Critical role for invariant chain in CD1d-mediated selection and maturation of Vα14-invariant NKT cells

The development and maturation of Vα14 invariant (i)NKT cells in mice requires CD1d-mediated lipid antigen presentation in the thymus and the periphery. Cortical thymocytes mediate positive selection, while professional APCs are involved in thymic negative selection and in terminal maturation of iNKT cells in the periphery. CD1d requires entry in the endosomal pathway to allow antigen acquisition for assembly as lipid/CD1d complexes for display to iNKT cells. This process involves tyrosine-based sorting motifs in the CD1d cytoplasmic tail and invariant chain (Ii) that CD1d associates with in the endoplasmic reticulum. The function of Ii in iNKT cell thymic development and peripheral maturation had not been fully understood. Using mice deficient in Ii and the Ii-processing enzyme cathepsin S (catS), we addressed this question. Ii(-/-) mice but not catS(-/-) mice developed significantly fewer iNKT cells in thymus, that were less mature as measured by CD44 and NK1.1 expression. Ii(-/-) mice but not catS(-/-) mice developed fewer Vβ7(+) cells in their iNKT TCR repertoire than WT counterparts, indicative of a change in endogenous glycolipid antigen/CD1d-mediated iNKT cell selection. Finally, using a Mycobacterium tuberculosis infection model in macrophages, we show that iNKT developed in Ii(-/-) but not catS(-/-) mice have defective effector function. Our data support a role for professional APCs expressing Ii, but no role for catS in the thymic development and peripheral terminal maturation of iNKT cells.     

IL-6-STAT3 controls intracellular MHC class II alphabeta dimer level through cathepsin S activity in dendritic cells

We found IL-6-STAT3 pathway suppresses MHC class II (MHCII) expression on dendritic cells (DCs) and attenuates T cell activation. Here, we showed that IL-6-STAT3 signaling reduced intracellular MHCII alphabeta dimmer, Ii, and H2-DM levels in DCs. IL-6-mediated STAT3 activation decreased cystatin C level, an endogenous inhibitor of cathepsins, and enhanced cathepsin activities. Importantly, cathepsin S inhibitors blocked reduction of MHCII alphabeta dimer, Ii, and H2-DM in the IL-6-treated DCs. Overexpression of cystatin C suppressed IL-6-STAT3-mediated increase of cathepsin S activity and reduction of MHCII alphabeta dimer, Ii, and H2-DM levels in DCs. Cathepsin S overexpression in DCs decreased intracellular MHCII alphabeta dimer, Ii, and H2-DM levels, LPS-mediated surface expression of MHCII and suppressed CD4(+) T cell activation. IL-6-gp130-STAT3 signaling in vivo decreased cystatin C expression and MHCII alphabeta dimer level in DCs. Thus, IL-6-STAT3-mediated increase of cathepsin S activity reduces the MHCII alphabeta dimer, Ii, and H2-DM levels in DCs, and suppresses CD4(+) T cell-mediated immune responses.     

Induction of NK1.1(+) alpha beta TCR(+) T cells by bypassing TCR signals in ZAP-70 deficient mice

The mechanism of development of a unique subset of T cells, thymic NK1.1(+) alpha beta T cells, has been poorly understood. We found that the development of thymic NK1.1(+) alpha beta T cells was defective in mice deficient in ZAP-70. Instead, an accumulation of NK1.1(+) TCR beta(-) NK-like population was detected in the thymus and spleen of the ZAP-70 deficient (ZAP -/-) mouse. In the present report, we examined whether biochemical treatments that replace TCR-mediated positive selection signals could restore the generation of thymic NK1.1(+) alpha beta T cells in ZAP -/- mice using the thymus organ culture. We found that a higher concentration of phorbol ester (PMA) than that required for CD4(+) T cell generation and ionomycin induced the generation of NK1.1(+) alpha beta T cells. Phenotypic analysis of the induced NK1.1(+) alpha beta T cell population suggested that these cells expressed CD8 but not CD4 molecules, which is a different characteristic from ordinary thymic NK1.1(+) alpha beta T cells. These results suggest that differential signaling is required for the generation of mainstream T cells and thymic NK1.1(+) alpha beta T cells.     

Thymocyte expression of cathepsin L is essential for NKT cell development

CD1d antigen presentation to natural killer T (NKT) cells expressing the semi-invariant T cell receptor V(alpha)14J(alpha)18 requires CD1d trafficking through endosomal compartments; however, the endosomal events remain undefined. We show that mice lacking the endosomal protease cathepsin L (catL) have greatly reduced numbers of V(alpha)14(+)NK1.1(+) T cells. In addition, catL expression in thymocytes is critical not only for selection of these cells in vivo but also for stimulation of V(alpha)14(+)NK1.1(+) T cells in vitro. CD1d cell-surface expression and intracellular localization appear normal in catL-deficient thymocytes, as does the lysosomal morphology; this implies a specific role for catL in regulating presentation of natural CD1d ligands mediating V(alpha)14(+)NK1.1(+) T cell selection. These data implicate lysosomal proteases as key regulators of not only classical major histocompatibility complex class II antigen presentation but also nonclassical CD1d presentation.     

The role of CD11c(+) hepatic dendritic cells in the induction of innate immune responses

The role of the liver in the initiation and maintenance of tolerance is a critical immune function that involves multiple lineages of immune cells. Included within these populations are liver dendritic cells (DCs). Although there has been significant work on the phenotypic and functional roles of splenic and bone marrow dendritic cells, as well as their subsets, comparable studies in liver have often been difficult. To address this issue we have isolated, from C57BL/6 mice, relatively pure populations of DCs and compared phenotype and function to the data from spleen using flow cytometry, cell sorter assisted purification and culture, morphology by cytospin and May-Giemsa staining, cell cycle progression, antigen uptake, cytokine production and allo-activation potential. natural killer (NK)1.1(-)CD11c(+) liver DC subsets (conventional DCs, T cell receptor (TcR)beta(-)NK1.1(-)CD11c(+)B220(-) and plasmacytoid DCs, TcRbeta(-)NK1.1(-)CD11c(+)B220(+)) efficiently endocytose dextran and produce significant levels of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-12 p40 in response to Toll-like receptor (TLR) ligands, with responses higher than splenic DCs. There is also a differential capability of hepatic DCs to respond to innate signals. Indeed, CD11c(+) hepatic DCs have a greater capacity to respond to innate stimulation but are less capable of inducing CpG activated-allogeneic T cells. These data suggest that hepatic dendritic cells function as a critical bridge between innate and adaptive immunity and are capable of inducing stronger innate responses with a lower capacity for allo-stimulation than splenic dendritic cells. These properties of liver dendritic cells contribute to their unique role in the induction of tolerance.     

Interleukin-21 receptor-mediated signals control autoreactive T cell infiltration in pancreatic islets

It remains unclear how interleukin-21 receptor (IL-21R) contributes to type 1 diabetes. Here we?have shown that dendritic cells (DCs) in the pancreas required IL-21R not for antigen uptake, but to acquire the chemokine receptor CCR7 and migrate into the?draining lymph node. Consequently, less antigen, major histocompatibility complex (MHC) class II, and CD86 was provided to autoreactive effector cells in?Il21r(-/-) mice, impairing CD4(+) T?cell activation, CD40:CD40L interactions, and pancreatic infiltration by autoreactive T?cells. CD40 crosslinking restored defective CD4(+) cell expansion and CD4 independently expanded autoreactive CD8(+) cells, but CD8(+) cells still required CD4(+) cells to reach the pancreas and induce diabetes. Diabetes induction by transferred T?cells required IL-21R-sufficient host antigen-presenting cells. Transferring IL-21R-sufficient DCs broke diabetes resistance in Il21r(-/-) mice. We conclude that IL-21R controls both antigen transport by DCs and the crucial beacon function of CD4(+) cells for autoreactive CD8(+) cells to reach the islets.     

Natural killer dendritic cells are an intermediate of developing dendritic cells

NK dendritic cells (DCs; NKDCs) appear to emerge as a distinct DC subset in humans and rodents, which have the functions of NK cells and DCs. However, the developmental relationship of NKDCs (CD11c(+)NK1.1(+)) to CD11c(+)NK1.1(-) DCs has not been addressed. Herein, we show that NKDCs exist exclusively in the compartment of CD11c(+)MHC II(-) cells in the steady state and express variable levels of DC subset markers, such as the IFN-producing killer DC marker B220, in a tissue-dependent manner. They can differentiate into NK1.1(-) DCs, which is accompanied by the up-regulation of MHC Class II molecules and down-regulation of NK1.1 upon adoptive transfer. However, NK cells (NK(+)CD11c(-)) did not differentiate into NK1.1(+)CD11c(+) cells upon adoptive transfer. Bone marrow-derived Ly6C(+) monocytes can be a potential progenitor of NKDCs, as some of them can differentiate into CD11c(+)NK1.1(+) as well as CD11c(+)NK1.1(-) cells in vivo. The steady-state NKDCs have a great capacity to lyse tumor cells but little capability to present antigens. Our studies suggest that NKDCs are an intermediate of developing DCs. These cells appear to bear the unique surface phenotype of CD11c(+)NK1.1(+)MHC II(-) and possess strong cytotoxic function yet show a poor ability to present antigen in the steady state. These findings suggest that NKDCs may play a critical role in linking innate and adaptive immunity.     

Suppression of major histocompatibility complex class II-associated invariant chain enhances the potency of an HIV gp120 DNA vaccine

Summary One function of the major histocompatibility complex (MHC) class II-associated invariant chain (Ii) is to prevent MHC class II molecules from binding endogenously generated antigenic epitopes. Ii inhibition leads to MHC class II presentation of endogenous antigens by APC without interrupting MHC class I presentation. We present data that in vivo immunization of BALB/c mice with HIV gp120 cDNA plus an Ii suppressive construct significantly enhances the activation of both gp120-specific T helper (Th) cells and cytotoxic T lymphocytes (CTL). Our results support the concept that MHC class II-positive/Ii-negative (class II(+)/Ii(-)) antigen-presenting cells (APC) present endogenously synthesized vaccine antigens simultaneously by MHC class II and class I molecules, activating both CD4(+) and CD8(+) T cells. Activated CD4(+) T cells locally strengthen the response of CD8(+) CTL, thus enhancing the potency of a DNA vaccine.     

Cytokines production of U5A2-13-positive T cells by stimulation with glycolipid alpha-galactosylceramide

We have previously established and reported a novel monoclonal antibody (mAb), U5A2-13, which recognizes a phenotypically similar population of natural killer (NK)-like T cells. Using U5A2-13 mAb, we now describe the functional properties of U5A2-13(+) T cells in both NK1.1-positive or -negative mouse strains. Similar to NK1.1(+) T cells, hepatic U5A2-13(+) T cells of C57BL/6 (NK1.1(+) strain) mice, but not U5A2-13(-) T cells, could be induced to produce large amounts of IL-4 and IFN-gamma by stimulation with glycolipid alpha-galactosylceramide (alpha-GalCer) present on dendritic cells (DC) in a dose-dependent manner. The abundant production of these cytokines from U5A2-13(+) T cells of BALB/c (NK1.1(-) strain) mice is similar to that noted in C57BL/6 mice. Cytokine production by cultures stimulated with DC of beta2-microglobulin-deficient mice was significantly less than that of cultures stimulated with DC of intact mice. Overall, U5A2-13(+) T cells recognize alpha-GalCer presented by CD1d, indicating that U5A2-13(+) T cells can be used to analyze NK-like T cell function in various strains of mice.     

Characterization of the protective T-cell response generated in CD4-deficient mice by a live attenuated Mycobacterium tuberculosis vaccine

The global epidemic of tuberculosis, fuelled by acquired immune-deficiency syndrome, necessitates the development of a safe and effective vaccine. We have constructed a DeltaRD1DeltapanCD mutant of Mycobacterium tuberculosis (mc(2)6030) that undergoes limited replication and is severely attenuated in immunocompromised mice, yet induces significant protection against tuberculosis in wild-type mice and even in mice that completely lack CD4(+) T cells as a result of targeted disruption of their CD4 genes (CD4(-/-) mice). Ex vivo studies of T cells from mc(2)6030-immunized mice showed that these immune cells responded to protein antigens of M. tuberculosis in a major histocompatibility complex (MHC) class II-restricted manner. Antibody depletion experiments showed that antituberculosis protective responses in the lung were not diminished by removal of CD8(+), T-cell receptor gammadelta (TCR-gammadelta(+)) and NK1.1(+) T cells from vaccinated CD4(-/-) mice before challenge, implying that the observed recall and immune effector functions resulting from vaccination of CD4(-/-) mice with mc(2)6030 were attributable to a population of CD4(-) CD8(-) (double-negative) TCR-alphabeta(+), TCR-gammadelta(-), NK1.1(-) T cells. Transfer of highly enriched double-negative TCR-alphabeta(+) T cells from mc(2)6030-immunized CD4(-/-) mice into naive CD4(-/-) mice resulted in significant protection against an aerosol tuberculosis challenge. Enriched pulmonary double-negative T cells transcribed significantly more interferon-gamma and interleukin-2 mRNA than double-negative T cells from naive mice after a tuberculous challenge. These results confirmed previous findings on the potential for a subset of MHC class II-restricted T cells to develop and function without expression of CD4 and suggest novel vaccination strategies to assist in the control of tuberculosis in human immunodeficiency virus-infected humans who have chronic depletion of their CD4(+) T cells.     

Impaired invariant chain degradation and antigen presentation and diminished collagen-induced arthritis in cathepsin S null mice

Cathepsins have been implicated in the degradation of proteins destined for the MHC class II processing pathway and in the proteolytic removal of invariant chain (Ii), a critical regulator of MHC class II function. Mice lacking the lysosomal cysteine proteinase cathepsin S (catS) demonstrated a profound inhibition of Ii degradation in professional APC in vivo. A marked variation in the generation of MHC class II-bound Ii fragments and presentation of exogenous proteins was observed between B cells, dendritic cells, and macrophages lacking catS. CatS-deficient mice showed diminished susceptibility to collagen-induced arthritis, suggesting a potential therapeutic target for regulation of immune responsiveness.     

Involvement of NK 1.1-positive γδT cells in interleukin-18 plus interleukin-2-induced interstitial lung disease

Interstitial lung disease (ILD) is induced by various factors in humans. However, the exact mechanism of ILD remains elusive. This study sought to determine the role of natural killer (NK) 1.1(+) γδT cells in ILD. The injection of IL-18 plus IL-2 (IL-18/IL-2) into C57BL6 (B6) mice induced acute ILD that resembled early-stage human ILD. An accumulation of NK1.1(+) γδT cells similar to NK cells was evident in the lungs. The T Cell Receptor (TCR) Vγ and Vδ repertoires of NK1.1(+) γδT cells indicated polyclonal expansion. The expression of IL-2 receptor β (Rβ) and IL-18Rβ in NK1.1(+) γδT cells was higher than in NK1.1(-) γδT cells. IL-18/IL-2 stimulated the proliferation of NK1.1(+) γδT cells, but not NK1.1(-) γδT cells. The IL-18/IL-2-stimulated NK1.1(+) γδT cells produced higher concentrations of IFN-γ than did NK1.1(-) γδT cells. Moreover, NK1.1(+) γδT and NK1.1(-) γδT cells constituted completely different cell populations. The IL-18/IL-2-induced ILD was milder in TCRδ(-/-) and IFN-γ(-/-) mice, compared with B6 mice. Furthermore, cell-transfer experiments demonstrated that NK1.1(+) γδT cells could induce the expansion of NK cells and IFN-γ mRNA in the lung by IL-18/IL-2. Our results suggest that NK1.1(+) γδT cells function as inflammatory mediators in the early phase of IL-18/IL-2-induced ILD.     

Critical role of NK but not NKT cells in acute rejection of parental bone marrow cells in F1 hybrid mice.

F1 hybrid mice vigorously reject transplanted parental bone marrow (BM) cells, which is a phenomenon called "hybrid resistance (HR)". Since NK1.1(+) cells play crucial role in HR, both NK1.1(+)CD3(+) NKT cells and NK1.1(+)CD3(-) NK cells have been possible candidates of effector cells. To elucidate the major effector cells in HR, we employed Rag-2(-/-) mice devoid of T, B, and NKT cells and cytokine receptor common gamma subunit and Rag-2 double-deficient (gamma(c)(-/-(y))-Rag-2(-/-)) mice lacking all lymphoid cells including NK cells. Rag-2(-/-) F1 hybrid mice rejected parental BM cells to the extent similar to wild-type (WT) F1 hybrids. In contrast, male gamma(c)(-/y)-Rag-2(-/-) F1 hybrid mice were unable to reject parental BM cells. After reconstitution with NK but not NKT cells, male gamma(c)(-/y)-Rag-2(-/-) F1 hybrid mice restored the ability to reject parental BM cells. Collectively, it is concluded that NKT cells play little role, if any, and NK cells are the only cells involved in HR.     

TSLP-induced placental DC activation and IL-10(+) NK cell expansion: comparative study based on BALB/c x C57BL/6 and NOD/SCID x C57BL/6 pregnant models

Thymic stromal lymphopoietin (TSLP)-TSLP receptor (TSLP-R) interactions activate CD11c(+) dendritic cells (DCs) and increase epithelial cell Th2-type cytokine production. We detected intracellular TSLP expression on CK7(+) trophoblast cells and TSLP-R expression on placental DCs from pregnant BALB/cxC57BL/6 and NOD/SCIDxC57BL/6 mice on gestational day 12.5. Murine recombinant TSLP activated DCs from BALB/c mice, with increased CD80 and CD83 expressions; TSLP-activated DCs induced IL-10-producing NK cell expansion. This was abrogated by anti-TSLP Ab or by culturing CD49b(+) NK cells alone. No TSLP-DC-induced IL-10(+)CD49b(+) cell expansion occurred when DCs and CD49b(+) cells were cultured separately. Although TSLP-induced DC activation occurred in NOD/SCID mice, the IL-10(+) NK cell percentage was unchanged. CK7(+) trophoblast cells may activate placental DCs via a TSLP-TSLP-R interaction and induce DC-dependent placental NK cell IL-10 production. TSLP-DC and NK cell contact appears necessary for IL-10(+)CD49b(+) cell expansion. Placental NK cells from NOD/SCIDxC57BL/6 mice appear less sensitive to TSLP-DC induction.     

Study of the NKT cell subsets with superantigen SEB-activated tolerance

AIM: To study the NKT cell subsets and their differentiation. METHODS: Splenic lymphocytes from C57BL/J mice that had received SEB treatment were collected as effector cells on the 10(th) day. The cells were cultured in medium containing ConA, LPS and IL-2 for 3 days and measured their response to mitogens and cytokine. The inhibitory action of the effector cells was examined. The effector cells were cultured with normal lymphocytes and above mitogens or cytokine for 3 day. The cells proliferation was assessed with MTT method.The NKT cell subsets among these effector cells with the tolerance function were analyzed and their differentiation sources and correlation of functions were detected by flow cytometry. RESULTS: The response of SEB-activated effector cells to ConA, LPS and IL-2 was significantly decreased compared with that of normal lymphocytes. The A values of cell proliferation were decreased from 0.80+/-0.04, 0.60+/-0.03 and 0.55+/-0.07 in control groups to 0.60+/-0.05, 0.30+/-0.05 and 0.27+/-0.04 in effector groups, respectively (P<0.01, n=3).The inhibitory ability of effectors cells against the response of normal lymphocytes to ConA, LPS and IL-2 were clearly observed. They inhibited the response of normal lymphocytes to several mitogens and cytokine. And the A values of cell proliferation were decreased to 0.26+/-0.02, 0.48+/-0.04 and 0.34+/-0.02, respectively (P<0.01, n=3). The CD4(+)NK1.1(+), CD8(+)NK1.1(+), TcRV8(+)NK1.1(+) NKT cell subsets among SEB-activated effector cells with tolerance function were significantly increased and shown that they come from T cell population. And the CD4(-)CD8(-)/NK1.1(+)CD3(+)NKT cells by ConA or SEB-activated were shown coming from NK cell population. CONCLUSION: The effector cells with tolerance function activated by superantigen SEB relate to CD4(+)NK1.1(+), CD8(+)NK1.1(+), TcRVbeta8(+)NK1.1(+) NKT cell subsets. The NKT cell subsets come from T cells. The CD4(-)CD8(-)/NK1.1(+)CD3(+)NKT cells differentiating from NK cells are not involved in the regulation of tolerance.     

Characterization of the phenotype and function of CD8(+), alpha / beta(+) NKT cells from tumor-bearing mice that show a natural killer cell activity and lyse multiple tumor targets

Natural Killer (NK) T cells are a specialized T cell population that co-expresses receptors of the NK lineage with the alpha / beta TCR receptor and other T cell surface markers. Their functions, regulation and relationship to other cells in the immune system are not fully understood. This report demonstrates that tumor-bearing C57BL / 6 mice have a population of NKT cells that co-express CD8 and CD161 (NK1.1) surface markers. These cells are maintained in long-term culture with T helper 2 (Th2) cytokine interleukin-4 (IL-4), but produce large amounts of Th1 cytokine interferon-gamma (IFN-gamma) following activation. NK1.1(+)CD8(+) T cells show a potent NK-like cytotoxic activity against multiple tumor targets, and lysis is independent of major histocompatibility complex (MHC)-class I or non-classical MHC-class I molecules (Qa, TL). The NK1.1(+)CD8(+) T cells express Vbeta14 chain of the TCR. These NKT cells are not CD1d restricted, and their cytotoxic activity is CD1d independent. Therefore, they represent a unique subset of T cells with an unknown restriction element which produce large quantities of IFN-gamma following expansion with IL-4. Furthermore, their cytotoxic activity is enhanced by B7 co-stimulatory molecules present on tumor cells. CD161(+) T cells that are expanded in tumor-bearing hosts may function as a part of the innate immune system with potential role(s) in tumor surveillance.     

Role of Qa-1(b)-binding receptors in the specificity of developing NK cells

NK cells acquire the ability to recognize MHC class I molecules during development. Studies with Qa-1(b) tetramers (Qa-1 tetramers) showed that nearly all NK1.1(+) cells from newborn C57BL/6 mice express Qa-1-binding receptors. Cytotoxic activity of these cells is fully inhibited by Qa-1 ligands on target cells. In contrast, neither receptors for H-2K(b) nor H-2D(b) were observed on NK1.1(+) cells from newborn mice. After birth, frequencies of Qa-1 tetramer(+)/ NK1.1(+) cells gradually decrease as the number of Ly49(+) /NK1.1(+) cells increases. Cell transfer studies showed that Qa-1 tetramer(+) cells from newborn mice do not lose expression of Qa-1 receptors, but that they further acquire expression of Ly49 molecules. Acquisition of Qa-1-binding receptors appears largely independent of host MHC class I molecules, as observed in studies using beta2-microglobulin-deficient (beta2m(-/-)) mice as well as K(b)/ D(b-/-) and K(b)/D(b)/beta2m(-/-) mice. The present results suggest that Qa-1-binding receptors play an important role in the specificity of developing NK cells, and suggest that these cells rely mainly on inhibitory receptors specific for non-classical MHC class I molecules to maintain self tolerance during the first weeks of life.