Interleukin 4-producing CD4 T cells arise from different precursors depending on the conditions of antigen exposure in vivo

CD4+ virtual memory: Antigen-inexperienced T cells reside in the naïve, regulatory, and memory T cell compartments at similar frequencies, implications for autoimmunity

It is widely accepted that central and effector memory CD4⁺ T cells originate from naïve T cells after they have encountered their cognate antigen in the setting of appropriate co-stimulation. However, if this were true the diversity of T cell receptor (TCR) sequences within the naïve T cell compartment should be far greater than that of the memory T cell compartment, which is not supported by TCR sequencing data. Here we demonstrate that aged mice with far fewer naïve T cells, respond to the model antigen, hen eggwhite lysozyme (HEL), by utilizing the same TCR sequence as their younger counterparts. CD4⁺ T cell repertoire analysis of highly purified T cell populations from naive animals revealed that the HEL-specific clones displayed effector and central "memory" cell surface phenotypes even prior to having encountered their cognate antigen. Furthermore, HEL-inexperienced CD4⁺ T cells were found to reside within the naïve, regulatory, central memory, and effector memory T cell populations at similar frequencies and the majority of the CD4⁺ T cells within the regulatory and memory populations were unexpanded. These findings support a new paradigm for CD4⁺ T cell maturation in which a specific clone can undergo a differentiation process to exhibit a "memory" or regulatory phenotype without having undergone a clonal expansion event. It also demonstrates that a foreign-specific T cell is just as likely to reside within the regulatory T cell compartment as it would the naïve compartment, arguing against the specificity of the regulatory T cell compartment being skewed towards self-reactive T cell clones. Finally, we demonstrate that the same set of foreign and autoreactive CD4⁺ T cell clones are repetitively generated throughout adulthood. The latter observation argues against T cell-depleting strategies or autologous stem cell transplantation as therapies for autoimmunity-as the immune system has the ability to regenerate pathogenic clones.

Endogenous regulation of inflammatory pain by T-cell-derived opioids: when friend turns to foe

Painful sensation is a hallmark of microbe-induced inflammation. This inflammatory pain is downregulated a few days after infection by opioids locally released by effector T lymphocytes generated in response to microbe-derived antigens. This review focuses on the endogenous regulation of inflammatory pain associated with adaptive T-cell response and puts in perspective the clinical consequences of the opioid-mediated analgesic activity of colitogenic T lymphocytes in inflammatory bowel disease.

Singularities of calcium signaling in effector T-lymphocytes

CD4(+) helper T (Th) lymphocytes orchestrate the immune response and include several types of effectors such as Th1, Th17 and Th2 cells. They fight against intracellular, extracellular pathogens and parasites respectively. They may also cause distinct immunopathological disorders. Th1 and Th17 are implicated in the development of autoimmune diseases while Th2 cells can initiate allergic diseases. These subsets differ by their TCR-associated signaling. In addition, the regulation of intracellular calcium concentration is not the same in Th1, Th2 and 17 cells. Our group showed that Th2 cells selectively overexpressed voltage-activated calcium (Cav1)-related channels. An increasing number of groups report the presence of Cav1-related products in T-lymphocyte subsets. This is a matter of debate since these calcium channels are classically defined as activated by high cell membrane depolarization in excitable cells. However, the use of mice with ablation of some Cav1 subunits shows undoubtedly an immune phenotype raising the question of how Cav1 channels are regulated in lymphocytes. We showed that knocking down Cav1.2 and/or Cav1.3 subunits impairs the functions of Th2 lymphocytes and is beneficial in experimental models of asthma, while it has no effect on Th1 cell functions. Beyond the role of Cav1 channels in T-lymphocytes, the identification of key components selectively implicated in one or the other T cell subset paves the way for the design of new selective therapeutic targets in the treatment of immune disorders while preserving the other T-cell subsets. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

Transforming growth factor activity is a key determinant for the effect of estradiol on fatty streak deposit in hypercholesterolemic mice

OBJECTIVE

Whereas estradiol prevents fatty streak deposit in immunocompetent apoE-/- or LDLr-/- mice, it is totally ineffective in immunodeficient mice, underlining the key role of immunoinflammation in this effect. In the present work, the role of several major pro- and antiinflammatory cytokines involved in the atheromatous process was evaluated in the effect of estradiol on fatty streak constitution.

METHODS AND RESULTS

The preventive effect of estradiol was fully maintained in LDLr-/- mice grafted with bone marrow from either IFN-gamma or interleukin (IL)-12-deficient mice, showing that this beneficial effect was not mediated through a specific decrease in the production of these 2 proinflammatory cytokines. Furthermore, IL-10-/- apoE-/- mice remained protected by estradiol, excluding a significant contribution of this antiinflammatory cytokine. In contrast, the protective effect of estradiol was (1) associated with enhanced aortic expression of TGF-beta1 in apoE-/- mice during early steps of atherogenesis; (2) abolished and even reversed in apoE-/- mice administered with a neutralizing anti-TGF-beta antibody; (3) abolished in LDLr-/- mice grafted with bone marrow from Smad3-deficient mice.

CONCLUSIONS

The status of the TGF-beta pathway crucially determines the antiatherogenic effect of estradiol in hypercholesterolemic mice, whereas neither IFN-gamma, IL-12, nor IL-10 are specifically involved in this protection.

Opioid receptor blockade increases the number of lymphocytes without altering T cell response in draining lymph nodes in vivo

A number of studies have been dedicated to estimate the consequences on immunity of the clinical use of opioids by focusing on mitogen-induced polyclonal proliferation of T cells from blood or spleen. Here we examined, under physiological conditions, the contribution of endogenous opioids in the development of a CD4(+) T cell response within draining lymph nodes. We show in OVA-primed DO11.10 mice that delta-opioid receptors were up-regulated upon T cell activation in vivo and that opioid receptor neutralization increased the number of specific anti-OVA T lymphocytes without promoting their capacity to proliferate. The sensitivity to Fas-mediated apoptosis of T lymphocytes and the synthesis of homeostatic lymphoid chemokines were not either affected suggesting that opioids operate mainly before the entry of T lymphocytes into lymph nodes.

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.

Transcriptional repressor DREAM regulates T-lymphocyte proliferation and cytokine gene expression

Downstream Regulatory Element Antagonist Modulator (DREAM) is a Ca2+-dependent transcriptional repressor expressed in the brain, thyroid gland and thymus. Here, we analyzed the function of DREAM and the related protein KChIP-2 in the immune system using transgenic (tg) mice expressing a cross-dominant active mutant (EFmDREAM) for DREAM and KChIPs Ca2+-dependent transcriptional derepression. EFmDREAM tg mice showed reduced T-cell proliferation. Tg T cells exhibited decreased interleukin (IL)-2, -4 and interferon (IFN)gamma production after polyclonal activation and following antigen-specific response. Chromatin immunoprecipitation and transfection assays showed that DREAM binds to and represses transcription from these cytokine promoters. Importantly, specific transient knockdown of DREAM or KChIP-2 induced basal expression of IL-2 and IFNgamma in wild-type splenocytes. These data propose DREAM and KChIP-2 as Ca2+-dependent repressors of the immune response.

Diminished monocyte function in microfilaremic patients with lymphatic filariasis and its relationship to altered lymphoproliferative responses

Antigen-specific hyporesponsiveness to filarial antigens is a phenomenon observed in patent infection with lymph-dwelling filarial parasites of humans. This phenomenon has been attributed to a multitude of factors, one of which is altered monocyte function. To examine the role played by monocytes in filarial infection, we assessed the responses of monocytes obtained from normal and filarial parasite-infected individuals to both crude filarial antigen and purified recombinant filarial antigen WbSXP-1 and attempted to relate these to the altered lymphoproliferative responses seen in filarial infection. Monocytes from microfilaremic (MF) patients demonstrated an inability to respond to lipopolysaccharide compared to monocytes from endemic normal persons or from lymphedema patients. Indeed, interleukin 1beta (IL-1beta) production was severely limited, a finding that did not extend to monocyte responses to filarial antigens. Serum from MF patients reduced adherence and spreading of normal monocytes, a finding not seen with serum from the other clinical groups. Interestingly, there was a significant correlation between the production of IL-1beta and adherence. Moreover, the levels of spontaneous production of IL-1beta correlated with high levels of spontaneous secretion of IL-10. The effects observed were not a result of diminished viability or alteration in the expression of the cell surface markers CD14 and HLA-DR. These data suggest that monocyte function is dampened in MF patients, a finding which could alter lymphoproliferative responses during patent infection.

Valpha and Vbeta public repertoires are highly conserved in terminal deoxynucleotidyl transferase-deficient mice

T cell repertoires observed in response to immunodominant and subdominant peptides include private, i.e., specific for each individual, as well as public, i.e., common to all mice or humans of the same MHC haplotype, Valpha-Jalpha and Vbeta-Dbeta-Jbeta rearrangements. To measure the impact of N-region diversity on public repertoires, we have characterized the alphabeta TCRs specific for several CD4 or CD8 epitopes of wild-type mice and of mice deficient in the enzyme TdT. We find that V, (D), J usage identified in public repertoires is strikingly conserved in TdT(o/o) mice, even for the CDR3 loops which are shorter than those found in TdT(+/+) animals. Moreover, the 10- to 20-fold decrease in alphabeta T cell diversity in TdT(o/o) mice did not prevent T cells from undergoing affinity maturation during secondary responses. A comparison of the CDR3beta in published public and private repertoires indicates significantly reduced N-region diversity in public CDR3beta. We interpret our findings as suggesting that public repertoires are produced more efficiently than private ones by the recombination machinery. Alternatively, selection may be biased in favor of public repertoires in the context of the interactions between TCR and MHC peptide complexes and we hypothesize that MHCalpha helices are involved in the selection of public repertoires.

Selection of similar naive T cell repertoires but induction of distinct T cell responses by native and modified antigen

To study the T cell responses induced by native and modified Ag, we have followed in vivo TCR selection and cytokine profile of T cells, as well as the isotype of induced Abs, in response to the model Ag hen egg-white lysozyme (HEL) and its reduced and carboxymethylated form (RCM-HEL). RCM-HEL induces in vivo a T cell response focused on the same immunodominant determinant characterizing the response to native HEL, but further skewed to the Th1 pathway. No difference between HEL and RCM-HEL could be observed in the efficiency of processing, nor in the type of APCs involved. In vivo experiments show that coimmunization with HEL and RCM-HEL generates distinct Th2 or Th1 responses in naive mice, but the two forms of Ag expand the same HEL-specific public clonotype, characterized by the Vbeta8.2-Jbeta1.5 rearrangement, indicating that the populations of naive T cells activated by the two Ag forms overlap. T cells primed by RCM-HEL are restimulated by soluble HEL in vivo, but divert the phenotype of the HEL-specific response to Th1, implying that priming of naive T cells by a structurally modified Ag can induce Th1-type memory/effector T cells more efficiently than native Ag.

Mouse V alpha 14i natural killer T cells are resistant to cytokine polarization in vivo

Under different circumstances, natural killer T (NKT) cells can cause a T helper (Th) 1 or a Th2 polarization of immune responses. We show here, however, that mouse NKT cells with an invariant V alpha 14 rearrangement (V alpha 14i NKT cells) rapidly produce both IL-4 and IFN-gamma, and this pattern could not be altered by methods that polarize naive CD4+ T cells. Surprisingly, although cytokine protein was detected only after activation, resting V alpha 14i NKT cells contained IL-4 and IFN-gamma mRNAs. Despite this finding, in vivo priming of mice with the glycolipid antigen recognized by V alpha 14i NKT cells resulted in a more Th2-oriented response upon antigen re-exposure. The V alpha 14i NKT cells from primed mice retain the ability to produce IL-4 and IFN-gamma, but they are less effective at activating NK cells to produce IFN-gamma. Our data therefore indicate that V alpha 14i NKT cells have a relatively inflexible immediate cytokine response, but that changes in their ability to induce IFN-gamma secretion by NK cells may determine the extent to which they promote Th1 responses.

Tracking T cell clonotypes in complex T lymphocyte populations by real-time quantitative PCR using fluorogenic complementarity-determining region-3-specific probes

The T cell receptor (TCR) alpha and beta chains are encoded by a series of stochastic rearrangements between variable (V), diversity (D) for TCR beta chain only, and joining (J) gene segments, creating hypervariable complementarity-determining region 3 (CDR3) regions that contact the peptide/MHC complex and confer specificity. In the present paper, we applied the recently developed real-time quantitative RT-PCR technique to the detection of rearranged TCR beta chain mRNA transcripts. We designed BV- and BJ-specific primers together with TaqMan probes specific for the CDR3 regions of the clones of interest. As an external reference, we used plasmids containing the entire TCR beta chains, making it possible to normalize the number of specific rearranged BV-J mRNA copies among the total number of TCR beta chains. Here, we present data validating this fluorogenic PCR-based method for the quantification of several TCR clonotypes characteristic of the CD4 T cell response to hen egg white lysozyme (HEL) in mice of the H-2d haplotype. This accurate and sensitive procedure permits the precise determination of T cell clone frequencies ranging from 10(-2) to less than 10(-5) in normal biological samples; it may provide an alternative approach when frequencies are too low to be assessed by flow cytometry.

Preventing NK cell activation by donor dendritic cells enhances allospecific CD4 T cell priming and promotes Th type 2 responses to transplantation antigens

Although much progress has been made in understanding the role of NK cells in bone marrow transplantation, little is known about their function in CD4 T cell-mediated allograft rejection. We have previously shown that in the absence of CD8 T lymphocyte priming, the in vivo default development pathway of alloreactive CD4 T cells was strongly biased toward Th2 phenotype acquisition. In this study, we investigate the impact of NK cells on the activation and differentiation of alloreactive CD4 T cells in various donor/recipient combinations. Our data demonstrate that defective inhibition of host NK cells by donor APCs including dendritic cells (DCs) results in diminished allospecific Th cell responses associated with the development of effector Th cells producing IFN-gamma rather than type 2 cytokines. Turning host NK cells off was sufficient to restore strong alloreactive CD4 T cell priming and Th2 cell development. Similar results were obtained by analyzing the effect of NK cell activation on CD4 T cell responses to skin allografts. However, despite the dramatic effect of NK cells on alloreactive Th1/Th2 cell development, the kinetics of skin graft rejection were not affected. Thus, Th2 differentiation is a major pathway of alloreactive CD4 T cell development during solid organ transplant rejection, as long as host NK and CD8 T cells are not activated. We propose the hypothesis that MHC class I-driven interactions between donor DCs and host NK cells or CD8 T cells might result in DC-carried signals controlling the dynamics of alloreactive CD4 T cell priming and polarization.

Intracellular T cell cytokines in patients with B cell chronic lymphocytic leukaemia (B-CLL)

Analysis of cytokine production is a tool to functionally characterise T cells. In this study, spontaneous and polyclonal activation induced cytokine production in T cells were assessed by flow cytometry in patients with B-CLL. Patients with progressive disease had a significantly increased number of T cells spontaneously producing IL-2, IL-4 and GM-CSF as compared to healthy donors and patients with non-progressive CLL, which was not the case for TNF-alpha and IFN-gamma producing T cells. However, no difference in the frequency of T cells producing these cytokines was seen comparing patients with non-progressive disease to control donors. Polyclonal activation of B-CLL T cells in vitro induced an increased proportion of T cells producing these five cytokines in patients as well as in control donors, indicating that T cells in CLL patients might have a relatively well preserved functional capacity. However, the increase in GM-CSF, TNF-alpha and IL-4 producing T cells was more marked in CLL patients than in controls. Furthermore, following activation, a higher frequency of cytokine-producing T cells was noted in patients with progressive disease as compared to those with non-progressive disease. The augmented number of cytokine-producing T cells in CLL may indicate an up-regulated capability of T cells to secrete cytokines, especially in patients with progressive CLL. The increased production of the T cell derived cytokines GM-CSF, TNF-alpha, IL-4 and IL-2 is interesting, as these cytokines have previously been shown to support growth of B-CLL leukaemic cells in vitro and as T cells might specifically recognise the autologous leukaemic B cells in vivo. The findings may suggest a role for T cells in the pathogenesis of B-CLL.

The kinetics of in vivo priming of CD4 and CD8 T cells by dendritic/tumor fusion cells in MUC1-transgenic mice

Previous work has demonstrated that dendritic/tumor fusion cells induce potent antitumor immune responses in vivo and in vitro. However, little is known about the migration and homing of fusion cells after s.c. injection or the kinetics of CD4+ and CD8+ T cell activation. In the present study, fluorescence-labeled dendritic/MUC1-positive tumor fusion cells (FC/MUC1) were injected s.c. into MUC1-transgenic mice. The FC/MUC1 migrated to draining lymph nodes and were closely associated with T cells in a pattern comparable with that of unfused dendritic cells. Immunization of MUC1-transgenic mice with FC/MUC1 resulted in proliferation of T cells and induced MUC1-specific CD8+ CTL. Moreover, CD4+ T cells activated by FC/MUC1 were multifunctional effectors that produced IL-2, IFN-gamma, IL-4, and IL-10. These findings indicate that both CD4+ and CD8+ T cells can be primed in vivo by FC/MUC1 immunization.

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.

Transmission intensity and human immune responses to lymphatic filariasis

Our understanding of how the host immune response influences the risk of developing disease has changed dramatically over the past decade. Previously, the spectrum of disease associated with lymphatic filariasis was largely attributed to the nature of the host immune response. Now, we appreciate that the duration and intensity of infection and possibly the direct influence of parasite-derived molecules also determine the risk of disease. Individuals chronically infected with lymphatic filariasis generally have an impaired lymphocyte proliferation response to filarial antigens and favour Th2-type cytokine responses. This ability to down-modulate the host immune response may help protect the host from disease. Defects in antigen-presenting cell (APC) function appear to participate in this acquired immune hyporesponsiveness, although the mechanisms as to how this occurs are poorly understood. Here, we present evidence that repeated exposure to infective stage larvae and their secreted products may stimulate basophils and mast cells to related products that may impair APC function.

Transmission intensity determines lymphocyte responsiveness and cytokine bias in human lymphatic filariasis

Humans living in areas where filariasis is endemic vary greatly in their exposure to mosquito-borne infective third-stage larvae (L3) of these parasitic helminths. Because the intensity of exposure to Ags affects T cell differentiation and susceptibility to parasitic infections in murine models, we compared T cell and cytokine responses in 97 residents of two villages in Papua New Guinea, where transmission intensity of Wuchereria bancrofti differed by 63-fold (37 vs 2355 L3 per person per year). Residents of the high transmission village had 4- to 11-fold lower proliferation and IFN-gamma responses to filarial Ags, nonparasite Ag, and PHA by PBMC compared with the low transmission village (p < 0.01) even when subjects were matched for intensity of infection. In contrast, filarial Ag-driven IL-5 production was 5.5-fold greater (p < 0.001), and plasma IL-4 and TGF-beta levels were 4-fold and 34% higher, respectively, in residents of the high transmission village. IL-4 and IL-10 responses by PBMC differed little according to village, and increased production of the counterregulatory cytokines IL-10 or TGF-beta by PBMC did not correlate with weak proliferation and IFN-gamma responses. Plasma IL-5, IFN-gamma, and IL-10 levels were similar in the two villages. These data demonstrate that the intensity of exposure to L3 affects lymphocyte responsiveness and cytokine bias possibly by a mechanism that alters APC function.

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.

Immunogenicity of self antigens is unrelated to MHC-binding affinity: T-cell determinant structure of Golli-MBP in the BALB/c mouse

The 'classical' myelin basic protein (MBP) exons belong to a much larger unit, termed the 'Golli-MBP' gene. Here we have examined the T-cell determinant structure of the Golli protein region in the BALB/c mouse. Golli p10-24, which was shown to have the strongest affinity for I-A(d), could not induce T-cell activation. Paradoxically, the poorer binding, overlapping p5-19 was effective at inducing T-cell proliferation. Thus, immunogenicity is not necessarily related to the MHC-binding affinity of self-peptides. In addition, MBP: p151-168-specific T cell clones responded only poorly to J37, a Golli-MBP protein, while MBP: 59-76-specific clones responded well to J37.