Chromatofocusing purification of CD1b-antigen complexes and their analysis by isoelectric focusing.

The presentation of lipid antigens to T cells is mediated by the CD1 proteins. Purified functional CD1/lipid complexes are valuable tools to investigate such immune processes. Here, we describe how these complexes can be prepared in vitro, how they can be purified by chromatofocusing and how to control their antigen-loading status by isoelectric focusing.

Discovery of deoxyceramides and diacylglycerols as CD1b scaffold lipids among diverse groove-blocking lipids of the human CD1 system.

Unlike the dominant role of one class II invariant chain peptide (CLIP) in blocking MHC class II, comparative lipidomics analysis shows that human cluster of differentiation (CD) proteins CD1a, CD1b, CD1c, and CD1d bind lipids corresponding to hundreds of diverse accurate mass retention time values. Although most ions were observed in association with several CD1 proteins, ligands binding selectively to one CD1 isoform allowed the study of how differing antigen-binding grooves influence lipid capture. Although the CD1b groove is distinguished by its unusually large volume (2,200 Å(3)) and the T' tunnel, the average mass of compounds eluted from CD1b was similar to that of lipids from CD1 proteins with smaller grooves. Elution of small ligands from the large CD1b groove might be explained if two small lipids bind simultaneously in the groove. Crystal structures indicate that all CD1 proteins can capture one antigen with its hydrophilic head group exposed for T-cell recognition, but CD1b structures show scaffold lipids seated below the antigen. We found that ligands selectively associated with CD1b lacked the hydrophilic head group that is generally needed for antigen recognition but interferes with scaffold function. Furthermore, we identified the scaffolds as deoxyceramides and diacylglycerols and directly demonstrate a function in augmenting presentation of a small glycolipid antigen to T cells. Thus, unlike MHC class II, CD1 proteins capture highly diverse ligands in the secretory pathway. CD1b has a mechanism for presenting either two small or one large lipid, allowing presentation of antigens with an unusually broad range of chain lengths.

Generation and characterisation of CD1d tetramer produced by a lentiviral expression system.

The alpha-galactosylceramide (alphaGalCer)-loaded CD1d tetramer remains the most powerful tool in identifying natural killer T (NKT) cells, a subpopulation of T cells that express an unusual semi-invariant T cell antigen receptor, and mediate a variety of proinflammatory and immunoregulatory functions. The difficulty of generating large amounts of the alphaGalCer-CD1d tetramer has limited its availability and consequently hampered the study of NKT cells. In this report, we used a lentiviral system to generate stable cell lines producing beta2m-CD1d single chain protein in large quantities and in a relatively short period of time. When the protein was loaded with alphaGalCer and tetramerised with fluorescence-labelled streptavidin, its ability to efficiently bind to NKT cells was confirmed both by phenotype analysis and functional study. The CD1d tetramer generated from these stable cell lines should facilitate a wide range of studies on the biology and clinical applications of CD1d-restricted NKT cells.

Characterization and functional analysis of mouse invariant natural T (iNKT) cells.

Invariant natural T (iNKT) cells are innate lymphocytes that recognize CD1d-restricted lipid antigens and have immunoregulatory properties. Human and mouse CD1d-restricted glycolipid antigen(s) and the iNKT cell functions they elicit are highly conserved, whereby, making the mouse an excellent animal model for understanding iNKT cell biology in vivo. This unit describes basic methods for the characterization and quantification (see Basic Protocol 1) and functional analysis of murine iNKT cells in vivo or in vitro (see Basic Protocols 2, 3, and 4). This unit also contains protocols that describe enrichment of iNKT cells (see Support Protocol 1), generation of CD1d-tetramer (see Support Protocol 2), and lipid antigen loading on cell-bound (see Support Protocol 3) or soluble (see Support Protocol 3) CD1d.

Group 1 CD1 genes in rabbit.

CD1 is an Ag-presenting molecule that can present lipids and glycolipids to T cells. The CD1 genes were first identified in the human, and since then, homologs have been identified in every mammalian species examined to date. Over a decade ago, CD1B and CD1D homologs were identified in the rabbit. We have extended this earlier study by identifying additional CD1 genes with the goal of developing the rabbit as an animal model to study the function of CD1 proteins. We constructed a thymocyte cDNA library and screened the library with CD1-specific probes. Based on nucleotide sequence analyses of the CD1(+) cDNA clones obtained from the library, we have identified two CD1A genes and one CD1E gene as well as determined the complete sequence of the previously identified CD1B gene. The CD1E(+) cDNA clones lacked the transmembrane and cytoplasmic domains and, if translated, would encode for a soluble or secreted CD1E protein. In addition, expression studies demonstrated that the CD1 genes were expressed in peripheral lymphoid tissues as well as in skin, gut, and lung. Of interest is the finding that CD1A2, CD1B, and CD1E genes were found to be expressed by rabbit B cell populations. The rabbit, with a complex CD1 locus composed of at least two CD1A genes, one CD1B gene, one CD1D gene, and one CD1E gene, is an excellent candidate as an animal model to study CD1 proteins.

Expression of CD1d in the duodenum of patients with cow's milk hypersensitivity.

CD1 cell surface glycoproteins represent a family of non-major histocompatibility complex (MHC) encoded antigen-presenting molecules. All members of the CD1 family appear to mediate the recognition of microbial or endogenous lipid and glycolipid antigens. The recognition of CD1d by a unique subset of natural killer (NK) T cells that leads to rapid production of large amounts of both type 1 and type 2 cytokines can be augmented by some synthetic glycolipids. Because of the proposed role of such CD1d-restricted T cells in immunoregulation, we hypothesized that CD1d molecules participate in mucosal immune responses in patients with gastrointestinal symptoms owing to food hypersensitivity. Patients of that category represent a heterogeneous group in which poorly defined immunological mechanisms are believed to contribute to disease pathogenesis. The expression of CD1 in duodenal biopsy samples from six patients with verified intolerance to cow's milk and six healthy controls was studied by immunoperoxidase staining of cryostat sections using a panel of mouse monoclonal antibodies (MoAbs) specific for CD1a, b, c, and d. Large numbers of CD1d positive cells were found in the lamina propria of all the patients, both during the symptomatic and the asymptomatic periods, whereas healthy controls were virtually devoid of CD1d expression in the duodenum. The localization of CD1d positive cells corresponded to areas where B cells, plasma cells and dendritic cells (DC) were present. A positive correlation was found between the numbers of CD1d(+) and CD19(+) cells in the lamina propria. In contrast to previous reports, no CD1d expression was found on the epithelial cells. Although less numerous than CD1d(+) the CD1c(+) cells were also present in all the patients and in five out of six controls. No staining for CD1a or CD1b was detected in the duodenal biopsy samples from any of the subjects. The exclusive presence of CD1d in the duodenal lamina propria of the patients with cow's milk hypersensitivity might suggest the participation of these molecules in the pathogenesis of allergic reactions to food.

Conservation of a CD1 multigene family in the guinea pig.

CD1 is a family of cell-surface molecules capable of presenting microbial lipid Ags to specific T cells. Here we describe the CD1 gene family of the guinea pig (Cavia porcellus). Eight distinct cDNA clones corresponding to CD1 transcripts were isolated from a guinea pig thymocyte cDNA library and completely sequenced. The guinea pig CD1 proteins predicted by translation of the cDNAs included four that can be classified as homologues of human CD1b, three that were homologues of human CD1c, and a single CD1e homologue. These guinea pig CD1 protein sequences contain conserved amino acid residues and hydrophobic domains within the putative Ag binding pocket. A mAb specific for human CD1b cross-reacted with multiple guinea pig CD1 isoforms, thus allowing direct analysis of the structure and expression of at least a subset of guinea pig CD1 proteins. Cell-surface expression of CD1 was detected on cortical thymocytes, dermal dendritic cells in the skin, follicular dendritic cells of lymph nodes, and in the B cell regions within the lymph nodes and spleen. CD1 proteins were also detected on a subset of PBMCs consistent with expression on circulating B cells. This distribution of CD1 staining in guinea pig tissues was thus similar to that seen in other mammals. These data provide the foundation for the development of the guinea pig as an animal model to study the in vivo function of CD1.

Functional and phenotypic analysis of thymic CD34+CD1a- progenitor-derived dendritic cells: predominance of CD1a+ differentiation pathway.

Whether thymic dendritic cells (DC) are phenotypically and functionally distinct from the monocyte lineage DC is an important question. Human thymic progenitors differentiate into T, NK, and DC. The latter induce clonal deletion of autoreactive thymocytes and therefore might be different from their monocyte-derived counterparts. The cytokines needed for the differentiation of DC from thymic progenitors were also questioned, particularly the need for GM-CSF. We show that various cytokine combinations with or without GM-CSF generated DC from CD34+CD1a- but not from CD34+CD1a+ thymocytes. CD34+ thymic cells generated far fewer DC than their counterparts from the cord blood. The requirement for IL-7 was strict whereas GM-CSF was dispensable but nonetheless improved the yield of DC. CD14+ monocytic intermediates were not detected in these cultures unless macrophage-CSF (M-CSF) was added. Cultures in M-CSF generated CD14-CD1a+ DC precursors but also CD14+CD1a- cells. When sorted and recultured in GM-CSF, CD14+ cells down-regulated CD14 and up-regulated CD1a. TNF-alpha accelerated the differentiation of progenitors into DC and augmented MHC class II transport to the membrane, resulting in improved capacity to induce MLR. The trafficking of MHC class II molecules was studied by metabolic labeling and immunoprecipitation. MHC class II molecules were transported to the membrane in association with invariant chain isoforms in CD14+ (monocyte)-derived and in CD1a+ thymic-derived DC but not in monocytes. Thus, thymic progenitors can differentiate into DC along a preferential CD1a+ pathway but have conserved a CD14+ maturation capacity under M-CSF. Finally, CD1a+-derived thymic DC and monocyte-derived DC share very close Ag-processing machinery.

Immunolocalization of CD1d in human intestinal epithelial cells and identification of a beta2-microglobulin-associated form.

In order to better understand the role of intestinal CD1d, we sought to define the cellular localization and further characterize the biochemical structure of CD1d in human intestinal epithelial cells (IEC). Using a CD1d-specific rabbit anti-gst-CD1d antibody, immunoprecipitation of radiolabeled cell surface proteins detected a previously identified 37 kDa protein as well as a 48-50 kDa protein which were confirmed by Western blotting with a CD1d-specific mAb, D5. Immunoprecipitation of protein lysates with the CD1d-specific mAb, D5 and 51.1.3, and the beta2-microglobulin (beta2m)-specific mAb, BBM.1, followed by N-glycanase digestion and Western blotting with the D5 mAb showed that the 48-50 kDa protein was a beta2m-associated, CD1d glycoprotein. CD1d was immunolocalized to the apical and lateral regions of native small and large intestinal IEC as defined by confocal laser microscopy using the D5 mAb and the rabbit anti-gst-CD1d antibody. In addition, a large apical intracellular pool of CD1d was identified. Identical observations were made with polarized T84 cells. Selective biotin labeling of apical and basolateral cell surfaces followed by immunoprecipitation with the D5 mAb, N-glycanase digestion and avidin blotting confirmed the presence of glycosylated CD1d on both cell surfaces and immunolocalization of the 37 kDa non-glycosylated form of CD1d to the apical cell surface. These studies show that CD1d is located in an ideal position for luminal antigen sampling and presentation to subjacent intraepithelial lymphocytes.

Amino-terminal sequencing of sheep CD1 antigens and identification of a sheep CD1D gene.

The anti-CD1 monoclonal antibodies IAH-CC14 and SBU-T6 were used to immunopurify CD1 antigens from sheep thymocytes. The amino-terminal sequence of IAH-CC14 yielded 13 amino acids, and 29 amino acids were obtained from the SBU-T6 antigen. The sequence of the IAH-CC14 antigen was 100% identical to the predicted sequence of the sheep CD1B clone, SCD1B-42. The 29 amino acid sequence of the SBU-T6 antigen did not match identically with the derived amino acid sequence of any of the previously reported sheep CD1 genes but had closest similarity to the derived sequence of human CD1E. Degenerate polymerase chain reaction primers based on this sequence identified a group 2 sheep CD1 gene. The predicted amino acid sequence of this gene shows that it is not identical to the SBU-T6 peptide, indicating that a different, CD1D-like gene was cloned.

Tissue distribution, regulation and intracellular localization of murine CD1 molecules.

CD1 molecules are MHC-unlinked class Ib molecules consisting of classical (human CD 1a-c) and non-classical subsets (human CD1d and murine CD1). The characterization of non-classical subsets of CD1 is limited due to the lack of reagents. In this study, we have generated two new anti-mouse CD1 monoclonal antibodies, 3H3 and 5C6, by immunization of hamsters with purified CD1 protein. These antibodies recognize CD1-transfected cells and have no reactivity to cells isolated from CD1-/- mice. Both antibodies precipitate the 52 kDa heavy chain and 12 kDa beta2m from thymocytes and splenocytes by radio-immunoprecipitation. Deglycosylation of CD1 reduces molecular mass of the heavy chain by 7.5 kDa, which can be detected by 3H3 but not 5C6. 3H3 and 5C6 detect surface CD1 expression on cells from the thymus, spleen, lymph node and bone marrow, but not on intestinal epithelial cells. Developmentally, CD1 is expressed on thymocytes prior to TCR rearrangement and remains constant throughout thymic development. CD1 is expressed early in the fetal liver (day 14) and remains expressed in hepatocytes postnatally. These data support evidence of a role for CD1 in the selection and/or expansion of NK1- T cells of both thymic origin and extrathymic origin. Unlike classical class I molecules, murine CD1 levels are not affected by IFN-gamma, but like human CD1b can be up-regulated by IL-4 and GM-CSF although only moderately. Similar to human CD1b, murine CD1 is found by immunofluorescence microscopy on the cell surface, and in various intracellular vesicles, including early and late endosomes. Localization in endocytic compartments indicates that murine CD1 may be capable of binding endocytosed antigens.

Natural ligand of mouse CD1d1: cellular glycosylphosphatidylinositol.

Mouse CD1d1, a member of the CD1 family of evolutionarily conserved major histocompatibility antigen-like molecules, controls the differentiation and function of a T lymphocyte subset, NK1+ natural T cells, proposed to regulate immune responses. The CD1d1 crystal structure revealed a large hydrophobic binding site occupied by a ligand of unknown chemical nature. Mass spectrometry and metabolic radiolabeling were used to identify cellular glycosylphosphatidylinositol as a major natural ligand of CD1d1. CD1d1 bound glycosylphosphatidylinositol through its phosphatidylinositol aspect with high affinity. Glycosylphosphatidylinositol or another glycolipid could be a candidate natural ligand for CD1d1-restricted T cells.