CD1d1 mutant mice are deficient in natural T cells that promptly produce IL-4

CD1d on myeloid dendritic cells stimulates cytokine secretion from and cytolytic activity of V alpha 24J alpha Q T cells: a feedback mechanism for immune regulation

The precise immunologic functions of CD1d-restricted, CD161+ AV24AJ18 (Valpha24JalphaQ) T cells are not well defined, although production of IL-4 has been suggested as important for priming Th2 responses. However, activation of human Valpha24JalphaQ T cell clones by anti-CD3 resulted in the secretion of multiple cytokines notably important for the recruitment and differentiation of myeloid dendritic cells. Specific activation of Valpha24JalphaQ T cells was CD1d restricted. Expression of CD1d was found on monocyte-derived dendritic cells in vitro, and immunohistochemical staining directly revealed CD1d preferentially expressed on dendritic cells in the paracortical T cell zones of lymph nodes. Moreover, myeloid dendritic cells both activated Valpha24JalphaQ T cells and were susceptible to lysis by these same regulatory T cells. Because myeloid dendritic cells are a major source of IL-12 and control Th1 cell differentiation, their elimination by lysis is a mechanism for limiting the generation of Th1 cells and thus regulating Th1/Th2 responses.

A NK1.1+ thymocyte-derived TCR beta-chain transgene promotes positive selection of thymic NK1.1+ alpha beta T cells

As a consequence of the peptide specificity of intrathymic positive selection, mice transgenic for a rearranged TCR beta-chain derived from conventional alphabeta T lymphocytes frequently carry mature T cells with significant skewing in the repertoire of the companion alpha-chain. To assess the generality of such an influence, we generated transgenic (Tg) mice expressing a beta-chain derived from nonclassical, NK1.1+ alphabeta T cells, the thymus-derived, CD1. 1-specific DN32H6 T cell hybridoma. Results of the sequence analysis of genomic DNA from developing DN32H6 beta Tg thymocytes revealed that the frequency of the parental alpha-chain sequence, in this instance the Valpha14-Jalpha281 canonical alpha-chain, is specifically and in a CD1.1-dependent manner, increased in the postselection thymocyte population. In accordance, we found phenotypic and functional evidence for an increased frequency of thymic, but interestingly not peripheral, NK1.1+ alphabeta T cells in DN32H6 beta Tg mice, possibly indicating a thymic determinant-dependent maintenance. Thus, in vivo expression of the rearranged TCR beta-chain from a thymus-derived NK1.1+ Valpha14+ T cell hybridoma promotes positive selection of thymic NK1.1+ alphabeta T cells. These observations indicate that the strong influence of productive beta-chain rearrangements on the TCR sequence and specificity of developing thymocytes, which operates through positive selection on self-determinants, applies to both classical and nonclassical alphabeta T cells and therefore represents a general phenomenon in intrathymic alphabeta T lymphocyte development.

Natural killer cells determine the outcome of B cell-mediated autoimmunity

Natural killer (NK) cells can affect the outcome of adaptive immune responses. NK cells, but not NK1.1+T cells, were found to participate in the development of myasthenia gravis (a T cell-dependent, B cell- and antibody-mediated autoimmune disease) in C57BL/6 mice. The requirement for NK cells was reflected by the lack of a type I helper T cell response and antibodies to the acetylcholine receptor in both NK1.1+ cell-depleted and NK cell-deficient IL-18-/- mice. These findings establish a previously unrecognized link between NK cells and autoreactive T and B cells.

Functional alteration of granulocytes, NK cells, and natural killer T cells in centenarians

The immune system in centenarians was characterized as elevated levels in the proportion and number of granulocytes, NK cells, and extrathymic T cells (including NKT cells) in the peripheral blood. Conventional T cells, abundant in youth, were decreased in proportion and number. In addition to this numerical change in centenarians, the function was significantly altered in comparison with that in middle-aged subjects. The phagocytic function and cytokine production of granulocytes in centenarians increased whereas the production of superoxides from granulocytes decreased. This tendency was almost the same in both healthy and unhealthy centenarians. IFN gamma production by NK and extrathymic T cells in centenarians seemed to be augmented and resulted in an elevated level of serum IFN gamma. Possibly due to the effect of this endogenous IFN gamma, the proportion of CD64(+) (Fc gamma RI) cells among granulocytes was elevated. The expansion of CD64 antigens on granulocytes is known to be regulated by IFN gamma and to be associated with their induction of phagocytosis. These results suggest that the immune system of centenarians is not merely impaired, but altered in terms of the number and functions of granulocytes, NK cells, NKT cells.

Cutting edge: contribution of NK cells to the homing of thymic CD4+NKT cells to the liver

In contrast to peripheral lymphoid organs, in the liver a high proportion of T cells are CD4+NKT cells. We have previously reported that LFA-1 plays a pivotal role in the homing of thymic CD4+NKT cells to the liver. In the present study, we further assessed which cell type participates in the homing of thymic CD4+NKT cells to the liver. The accumulation of donor thymocyte-derived CD4+NKT cells in the liver of SCID mice that had been reconstituted with thymocytes from C57BL/6 mice was severely impaired by in vivo depletion of NK cells, but not Kupffer cells in recipients. These results suggest that NK cells participate in the homing of thymic CD4+NKT cells to the liver. We assume that LFA-1 expressed on NK cells is involved in this mechanism.

Cd1d-restricted cellular lysis by peripheral blood lymphocytes: relevance to the inflammatory bowel diseases

The CD1d molecule has been implicated to play a role in inflammatory bowel diseases (IBD), possibly through its presentation of an intestinal antigen trigger. To understand the role of the CD1d class I-like protein in IBD, we investigated the molecule's expression in diseased intestinal tissue and determined its potential to undergo specific recognition by intraepithelial and peripheral blood lymphocytes (PBLs) derived from IBD patients. We have observed an increase in precipitable CD1d in inflamed tissues, which suggests CD1d up-regulation in IBD; this was not accompanied by the occurrence of CD1d-specific cytotoxicity by lymphocytes isolated from the same tissue sites. In contrast, we have observed CD1d-specific cytotoxicity by PBLs from both patients and normal controls mediated by a possibly unique type of lymphocytic cell. These observations support a model in which intestinal inflammation may be initiated by circulating PBLs following the tissue-specific upregulation of CD1d. These activated PBLs may then be the source of the extraintestinal manifestations observed with IBD. We therefore propose that the cells responsible for this activity may play a role in regulating immune responses through the specific recognition of CD1d-specific antigen(s).

alpha -galactosylceramide-activated Valpha 14 natural killer T cells mediate protection against murine malaria

Natural killer T (NKT) cells are a unique population of lymphocytes that coexpress a semiinvariant T cell and natural killer cell receptors, which are particularly abundant in the liver. To investigate the possible effect of these cells on the development of the liver stages of malaria parasites, a glycolipid, alpha-galactosylceramide (alpha-GalCer), known to selectively activate Valpha14 NKT cells in the context of CD1d molecules, was administered to sporozoite-inoculated mice. The administration of alpha-GalCer resulted in rapid, strong antimalaria activity, inhibiting the development of the intrahepatocytic stages of the rodent malaria parasites Plasmodium yoelii and Plasmodium berghei. The antimalaria activity mediated by alpha-GalCer is stage-specific, since the course of blood-stage-induced infection was not inhibited by administration of this glycolipid. Furthermore, it was determined that IFN-gamma is essential for the antimalaria activity mediated by the glycolipid. Taken together, our results provide the clear evidence that NKT cells can mediate protection against an intracellular microbial infection.

Membrane lymphotoxin is required for the development of different subpopulations of NK T cells

The development of lymphoid organs requires membrane-bound lymphotoxin (LT), a heterotrimer containing LTalpha and LTbeta, but the effects of LT on T cell function have not been characterized extensively. Upon TCR cross-linking in vitro, splenocytes from both LTalpha-/- and LTbeta-/- mice failed to produce IL-4 and IL-10 due to a reduction in NK T cells. Concordantly, LTalpha-/- and LTbeta-/- mice did not respond to the lipoglycan alpha-galactosylceramide, which is presented by mouse CD1 to Valpha14+ NK T cells. Interestingly, both populations of NK T cells, including those that are mouse CD1 dependent and alpha-galactosylceramide reactive and those that are not, were affected by disruption of the LTalpha and LTbeta genes. NK T cells were not affected, however, in transgenic mice in which LT signaling is blocked, beginning on day 3 after birth, by expression of a soluble decoy LTbeta receptor. This suggests that membrane-bound LT is critical for NK T cells early in ontogeny, but not for the homeostasis of mature cells.

CD1-Restricted T cells: T cells with a unique immunological niche

Until recently, antigen presentation to T cells was defined only by proteins encoded within the MHC locus. That definition has now been expanded to include proteins encoded outside the MHC locus, most notably the CD1 family of proteins. The pathway of CD1-presented antigens diverges from that of MHC processing, indicating that the CD1 antigen-processing pathway may be complementary to the MHC pathways. The most surprising finding of the CD1 antigen-presenting system is that the antigens presented by CD1 are not peptides, but rather lipid and glycolipid in nature. The most compelling evidence for the role of CD1-restricted T cells in immune homeostasis stems from studies of mycobacterial infection and autoimmunity. These studies suggest that CD1-restricted T cells promote cell-mediated immune responses to intracellular infection and protect against anti-self responses.

Functional natural killer T cells in experimental mouse strains, including NK1.1- strains

Natural killer T (NKT) cells are a newly discovered subset of lymphocytes. It appears that this subset has potential as important regulators of immune responses. But because there are relatively few NKT cells in lymphoid organs and because of technical difficulties in detecting NKT cells in most mouse strains, the roles of NKT cells have not been fully identified and little attention has been paid to the roles of NKT cells in immunological experiments in which NK1.1- strains were used. To examine the existence of functional NKT cells in various strains of experimental mice, including NK1.1- strains, we utilized alpha-galactosylceramide (KRN7000) which is thought to react specifically with NKT cells. Indeed, we could confirm that early cytokine (IL-4 and IFN-gamma) secretion at 2 h after the injection of KRN7000 was dependent on NKT cells. With this in vivo system, we have successfully detected the presence of functional NKT cells in various mouse strains, including AKR/N, BALB/c, C3H/HeJ, C3H/HeN, C57BL/6, C.B-17, CBA/N, NC, NOD, SJL, W/Wv, aly/aly and aly/+. Notable increases of serum IL-4 were detected in W/Wv and aly/+ strains, and defective response of IFN-gamma in SJL mice and that of IL-4 in NOD mice were observed. This is the first report to show the functional significance of NKT cells in cytokine secretion in various mouse strains in response to a ligand for the T cell receptor of NKT cells.

Activation of natural killer T cells by alpha-galactosylceramide in the presence of CD1d provides protection against colitis in mice

BACKGROUND & AIMS

CD1d is a major histocompatibility complex class I-like molecule that presents glycolipid antigens to a subset of natural killer (NK)1.1(+) T cells. These NK T cells exhibit important immunoregulatory functions in several autoimmune disease models.

METHODS

To investigate whether CD1d and NK T cells have a similar role in intestinal inflammation, the effects of the glycolipid, alpha-galactosylceramide (alpha-GalCer), on dextran sodium sulfate (DSS)-induced colitis were examined. Wild-type (WT), CD1d(-/-), and RAG(-/-) mice were examined for their response to either alpha-GalCer or the control analogue, alpha-mannosylceramide (alpha-ManCer).

RESULTS

WT mice, but not CD1d(-/-) and RAG(-/-) mice, receiving alpha-GalCer had a significant improvement in DSS-induced colitis based on body weight, bleeding, diarrhea, and survival when compared with those receiving alpha-ManCer. Elimination of NK T cells through antibody-mediated depletion resulted in a reduction of the effect of alpha-GalCer. Furthermore, adoptive transfer of NK T cells preactivated by alpha-GalCer, but not alpha-ManCer, resulted in diminished colitis. Using a fluorescent-labeled analogue of alpha-GalCer, confocal microscopy localized alpha-GalCer to the colonic surface epithelium of WT but not CD1d(-/-) mice, indicating alpha-GalCer binds CD1d in the intestinal epithelium and may be functionally active at this site.

CONCLUSIONS

These results show an important functional role for NK T cells, activated by alpha-GalCer in a CD1d-restricted manner, in regulating intestinal inflammation.

The interface between innate and acquired immunity: glycolipid antigen presentation by CD1d-expressing dendritic cells to NKT cells induces the differentiation of antigen-specific cytotoxic T lymphocytes

In vivo administration of NKT cell ligand, alpha-galactosylceramide (alpha-GalCer), caused the activation of NKT cells to induce a strong NK activity and cytokine production by CD1d-restricted mechanisms. Surprisingly, we also found that alpha-GalCer induced the activation of immunoregulatory cells involved in acquired immunity. Specifically, in vivo administration of alpha-GalCer resulted in the induction of the early activation marker CD69 on CD4(+) T cells, CD8(+) T cells and B cells in addition to macrophages and NKT cells. However, no significant induction of CD69 was observed on cells from CD1d- or V(alpha)14 NKT-deficient mice, indicating an essential role for the interaction between NKT cells and CD1d-expressing dendritic cells (DC) in the activation of acquired immunity in response to alpha-GalCer. Indeed, in vivo injection of alpha-GalCer resulted not only in the activation of NKT cells but also in the generation of CD69(+)CD8(+) T cells possessing both cytotoxic T lymphocyte (CTL) activity and IFN-gamma-producing ability. Tumor-specific CTL generation was also accelerated by alpha-GalCer. The critical role of CD40-CD40 ligand (CD40L)-mediated NKT-DC interaction during the development of CD69(+)CD8(+) CTL by alpha-GalCer was demonstrated by blocking experiments using anti-CD40L mAb. These findings provide direct evidence for a critical role of CD1d-restricted NKT cells and DC in bridging innate and acquired immunity.

CD1d-specific NK1.1+ T cells with a transgenic variant TCR

The majority of T lymphocytes carrying the NK cell marker NK1.1 (NKT cells) depend on the CD1d molecule for their development and are distinguished by their potent capacity to rapidly secrete cytokines upon activation. A substantial fraction of NKT cells express a restricted TCR repertiore using an invariant TCR Valpha14-Jalpha281 rearrangement and a limited set of TCR Vbeta segments, implying recognition of a limited set of CD1d-associated ligands. A second group of CD1d-reactive T cells use diverse TCR potentially recognizing a larger diversity of ligands presented on CD1d. In TCR-transgenic mice carrying rearranged TCR genes from a CD1d-reactive T cell with the diverse type receptor (using Valpha3. 2/Vbeta9 rearrangements), the majority of T cells expressing the transgenic TCR had the typical phenotype of NKT cells. They expressed NK1.1, CD122, intermediate TCR levels, and markers indicating previous activation and were CD4/CD8 double negative or CD4+. Upon activation in vitro, the cells secreted large amounts of IL-4 and IFN-gamma, a characteristic of NKT cells. In mice lacking CD1d, TCR-transgenic cells with the NKT phenotype were absent. This demonstrates that a CD1d-reactive TCR of the "non-Valpha 14" diverse type can, in a ligand-dependent way, direct development of NK1.1+ T cells expressing expected functional and cell-surface phenotype characteristics.

Multiple differences in gene expression in regulatory Valpha 24Jalpha Q T cells from identical twins discordant for type I diabetes

Quantitative and qualitative defects in CD1d-restricted T cells have been demonstrated in human and murine autoimmune diseases. To investigate the transcriptional consequences of T cell receptor activation in human Valpha24JalphaQ T cell clones, DNA microarrays were used to quantitate changes in mRNA levels after anti-CD3 stimulation of clones derived from identical twins discordant for type 1 diabetes and IL-4 secretion. Activation resulted in significant modulation of 226 transcripts in the IL-4 secreting clone and 86 in the IL-4-null clone. Only 28 of these genes were in common. The differences observed suggest both ineffective differentiation of diabetic Valpha24JalphaQ T cells and a role for invariant T cells in the recruitment and activation of cells from the myeloid lineage.

Mouse CD8+ CD122+ T cells with intermediate TCR increasing with age provide a source of early IFN-gamma production

Although CD8+ IL-2Rbeta (CD122)+ T cells with intermediate TCR reportedly develop extrathymically, their functions still remain largely unknown. In the present study, we characterized the function of CD8+ CD122+ T cells with intermediate TCR of C57BL/6 mice. The proportion of CD8+ CD122+ T cells in splenocytes gradually increased with age, whereas CD8+ IL-2Rbeta-negative or -low (CD122-) T cells conversely decreased. The IFN-gamma production from splenocytes stimulated with immobilized anti-CD3 Ab in vitro increased with age, whereas the IL-4 production decreased. When sorted CD8+ CD122+ T cells were stimulated in vitro by the anti-CD3 Ab, they promptly produced a much larger amount of IFN-gamma than did CD8+ CD122- T cells or CD4+ T cells, whereas only CD4+ T cells produced IL-4. The depletion of CD8+ CD122+ T cells from whole splenocytes greatly decreased the CD3-stimulated IFN-gamma production and increased the IL-4 production, whereas the addition of sorted CD8+ CD122+ T cells to CD8+ CD122+ T cell-depleted splenocytes restored the IFN-gamma production and partially decreased IL-4 production. It is of interest that CD8+ CD122+ T cells stimulated CD4+ T cells to produce IFN-gamma. The CD3-stimulated IFN-gamma production from each T cell subset was augmented by macrophages. Furthermore, CD3-stimulated CD8+ CD122+ T cells produced an even greater amount of IFN-gamma than did liver NK1.1+ T cells and also showed antitumor cytotoxicity. These results show that CD8+ CD122+ T cells may thus be an important source of early IFN-gamma production and are suggested to be involved in the immunological changes with aging.

Relative contribution of NK and NKT cells to the anti-metastatic activities of IL-12

Conventional T cells, NK cells and NKT cells have been implicated in the anti-tumor activities induced by IL-12. Here we show that IL-12-induced immune responses are partially impaired in T and NKT cell-deficient RAG-2(-/-) mice, and in NKT cell-deficient CD1(-/-) mice. In response to a small dose (<1000 U) of IL-12, RAG-2(-/-) and CD1(-/-) mice demonstrated reduced cytotoxicity, serum IFN-gamma elevation and anti-metastatic activities; in contrast, in response to a high dose (>2000 U) of IL-12, the IL-12-induced immune responses of RAG-2(-/-) and CD1(-/-) mice were indistinguishable from wild-type mice. The defective responses to low-dose IL-12 of RAG-2(-/-) mice were corrected by adoptive transfer of NKT cells but not NK cells. These findings indicate that both NK and NKT cells contribute to the anti-metastatic responses induced by IL-12, and that NKT cells are mostly responsible for the low-dose activities of this cytokine.

Critical contribution of liver natural killer T cells to a murine model of hepatitis

Natural killer T (NKT) cells constitute a distinct subpopulation of T cells with a unique antigen specificity, prompt effector functions, and an unusual tissue distribution. NKT cells are especially abundant in the liver, but their physiological function in this organ remains unclear. In the present study, we examined the possible contribution of NKT cells to a murine model of hepatitis induced by i.v. injection of Con A. CD1-deficient mice lacking NKT cells were highly resistant to Con A-induced hepatitis. Adoptive transfer of hepatic NKT cells isolated from wild-type mice, but not from FasL-deficient gld mice, sensitized CD1-deficient mice to Con A-induced hepatitis. Furthermore, adoptive transfer of hepatic mononuclear cells from wild-type mice, but not from CD1-deficient mice, sensitized gld mice to Con A-induced hepatitis. Upon Con A administration, hepatic NKT cells rapidly up-regulated cell surface FasL expression and FasL-mediated cytotoxicity. At the same time, NKT cells underwent apoptosis leading to their rapid disappearance in the liver. These results implicated FasL expression on liver NKT cells in the pathogenesis of Con A-induced hepatitis, suggesting a similar pathogenic role in human liver diseases such as autoimmune hepatitis.

CD1-mediated antigen presentation of glycosphingolipids

CD1 proteins are distinguished by their ability to present lipid antigens to T cells. Group II CD1 or CD1d molecules are recognized by the specialized NK T-cell subset, and this reactivity can be greatly augmented by alpha-galactosylceramide, a glycosphingolipid derived from a marine sponge. Human CD1b, which is only distantly related to the CD1d molecules, can present mammalian glycosphingolipids (gangliosides) to autoreactive T-cell clones derived from multiple sclerosis patients. Thus, CD1 responsive and glycosphingolipid-reactive cells may play an important immune regulatory role, in addition to their well-characterized role in the response to microbial lipids.

Evidence for human CD4+ T cells in the CD1-restricted repertoire: derivation of mycobacteria-reactive T cells from leprosy lesions

Both the CD4-CD8- (double negative) and CD4-CD8+ T cell lineages have been shown to contain T cells which recognize microbial lipid and glycolipid Ags in the context of human CD1 molecules. To determine whether T cells expressing the CD4 coreceptor could recognize Ag in the context of CD1, we derived CD4+ T cell lines from the lesions of leprosy patients. We identified three CD4+ Mycobacterium leprae-reactive, CD1-restricted T cell lines: two CD1b restricted and one CD1c restricted. These T cell lines recognize mycobacterial Ags, one of which has not been previously described for CD1-restricted T cells. The response of CD4+ CD1-restricted T cells, unlike MHC class II-restricted T cells, was not inhibited by anti-CD4 mAb, suggesting that the CD4 coreceptor does not impact positive or negative selection of CD1-restricted T cells. The CD4+ CD1-restricted T cell lines produced IFN-gamma and GM-CSF, the Th1 pattern of cytokines required for cell-mediated immunity against intracellular pathogens, but no detectable IL-4. The existence of CD4+ CD1-restricted T cells that produce a Th1 cytokine pattern suggests a contributory role in immunity to mycobacterial infection.

Differential expression of NK T cell V alpha 24J alpha Q invariant TCR chain in the lesions of multiple sclerosis and chronic inflammatory demyelinating polyneuropathy

Human V alpha 24+ NK T cells are a unique subset of lymphocytes expressing the V alpha 24J alpha Q invariant TCR chain. Because they can rapidly produce large amounts of regulatory cytokines, a reduction of NK T cells may lead to the development of certain autoimmune diseases. Using a single-strand conformation polymorphism method, we demonstrate that a great reduction of V alpha 24J alpha Q NK T cells in the peripheral blood is an immunological hallmark of multiple sclerosis, whereas it is not appreciable in other autoimmune/inflammatory diseases such as chronic inflammatory demyelinating polyneuropathy. The chronic inflammatory demyelinating polyneuropathy lesions were often found to be infiltrated with V alpha 24J alpha Q NK T cells, but multiple sclerosis lesions only rarely expressed the V alpha 24J alpha Q TCR. It is therefore possible that the extent of NK T cell alteration may be a critical factor which would define the clinical and pathological features of autoimmune disease. Although the mechanism underlying the NK T cell deletion remains largely unclear, a remarkable contrast between the CNS and peripheral nervous system diseases allows us to speculate a role of tissue-specific elements such as the level of CD1d expression or differences in the CD1d-bound glycolipid.

Relative contributions of distinct MHC class I-dependent cell populations in protection to tuberculosis infection in mice

A necessary role for cytotoxic T lymphocytes in protection against Mycobacterium tuberculosis (MTB) has been suggested by studies of the beta2-microglobulin-deficient mouse, which is unable to present antigens through MHC class I and class I-like molecules and invariably succumbs early after infection. To identify the relative contributions of distinct putative MHC class I-dependent cell populations in protection against tuberculosis, we compared a variety of gene-disrupted mouse strains for susceptibility to MTB infection. Among the strains tested, the most susceptible mice, as measured by survival time and bacterial loads, were the beta2-microglobulin(-/-), followed by transporter associated with antigen processing deficient (TAP1(-/-)), CD8alpha(-/-), perforin(-/-), and CD1d(-/-) mice. These findings indicated that (i) CD8(+) T cells contribute to protection against MTB, and their protective activity is only partially dependent on perforin; (ii) beta2-microglobulin-dependent T cell populations distinct from CD8(+) T cells also contribute to anti-MTB immunity; and (iii) protective immune mechanisms are predominantly TAP-dependent, although TAP-independent mechanisms also contribute to protection. Because CD1d-deficient animals were fully resistant to MTB, other TAP-independent mechanisms must contribute to protection. We suggest here that both classical and nonclassical MHC class I-restricted T cells, distinct from CD1d-restricted cells, may be involved in protective immune responses against tuberculosis.

Synergistic effect of KRN7000 with interleukin-15, -7, and -2 on the expansion of human V alpha 24+V beta 11+ T cells in vitro

KRN7000, (2S, 3S, 4R)-1-O-(alpha-D-galactopyranosyl)-2-(N-hexacosanoylamino)-1, 3, 4-octadecanetriol, has been shown to prevent tumor metastasis to the liver through the activation of natural killer (NK) T cells in mice. In this study, the proliferation of human NK T cells, which express an invariant T cell antigen receptor (TCR) consisting of a Valpha24 chain and a Vbeta11 chain, was investigated using KRN7000, interleukin (IL)-15, IL-7, and IL-2 in vitro. KRN7000 stimulated the expansion of Valpha24(+)Vbeta11(+) T cells derived from peripheral blood mononuclear cells in a dose-dependent fashion, with some fluctuation between donors. IL-15, IL-7, and IL-2 synergistically stimulated the expansion of Valpha24(+)Vbeta11(+) T cells when combined with KRN7000. Intracellular expression of interferon (IFN)-gamma and IL-4 in Valpha24(+)Vbeta11(+) T cells expanded in the presence of KRN7000 was identified using flow cytometry. Valpha24(+)Vbeta11(+) T cells, expanded in the presence of KRN7000, contained granzyme (Gr) B-positive granules and perforin-positive granules. The addition of IL-15 to the culture containing KRN7000 increased GrB expression in Valpha24(+)Vbeta11(+) T cells while IL-7 and IL-2 failed to do it. In conclusion, the antitumor effect of KRN7000 may depend, in part, on granule-mediated cell killing through the activation of NK T cells and IL-15 may potentiate this effect.

Cutting edge: the Ets1 transcription factor is required for the development of NK T cells in mice

Ets1-deficient mice develop B and T cells but display a severe defect in the development of the NK cell lineage. In this report, we demonstrate that Ets1 is also required for the development of NK1.1+ T (NK T) cells. We observed significantly decreased numbers of NK T cells in the thymus, spleen, and liver of Ets1-deficient mice. These organs also contained markedly decreased levels of the canonical Valpha14-Jalpha281 TCRalpha transcript seen in NK T cells. Unlike wild-type NK T cells, Ets1-deficient thymocytes failed to produce detectable levels of IL-4 following anti-CD3 stimulation. The absence of NK T cells in the Ets1-deficient mice was not associated with defective expression of CD1, an MHC class I molecule required for NK T cell development. We conclude that Ets1 defines a novel transcriptional regulatory pathway that is required for the development of both the NK and NK T cell lineages.

NKT cells in the rat: organ-specific distribution of NK T cells expressing distinct V alpha 14 chains

Rat invariant TCR alpha-chains and NKT cells were investigated to clarify whether CD1d-mediated recognition by NKT cells is conserved further in evolution. Rats had multiple-copies of TRAV14 genes, which can be categorized into two types according to the diversity accumulated in the CDR2 region. Rats retained invariant TCR alpha forms with the homogeneous junctional region similar to mouse invariant TRAV14-J281. The proportion of invariant TCR among V alpha 14+ clones was 12.9% in the thymus and increased in the periphery, 31% in the spleen and 95% in hepatic sinusoidal cells. The invariant TRAV14-J281 was expressed by liver sinusoidal and splenic NKT cells with CD8, CD44high, and TCR V beta 8. Type 1 invariant TCR alpha was expressed more frequently in hepatic lymphocytes, while type 2 invariant TCR alpha was expressed predominantly in the spleen. Both types of cells cytolyzed to and were stimulated to proliferate by CD1d-expressing cells in a CD1d-restricted manner. These results suggested that rat NKT cells bearing distinct V alpha 14 chains are distributed in a tissue-specific pattern. NKT cell populations in rats were more variable than those in mice, indicating that they play novel roles in nature. The implication of the molecular interaction between the structurally diverse invariant TCR alpha and CD1d/ligand complex in different organs is discussed.

Reversible defects in natural killer and memory CD8 T cell lineages in interleukin 15-deficient mice

C57BL/6 mice genetically deficient in interleukin 15 (IL-15(-/-) mice) were generated by gene targeting. IL-15(-/-) mice displayed marked reductions in numbers of thymic and peripheral natural killer (NK) T cells, memory phenotype CD8(+) T cells, and distinct subpopulations of intestinal intraepithelial lymphocytes (IELs). The reduction but not absence of these populations in IL-15(-/-) mice likely reflects an important role for IL-15 for expansion and/or survival of these cells. IL-15(-/-) mice lacked NK cells, as assessed by both immunophenotyping and functional criteria, indicating an obligate role for IL-15 in the development and functional maturation of NK cells. Specific defects associated with IL-15 deficiency were reversed by in vivo administration of exogenous IL-15. Despite their immunological defects, IL-15(-/-) mice remained healthy when maintained under specific pathogen-free conditions. However, IL-15(-/-) mice are likely to have compromised host defense responses to various pathogens, as they were unable to mount a protective response to challenge with vaccinia virus. These data reveal critical roles for IL-15 in the development of specific lymphoid lineages. Moreover, the ability to rescue lymphoid defects in IL-15(-/-) mice by IL-15 administration represents a powerful means by which to further elucidate the biological roles of this cytokine.

CD4-CD8- T cells bearing invariant Valpha24JalphaQ TCR alpha-chain are decreased in patients with atopic diseases

Atopic disorders are caused by disregulated activation of T helper 2 (Th2) cells that produce IL-4 and IL-5. Because the presence of IL-4 potently augments the differentiation of naive T cells into Th2 cells, it is important to seek the cell population which provides IL-4 for naive T cells. Recently, a unique subpopulation of T cells, natural killer (NK) T cells, has been shown to produce a large amount of IL-4 upon activation, suggesting their regulatory role in initiation of Th2 cell differentiation. To determine whether NK T cells play a regulatory role in human Th2 cell-mediated atopic diseases, we analysed the frequency of invariant Valpha24JalphaQ CD4-CD8- double-negative (DN) T cells, human NK T cells, in patients with atopic asthma and atopic dermatitis. We also studied cytokine production from Valpha24+ Vbeta11+ DN T cells, which comprise most of Valpha24JalphaQ DN T cells. We found that the invariant Valpha24JalphaQ DN T cells were greatly diminished in patients with asthma and atopic dermatitis. On the other hand, there was no significant difference in Valpha24+ CD4+ T cells possessing invariant Valpha24JalphaQ TCR between healthy subjects and atopic patients. We also found that Valpha24+ Vbeta11+ DN T cells from healthy subjects predominantly produced interferon-gamma (IFN-gamma) but not IL-4 upon activation. These results suggest that NK T cells may not be essential for human atopic disease and that the disappearance of NK T cells, most of which produce IFN-gamma, may be involved in the pathogenesis of atopic diseases.

NK1.1+ T cells in the liver arise in the thymus and are selected by interactions with class I molecules on CD4+CD8+ cells

NK1.1+ T cells represent a specialized T cell subset specific for CD1d, a nonclassical MHC class I-restricting element. They are believed to function as regulatory T cells. NK1.1+ T cell development depends on interactions with CD1d molecules presented by hematopoietic cells rather than thymic epithelial cells. NK1.1+ T cells are found in the thymus as well as in peripheral organs such as the liver, spleen, and bone marrow. The site of development of peripheral NK1.1+ T cells is controversial, as is the nature of the CD1d-expressing cell that selects them. With the use of nude mice, thymectomized mice reconstituted with fetal liver cells, and thymus-grafted mice, we provide direct evidence that NK1.1+ T cells in the liver are thymus dependent and can arise in the thymus from fetal liver precursor cells. We show that the class I+ (CD1d+) cell type necessary to select NK1.1+ T cells can originate from TCRalpha-/- precursors but not from TCRbeta-/- precursors, indicating that the selecting cell is a CD4+CD8+ thymocyte. 5-Bromo-2'-deoxyuridine-labeling experiments suggest that the thymic NK1.1+ T cell population arises from proliferating precursor cells, but is a mostly sessile population that turns over very slowly. Since liver NK1.1+ T cells incorporate 5-bromo-2'-deoxyuridine more rapidly than thymic NK1.1+ T cells, it appears that liver NK1.1+ T cells either represent a subset of thymic NK1.1+ T cells or are induced to proliferate after having left the thymus. The results indicate that NK1.1+ T cells, like conventional T cells, arise in the thymus where they are selected by interactions with restricting molecules.

Comparative contribution of CD1 on the development of CD4+ and CD8+ T cell compartments

CD1 molecules are MHC class I-like glycoproteins whose expression is essential for the development of a unique subset of T cells, the NK T cells. To evaluate to what extent CD1 contributes to the development of CD4+ and CD8+ T cells, we generated CD1oIIo and CD1oTAPo mice and compared the generation of T cells in these double-mutant mice and IIo or TAPo mice. FACS analysis showed that the number of CD4+ T cells in CD1oIIo mice was reduced significantly compared with the corresponding population in IIo mice. Both CD4+ NK1.1+ and the CD4+ NK1.1- population were reduced in CD1oIIo mice, suggesting that CD1 can select not only CD4+ NK1.1+ T cells but also some NK1.1- CD4+ T cells. Functional analysis showed that the residual CD4+ cells in CD1oIIo can secrete large amounts of IFN-gamma and a significant amount of IL-4 during primary stimulation with anti-CD3, suggesting that this population may be enriched for NK T cells restricted by other class I molecules. In contrast to the CD4+ population, no significant differences in the CD8+ T cell compartment can be detected between TAPo and CD1oTAPo mice in all lymphoid tissues tested, including intestinal intraepithelial lymphocytes. Our data suggest that, unlike other MHC class I molecules, CD1 does not contribute in a major way to the development of CD8+ T cells.

Cell fate decision: T-helper 1 and 2 subsets in immune responses

After activation CD4(+) helper T cells differentiate into T-helper (Th) 1 or Th2 effector cells. These two subsets are characterized by their distinct cytokine expression pattern and the immune function they mediate. Over the past years, a number of factors have been identified to affect helper T cell lineage determination, including antigen receptor, coreceptors and, most importantly, cytokine environment. In this review, we also summarize recent advancement in understanding of transcriptional and signaling regulation of the differentiation process. This knowledge will become important in the future to develop means in treating immune disorders.

Stat6-independent GATA-3 autoactivation directs IL-4-independent Th2 development and commitment

The initial source of IL-4-inducing Th2 development and the mechanism of stable Th2 commitment remain obscure. We found the reduced level of IL-4 production in Stat6-deficient T cells to be significantly higher than in Th1 controls. Using a novel cell surface affinity matrix technique, we found that IL-4-secreting Stat6-deficient T cells stably expressed GATA-3 and Th2 phenotype. Introducing GATA-3 into Stat6-deficient T cells completely restored Th2 development, inducing c-Maf, Th2-specific DNase I hypersensitive sites in the IL-4 locus, and Th2 cytokine expression. The fact that GATA-3 fully reconstitutes Th2 development in Stat6-deficient T cells indicates it is a master switch in Th2 development. Finally, GATA-3 exerts Stat6-independent autoactivation, creating a feedback pathway stabilizing Th2 commitment.

Positive selection of NKT cells by CD1(+), CD11c(+) non-lymphoid cells residing in the extrathymic organs

Previously, we found that NK1.1(+), TCRalpha beta(+) natural killer T (NKT) cells develop in cytokine-supplemented suspension cultures of fetal liver established from normal, but not from beta2 microglobulin-deficient [beta2m(- / -)] mice, and that recombination-deficient SCID fetal liver can reconstiute NKT cell development in beta2m(- / -) fetal liver cultures. We found here that cells of SCID adult liver, bone marrow, spleen and thymus were able to reconstitute NKT cell development in the former culture system with efficiency comparable to normal thymic cells. The reconstitution of NKT cells was also seen in the bone marrow chimeras that had been administered a combination of beta2m(- / -) and Rag-2(- / -) bone marrow cells. Development of NKT cells was hampered by depletion of CD11c(+) or CD11b(+) cells, but not by removal of B220(+) or Gr-1(+) cells from cultures of normal fetal liver cells. Furthermore CD11c(+), CD11b(+) and / or CD11c(+) CD11b(-) cells (both populations were CD1-dull positive) enriched from Rag-2-deficient fetal livers and pulsed with alpha-galactosylceramide, a possible antigen for NKT cells, were shown to reconstitute the NKT cell development in beta2m(- / -) fetal liver cultures. Collectively, our findings suggest that non-lymphoid cells, presumably CD11c(+), CD11b(+) and / or CD11c(+), CD11b(-) dendritic cells, are involved in the mechanism of positive selection of NKT cells in the thymus and extrathymic organs.

Heterogeneity of NK1.1+ T Cells in the Bone Marrow: Divergence from the Thymus

NK1.1+ T cells in the mouse thymus and bone marrow were compared because some marrow NK1.1+ T cells have been reported to be extrathymically derived. Almost all NK1.1+ T cells in the thymus were depleted in the CD1−/−, β2m−/−, and Jα281−/− mice as compared with wild-type mice. CD8+NK1.1+ T cells were not clearly detected, even in the wild-type mice. In bone marrow from the wild-type mice, CD8+NK1.1+ T cells were easily detected, about twice as numerous as CD4+NK1.1+ T cells, and were similar in number to CD4−CD8−NK1.1+ T cells. All three marrow NK1.1+ T cell subsets were reduced about 4-fold in CD1−/− mice. No reduction was observed in CD8+NK1.1+ T cells in the bone marrow of Jα281−/− mice, but marrow CD8+NK1.1+ T cells were markedly depleted in β2m−/− mice. All NK1.1+ T cell subsets in the marrow of wild-type mice produced high levels of IFN-γ, IL-4, and IL-10. Although the numbers of marrow CD4−CD8−NK1.1+ T cells in β2m−/− and Jα281−/− mice were similar to those in wild-type mice, these cells had a Th1-like pattern (high IFN-γ, and low IL-4 and IL-10). In conclusion, the large majority of NK1.1+ T cells in the bone marrow are CD1 dependent. Marrow NK1.1+ T cells include CD8+, Vα14-Jα281−, and β2m-independent subsets that are not clearly detected in the thymus.

Noncanonical Valpha24JalphaQ T cells with conservative alpha chain CDR3 region amino acid substitutions are restricted by CD1d

Human NKRP-1A (CD161)+ T cells include members of a family of CD4+ or CD4-/CD8- lymphocytes that utilize an invariant alpha chain in the T-cell receptor (TCR). The alpha chain consists of the Valpha24 segment joined to Jalpha18 (JalphaQ) (TCRAV24/AJ18). These families of T cells rapidly produce both interleukin-4 and interferon-gamma upon TCR cross-linking, and are restricted by CD1d. To determine the spectrum of allowable V/J rearrangements in the Valpha24+ CD4-/CD8- family, TCR Valpha24 chain transcripts derived from the total CD4-/CD8- population in peripheral blood mononuclear cells were sequenced. A second invariant rearrangement, Valpha24Jalpha45, was found in two donors. In addition, a subset of 15 clones with single amino acid substitutions in the CDR3 were identified and used to define CD1d restriction. All 15 variant clones were indistinguishable from invariant clones on the basis of surface phenotype and response to CD3 cross-linking. However, CD1d was the restriction element only for those clones with the conservative substitution of threonine or asparagine for serine at the V/J junction. Thus, the family of human CD161+ T cells can be extended to include a subset of Valpha24-JalphaQ rearrangements with a single amino acid substitution that defines a Valpha24 CDR3 residue critical for CD1d restriction.

CD1-reactive natural killer T cells are required for development of systemic tolerance through an immune-privileged site

Systemic tolerance can be elicited by introducing antigen into an immune-privileged site, such as the eye, or directly into the blood. Both routes of immunization result in a selective deficiency of systemic delayed type hypersensitivity. Although the experimental animal model of anterior chamber-associated immune deviation (ACAID) occurs in most mouse strains, ACAID cannot be induced in several mutant mouse strains that are coincidentally deficient in natural killer T (NKT) cells. Therefore, this model for immune-privileged site-mediated tolerance provided us with an excellent format for studying the role of NKT cells in the development of tolerance. The following data show that CD1-reactive NKT cells are required for the development of systemic tolerance induced via the eye as follows: (a) CD1 knockout mice were unable to develop ACAID unless they were reconstituted with NKT cells together with CD1(+) antigen-presenting cells; (b) specific antibody depletion of NKT cells in vivo abrogated the development of ACAID; and (c) anti-CD1 monoclonal antibody treatment of wild-type mice prevented ACAID development. Significantly, CD1-reactive NKT cells were not required for intravenously induced systemic tolerance, thereby establishing that different mechanisms mediate development of tolerance to antigens inoculated by these routes. A critical role for NKT cells in the development of systemic tolerance associated with an immune-privileged site suggests a mechanism involving NKT cells in self-tolerance and their defects in autoimmunity.

Age-Associated Rapid and Stat6-Independent IL-4 Production by NK1−CD4+8− Thymus T Lymphocytes

The source of IL-4 required for priming naive T cells into IL-4-secreting effectors has not been clearly identified. Here we show that upon TCR stimulation, thymus NK1−CD4+8− T cells produced IL-4, the magnitude of which was inversely correlated with age. This IL-4 production response by Th2-prone BALB/c mice was ∼9-fold that of Th1-prone C57BL/10 mice. More than 90% of activated NK1−CD4+8− thymocytes did not use the invariant Vα14-Jα281 chain characteristic of typical CD1-restricted NK1+CD4+ T cells. Stat6-null NK1−CD4+8− thymocytes produced bioactive IL-4, with induction of IL-4 mRNA expression within 1 h of stimulation. Our results support the possibility that TCR repertoire-diverse conventional NK1−CD4+ T cells are a potential IL-4 source for directing naive T cells toward Th2/type 2 CD8+ T cell (Tc2) effector development.

Impaired NK1.1 T cell development in mice transgenic for a T cell receptor beta chain lacking the large, solvent-exposed cbeta FG loop

A striking feature of the T cell receptor (TCR) beta chain structure is the large FG loop that protrudes freely into the solvent on the external face of the Cbeta domain. We have already shown that a transgene-encoded Vbeta8.2(+) TCR beta chain lacking the complete Cbeta FG loop supports normal development and function of conventional alpha/beta T cells. Thus, the FG loop is not absolutely necessary for TCR signaling. However, further analysis has revealed that a small population of alpha/beta T cells coexpressing NK1.1 are severely depleted in these transgenic mice. The few remaining NK1.1 T cells have a normal phenotype but express very low levels of TCR. We find that the TCR Vbeta8.2(+) chain lacking the Cbeta FG loop cannot pair efficiently with the invariant Valpha14-Jalpha281 TCR alpha chain commonly expressed by this T cell family. Consequently, fewer NK1.1 T cells develop in these mice. Our results suggest that expression of the Valpha14(+) TCR alpha chain is particularly sensitive to TCR-beta conformation. Development of NK1.1 T cells appears to need a TCR-beta conformation dependent on the presence of the Cbeta loop that is not necessarily required for assembly and function of TCRs on most alpha/beta T cells.

The Src family tyrosine kinase Fyn regulates natural killer T cell development

T lymphocytes express two Src tyrosine kinases, Lck and Fyn. While thymocyte and T cell subsets are largely normal in fyn(-/-) mice, animals lacking Lck have impaired T cell development. Here, it is shown that Fyn is required for the rapid burst of interleukin (IL)-4 and IL-13 synthesis, which occurs promptly after T cell receptor activation. The lack of cytokine induction in fyn mutant mice is due to a block in natural killer (NK) T cell development. Studies using bone marrow chimeras indicate that the defect behaves in a cell-autonomous manner, and the lack of NK T cells is probably not caused by inappropriate microenvironmental cues. Both NK T cells and conventional T cells express similar levels of Lck, implying that Fyn and Lck have distinct roles in regulating NK T cell ontogeny. The fyn mutation defines the first signaling molecule that is selectively required for NK T cell, but not for T lymphocyte or NK cell development.

Cutting Edge: NKT Cell Development Is Selectively Impaired in Fyn- Deficient Mice

Most NK1.1+ T (NKT) cells express a biased TCRαβ repertoire that is positively selected by the monomorphic MHC class I-like molecule CD1d. The development of CD1d-dependent NKT cells is thymus dependent but, in contrast to conventional T cells, requires positive selection by cells of hemopoietic origin. Here, we show that the Src protein tyrosine kinase Fyn is required for development of CD1d-dependent NKT cells but not for the development of conventional T cells. In contrast, another Src kinase, Lck, is required for the development of both NKT and T cells. Impaired NKT cell development in Fyn-deficient mice cannot be rescued by transgenic expression of CD8, which is believed to increase the avidity of CD1d recognition by NKT cells. Taken together, our data reveal a selective and nonredundant role for Fyn in NKT cell development.

A defect in interleukin 12-induced activation and interferon gamma secretion of peripheral natural killer T cells in nonobese diabetic mice suggests new pathogenic mechanisms for insulin-dependent diabetes mellitus

The function of natural killer T (NKT) cells in the immune system has yet to be determined. There is some evidence that their defect is associated with autoimmunity, but it is still unclear how they play a role in regulating the pathogenesis of T cell-mediated autoimmune diseases. It was originally proposed that NKT cells could control autoimmunity by shifting the cytokine profile of autoimmune T cells toward a protective T helper 2 cell (Th2) type. However, it is now clear that the major function of NKT cells in the immune system is not related to their interleukin (IL)-4 secretion. In fact, NKT cells mainly secrete interferon (IFN)-gamma and, activated in the presence of IL-12, acquire a strong inflammatory phenotype and cytotoxic function.

Inhibition of T helper cell type 2 cell differentiation and immunoglobulin E response by ligand-activated Valpha14 natural killer T cells

Murine Valpha14 natural killer T (NKT) cells are thought to play a crucial role in various immune responses, including infectious, allergic, and autoimmune diseases. Because Valpha14 NKT cells produce large amounts of both interleukin (IL)-4 and interferon (IFN)-gamma upon in vivo stimulation with a specific ligand, alpha-galactosylceramide (alpha-GalCer), or after treatment with anti-CD3 antibody, a regulatory role on helper T (Th) cell differentiation has been proposed for these cells. However, the identity of the cytokine produced by Valpha14 NKT cells that play a dominant role on the Th cell differentiation still remains controversial. Here, we demonstrate by using Valpha14 NKT-deficient mice that Valpha14 NKT cells are dispensable for the induction of antigen-specific immunoglobulin (Ig)E responses induced by ovalbumin immunization or Nippostrongylus brasiliensis infection. However, upon in vivo activation with alpha-GalCer, Valpha14 NKT cells are found to suppress antigen-specific IgE production. The suppression appeared to be IgE specific, and was not detected in either Valpha14 NKT- or IFN-gamma-deficient mice. Consistent with these results, we also found that ligand-activated Valpha14 NKT cells inhibited Th2 cell differentiation in an in vitro induction culture system. Thus, it is likely that activated Valpha14 NKT cells exert a potent inhibitory effect on Th2 cell differentiation and subsequent IgE production by producing a large amount of IFN-gamma. In marked contrast, our studies have revealed that IL-4 produced by Valpha14 NKT cells has only a minor effect on Th2 cell differentiation.

IL-4-Producing γδ T Cells That Express a Very Restricted TCR Repertoire Are Preferentially Localized in Liver and Spleen

IL-4-producing γδ thymocytes in normal mice belong to a distinct subset of γδ T cells characterized by low expression of Thy-1. This γδ thymocyte subset shares a number of phenotypic and functional properties with the NK T cell population. Thy-1dull γδ thymocytes in DBA/2 mice express a restricted repertoire of TCRs that are composed of the Vγ1 gene product mainly associated with the Vδ6.4 chain and exhibit limited junctional sequence diversity. Using mice transgenic for a rearranged Vγ1Jγ4Cγ4 chain and a novel mAb (9D3) specific for the Vδ6.3 and Vδ6.4 murine TCRδ chains, we have analyzed the peripheral localization and functional properties of γδ T cells displaying a similarly restricted TCR repertoire. In transgenic mice, IL-4 production by peripheral γδ T cells was confined to the γδ+9D3+ subset, which contains cells with a TCR repertoire similar to that found in Thy-1dull γδ thymocytes. In normal DBA/2 mice such cells represent close to half of the γδ T cells present in the liver and around 20% of the splenic γδ T cells.

Cutting Edge: Activation of NK T Cells by CD1d and α-Galactosylceramide Directs Conventional T Cells to the Acquisition of a Th2 Phenotype

NK T cells recognize glycolipid Ags such as α-galactosylceramide (α-GalCer) presented by the MHC class I-like molecule CD1d. In this paper we have studied the in vivo effects of α-GalCer on the generation of adaptive immune responses. Treatment of mice with α-GalCer resulted in rapid activation of NK T cells and production of the cytokines IL-4 and IFN-γ. However, after this initial stimulation, NK T cells became polarized for the production of IL-4. Further, as soon as 6 days after α-GalCer injection, a marked increase in serum IgE levels was observed. Administration of α-GalCer at the time of priming of mice with protein Ag resulted in the generation of Ag-specific Th2 cells and a profound increase in the production of IgE. Collectively, these findings indicate that α-GalCer may be useful for modulating immune responses toward a Th2 phenotype during prophylaxis and therapy.

Regulatory Role of Peritoneal NK1.1+αβ T Cells in IL-12 Production During Salmonella Infection

NK1.1+αβ T cells emerge in the peritoneal cavity after an i.p. infection with Salmonella choleraesuis in mice. To elucidate the role of the NK1.1+αβ T cells during murine salmonellosis, mice lacking NK1.1+αβ T cells by disruption of TCRβ (TCRβ−/−), β2m (β2m−/−), or Jα281 (Jα281−/−) gene were i.p. inoculated with S. choleraesuis. The peritoneal exudate T cells in wild type (wt) mice on day 3 after infection produced IL-4 upon TCRαβ stimulation, whereas those in TCRβ−/−, β2m−/−, or Jα281−/− mice showed no IL-4 production upon the stimulation, indicating that NK1.1+αβ T cells are the main source of IL-4 production at the early phase of Salmonella infection. Neutralization of endogenous IL-4 by administration of anti-IL-4 mAb to wt mice reduced the number of Salmonella accompanied by increased IL-12 production by macrophages after Salmonella infection. The IL-12 production by the peritoneal macrophages was significantly augmented in mice lacking NK1.1+αβ T cells after Salmonella infection accompanied by increased serum IFN-γ level. The aberrantly increased IL-12 production in infected TCRβ−/− or Jα281−/− mice was suppressed by adoptive transfer of T cells containing NK1.1+αβ T cells but not by the transfer of T cells depleted of NK1.1+αβ T cells or T cells from Jα281−/− mice. Taken together, it is suggested that NK1.1+αβ T cells eliciting IL-4 have a regulatory function in the IL-12 production by macrophages at the early phase of Salmonella infection.

Activation of mouse liver natural killer cells and NK1.1(+) T cells by bacterial superantigen-primed Kupffer cells

Although bacterial superantigens have been well characterized as potent stimulators of T cells, their role in natural killer (NK)-type cells remains largely unknown. In the present study, we examined the effect of bacterial superantigens on mouse liver NK cells and NK1.1 Ag(+) (NK1(+)) T cells. C57BL/6 mice were intravenously injected with staphylococcal enterotoxin B (SEB) or streptococcal pyrogenic exotoxin A (SPE-A), and mononuclear cells (MNC) of various organs were obtained from mice 4 hours after being injected with superantigen. MNC were cultured for 48 hours, and interferon gamma (IFN-gamma) levels of supernatants were measured. The antitumor cytotoxicities of the liver and spleen MNC were also evaluated 24 hours after the mice were injected with superantigen. Liver MNC produced more IFN-gamma than did splenocytes, and peripheral blood and lung MNC did not produce any detectable IFN-gamma. In addition, liver MNC acquired a potent antitumor cytotoxicity by the SEB injection, and both NK cells and NK1(+)T cells but not cluster of differentiation (CD)8(+) T cells were responsible for the cytotoxicity as demonstrated by either in vivo or in vitro cell depletion experiments, and the NK-type cells were partly responsible for the increased serum IFN-gamma. Activation of liver NK-type cells was also supported by the fact that liver NK cells proportionally increased and NK1(+) T cells augmented their CD11a expressions after SEB injection. The pretreatment of mice with anti-IFN-gamma Ab and/or with anti-interleukin-12 (IL-12) Ab diminished the SEB-induced cytotoxicity of liver MNC. Furthermore, the in vivo depletion of Kupffer cells decreased the SEB-induced cytotoxicity of liver MNC. Consistent with these results, liver MNC stimulated with superantigens in the presence of Kupffer cells in vitro produced a greater amount of IFN-gamma than did the liver MNC without Kupffer cells or splenocytes. Our results suggest that bacterial superantigen-primed Kupffer cells produce IL-12 and other monokines, while also nonspecifically activating both NK cells and NK1(+) T cells to produce IFN-gamma.

Selection of phenotypically distinct NK1.1+ T cells upon antigen expression in the thymus or in the liver

Unlike the main TCR alphabeta T cell lineage in which deletion occurs at the CD4+ CD8+ double-positive (DP) stage upon TCR engagement by antigen in the thymus, some T cells appear to require such engagement for their selection, either in the thymus or extrathymically. We used a transgenic TCR (tgTCR) model which, as we previously showed, led to selection upon expression of the corresponding antigen H-2Kb (Kb) in the thymus, of tgTCR/CD3(lo) CD4- CD8- double-negative (DN) thymocytes that expressed the NK1.1 marker (NK T cells) (Curnow, S. J., et al., Immunity 1995. 3: 427). We now report that antigen expression on medullary epithelial cells of the thymus failed to select the NK T cells, whereas its expression on thymocytes did, although tgTCR DP thymocyte development was affected under both conditions. Antigen expression on hepatocytes (Alb-Kb mice) did not perturb tgTCR DP thymocyte development. No enrichment in tgTCR NK T cells was detected in the periphery, except for the liver of the Alb-Kb/tgTCR mice. When reconstitution of thymectomized and irradiated H-2k hosts expressing or not Kb was performed with bone marrow from tgTCR H-2k mice, an enrichment in tgTCR+ NK T cells was found in the liver, but not in the spleen, of the hosts which expressed Kb, either selectively on hepatocytes or ubiquitously. Surprisingly, the majority of the hepatic tgTCR+ NK T cells also expressed the CD8 alpha/beta heterodimer. These results indicate that thymus-independent NK T cells with unique phenotypic characteristics can be selected upon antigen encounter in the liver.

Induction of differentiation of pre-NKT cells to mature Valpha14 NKT cells by granulocyte/macrophage colony-stimulating factor

Valpha14 NKT cells express an invariant antigen receptor encoded by Valpha14 and Jalpha281 gene segments as well as natural killer (NK) markers, including NK1.1. Here, we describe a precursor population of NKT cells (pre-NKT) that expresses NK1.1, T cell antigen receptor beta, pTalpha, and RAG1/2 but not Valpha14 and surface CD3epsilon. Such pre-NKT cells were differentiated successfully in vitro into mature CD3epsilon+ Valpha14(+) NKT cells by IL-15 and granulocyte/macrophage colony-stimulating factor (GM-CSF) in conjunction with stroma cells. Interestingly, only GM-CSF without stroma cells induced the Valpha14-Jalpha281 gene rearrangement in the pre-NKT cells. This also was confirmed by the findings that the number of mature Valpha14 NKT cells and the frequency of Valpha14-Jalpha281 rearrangements were decreased significantly in the mice lacking a GM-CSF receptor component, common beta-chain. These results suggest a crucial role of GM-CSF in the development of Valpha14 NKT cells in vivo.