Psychosine variants as antigens for natural killer T cells

Natural killer T (NKT) cells play a central role in the interface between innate and adaptive immunity, and alpha-galactosylceramide was recently shown to be an endogenous antigen for these cells. The source of alpha-galactosylceramide has not yet been determined; however, in vivo degradation of alpha-galactosylceramide involves generation of alpha-psychosine (alpha-galactosylsphingosine). Alpha-psychosine stimulates cytokine release from NKT cells and constitutes an endogenous antigen for these cells. Alpha-psychosine contains a single lipid chain, while most antigens for NKT cells have two lipid chains, and we have investigated if other glycolipids with one lipid chain, derived from know antigens for NKT cells, stimulate cytokine release from NKT cells. Only psychosine variants derived from the most potent NKT cell antigens cause stimulation, and this stimulation occurs in vitro as well as in vivo. Truncated forms of weak antigens for NKT cells are not stimulatory.

A peptide-free, liposome-based oligosaccharide vaccine, adjuvanted with a natural killer T cell antigen, generates robust antibody responses in vivo

Due to the prevalence of oligo- and polysaccharides on the surfaces of pathogenic organisms, carbohydrates are primary targets for recognition by antibodies generated by the immune systems of higher organisms. Consequently, substantial effort has been expended in efforts to develop vaccines based on carbohydrate epitopes. Typical approaches involve multivalent presentation of carbohydrate targets on antigenic peptides or proteins, which often involve substantial synthetic commitments and/or vaccines that are heterogeneous and difficult to characterize. We have developed a simple, liposome-based approach to generate multivalent carbohydrate vaccines, and in place of an antigenic peptide or protein, we have used a potent antigen for natural killer T cells. This vaccine, based on the Streptococcus pneumoniae serotype 14 polysaccharide, gave a response superior to that from a clinically used vaccine (Prevnar). The dependence of this response on liposome formation was demonstrated by comparison to a simple mixture of the oligosaccharide and the natural killer T cell adjuvant. The importance of the strength of the adjuvant was observed by use of a potent synthetic adjuvant and a weaker, bacterial derived glycolipid adjuvant. These results demonstrate the effectiveness of this novel and relatively simple means of generating carbohydrate-based vaccines.

CD1d endosomal trafficking is independently regulated by an intrinsic CD1d-encoded tyrosine motif and by the invariant chain

Endosomal trafficking is an essential component of the CD1 pathway of lipid antigen presentation to T cells. We demonstrate that CD1d access to endosomal compartments is under dual regulation by an intrinsic tyrosine-based motif, which governs intense recycling between the plasma membrane and the endosome, and by the invariant chain, with which CD1d associates in the endoplasmic reticulum. Both pathways independently enhance antigen presentation to V(alpha)14(+) NKT cells, the main subset of CD1d-restricted T cells. These results reveal the complexity of CD1d trafficking and suggest that the invariant chain was a component of ancestral antigen presentation pathways prior to the evolution of MHC and CD1.

Autoreactivity by design: innate B and T lymphocytes

Innate B and T lymphocytes are a subset of lymphocytes that express a restricted set of semi-invariant, germ-line-encoded, autoreactive antigen receptors. Although they have long been set apart from mainstream immunological thought, they now seem to represent a distinct immune-recognition strategy that targets conserved stress-induced self-structures, rather than variable foreign antigens. Innate lymphocytes regulate a range of infectious, tumour and autoimmune conditions. New studies have shed light on the principles and mechanisms that drive their unique development and function, and show their resemblance to another subset of innate lymphocytes, the natural killer cells.

Deficiency in beta(2)-microglobulin, but not CD1, accelerates spontaneous lupus skin disease while inhibiting nephritis in MRL-Fas(lpr) nice: an example of disease regulation at the organ level

When mutations that inactivate molecules that function in the immune system have been crossed to murine lupus strains, the result has generally been a uniform up-regulation or down-regulation of autoimmune disease in the end organs. In the current work we report an interesting dissociation of target organ disease in beta(2)-microglobulin (beta(2)m)-deficient MRL-Fas(lpr) (MRL/lpr) mice: lupus skin lesions are accelerated, whereas nephritis is ameliorated. beta(2)m deficiency affects the expression of classical and nonclassical MHC molecules and thus prevents the normal development of CD8- as well as CD1-dependent NK1(+) T cells. To further define the mechanism by which beta(2)m deficiency accelerates skin disease, we studied CD1-deficient MRL/lpr mice. These mice do not have accelerated skin disease, excluding a CD1 or NK1(+) T cell-dependent mechanism of beta(2)m deficiency. The data indicate that the regulation of systemic disease is not solely governed by regulation of initial activation of autoreactive lymphocytes in secondary lymphoid tissue, as this is equally relevant to renal and skin diseases. Rather, regulation of autoimmunity can also occur at the target organ level, explaining the divergence of disease in skin and kidney in beta(2)m-deficient mice.

The mouse CD1d-restricted repertoire is dominated by a few autoreactive T cell receptor families

To define the phenotype and T cell receptor (TCR) repertoire of CD1d-dependent T cells, we compared the populations of T cells that persisted in major histocompatibility complex (MHC)-deficient mice, which lack mainstream T cells, with those from MHC/CD1d doubly deficient mice, which lack both mainstream and CD1d-dependent T cells. Surprisingly, up to 80% of the CD1d-dependent T cells were stained by tetramers of CD1d/alpha-galactosylceramide, which specifically identify the previously described CD1d autoreactive Valpha14-Jalpha18/Vbeta8 natural killer (NK) T cells. Furthermore, zooming in on the CD1d-dependent non-Valpha14 T cells, we found that, like Valpha14 NK T cells, they mainly expressed recurrent, CD1d autoreactive TCR families and had a natural memory phenotype. Thus, CD1d-restricted T cells differ profoundly from MHC-peptide-specific T cells by their predominant use of autoreactive and semiinvariant, rather than naive and diverse, TCRs. They more closely resemble other lineages of innate lymphocytes such as B-1 B cells, gammadelta T cells, and NK cells, which express invariant or semiinvariant autoreactive receptors. Finally, we demonstrate that the MHC-restricted TCR repertoire is essentially non-cross-reactive to CD1d. Altogether, these findings imply that lipid recognition by CD1d-restricted T cells may have largely evolved as an innate rather than an adaptive arm of the mouse immune system.

CD1 and lipid antigens: intracellular pathways for antigen presentation

Recently, different members of the CD1 family of MHC-like molecules have been shown to sample different intracellular compartments to present lipid and glycolipid antigens to T cells. Emerging models suggest that CD1 may have evolved to monitor the integrity of membrane lipids and/or to present microbial lipid antigens to both alpha beta and gamma delta T cells.

CD1d-restricted mouse V alpha 14 and human V alpha 24 T cells: lymphocytes of innate immunity

Mouse V alpha 14 T cells and their human homologs, V alpha 24 T cells, are prominent subsets of CD1d-restricted T cells. Here we discuss their striking similarities to B-1 B cells and gammadelta T cells and propose that these immune cells mediate various innate strategies in response to endogenous or exogenous danger signals.

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.

CD1-restricted T-cell responses and microbial infection

CD1, a conserved family of major histocompatibility (MHC)-like glycoproteins in mammals, specializes in capturing lipid rather than peptide antigen for presentation to T lymphocytes. The principles and mechanisms of this newly discovered immune strategy differ markedly from those governing classical MHC-peptide presentation. They might be exploited for the design of new lipid-based microbial vaccines and adjuvants.

A novel nonclassic beta2-microglobulin-restricted mechanism influencing early lymphocyte accumulation and subsequent resistance to tuberculosis in the lung

In this study, we compared the course of a low-dose aerosol Mycobacterium tuberculosis infection in mice bearing gene disruptions for the beta2-microglobulin molecule, the CD8 molecule, and the CD1 molecule. Over the first 50 d of infection, the CD8- and CD1-disrupted mice were no more susceptible to infection than were the control mice. In contrast, the bacterial load in beta2-microglobulin gene-disrupted mice increased rapidly and attained much higher levels than that observed in the other gene-disrupted mice and in control mice. A second major difference between the beta2-microglobulin gene-disrupted mice and the other animals was the development of lung granulomas; both the CD8- and CD1-disrupted mice developed essentially normal granulomas except for an apparent increased lymphocyte influx in the CD8-disrupted mice. The beta2-microglobulin gene-disrupted mice, on the other hand, developed granulomas virtually devoid of lymphocytes, with these cells instead localized within prominent perivascular cuffing adjacent to the lesions. These data support the hypothesis that a beta2-microglobulin-dependent, non-CD8- and non-CD1-dependent mechanism controls the early and efficient influx of protective lymphocytes into infected lesions, and that the absence of this mechanism decreases the capacity of the animal to initially deal with pulmonary tuberculosis.

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.

Cutting edge: the IgG response to the circumsporozoite protein is MHC class II-dependent and CD1d-independent: exploring the role of GPIs in NK T cell activation and antimalarial responses

Biochemical analysis has suggested that self GPI anchors are the main natural ligand associated with mouse CD1d molecules. A recent study reported that Valpha14+ NK T cells responded to self as well as foreign (parasite-derived) GPIs in a CD1d-dependent manner. It further reported that the IgG response to the Plasmodium berghei malarial circumsporozoite (CS) protein was severely impaired in CD1d-deficient mice, leading to a model whereby NK T cells, upon recognition of CD1d molecules presenting the CS-derived GPI anchor, provide help for B cells secreting anti-CS Abs. We tested this model by comparing the anti-CS Ab responses of wild-type, CD1d-deficient, and MHC class II-deficient mice. We found that the IgG response to the CS protein was solely MHC class II-dependent. Furthermore, by measuring the response of a broad panel of CD1d-autoreactive T cells to GPI-deficient CD1d-expressing cells, we found that GPIs were not required for autoreactive responses.

Unaltered phenotype, tissue distribution and function of Valpha14(+) NKT cells in germ-free mice

The expression pattern of mouse CD1d and the tissue distribution of CD1d-restricted Valpha14-Jalpha281 NKT cells suggest that the liver and the marginal zone of the spleen might be preferred sites of activation of this potent innate pathway of early cytokine secretion. Because these tissues are particularly involved with the filtration of blood-borne pathogens, and because NKT cells with an activated / memory phenotype accumulate over the first weeks of life and their CD1 ligands bind microbial glycolipids, it has been hypothesized that expansion of the NKT cell subset may be driven by exposure to the microbial environment. To test this hypothesis, we analyzed the frequency, surface phenotype and functional properties of NKT cells in normal and in germ-free C57BL / 6 mice. Surprisingly, we found that the NKT cell subset develops in the presence or absence of a microbial environment. Although these results do not rule out the possibility that NKT cells exert a protective function against some microbial agents, they demonstrate that non microbial ligands, possibly self-antigens are sufficient for the generation, maturation and peripheral accumulation of NKT cells.

Unaltered phenotype, tissue distribution and function of Valpha14(+) NKT cells in germ-free mice

The expression pattern of mouse CD1d and the tissue distribution of CD1d-restricted Valpha14-Jalpha281 NKT cells suggest that the liver and the marginal zone of the spleen might be preferred sites of activation of this potent innate pathway of early cytokine secretion. Because these tissues are particularly involved with the filtration of blood-borne pathogens, and because NKT cells with an activated / memory phenotype accumulate over the first weeks of life and their CD1 ligands bind microbial glycolipids, it has been hypothesized that expansion of the NKT cell subset may be driven by exposure to the microbial environment. To test this hypothesis, we analyzed the frequency, surface phenotype and functional properties of NKT cells in normal and in germ-free C57BL / 6 mice. Surprisingly, we found that the NKT cell subset develops in the presence or absence of a microbial environment. Although these results do not rule out the possibility that NKT cells exert a protective function against some microbial agents, they demonstrate that non microbial ligands, possibly self-antigens are sufficient for the generation, maturation and peripheral accumulation of NKT cells.

Cutting edge: Cross-talk between cells of the innate immune system: NKT cells rapidly activate NK cells

alpha-Galactosylceramide (alpha-GalCer) is a glycolipid with potent antitumor properties that binds to CD1d molecules and activates mouse Valpha14 and human Valpha24 NKT cells. Surprisingly, we found that, as early as 90 min after alpha-GalCer injection in vivo, NK cells also displayed considerable signs of activation, including IFN-gamma production and CD69 induction. NK activation was not observed in RAG- or CD1-deficient mice, and it was decreased by pretreatment with anti-IFN-gamma Abs, suggesting that, despite its rapid induction, it was a secondary event that depended on IFN-gamma release by NKT cells. At later time points, B cells and CD8 T cells also began to express CD69. These findings identify a high-speed communication network between the innate and adaptive immune systems in vivo that is initiated upon NKT cell activation. They also suggest that the antitumor effects of alpha-GalCer result from the sequential recruitment of distinct innate and adaptive effector lymphocytes.

Thymic dependence of invariant V alpha 14+ natural killer-T cell development

Both thymic and extrathymic bone marrow (BM)-derived pathways for the development of CD1 reactive, Valpha14-Jalpha281(+) NK1.1(+) T cells have been suggested. In this report, we sought evidence for extrathymic NK-T cell development using two approaches. First, BM cells from gammac-deficient mice were examined for the presence of Valpha14-Jalpha281 transcripts. Since intrathymic NK-T cell selection is gammac independent, we predicted that gammac(-) BM cells should also harbor these specific TCRalpha chains. Second, Valpha14-Jalpha281 transcripts were analyzed in BM cells from lethally irradiated, thymectomized mice reconstituted with fetal liver hematopoietic precursors. All donor-derived T cell development in these chimeras is by definition extrathymic. In both cases, we failed to detect invariant Valpha14(+) TCRalpha chain transcripts. These experiments call into question the significance of an extrathymic pathway of development for Valpha14(+) NK1.1(+) CD1-reactive T cells.

An invariant T cell receptor alpha chain defines a novel TAP-independent major histocompatibility complex class Ib-restricted alpha/beta T cell subpopulation in mammals

We describe here a new subset of T cells, found in humans, mice, and cattle. These cells bear a canonical T cell receptor (TCR) alpha chain containing hAV7S2 and AJ33 in humans and the homologous AV19-AJ33 in mice and cattle with a CDR3 of constant length. These T cells are CD4(-)CD8(-) double-negative (DN) T cells in the three species and also CD8alphaalpha in humans. In humans, their frequency was approximately 1/10 in DN, 1/50 in CD8alpha+, and 1/6,000 in CD4(+) lymphocytes, and they display an activated/memory phenotype (CD45RAloCD45RO+). They preferentially use hBV2S1 and hBV13 segments and have an oligoclonal Vbeta repertoire suggesting peripheral expansions. These cells were present in major histocompatibility complex (MHC) class II- and transporter associated with antigen processing (TAP)-deficient humans and mice and also in classical MHC class I- and CD1-deficient mice but were absent from beta2-microglobulin-deficient mice, indicating their probable selection by a nonclassical MHC class Ib molecule distinct from CD1. The conservation between mammalian species, the abundance, and the unique selection pattern suggest an important role for cells using this novel canonical TCR alpha chain.

Distinct subsets of CD1d-restricted T cells recognize self-antigens loaded in different cellular compartments

Although recent studies have indicated that the major histocompatibility complex-like, beta2-microglobulin-associated CD1 molecules might function to present a novel chemical class of antigens, lipids and glycolipids, to alpha/beta T cells, little is known about the T cell subsets that interact with CD1. A subset of CD1d-autoreactive, natural killer (NK)1.1 receptor-expressing alpha/beta T cells has recently been identified. These cells, which include both CD4(-)CD8(-) and CD4(+) T cells, preferentially use an invariant Valpha14-Jalpha281 T cell receptor (TCR) alpha chain paired with a Vbeta8 TCR beta chain in mice, or the homologous Valpha24-JalphaQ/Vbeta11 in humans. This cell subset can explosively release key cytokines such as interleukin (IL)-4 and interferon (IFN)-gamma upon TCR engagement and may regulate a variety of infectious and autoimmune conditions. Here, we report the existence of a second subset of CD1d-restricted CD4(+) T cells that do not express the NK1.1 receptor or the Valpha14 TCR. Like the Valpha14(+) NK1.1(+) T cells, these T cells exhibit a high frequency of autoreactivity to CD1d, use a restricted albeit distinct set of TCR gene families, and contribute to the early burst of IL-4 and IFN-gamma induced by intravenous injection of anti-CD3. However, the Valpha14(+) NK1.1(+) and Valpha14(-) NK1.1(-) T cells differ markedly in their requirements for self-antigen presentation. Antigen presentation to the Valpha14(+) NK1.1(+) cells requires endosomal targeting of CD1d through a tail-encoded tyrosine-based motif, whereas antigen presentation to the Valpha14(-) NK1.1(-) cells does not. These experiments suggest the existence of two phenotypically different subsets of CD1d-restricted T cells that survey self-antigens loaded in distinct cellular compartments.

Overexpression of natural killer T cells protects Valpha14- Jalpha281 transgenic nonobese diabetic mice against diabetes

Progression to destructive insulitis in nonobese diabetic (NOD) mice is linked to the failure of regulatory cells, possibly involving T helper type 2 (Th2) cells. Natural killer (NK) T cells might be involved in diabetes, given their deficiency in NOD mice and the prevention of diabetes by adoptive transfer of alpha/beta double-negative thymocytes. Here, we evaluated the role of NK T cells in diabetes by using transgenic NOD mice expressing the T cell antigen receptor (TCR) alpha chain Valpha14-Jalpha281 characteristic of NK T cells. Precise identification of NK1.1(+) T cells was based on out-cross with congenic NK1.1 NOD mice. All six transgenic lines showed, to various degrees, elevated numbers of NK1.1(+) T cells, enhanced production of interleukin (IL)-4, and increased levels of serum immunoglobulin E. Only the transgenic lines with the largest numbers of NK T cells and the most vigorous burst of IL-4 production were protected from diabetes. Transfer and cotransfer experiments with transgenic splenocytes demonstrated that Valpha14-Jalpha281 transgenic NOD mice, although protected from overt diabetes, developed a diabetogenic T cell repertoire, and that NK T cells actively inhibited the pathogenic action of T cells. These results indicate that the number of NK T cells strongly influences the development of diabetes.

Innate and adaptive functions of the CD1 pathway of antigen presentation

In the past few years, several studies have unravelled a novel pathway of antigen presentation to T cells of the mammalian immune system. The antigens are presented by CD1, which appears to have evolved to present glycolipid antigens to alphabeta T cells. CD1-restricted T cells are frequently autoreactive, and can promptly release key regulatory cytokines such as IL-4 and IFN-gamma. They have been implicated in a variety of autoimmune diseases including type I diabetes and lupus, in intracellular bacterial infections, and in tumor rejection. They are likely to be involved at the early, innate phase of these immune responses, providing a unique model to study the interface between the innate and adaptive immune systems.

Tissue-specific recognition of mouse CD1 molecules

Although there is evidence that some members of the CD1 gene family may present particular types of foreign Ags, such as mycobacterial lipid Ags or synthetic hydrophobic peptides, to alphabeta T cells, most CD1 isotypes share the unusual property of being recognized by a high frequency of naturally autoreactive alphabeta T cells. In the case of mouse CD1.1 and its human counterpart CD1d, a significant fraction of the autoreactive T cells express semi-invariant TCRs. CD1.1-specific T cells have a restricted tissue distribution and very promptly secrete a large panel of potent cytokines, including IL-4 and IFN-gamma, upon primary activation through their TCR, suggesting that they might regulate some immune responses in these tissues. We show here that their autorecognition of mouse CD1.1 is highly dependent upon the cell type in which CD1.1 is expressed. For example, some of these T cells only respond to CD1.1 expressed by splenic dendritic cells, some respond preferentially to cortical thymocytes, and others respond to splenic B cells. Tissue specificity of CD1.1 recognition is also observed with various cell lines transfected with CD1.1 cDNA. These results show that different CD1.1 self Ags are expressed in different tissues and can be specifically recognized by autoreactive T cells. They suggest that CD1.1 may be naturally associated with a variety of self ligands that overlap only partially in different cell types.

CD1.1 expression by mouse antigen-presenting cells and marginal zone B cells

Mouse CD1.1 is an MHC class I-like, non-MHC-encoded, surface glycoprotein that can be recognized by T cells, in particular NK1.1+ T cells, a subset of alphabeta T cells with semiinvariant TCRs that promptly releases potent cytokines such as IL-4 and IFN-gamma upon stimulation. To gain insight into the function of CD1.1, a panel of nine mAbs was generated and used to biochemically characterize and monitor the surface expression of CD1.1 on different cell types. CD1.1 is a heavily glycosylated, beta2-microglobulin-associated surface protein. Its recognition by a panel of 12 V alpha14-positive and -negative CD1-specific alphabeta T cell hybridomas was blocked by two groups of mAbs that bound to adjacent clusters of epitopes, indicating that different alphabeta TCRs bind to the same region of CD1.1, presumably above the groove. Remarkably, CD1.1 was mainly expressed by dendritic cells, B cells, and macrophages, suggesting a function in Ag presentation to Th cells. Furthermore, the cell type that expressed the highest levels of CD1.1 was the splenic marginal zone B cell, a distinct subset of B cells that also expresses CD21 (the C3d receptor) and may be involved in natural responses to bacterial Ags. Altogether, the results support the idea that CD1.1 may function in recruiting a form of innate help from specialized cytokine producer alphabeta T cells to APCs, a role that might be important at the preadaptive phase of immune responses to some microbial pathogens.

Mouse CD1-specific NK1 T cells: development, specificity, and function

NK1 T cells are a specialized population of alpha/beta T cells that coexpress receptors of the NK lineage and have the unique potential to very rapidly secrete large amounts of cytokines, providing early help for effector cells and regulating the Th1 or Th2 differentiation of some immune responses. NK1 T cells express a restricted TCR repertoire made of an invariant TCR alpha chain, V alpha 14-J alpha 281, associated with polyclonal V beta 8, V beta 7, and V beta 2 TCR beta chains. NK1 T cells recognize the products of the conserved family of MHC class I-like CD1 genes, apparently in the absence of foreign antigens. Thus, this novel regulatory pathway, which straddles the innate and the adaptive immune systems, is unique in that its activation may not require associative recognition of antigen. Here, we review the specificity and function of mouse NK1 T cells, and we discuss the relationship of this lineage to mainstream T cells and NK cells.

Increased interleukin 4 and immunoglobulin E production in transgenic mice overexpressing NK1 T cells

Natural Killer (NK)1.1+ (NK1) T cells are a specialized subset of alpha/beta T cells that coexpress surface receptors that are normally associated with the NK cell lineage of the innate immune system. On recognition of the conserved, major histocompatibility complex class I-like CD1 molecule, these cells are able to release explosive bursts of interleukin 4 (IL-4), a cytokine that promotes the T helper type 2 (Th2) effector class of an immune response. A unique feature of their T cell receptor (TCR) repertoire is the expression of an invariant TCR alpha chain, V alpha 14-J alpha 281, and of a restricted but polyclonal set of V beta gene families, V beta 8, V beta 7, and V beta 2. Here, we show that transgenic expression of this TCR alpha chain during thymic development is sufficient information to bias the differentiation of mainstream thymocytes towards the NK1 developmental pathway. It markedly increases the frequency of cells with the NK1 pattern of T cell differentiation and also has drastic consequences for the selection of the V beta repertoire. Transgenic CD4 cells exhibited a 10-100-fold increase in IL-4 production on mitogen stimulation in vitro and in vivo, and baseline levels of the Th2-controlled serum immunoglobulin isotypes, IgE and IgG1, were also selectively elevated in vivo.

Role of NK1.1+ T cells in a TH2 response and in immunoglobulin E production

Immune responses dominated by interleukin-4 (IL-4)-producing T helper type 2 (TH2) cells or by interferon gamma (IFN-gamma)-producing T helper type 1 (TH1) cells express distinctive protection against infection with different pathogens. Interleukin-4 promotes the differentiation of naïve CD4+ T cells into IL-4 producers and suppresses their development into IFN-gamma producers. CD1-specific splenic CD4+NK1.1+ T cells, a numerically minor population, produced IL-4 promptly on in vivo stimulation. This T cell population was essential for the induction of IL-4-producing cells and for switching to immunoglobulin E, an IL-4-dependent event, in response to injection of antibodies to immunoglobulin D.

Defective IgE production by SJL mice is linked to the absence of CD4+, NK1.1+ T cells that promptly produce interleukin 4

SJL mice produce little or no IgE in response to polyclonal stimulation with anti-IgD antibody and fail to express interleukin 4 (IL-4) mRNA in the spleen 5 days after injection of anti-IgD, in contrast to other mouse strains that produce substantial amounts of IgE and IL-4. Because IL-4 is critical in IgE production, the possibility that SJL mice are poor IgE producers because their naive T cells fail to differentiate into IL-4 producers must be seriously considered. IL-4 itself is the principal factor determining that naive T cells develop into IL-4 producers. A major source of IL-4 for such differentiation is a population of CD1-specific CD4+ T cells that express NK1.1. These cells produce IL-4 within 90 min of anti-CD3 injection. T cells from SJL mice fail to produce IL-4 in response to injection of anti-CD3. Similarly, SJL T cells and CD4+ thymocytes do not produce IL-4 in response to acute in vitro stimulation. SJL T cells show a marked deficiency in CD4+ cells that express the surface receptors associated with the NK1.1+ T-cell phenotype. This result indicates that the SJL defect in IgE and IL-4 production is associated with, and may be due to, the absence of the CD4+, NK1.1+ T-cell population.

Positive selection of mouse NK1+ T cells by CD1-expressing cortical thymocytes

Mouse NK1+ T cells constitute a subset of alpha/beta TCR+ T cells that specialize in the rapid production of cytokines, in particular IL-4, and may promote the differentiation of Th2-type CD4 T cells. Their TCRs, like those of a homologous subset of human T cells, use an invariant TCR alpha chain and were recently shown to be specific for the beta 2-microglobulin-associated, MHC class I-like CD1 molecules, which are encoded outside the MHC. In contrast to mainstream thymocytes, which recognize their positively selecting MHC ligand on thymic epithelial cells, positive selection of NK1+ T cells requires their CD1 ligand to be expressed on bone marrow-derived cells. To investigate the nature of the bone marrow-derived cell involved, chimeric mice were constructed with tissues from normal, SCID, and MHC-deficient mice, so that CD1 could be selectively expressed by different subsets of bone marrow-derived cells in the thymus. CD1 expression was also directly assessed using an anti-CD1 mAb, and a CD1-specific T cell hybridoma. The results suggest that immature (CD4+8+ double-positive) cortical thymocytes are the source of CD1 presentation for positive selection of NK1+ T cells.

TAP-independent, beta 2-microglobulin-dependent surface expression of functional mouse CD1.1

CD1 molecules consist of beta 2-microglobulin (beta 2m) noncovalently complexed to a non-major histocompatibility complex (MHC)-encoded monomorphic integral membrane protein homologous to MHC class I alpha chains. Little is known about the requirements for cell surface expression and T cell recognition of CD1. We inserted the mouse CD1.1 gene into vaccinia virus to create a recombinant virus expressing CD1.1 under the control of a viral promoter. Using this recombinant virus to infect normal or mutant cell lines, we found that the expression of molecules reactive with the CD1.1-specific monoclonal antibody 3C11 requires the expression of beta 2m but was not affected by the absence of the MHC-encoded peptide transporter (TAP). Consistent with these results, IL-2 production by the mCD1.1-specific T cell hybridoma DN32.D3 was induced by thymocytes from normal mice or mice with a homozygous deletion of the TAP1 gene, but not by thymocytes from mice with a homozygous deletion of the beta 2m gene. These results indicate that expression of functional mCD1.1 occurs in a beta 2m-dependent, TAP-independent manner.

Mouse NK1+ T cells

Mouse NK1+ T cells constitute a special subset of alpha beta TCR+ T cells that express natural killer surface receptors and are thought to play an immunoregulatory role because of their unique ability to secrete IL-4 within minutes of primary activation. The recent discovery that they recognize non-polymorphic MHC class I like ligands encoded by CD1 family genes sheds a new light on unusual aspects of their development as well as on some of the possible ways in which they might influence the regulation of the T-helper cell (types 1 and 2) classes of immune responses.

CD1 recognition by mouse NK1+ T lymphocytes

Rare major histocompatibility complex (MHC) class I-like CD1-specific T cells have been isolated from human blood, but it has not been determined whether these clones are part of a defined subset of CD1-specific T cells selected during T cell development, or whether their recognition of CD1 is a fortuitous cross-reaction. In mice, an entire subset of alpha beta thymocytes with a unique phenotype was found to be CD1-specific. This particular subset, and its human counterpart, provide evidence that CD1 has a general role in selecting and interacting with specialized alpha beta T cells.

An invariant T cell receptor alpha chain is used by a unique subset of major histocompatibility complex class I-specific CD4+ and CD4-8- T cells in mice and humans

The mouse thymus contains a mature T cell subset that is distinguishable from the mainstream thymocytes by several characteristics. It is restricted in its usage of T cell receptor (TCR) V beta genes to V beta 8, V beta 7, and V beta 2. Its surface phenotype is that of activated/memory cells. It carries the natural killer NK1.1 surface marker. Furthermore, though it consists entirely of CD4+ and CD4-8- cells, its selection in the thymus depends solely upon major histocompatibility complex (MHC) class I expression by cells of hematopoietic origin. Forced persistence of CD8, in fact, imparts negative selection. Here, we have studied the TCR repertoire of this subset and found that, whereas the beta chain V-D-J junctions are quite variable, a single invariant alpha chain V alpha 14-J281 is used by a majority of the TCRs. This surprisingly restricted usage of the V alpha 14-J281 alpha chain is dependent on MHC class I expression, but independent of the MHC haplotype. In humans, a similar unusual population including CD4-8- cells can also be found that uses a strikingly homologous, invariant alpha chain V alpha 24-JQ. Thus, this unique V alpha-J alpha combination has been conserved in both species, conferring specificity to some shared nonpolymorphic MHC class I/peptide self-ligand(s). This implies that the T cell subset that it defines has a specialized and important role, perhaps related to its unique ability to secrete a large set of lymphokines including interleukin 4, upon primary stimulation in vitro and in vivo.

A subset of CD4+ thymocytes selected by MHC class I molecules

To complete their maturation, most immature thymocytes depend on the simultaneous engagement of their antigen receptor [alpha beta T cell receptor (TCR)] and their CD4 or CD8 coreceptors with major histocompatibility complex class II or I ligands, respectively. However, a normal subset of mature alpha beta TCR+ thymocytes did not follow these rules. These thymocytes expressed NK1.1 and a restricted set of alpha beta TCRs that are intrinsically class I-reactive because their positive selection was class I-dependent but CD8-independent. These cells were CD4+ and CD4-8- but never CD8+, because the presence of CD8 caused negative selection. Thus, neither CD4 nor CD8 contributes signals that direct their maturation into the CD4+ and CD4-8- lineages.

Evidence for a preferential V beta usage by the T cells which adoptively transfer diabetes in NOD mice

Non-obese diabetic (NOD) mice become spontaneously diabetic as a result of a genetically programmed autoimmune process mediated by autoreactive T lymphocytes and directed against beta cell antigen(s). Studies dealing with T cell receptor (TcR) variable (V) gene usage by such autoreactive T lymphocytes have given contrasted results. Various reasons may explain these discrepancies: the multiplicity of antigenic epitopes putatively recognized by T cells, the ambiguity between specifically committed T cells and passenger lymphocytes homing randomly to the pancreas, the necessarily limited size of the T cell clone panels which have been analyzed for TcR rearrangements and, last but not least, the flexibility of T cell repertoires. To circumvent some of these difficulties, we have decided to concentrate upon the T cell population present in diseased animals and capable of transferring diabetes into young naive NOD recipients. This population, composed of CD4+ and CD8+ T cells, is presumably committed against the relevant beta cell antigens and is the most likely to reveal a bias in V gene usage if such a bias does indeed exist. To find out whether certain V beta genes are more frequently used than others by such pathogenic T cells, T lymphocytes from diabetic donors have been depleted in vitro of defined V beta subsets before being reinoculated into permissive recipients. Out of four V beta families probed under such conditions, three (V beta 8, V beta 5 and V beta 11) are neutral. Their absence neither increases nor reduces the final incidence of successful transfers, indicating that these gene segments are not preferentially used. In contrast, the depletion of V beta 6-positive T cells results in a severe reduction of transfers, suggesting that V beta 6 gene is used with a relatively high frequency by diabetogenic CD4+ and/or CD8+ T cells. To define more precisely which subset uses V beta 6 gene preferentially, we have performed mixing experiments with deleted and intact subsets. The results, based on disease transfer and insulitis severity, indicate that the V beta 6 bias affects predominantly the CD4+ subset. Thus, at variance with several studies concluding that V gene usage in NOD mice is heterogeneous, our present data suggest that disease transferring T cells use a relatively restricted set of V beta genes.

Intrathymic activation events and the generation of IL-4 producer CD4+8- thymocytes

The generation of mouse CD4+8- thymocytes appears to involve an activation process. CD69, an early activation marker, is first expressed on 3% of TCRlo/med double-positive thymocytes and peaks (70-90%) at the HSAhi TCRmed CD4+8lo and the HSAhi TCRhi CD4+8- stages, before being downmodulated. CD44, a marker of a later stage of activation is selectively expressed at the HSAlo CD4+8- stage. Functional changes associated with the late activated state, such as the transient acquisition of the potential to secrete IL-4 upon stimulation, are also induced at the HSAlo CD4+8- stage and are still evident after export to the periphery. During thymic selection, interactions of different affinities between TCR/CD4 and self ligand/MHC class II, are likely to induce different degrees of activation. This may impart different functional capabilities--such as the potential to secrete IL-4--to a subset of emerging CD4+ T lymphocytes that express TCRs with intermediate affinities for self. Such a pathway may be involved in the maintenance of tolerance and the prevention of some deleterious autoimmune reactions.

Activation events during thymic selection

During their differentiation in the mouse thymus, CD4+8- cells undergo several of the sequential changes observed upon normal activation of mature, peripheral CD4+ lymphocytes. Expression of CD69, an early activation marker, is first observed on a minority of cells at the T cell receptor (TCR)lo/med double-positive stage, is maximal (50-90%) on heat-stable antigen (HSA)hi TCRhi double-positive, HSAhi TCRmed CD4+8lo, and HSAhi TCRhi CD4+8- cells, and is downmodulated at the mature HSAlo CD4+8- stage. In contrast, CD44, a late activation marker, is selectively expressed at the HSAlo stage. The set of lymphokines that CD4+8- thymocytes can produce upon stimulation also characteristically expands from mainly interleukin 2 (IL-2) at the HSAhi stage, to IL-2 and very large amounts of IL-4, IL-5, IL-10, and interferon gamma (IFN-gamma) at the HSAlo stage. 1 in 30 HSAlo CD4+8- adult thymocytes secrete IL-4 upon stimulation through their TCR. This frequency is 25% of the frequency of IL-2 producers, about 100-fold above that of peripheral (mainly resting) CD4+ T cells. With time after their generation in organ culture, CD4+8- thymocytes lose their capacity to secrete IL-4, IL-5, and IFN-gamma, but not IL-2. Similarly, the frequency of IL-4, but not of IL-2, producers progressively decreases after emigration to the periphery as judged by direct comparison between thymic and splenic CD4+ cells in newborns, or by following the fate of intrathymically labeled CD4+8- cells in adults after their migration to the spleen. This sequence suggests that thymic selection results from an activation process rather than a simple rescue from death at the double-positive stage, and shows that the functional changes induced after intrathymic activation, although transient, are still evident after export to the periphery.

Th0 cells in the thymus: the question of T-helper lineages

Although peripheral naive cells only secrete IL-2 upon primary stimulation, their presumptive immediate precursors, HSAlow CD4+8- thymocytes, can produce a large amount of the set of lymphokines usually associated with preactivated or memory CD4+ lymphocytes: IL-4, IL-5, IL-10 and gamma-IFN. This phenotype can be attributed to true virgin thymocytes and not only to recirculating lymphocytes, because it is found in newborn thymuses and in fetal thymic organ culture. This mature stage of CD4+8- thymocytes is itself preceded by an immature stage (HSAhigh) where only IL-2 and small amounts of gamma-IFN can be elicited by the combination of calcium ionophore and phorbol ester, but not by TCR cross-linking. CD8+4- thymocytes pass through a similar immature HSAhigh stage, where their pattern of lymphokine secretion is not yet differentiated from that of CD4+8- HSA high thymocytes. The subsets acquire their specific profiles at the HSAlow stage. We propose that recent thymic CD4+8- emigrant cells include a significant proportion of Th0 type cells, and that their role is critical to prime the immune system for IL-4 production, as well as to explain the longstanding observations of synergy between helper cell subpopulations in the periphery.

CD4+ and CD8+ T cells acquire specific lymphokine secretion potentials during thymic maturation

Peripheral CD4+ and CD8+ T lymphocytes carry out different functions during immune reactions, partly as a result of the distinct patterns of lymphokines that they secrete upon stimulation. Using thymic cells from adult and newborn mice as well as from fetal organ cultures, we show here that this functional differentiation occurs inside the thymus and is completed during the single positive stage by the time the T-cell receptor becomes fully coupled to the intracellular activation pathways leading to lymphokine secretion. Surprisingly, CD4+8- thymocytes differ from their immediate progeny, naive peripheral CD4+ cells, in that they secrete a broader range of lymphokines, including interleukins 4, 5 and 10 and gamma-interferon, and more closely resemble immunologically experienced (activated or memory) CD4+ lymphocytes.

CD8+ T cell homing to the pancreas in the nonobese diabetic mouse is CD4+ T cell-dependent

The adoptive transfer of type I diabetes in nonobese diabetic mice requires the contribution of both CD4+ and CD8+ T cells. To further elucidate the cellular pathway(s) of beta-cell destruction and the responsibility of each subset, high doses of committed T cells from diabetic mice purified to single subsets, were injected into syngeneic nonobese diabetic neonates. The recipients of single or mixed subsets were followed for clinical manifestations of diabetes and examined at 30 days of age for in situ lesions. None of the animals injected with either CD4+ or CD8+ T cells became overtly diabetic during the 30 days of observation whereas 8 of 23 mice inoculated with a mixture of the two subsets developed glycosuria and hyperglycemia. However, insulitis was found in 6 of the 13 mice injected with CD4+ T cells whereas only 1 of the 9 mice injected with CD8+ T cells showed marginal infiltration of the pancreas. The lesions initiated by CD4+ T cells alone were considerably less severe than those induced by the mixture of both subsets, corroborating the fact that overt disease did not occur in the former group. Together, these results suggest a distinct function for each diabetogenic T cell subset. CD4+ T cells, which have the capacity to home to the pancreas, promote in turn the influx of CD8+ effector T cells that do not by themselves accumulate in this organ. These results illustrate a novel form of T-T cell interactions leading to organ specific autoimmune lesions.

CD8+ T cell homing to the pancreas in the nonobese diabetic mouse is CD4+ T cell-dependent

The adoptive transfer of type I diabetes in nonobese diabetic mice requires the contribution of both CD4+ and CD8+ T cells. To further elucidate the cellular pathway(s) of beta-cell destruction and the responsibility of each subset, high doses of committed T cells from diabetic mice purified to single subsets, were injected into syngeneic nonobese diabetic neonates. The recipients of single or mixed subsets were followed for clinical manifestations of diabetes and examined at 30 days of age for in situ lesions. None of the animals injected with either CD4+ or CD8+ T cells became overtly diabetic during the 30 days of observation whereas 8 of 23 mice inoculated with a mixture of the two subsets developed glycosuria and hyperglycemia. However, insulitis was found in 6 of the 13 mice injected with CD4+ T cells whereas only 1 of the 9 mice injected with CD8+ T cells showed marginal infiltration of the pancreas. The lesions initiated by CD4+ T cells alone were considerably less severe than those induced by the mixture of both subsets, corroborating the fact that overt disease did not occur in the former group. Together, these results suggest a distinct function for each diabetogenic T cell subset. CD4+ T cells, which have the capacity to home to the pancreas, promote in turn the influx of CD8+ effector T cells that do not by themselves accumulate in this organ. These results illustrate a novel form of T-T cell interactions leading to organ specific autoimmune lesions.

Detection of Epstein-Barr virus in epidermal skin lesions of an immunocompromised patient

Using in-situ hybridizaiton, we showed the presence of the Epstein-Barr (EB) virus genome in epidermal cells from a patient with chronic lymphocytic leukemia and unusual cutaneous lesions characterized clinically by a maculopapular eruption and histologically by epidermal cell degeneration and lymphoid cell infiltration. Such histologic changes are similar to those seen in graft-versus-host disease. The EB virus genome was mainly detected in the basal, germinative cells of the abnormal epithelium. Specimens of our patient's healthy skin were negative. The presence of EB virus DNA in skin lesions was confirmed by polymerase chain reaction adapted for analysis of paraffin-embedded tissue. These findings indicate that EB virus can infect the human epidermis and that the viral infection may produce a distinctive cutaneous disease.

The nonobese diabetic mouse model. Independent expression of humoral and cell-mediated autoimmune features

Nonobese diabetic (NOD) mice present concomitant signs of cell-mediated and humoral autoimmunity. Whereas the involvement of the cell-mediated manifestations in the pathogenesis of diabetes has been clearly demonstrated, the origin and the relevance of the humoral manifestations is still unclear. In the present study, we have tried to determine whether the humoral manifestations observed in NOD mice were secondary to the cell-mediated antiislet reaction, or whether they resulted from an autonomous polyclonal activation of B cells, a possibility suggested by the notorious presence of antilymphocyte antibodies with thymocytotoxic properties, in the serum of old NOD females. To discriminate between the two alternatives, we have followed the titers of thymocytotoxic autoantibodies in aging males and females, as well as in F1 hybrids where the organ-specific disease is recessive, and in back-crossed mice where the susceptibility genes responsible for insulitis and diabetes have segregated. In addition to thymocytotoxic antibodies, we have also screened the sera of these animals for hyperglobulinemia, antiinsulin, and anti-DNA autoantibodies that are classically associated with polyclonal B cell activation in autoimmune strains of mice. The results indicate that these humoral anomalies are clearly disconnected from the occurrence of diabetes and even of insulitis. Lymphocytotoxic antibodies appear several weeks after the onset of insulitis in NOD mice, are not correlated with disease occurrence and have no predictive value for its onset. The humoral manifestations that include, beside thymocytotoxic antibodies, antiinsulin antibodies, hyperglobulinemia, but no anti-DNA antibodies, are found at the same frequency in F1 mice as in parental mice in spite of the fact that the former are practically free of insulitis lesions. These anomalies are also randomly distributed among back-crossed mice independently of the presence and the severity of the organ-specific lesions. Altogether, these results suggest that NOD mice, like other autoimmune strains, suffer from a genetically inherited defect of B cell regulation resulting in the hyperproduction of natural autoantibodies.

The nonobese diabetic mouse model. Independent expression of humoral and cell-mediated autoimmune features

Nonobese diabetic (NOD) mice present concomitant signs of cell-mediated and humoral autoimmunity. Whereas the involvement of the cell-mediated manifestations in the pathogenesis of diabetes has been clearly demonstrated, the origin and the relevance of the humoral manifestations is still unclear. In the present study, we have tried to determine whether the humoral manifestations observed in NOD mice were secondary to the cell-mediated antiislet reaction, or whether they resulted from an autonomous polyclonal activation of B cells, a possibility suggested by the notorious presence of antilymphocyte antibodies with thymocytotoxic properties, in the serum of old NOD females. To discriminate between the two alternatives, we have followed the titers of thymocytotoxic autoantibodies in aging males and females, as well as in F1 hybrids where the organ-specific disease is recessive, and in back-crossed mice where the susceptibility genes responsible for insulitis and diabetes have segregated. In addition to thymocytotoxic antibodies, we have also screened the sera of these animals for hyperglobulinemia, antiinsulin, and anti-DNA autoantibodies that are classically associated with polyclonal B cell activation in autoimmune strains of mice. The results indicate that these humoral anomalies are clearly disconnected from the occurrence of diabetes and even of insulitis. Lymphocytotoxic antibodies appear several weeks after the onset of insulitis in NOD mice, are not correlated with disease occurrence and have no predictive value for its onset. The humoral manifestations that include, beside thymocytotoxic antibodies, antiinsulin antibodies, hyperglobulinemia, but no anti-DNA antibodies, are found at the same frequency in F1 mice as in parental mice in spite of the fact that the former are practically free of insulitis lesions. These anomalies are also randomly distributed among back-crossed mice independently of the presence and the severity of the organ-specific lesions. Altogether, these results suggest that NOD mice, like other autoimmune strains, suffer from a genetically inherited defect of B cell regulation resulting in the hyperproduction of natural autoantibodies.