand and down-regulation of CD62L. More importantly, we find that expression of caNFATc1 in T cells maintained under either nonpolarizing or Th1-skewing conditions leads to a marked selective increase in the number of cells expressing the prototypical Th1 cytokine, IFN-gamma. Furthermore, when expressed in Th2-skewed cells, caNFATc1 appears to attenuate Th2 differentiation by decreasing production of IL-4 and promoting the expression of IFN-gamma. Finally, we find that caNFATc1 enhances expression of functional P-selectin glycoprotein ligand-1, up-regulates Fas ligand expression, and increases susceptibility to activation-induced cell death, cellular traits that are preferentially associated with Th1 effector cells. Taken together, these results suggest that sustained NFAT signaling, mediated by ectopic expression of caNFATc1, acts to promote a Th1-like pattern of gene expression and thereby serves to highlight the important relationship between the degree of NFAT signaling and the qualitative pattern of gene expression induced during T cell activation.

CD4 T cells selected by antigen under Th2 polarizing conditions favor an elongated TCR alpha chain complementarity-determining region 3

The affinity of the MHC/peptide/TCR interaction is thought to be one factor determining the differentiation of CD4+ T cells into Th1 or Th2 phenotypes. To study whether CD4+ cells generated under conditions favoring Th1 or Th2 responses select structurally different TCRs, Th1 and Th2 clones and lines were generated from nonobese diabetic and nonobese diabetic H2-E transgenic mice against the peptides proteolipoprotein 56-70, glutamic acid decarboxylase(65) 524-543, and heat shock protein-60 peptides 168-186 and 248-264. Th1/Th2 polarization allowed the generation of clones and lines with fixed peptide specificity and class II restriction but differing in Th1/Th2 phenotype in which the impact on TCR selection and structure could be studied. The Th2 clones tended to use longer TCR complementarity-determining region (CDR)3alpha loops than their Th1 counterparts. This trend was confirmed by analyzing TCRalpha transcripts from Th1 and Th2 polarized, bulk populations. Molecular modeling of Th1- and Th2-derived TCRs demonstrated that Th2 CDR3alpha comprised larger side chain residues than Th1 TCRs. The elongated, bulky Th2 CDR3alpha loops may be accommodated at the expense of less optimal interactions between the MHC class II/peptide and other CDR loops of the TCR. We propose that CD4+ T cells selected from the available repertoire under Th2 polarizing conditions tend to have elongated TCR CDR3alpha loops predicted to alter TCR binding, reducing contact at other interfaces and potentially leading to impeded TCR triggering.

Chronic soluble antigen sensitization primes a unique memory/effector T cell repertoire associated with th2 phenotype acquisition in vivo

Although much progress has been made in characterization of the signaling pathways that control Th cell commitment, little is known about the early events that govern differentiation of IL-4-producing T lymphocytes in vivo. We have previously shown that chronic administration of low dose, soluble hen egg white lysozyme (HEL) induced the selective development of Ag-specific Th2 in genetically predisposed BALB/c mice. Here, we show that these memory/effector Th2 cells express a unique TCR Vbeta repertoire, different from the TCR Vbeta profile of primary effector cells from HEL-adjuvant-primed mice. This Th2-associated repertoire contains a highly frequent public clonotype characterized by preferred TCR AV and BV gene segment usage along with conserved sequences in the third hypervariable regions of both TCR chains. This Th2 clonotype, which is not recruited in primary effector T cells from HEL-adjuvant-immunized mice, recognized an IA(d)-restricted HEL determinant, preferentially processed by dendritic cells, but not by B cells. Thus, IL-4-producing CD4 T cells that expand following chronic Ag sensitization emerge from a distinct pool of precursors, supporting the hypothesis that ligand-TCR interactions play a crucial role in the regulation of Ag-specific Th2 cell development in vivo.

Mutation of Tec family kinases alters T helper cell differentiation

The Tec kinases Rlk and Itk are critical for full T cell receptor (TCR)-induced activation of phospholipase C-gamma and mitogen-activated protein kinase. We show here that the mutation of Rlk and Itk impaired activation of the transcription factors NFAT and AP-1 and production of both T helper type 1 (TH1) and TH2 cytokines. Consistent with these biochemical defects, Itk-/- mice did not generate effective TH2 responses when challenged with Schistosoma mansoni eggs. Paradoxically, the more severely impaired Rlk-/-Itk-/- mice were able to mount a TH2 response and produced TH2 cytokines in response to this challenge. In addition, Rlk-/-Itk-/- cells showed impaired TCR-induced repression of the TH2-inducing transcription factor GATA-3, suggesting a potential mechanism for TH2 development in these hyporesponsive cells. Thus, mutations that affect Tec kinases lead to complex alterations in CD4+ TH cell differentiation.

Immunopathology in RSV infection is mediated by a discrete oligoclonal subset of antigen-specific CD4(+) T cells

Vaccination with the respiratory syncytial virus (RSV) attachment (G) protein results in immune-mediated lung injury after natural RSV infection with pathogenic features characteristic of an exaggerated Th2 response. Here we demonstrate that approximately half of the CD4(+) T cells infiltrating the lungs of G-primed mice utilize a single V beta gene (V beta 14) with remarkably limited CDR3 diversity. Furthermore, elimination of these V beta 14-bearing CD4(+) T cells in vivo abolishes the type 2-like pulmonary injury. These results suggest that a novel subset of CD4(+) T cells may be crucial in the development of pathology during human RSV infection and that genetic or environmental factors prior to or at the time of G antigen exposure may affect the commitment of this discrete antigen-specific T cell subset to Th2 differentiation.

Antigen-specific immunity. Th cell-dependent B cell responses

Helper T cell-regulated B cell responses constitute a major component of the primary immune response to many pathogens. The subsequent development of antigen-specific immune memory is one critical outcome of this primary adaptive immune response. Antigen-specific immunity develops through a series of intercellular information exchanges organized around cognate T cell receptor-peptide/MHC interactions. Here, we discuss these complex molecularevents andtheircellularconsequences in a serial synapsis model of adaptive immunity. Our laboratory has developed strategies to isolate antigen-specific Th cells and B cells to analyze gene expression and cellular function in single responding lymphocytes directly ex vivo. These studies provide insight into the regulation and cellular organization of antigen-specific immune responses in vivo.

Germinal center reaction

The germinal center reaction is one critical outcome of helper T-cell-dependent antigen-specific B-cell responses. Germinal center reactions are the culmination of an orchestrated series of intercellular information exchanges discussed here as the serial synapsis model of adaptive immunity. The main purpose of the germinal center reaction is the development of B-cell memory through iterative cycles of somatic antigen receptor diversification and the selection of B cells with receptors of best fit. Recent studies provide insight into the regulation of these complex processes in vivo with new information on the cellular organization of the memory B-cell compartment.

Antigen-specific T helper cell function: differential cytokine expression in primary and memory responses

Distinguishing between the development of functional potential in antigen-specific T helper (Th) cells and the delivery of these specialized functions in vivo has been difficult to resolve. Here, we quantify the frequency of cytokine-producing cells within the primary and memory B10.BR Th cell response to pigeon cytochrome c (PCC). In vitro analysis of acquired functional potential indicated no Th1/Th2 cytokine polarity at the peak of the primary response with surprisingly little evidence for the selective preservation of interleukin (IL)-2, tumor necrosis factor (TNF)-alpha, IL-4, and interferon (IFN)-gamma potentials into the memory compartment. However, the expression of these functional potentials appears tightly regulated in vivo. The staggered appearance of primary response cytokines directly ex vivo contrasts markedly with their rapid coordinate expression in the memory response. Frequencies of IL-2-, TNF-alpha-, IFN-gamma-, and IL-10-expressing memory responders increased over their primary response counterparts, but were still markedly lower than revealed in vitro. IL-4-, IFN-gamma-, and IL-10-expressing Th cells remained at low but stable frequencies over the first 6 d of the memory response. Analysis of T cell receptor beta chain sequences of IL-4- and TNF-alpha-expressing PCC-specific Th cells provides evidence for early functional commitment among clonal progeny. These data indicate that the development of functional potential is a consequence of initial antigen experience, but delivery of specialized functions is differentially regulated in primary and memory immune responses.

Review article: molecular signals and genetic reprogramming in peripheral T-cell differentiation

Rearrangement of gene segments occurs in T lymphocytes during thymic development as the T-cell receptor (TCR) is first expressed, allowing T cells to become central regulators of antigen specificity in the acquired immune system. However, further development of T cells occurs after population of peripheral lymphoid tissues, which can result in T-cell expansion and differentiation into effectors of various immune function, or progression to memory T cells, anergic cells or death by apoptosis. This review focuses on more recent developments concerning the choices that peripheral T cells make between first encountering antigen through TCR recognition and death. These decisions are associated with a process of genetic reprogramming that alters the behaviour of cells so that immune responses are appropriately regulated.