Induction of CD1-restricted immune responses in guinea pigs by immunization with mycobacterial lipid antigens

Group 1 CD1 molecules have been shown to present lipid and glycolipid Ags of mycobacteria to human T cells. However, a suitable animal model for the investigation of this component of antimycobacterial immunity has not yet been established. Previously, we found that guinea pigs express multiple isoforms of group 1 CD1 proteins that are homologous to human CD1b and CD1c. In this study, we show that CD1-restricted T cell responses can be generated in guinea pigs following immunization with lipid Ags from Mycobacterium tuberculosis. Splenic T cells from lipid Ag-immunized guinea pigs showed strong proliferative responses to total lipid Ags and partially purified glycolipid fractions from M. tuberculosis. These lipid Ag-reactive T cells were enriched in CD4-negative T cell fractions and showed cytotoxic activity against CD1-expressing guinea pig bone marrow-derived dendritic cells pulsed with M. tuberculosis lipid Ags. Using guinea pig cell lines transfected with individual CD1 isoforms as target cells in cytotoxic T cell assays, we found that guinea pig CD1b and CD1c molecules presented M. tuberculosis glycolipid Ags to T cells raised by mycobacterial lipid immunization. These results were confirmed using a T cell line derived from M. tuberculosis lipid Ag-immunized guinea pigs, which also showed CD1-restricted responses and cytolytic activity. Our results demonstrate that CD1-restricted responses against microbial glycolipid Ags can be generated in vivo by specific immunization and provide support for the use of the guinea pig as a relevant small animal model for the study of CD1-restricted immune responses to mycobacterial pathogens.     

Invariant NKT cells regulate experimental autoimmune encephalomyelitis and infiltrate the central nervous system in a CD1d-independent manner

Invariant NKT cells are CD1d-restricted T cells specific for glycolipid Ags. Their activation or transgenic enrichment abrogates the development of experimental autoimmune encephalomyelitis (EAE). Herein, we demonstrate that in NKT-enriched mice the protection from EAE is associated with the infiltration of NKT cells in the CNS and the local expression of CD1d. This indicates that the CNS acquires the potential for local glycolipid presentation when exposed to inflammatory stress, permitting the triggering of NKT cells. To address the importance of CD1d-mediated Ag presentation, we used transgenic mice that express CD1d solely in the thymus. Interestingly, enrichment of NKT cells in these mice also conferred resistance to EAE, with an efficacy indistinguishable from that of NKT-enriched CD1d-sufficient mice. This protection was due to an abrogation of the encephalitogenic Th1 and Th17 response in the spleen, revealing that endogenous glycolipid presentation is dispensable for the regulatory function of NKT cells in EAE. Moreover, abrogating extrathymic CD1d expression failed to affect both the recruitment of NKT cells and their effector phenotype. CNS-infiltrating NKT cells were characterized by a cytotoxic IFN-gamma(high)IL-4(low)IL-10(low)granzyme B(high) profile, irrespective of the local expression of CD1d. Glycolipid Ag presentation is therefore dispensable for the control of autoimmune demyelination by NKT cells, underlining the importance of alternative cognate and/or soluble factors in the control of NKT cell function.     

The A' and F' pockets of human CD1b are both required for optimal presentation of lipid antigens to T cells

CD1 proteins are unique in their ability to present lipid Ags to T cells. Human CD1b shares significant amino acid homology with mouse CD1d1, which contains an unusual putative Ag-binding groove formed by two large hydrophobic pockets, A' and F'. We investigated the function of the amino acid residues that line the A' and F' pockets of CD1b by engineering 36 alanine-substitution mutants and analyzing their ability to present mycobacterial glycolipid Ags. Two lipid Ags presented by CD1b were studied, a naturally occurring glucose monomycolate (GMM) isolated from mycobacteria, which contains two long alkyl chains (C54-C62 and C22-C24) and synthetic GMM (sGMM), which includes two short alkyl chains (C18 and C14). We identified eight residues in both the A' and F' pockets that were involved in the presentation of both GMM and sGMM to T cells. Interestingly, four additional residues located in the distal portion of the A' pocket were required for the optimal presentation of GMM, but not sGMM. Conversely, nine residues located between the center of the groove and the F' pocket were necessary for the optimal presentation of sGMM, but not GMM. These data indicate that both the A' and F' pockets of human CD1b are required for the presentation of lipid Ags to T cells.     

Deciphering the Role of CD1e Protein in Mycobacterial Phosphatidyl-myo-inositol Mannosides (PIM) Processing for Presentation by CD1b to T Lymphocytes

Lipids are important antigens that induce T cell-mediated specific immune responses. They are presented to T lymphocytes by a specific class of MHC-I like proteins, termed CD1. The majority of the described CD1-presented mycobacterial antigens are presented by the CD1b isoform. We previously demonstrated that the stimulation of CD1b-restricted T cells by the hexamannosylated phosphatidyl-myo-inositol (PIM(6)), a family of mycobacterial antigens, requires a prior partial digestion of the antigen oligomannoside moiety by α-mannosidase and that CD1e is an accessory protein absolutely required for the generation of the lipid immunogenic form. Here, we show that CD1e behaves as a lipid transfer protein influencing lipid immunoediting and membrane transfer of PIM lipids. CD1e selectively assists the α-mannosidase-dependent digestion of PIM(6) species according to their degree of acylation. Moreover, CD1e transfers only diacylated PIM from donor to acceptor liposomes and also from membranes to CD1b. This study provides new insight into the molecular mechanisms by which CD1e contributes to lipid immunoediting and CD1-restricted presentation to T cells.     

Distinct roles of dendritic cells and B cells in Va14Ja18 natural T cell activation in vivo

Va14Ja18 natural T (iNKT) cells are innate, immunoregulatory lymphocytes that recognize CD1d-restricted lipid Ags such as alpha-galactosylceramide (alpha GalCer). The immunoregulatory functions of iNKT cells are dependent upon either IFN-gamma or IL-4 production by these cells. We hypothesized that alpha GalCer presentation by different CD1d-positive cell types elicits distinct iNKT cell functions. In this study we report that dendritic cells (DC) play a critical role in alpha GalCer-mediated activation of iNKT cells and subsequent transactivation of NK cells. Remarkably, B lymphocytes suppress DC-mediated iNKT and NK cell activation. Nevertheless, alpha GalCer presentation by B cells elicits low IL-4 responses from iNKT cells. This finding is particularly interesting because we demonstrate that NOD DC are defective in eliciting iNKT cell function, but their B cells preferentially activate this T cell subset to secrete low levels of IL-4. Thus, the differential immune outcome based on the type of APC that displays glycolipid Ags in vivo has implications for the design of therapies that harness the immunoregulatory functions of iNKT cells.     

Lysosomal localization of murine CD1d mediated by AP-3 is necessary for NK T cell development

The presentation of lipid and glycolipid Ags to T cells is mediated through CD1 molecules. In the mouse and rat only a single isoform, CD1d, performs these functions, while humans and all other mammals studied have members of both group I (CD1a, -b, and -c) and group II (CD1d) isoforms. Murine CD1d contains a cytoplasmic tyrosine-based sorting motif that is similar to motifs recognized by adaptor protein complexes that sort transmembrane proteins. Here we show that the adaptor protein complex, AP-3, directly interacts with murine CD1d and controls its targeting to lysosomes. AP-3 deficiency results in a redistribution of CD1d from lysosomes to the cell surface of thymocytes, B cell-depleted splenocytes, and dendritic cells. The altered trafficking of CD1d in AP-3-deficient mice results in a significant reduction of NK1.1(+)TCR-beta(+) and CD1d tetramer-positive cells, consistent with a defect in CD1d self-Ag presentation and thymocyte-positive selection. The AP-3 complex has recently been shown to associate with the human CD1b isoform, which has an intracellular distribution pattern similar to that of murine CD1d. We propose that lysosomal sampling may be so critical for efficient host defense that mice have evolved mechanisms to target their single CD1 isoform to lysosomes for sampling lipid Ags. Here we show the dominant mechanism for this trafficking is mediated by AP-3.     

Human and Mouse Type I Natural Killer T Cell Antigen Receptors Exhibit Different Fine Specificities for CD1d-Antigen Complex

Human and mouse type I natural killer T (NKT) cells respond to a variety of CD1d-restricted glycolipid antigens (Ags), with their NKT cell antigen receptors (NKT TCRs) exhibiting reciprocal cross-species reactivity that is underpinned by a conserved NKT TCR-CD1d-Ag docking mode. Within this common docking footprint, the NKT TCR recognizes, to varying degrees of affinity, a range of Ags. Presently, it is unclear whether the human NKT TCRs will mirror the generalities underpinning the fine specificity of the mouse NKT TCR-CD1d-Ag interaction. Here, we assessed human NKT TCR recognition against altered glycolipid ligands of α-galactosylceramide (α-GalCer) and have determined the structures of a human NKT TCR in complex with CD1d-4′,4″-deoxy-α-GalCer and CD1d-α-GalCer with a shorter, di-unsaturated acyl chain (C20:2). Altered glycolipid ligands with acyl chain modifications did not affect the affinity of the human NKT TCR-CD1d-Ag interaction. Surprisingly, human NKT TCR recognition is more tolerant to modifications at the 4′-OH position in comparison with the 3′-OH position of α-GalCer, which contrasts the fine specificity of the mouse NKT TCR-CD1d-Ag recognition (4′-OH > 3′-OH). The fine specificity differences between human and mouse NKT TCRs was attributable to differing interactions between the respective complementarity-determining region 1α loops and the Ag. Accordingly, germline encoded fine-specificity differences underpin human and mouse type I NKT TCR interactions, which is an important consideration for therapeutic development and NKT cell physiology.     

Intersection of group I CD1 molecules and mycobacteria in different intracellular compartments of dendritic cells

Human CD1a, CD1b, and CD1c molecules can present mycobacterial glycolipids to T cells. Because phagosomes containing viable mycobacteria represent early endosomal compartments, we studied where mycobacterial glycolipids intersect with CD1 molecules in infected APC. CD1b and CD1c, but not CD1a, localized to late endosomes/lysosomes. CD1a and CD1c were predominantly expressed on the cell surface and in mycobacterial phagosomes of the early endosomal stage. In contrast, CD1b was present in a subset of mycobacterial phagosomes representing mature phagolysosomes. Released mycobacterial glycolipids including lipoarabinomannan and phosphatidylinositol mannosides were transported from the phagosome into late endosomes/lysosomes and to uninfected bystander cells. The macrophage mannose receptor, which has been implicated in glycolipid uptake by APC for CD1b-mediated presentation, was absent from mycobacterial phagosomes and may therefore not be involved in trafficking of glycolipids between phagosomes and late endosomes/lysosomes. In conclusion, all three CD1 molecules have access to mycobacteria and glycolipids thereof, but at different intracellular sites. This allows sampling by CD1a, CD1b, and CD1c of mycobacterial glycolipids from different intracellular sites of the infected cell, which has important implications for processing and presentation of such Ags during mycobacterial infections.     

Natural killer T cells restricted by the monomorphic MHC class 1b CD1d1 molecules behave like inflammatory cells.

Murine Valpha14(inv)T cells (NKT cells), restricted by the CD1d1 MHC 1b molecules, are a distinctive subset of T cells endowed with pleiotropic functions. CD1d1-restricted NKT cells infiltrate the granulomas induced by the s.c. injection of mycobacterial phosphatidylinositoldimannoside (PIM(2)) but not of its deacylated derivative. NKT cells are detectable as early as 6 hours following the injection. Although the molecular structure of PIM(2) meets the requirements for presentation by CD1d1, Ab blocking and adoptive transfer experiments of wild-type NKT cells into CD1d1(-/-) mice show that CD1d1 expression is not required for the early recruitment of NKT cells to the injection site. This conclusion was confirmed by the finding that IL-12Rbeta(-/-) and CD40(-/-) mice were able to recruit NKT cells after PIM(2) challenge. Moreover, the injection of alpha-galactosylceramide, an NKT cell ligand that is recognized in the context of CD1d1, promoted only a minor recruitment of NKT cells. By contrast, injection of beta-galactosylceramide, a synthetic glycolipid that binds to CD1d1 but does not activate the CD1d/TCR pathway, resulted in the development of large granulomas rich in NKT cells. Finally, local injection of TNF-alpha mimics the effect of glycolipids. It is concluded that NKT cells migrate to and accumulate at inflammatory sites in the same way as other cells of the innate immune system and that migration to and accumulation at inflammatory sites are processes independent of the CD1d1 molecule.     

Phosphatidylinositol mannoside from Mycobacterium tuberculosis binds alpha5beta1 integrin (VLA-5) on CD4+ T cells and induces adhesion to fibronectin

The pathological hallmark of the host response to Mycobacterium tuberculosis is the granuloma where T cells and macrophages interact with the extracellular matrix (ECM) to control the infection. Recruitment and retention of T cells within inflamed tissues depend on adhesion to the ECM. T cells use integrins to adhere to the ECM, and fibronectin (FN) is one of its major components. We have found that the major M. tuberculosis cell wall glycolipid, phosphatidylinositol mannoside (PIM), induces homotypic adhesion of human CD4+ T cells and T cell adhesion to immobilized FN. Treatment with EDTA and cytochalasin D prevented PIM-induced T cell adhesion. PIM-induced T cell adhesion to FN was blocked with mAbs against alpha5 integrin chain and with RGD-containing peptides. Alpha5beta1 (VLA-5) is one of two major FN receptors on T cells. PIM was found to bind directly to purified human VLA-5. Thus, PIM interacts directly with VLA-5 on CD4+ T lymphocytes, inducing activation of the integrin, and promoting adhesion to the ECM glycoprotein, FN. This is the first report of direct binding of a M. tuberculosis molecule to a receptor on human T cells resulting in a change in CD4+ T cell function.     

Vaccinia virus-specific CD4+ T cell responses target a set of antigens largely distinct from those targeted by CD8+ T cell responses

Recent studies have defined vaccinia virus (VACV)-specific CD8(+) T cell epitopes in mice and humans. However, little is known about the epitope specificities of CD4(+) T cell responses. In this study, we identified 14 I-A(b)-restricted VACV-specific CD4(+) T cell epitopes by screening a large set of 2146 different 15-mer peptides in C57BL/6 mice. These epitopes account for approximately 20% of the total anti-VACV CD4(+) T cell response and are derived from 13 different viral proteins. Surprisingly, none of the CD4(+) T cell epitopes identified was derived from VACV virulence factors. Although early Ags were recognized, late Ags predominated as CD4(+) T cell targets. These results are in contrast to what was previously found in CD8(+) T cells responses, where early Ags, including virulence factors, were prominently recognized. Taken together, these results highlight fundamental differences in immunodominance of CD4(+) and CD8(+) T cell responses to a complex pathogen.     

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.     

Cutting edge: major CD8 T cell response to live bacillus Calmette-Guérin is mediated by CD1 molecules

MHC class I-restricted CD8(+) T cells are a crucial component of the host defense against mycobacterial infection in mice, but it has often proved very difficult to identify the CD8 T cell response in humans. Human group 1 CD1 molecules (CD1a, -b, -c) mediate MHC-independent presentation of mycobacteria-derived lipid and glycolipid Ags to CD8(+) T cells, and their intracellular localization to the endocytic system may favor efficient monitoring of phagosome-resident mycobacteria. Here, we show that bacillus Calmette-Guérin (BCG)-immunized subjects contain a significant circulating pool of CD8(+) T cells that recognize BCG-infected DCs in a CD1-dependent, but MHC-independent, manner. These CD1-restricted T cells efficiently detected live, rather than dead, BCG and produced IFN-gamma, an important cytokine for protection against mycobacterial infection. These results emphasize that lipid-reactive CD8(+) T cells may contribute to host defense against mycobacterial infection.     

Glycosyl-phosphatidylinositol reanchoring unmasks distinct antigen-presenting pathways for CD1b and CD1c

Human CD1 proteins present lipid and glycolipid Ags to T cells. Cellular trafficking patterns of CD1 proteins may determine the ability of differing isoforms of CD1 to acquire, bind, and present these Ags to T cells. To test this hypothesis, glycosyl-phosphatidylinositol (GPI)-modified variants of CD1b and CD1c were engineered by chimerization with a GPI modification signal sequence derived from decay-accelerating factor (DAF). GPI reanchoring was confirmed by demonstrating the phosphatidylinositol-specific phospholipase C sensitivity of the CD1b. DAF and CD1c. DAF fusion proteins expressed on transfectant cell surfaces. Using cytotoxicity and cytokine release assays as functional readouts, we demonstrated that CD1c. DAF is as efficient as native CD1c in presenting mycobacterial Ags to the human CD1c-restricted T cell line CD8-1. In contrast, CD1b. DAF, although also capable of presenting Ag (in this case to the CD1b-restricted T cell line LDN5), was less efficient than its native CD1b counterpart. The data support the idea that CD1c. DAF maintains the capacity to access CD1c Ag-loading compartment(s), whereas CD1b. DAF is diverted by its GPI anchor away from the optimal CD1b Ag-loading compartment(s). This constitutes the first GPI reanchoring of CD1 proteins and provides evidence that CD1b and CD1c have nonoverlapping Ag-presenting pathways, suggesting that these two Ag-presenting molecules may have distinct roles in lipid Ag presentation.     

Distinct sequences in the cytoplasmic domain of complement receptor 2 are involved in antigen internalization and presentation

B cells express randomly rearranged surface Ig that forms part of a multiprotein complex known as the B cell receptor (BCR). Recognition of Ag via this receptor results in its capture, internalization, proteolysis and presentation to CD4+ T cells. The recognition of Ag by CD4+ T cells is critical for the selection of individual B cells, leading to the eventual secretion of a high affinity version of the BCR as an effective circulating Ab. B cells also express other receptors that recognize Ags associated with components of innate immunity. One of these receptors, CR2, binds Ags coated with activated complement components. Studies have shown that cross-linking CR2 and the BCR with complement-tagged Ags leads to enhanced Ag presentation by B cells. In addition, Ags targeted to B cell CR2 in the absence of BCR coligation are also efficiently presented to T cells. In this report, we identify several distinct sequences within the cytoplasmic domain of mouse CR2 (mCR2) that are essential for mCR2-mediated Ag presentation in both the presence and the absence of BCR cross-linking. The finding that distinct sequences in the cytoplasmic domain of mCR2 are essential for BCR-independent Ag presentation leads us to propose a novel role for CR2.     

CD1 molecules efficiently present antigen in immature dendritic cells and traffic independently of MHC class II during dendritic cell maturation

Upon exposure to Ag and inflammatory stimuli, dendritic cells (DCs) undergo a series of dynamic cellular events, referred to as DC maturation, that involve facilitated peptide Ag loading onto MHC class II molecules and their subsequent transport to the cell surface. Besides MHC molecules, human DCs prominently express molecules of the CD1 family (CD1a, -b, -c, and -d) and mediate CD1-dependent presentation of lipid and glycolipid Ags to T cells, but the impact of DC maturation upon CD1 trafficking and Ag presentation is unknown. Using monocyte-derived immature DCs and those stimulated with TNF-alpha for maturation, we observed that none of the CD1 isoforms underwent changes in intracellular trafficking that mimicked MHC class II molecules during DC maturation. In contrast to the striking increase in surface expression of MHC class II on mature DCs, the surface expression of CD1 molecules was either increased only slightly (for CD1b and CD1c) or decreased (for CD1a). In addition, unlike MHC class II, DC maturation-associated transport from lysosomes to the plasma membrane was not readily detected for CD1b despite the fact that both molecules were prominently expressed in the same MIIC lysosomal compartments before maturation. Consistent with this, DCs efficiently presented CD1b-restricted lipid Ags to specific T cells similarly in immature and mature DCs. Thus, DC maturation-independent pathways for lipid Ag presentation by CD1 may play a crucial role in host defense, even before DCs are able to induce maximum activation of peptide Ag-specific T cells.     

Interdependency of MHC class II/self-peptide and CD1d/self-glycolipid presentation by TNF-matured dendritic cells for protection from autoimmunity

Dendritic cells (DC) are key regulators of T cell immunity and tolerance. NKT cells are well-known enhancers of Th differentiation and regulatory T cell function. However, the nature of the DC directing T and NKT cell activation and polarization as well as the role of the respective CD1d Ags presented is still unclear. In this study, we show that peptide-specific CD4(+)IL-10(+) T cell-mediated full experimental autoimmune encephalomyelitis (EAE) protection by TNF-treated semimatured DCs was dependent on NKT cells recognizing an endogenous CD1d ligand. NKT cell activation by TNF-matured DCs induced high serum levels of IL-4 and IL-13 which are absent in NKT cell-deficient mice, whereas LPS plus anti-CD40-treated fully mature DCs induce serum IFN-gamma. In the absence of IL-4Ralpha chain signaling or NKT cells, no complete EAE protection was achieved by TNF-DCs, whereas transfer of NKT cells into Jalpha281(-/-) mice restored it. However, activation of NKT cells alone was not sufficient for EAE protection and early serum Th2 deviation. Simultaneous activation of NKT cells and CD4(+) T cells by the same DC was required for EAE protection. Blocking experiments demonstrated that NKT cells recognize an endogenous glycolipid presented on CD1d on the injected DC. Together, this indicates that concomitant and interdependent presentation of MHC II/self-peptide and CD1d/self-isoglobotrihexosylceramide to T and NKT cells by the same partially or fully matured DC determines protective and nonprotective immune responses in EAE.     

A bone marrow-derived APC in the gut-associated lymphoid tissue captures oral antigens and presents them to both CD4+ and CD8+ T cells

We have previously reported that feeding OVA to C57BL/6 mice can lead to a weak CTL response that is dependent on CD4+ T cell help and is capable of causing autoimmunity. In this study, we investigated the basis of the class I and class II-restricted Ag presentation required for such CTL induction. Two days after feeding OVA, Ag-specific CD4+ and CD8+ T cells were seen to proliferate in the Peyer's patches and mesenteric lymph nodes. Little proliferation was evident in other lymphoid tissues, except at high Ags doses, in which case some dividing CD4+ T cells were observed in the spleen and peripheral lymph nodes. Using chimeric mice, the APC responsible for presenting orally derived Ags was shown to be derived from the bone marrow. Examination of the Ag dose required to activate either CD4+ or CD8+ T cells indicated that a single dose of 6 mg OVA was the minimum dose that consistently stimulated either T cell subset. These data indicate that oral Ags can be transported from the gut into the gut-associated lymphoid tissue, where they are captured by a bone marrow-derived APC and presented to both CD4+ and CD8+ T cells.     

Genetic variation in PTPN22 corresponds to altered function of T and B lymphocytes

A variant of the PTPN22 gene, 1858C/T, is associated with an increased risk for the development of a wide array of autoimmune disorders. It is known that the protein tyrosine phosphatase Lyp encoded by this gene has an inhibitory effect on the proximal TCR signaling pathways. However, the consequences of carrying this variant and the mechanism by which it contributes to the development of autoimmunity are poorly understood. In this study, we demonstrate that homozygosity for this variant results in a profound deficit in T cell responsiveness to Ag stimulation. Heterozygosity for the variant allele is associated with reduced responsiveness of CD4+ memory T cells, characterized by diminished calcium mobilization, expression of CD25, and IL-10 production upon TCR stimulation. Additionally, the presence of the variant allele is associated with an increase in circulating memory T cells. We further demonstrate that these effects are not limited to the T cell compartment. Individuals with the variant allele have fewer memory B cells and these cells display a reduced response to stimulation via the BCR indicative of a B cell intrinsic defect. By identifying an immunologic phenotype in healthy subjects which correlates with the PTPN22 1858C/T genotype, we can now explore specific hypotheses regarding pathogenesis of diseases associated with the PTPN22 1858T variant.     

Mutation of a positively charged cytoplasmic motif within CD1d results in multiple defects in antigen presentation to NKT cells

CD1d is an MHC class I-like molecule that presents glycolipid Ags to types I and II NKT cells. The YxxI motif in the cytoplasmic tail of CD1d contributes to its intracellular localization to the endolysosomal compartment and is important for Ag presentation to type I NKT cells. In this study, we identified the (327-329)RRR motif in CD1d and showed that it is critical for the control of CD1d intracellular trafficking and Ag presentation. The replacement of the arginines in this motif with alanines resulted in the extensive accumulation of CD1d in lysosomes but did not affect the cell surface expression. The defect in its cellular localization was accompanied by defects in Ag presentation to both type I and type II NKT cells. These results demonstrated that the (327-329)RRR motif of CD1d is required for proper cellular distribution of CD1d and optimal Ag presentation to both type I and type II NKT cells.