Regulation of innate and acquired immunity in African trypanosomiasis

African trypanosomes are well known for their ability to avoid immune elimination by switching the immunodominant variant surface glycoprotein (VSG) coat during infection. However, antigenic variation is only one of several means by which trypanosomes manipulate the immune system of their hosts. In this article, the role of parasite factors such as GPI anchor residues of the shed VSG molecule and the release of CpG DNA, in addition to host factors such as IFN-gamma, in regulating key aspects of innate and acquired immunity during infection is examined. The biological relevance of these immunoregulatory events is discussed in the context of host and parasite survival.     

Increased CXCL-13 levels in human African trypanosomiasis meningo-encephalitis

Objectives  To determine the role of the B-cell attracting chemokine CXCL-13, which may initiate B-cell trafficking and IgM production in diagnosing HAT meningo-encephalitis.
Methods  We determined CXCL-13 levels by ELISA on paired sera and CSF of 26 patients from Angola and of 16 controls (six endemic and ten non-endemic). Results were compared to standard stage determination markers and IgM intrathecal synthesis.
Results  CXCL-13 levels in patients' sera had a median value of 386.6 pg/ml and increased levels were associated with presence of trypanosomes in the CSF but not with other stage markers. CXCL-13 levels in patients' CSF had a median value of 80.9 pg/ml and increased levels were associated with all standard stage determination markers and IgM intrathecal synthesis.
Conclusion  CXCL-13 levels in CSF increased significantly during the course of HAT. Hence the value of CXCL-13 for diagnosis, follow-up or as a marker of disease severity should be tested in a well-defined cohort study.     

Eflornithine is a cost-effective alternative to melarsoprol for the treatment of second-stage human West African trypanosomiasis in Caxito, Angola

Objective To compare the cost‐effectiveness of eflornithine and melarsoprol in the treatment of human African trypanosomiasis. Method We used data from a Médecins Sans Frontières treatment project in Caxito, Angola to do a formal cost‐effectiveness analysis, comparing the efficiency of an eflornithine‐based approach with melarsoprol. Endpoints calculated were: cost per death avoided; incremental cost per additional life saved; cost per years of life lost (YLL) averted; incremental cost per YLL averted. Sensitivity analysis was done for all parameters for which uncertainty existed over the plausible range. We did an analysis with and without cost of trypanocidal drugs included. Results Effectiveness was 95.6% for melarsoprol and 98.7% for eflornithine. Cost/patient was 504.6 for melarsoprol and 552.3 for eflornithine, cost per life saved was 527.5 USD for melarsoprol and 559.8 USD for eflornithine without cost of trypanocidal drugs but it increases to 600.4 USD and 844.6 USD per patient saved and 627.6 USD and 856.1 USD per life saved when cost of trypanocidal drugs are included. Incremental cost‐effectiveness ratio is 1596 USD per additional life saved and 58 USD per additional life year saved in the baseline scenario without cost of trypanocidal drugs but it increases to 8169 USD per additional life saved and 299 USD per additional life year saved if costs of trypanocidal drugs are included. Conclusion Eflornithine saves more lives than melarsoprol, but melarsoprol is slightly more cost‐effective. Switching from melarsoprol to eflornithine can be considered as a cost‐effective option according to the WHO choice criteria.     

Comparison of operational criteria for treatment outcome in gambiense human African trypanosomiasis

Objective  To develop a simple and standard operational decision tool for the diagnosis of relapse after treatment for human African trypanosomiasis (HAT), by evaluating the performance of several criteria currently used by HAT control programs and research projects.
Methods  We identified 10 different criteria for relapse, based on trypanosome presence and/or white blood cell count in cerebrospinal fluid, and compared their specificity, sensitivity and time to diagnosis on a data set containing 63 relapsed and 247 cured T.b. gambiense patients.
Results  At any time point, the criterion 'Trypanosomes present and/or a cerebrospinal white blood cell count ≥50/μl' allowed accurate and timely detection of HAT relapse, irrespective of disease stage. This criterion was 13–25% more sensitive ( P  ≤   0.013) than trypanosome detection alone and was >97% specific. Lumbar punctures at the end of treatment and at 3-month post-treatment provided limited clinical information.
Conclusions  Adequate detection of relapse was possible with a simple criterion but these findings should be validated in a prospective study before adoption in clinical practice.     

GABRG1 and GABRA2 variation associated with alcohol dependence in African Americans

Background: GABRG1 and GABRA2, genes that encode the γ1 and α2 subunits, respectively, of the GABA‐A receptor, are located in a cluster on chromosome 4p. Association of alcohol dependence (AD) with markers located at the 3′ region of GABRA2 has been replicated in several studies, but recent studies suggested the possibility that the signal may be attributable to the adjacent gene, GABRG1, located 90 kb distant in the 3′ direction. Owing to strong linkage disequilibrium (LD) in European Americans (EAs), the origin, or origins, of the association signal is very difficult to discern, but our previous population‐based study suggested that decreased LD across the GABRG1–GABRA2 region in African Americans (AAs) may be useful for fine mapping and resolution of the association signal in that population. Methods: To examine these associations in greater detail, we genotyped 13 single nucleotide polymorphisms (SNPs) spanning GABRG1 and GABRA2 in 380 AAs with AD and in 253 AA controls. Results: Although there was no association between any individual SNP and AD, a highly significant difference was shown between AD subjects and controls in the frequency of a 3‐SNP GABRA2 haplotype (global p = 0.00029). A similar level of significance was obtained in 6‐SNP haplotypes that combined tagging SNPs from both genes (global p = 0.00994). High statistical significance was also shown with a 6‐SNP haplotype (T‐G‐C‐G‐T‐A), p = 0.0033. The T‐G‐C‐G‐T‐A haplotype contains the most significant GABRA2 3‐SNP haplotype (p = 0.00019), G‐T‐A. Conclusions: These findings reflect the interrelationship between these 2 genes and the likelihood that risk loci exist in each of them. Study of an AA population allowed evaluation of these associations at higher genomic resolution than is possible in a EA population, owing to the much lower LD across these loci in AAs.     

Sleeping hearts: the role of the heart in sleeping sickness (human African trypanosomiasis)

Objectives To estimate the frequency and evolution of heart involvement in human African trypanosomiasis (HAT) using electrocardiogram (ECG) findings; to describe these findings and to assess the frequency and clinical relevance of symptoms and signs before and after treatment. Methods In a prospective cohort study ECG findings, signs and symptoms consistent with heart failure and cardiac laboratory parameters were studied at baseline, 2 days after the end of treatment and 3 months later. Results Major ECG alterations were significantly more frequent in HAT patients than in healthy controls (71%vs. 18%; P < 0.001); 31% were low voltage changes, 34% were repolarization changes. ECG signs of necrosis and conduction problems were rare. Symptoms consistent with heart failure such as exertional dyspnoea (19%vs. 1.7%; P = 0.002) or palpitations (18%vs. 5%; P = 0.28) occurred more frequently in patients than in controls. The median NT‐proBNP was significantly higher in HAT patients than in controls (85.2 vs. 28 pg/ml; P < 0.001). Troponin levels were normal. At the end of treatment repolarization changes appeared or worsened in 33.4%. Such changes improved or disappeared at follow‐up in 33.1% of the patients. Conclusions Cardiac involvement documented by ECG alterations is common in HAT patients, but cardiopathy rarely causes severe congestive heart failure and subsides after treatment. ECG alterations immediately after treatment and their improvement 3 months later may be the result of a treatment‐induced inflammatory reaction.     

Diversity of feeding behavior of Glossina palpalis palpalis in the forest belt of the Ivory Coast: relation to the prevalence of human African trypanosomiasis

Résumé Une analyse rétrospective des préférences trophiques de Glossina palpalis palpalis, vecteur majeur de la Trypanosomiase humaine africaine (THA) a été faite à partir des données recueillies entre 1984 et 1994 dans cinq foyers du secteur forestier, dans le centre‐ouest de la Côte d'Ivoire. Les auteurs ont comparé le régime alimentaire de ce vecteur dans ces différents foyers. L'objectif est de vérifier s'il existe une relation entre les préférences trophiques du vecteur et la prévalence de la THA. La diversité du régime alimentaire a étéévaluée par deux indices: l'indice de diversité de Shannon et Weaver (Ish) et un nouvel indice défini par le rapport pourcentage de repas de sang animal/pourcentage de repas de sang humain ou indice de zoophilie/ anthropophilie (Za). Il n'y a pas de correlation entre la DAP et le taux de prévalence. Des indices (Ish et Za) élevés, signe d'une diversité alimentaire, ont été observés dans les foyers de Vavoua, Zoukougbeu et Sinfra où les taux de prévalence de la THA étaient importants. Inversement des indices faibles ont été notés dans les zones de faible prévalence comme Daniafla et Gagnoa où la quasi totalité des repas de sang du vecteur était pris sur l'hôte humain. Il existe une corrélation forte mais non significative entre les deux indices entomologiques et la prévalence de la maladie. La corrélation est plus forte avec l'indice Za qu'avec l'indice Ish. La signification épidémiologique de ces observations est discutée. Summary The feeding habits of Glossina palpalis palpalis, the main vector of human African trypanosomiasis (HAT) were retrospectively analysed using data collected between 1984 and 1994 in five areas in the forest belt in the mid‐west of Côte d'Ivoire. The authors compare the feeding habits of the vector in these different foci. This analysis is aimed at determining if there is any relationship between the feeding pattern of tsetse‐flies and the prevalence rates of HAT. The feeding pattern was measured using two indices: the conventional index of Shannon and Weaver (Ish) and a new one, the zoophily/anthropophily index (Za). The latter is an estimate of the ratio of the percentage of animal blood meals divided by the percentage of human blood meals. There was no correlation between apparent density and prevalence rate. A high Ish and a high Za were observed in the foci of Vavoua, Zoukougbeu and Sinfra where prevalence rates of HAT were high. Conversely, a low Ish and a low Za were observed in the hypoendemic areas of Daniafla and Gagnoa. Both indices are highly but not significantly correlated with prevalence rates. The Za index seemed to be more strongly correlated to the disease rate as compared to the Ish index. The epidemiological significance of these observations is discussed.     

Delineation of a CD1d-restricted antigen presentation pathway associated with human and mouse intestinal epithelial cells

BACKGROUND & AIMS: CD1d, a major histocompatibility complex (MHC) class I-related molecule that is responsible for the presentation of glycolipid antigens to subsets of natural killer T (NK-T) cells, is expressed by intestinal epithelial cells (IECs). However, CD1d-restricted antigen presentation has not yet been examined on IECs. METHODS: A mouse intestinal epithelial cell line (MODE-K), a human epithelial cell line (T84), T84 cells transfected with CD1d and/or MHC class II, and freshly isolated human IECs were examined for their ability to present model glycolipid antigens to NK-T cells as defined by interleukin (IL)-2 or IL-4 secretion. RESULTS: MODE-K and freshly isolated human IECs exhibited dose-dependent, CD1d-restricted presentation of the functional glycolipid antigen, alpha-galactosylceramide (alpha GalCer), to the mouse NK-T cell hybridoma, DN32.D3. The human IEC line, T84, mainly presented alpha GalCer when transfected with human CD1d. Presentation of alpha GalCer by CD1d-transfected T84 cells (T84d) to DN32.D3 cells was greater along the basal surface in comparison with the apical surface. Induction of the MHC class II antigen presentation machinery by cotransfecting T84d with the MHC class I transactivator (CIITA) did not alter this polarity of presentation. Neither MODE-K nor T84 cells transfected with CD1d, CD1d plus CIITA, or CD1d plus HLA-DR were able to present glycolipid antigens requiring intracellular processing. The MODE-K cell line could also present alpha GalCer to primary mouse NK-T cells. CONCLUSIONS: CD1d is expressed functionally on IECs with a polarity of presentation (basal > apical) predicting a role in presentation of mucosal glycolipid antigens to local CD1d-restricted T cells.     

Proliferatory defect of invariant population and accumulation of non-invariant CD1d-restricted natural killer T cells in the joints of RA patients

Abstract

Objectives. While numerical and functional defects of invariant NKT cells have been demonstrated in rheumatoid arthritis (RA), the detailed characterization of proliferative and secretory responses following CD1d-mediated presentation is lacking; the presence of non-invariant populations has never been assessed in human autoimmunity. We have evaluated both invariant and non-invariant populations in the blood and synovial fluid from patients to assess feasibility of NKT cell-directed manipulations in RA.

Methods. NKT cell populations were quantified by anti-CD4/anti-Vα24 staining and/or CD1d tetramers. Proliferation was measured in cultures of mononuclear cells following stimulations with αGalCer and cytokine secretion determined by multi-bead assay.

Results. We have confirmed a proliferative defect of iNKT cells in both peripheral blood and synovial fluid from RA patients, but no changes in baseline frequencies. Moreover, we have detected an enlargement of non-invariant cell pool in synovial fluid samples. In addition, we noted an evident Th2 shift following exposure to αGalCer and pronounced IL-6 secretion.

Conclusions. While RA patients suffer from defective proliferative responses of invariant NKT cells, non-invariant cells accumulate at the site of inflammation. While stimulation with αGalCer results in reduced TNF-α and increased suppressive IL-10, abundantly produced IL-6 could potentially contribute to the induction of Th17 cells in the joints.     

Matrix metalloproteinase-9 and intercellular adhesion molecule 1 are powerful staging markers for human African trypanosomiasis

Objectives A critical step before treatment of human African trypanosomiasis (HAT) is the correct staging of the disease. As late stage is established when trypanosomes cross the blood–brain barrier and invade the central nervous system, we hypothesized that matrix metalloproteinases and cell adhesion molecules could indicate, alone or in combination, the disease progression from the first to the second stage of HAT. Methods We measured the levels of MMP‐2, MMP‐9, ICAM‐1, VCAM‐1 and E‐selectin in the cerebrospinal fluid (CSF) of 63 Trypanosoma brucei gambiense‐infected patients (15 stage 1 and 48 stage 2). Staging was based on counting of white blood cells (WBC) and/or parasite detection in CSF. Concentrations were obtained either by ELISA or multiplex bead suspension assays, and results were compared with three known HAT staging markers (CXCL10, CXCL8 and H‐FABP). Results ICAM‐1 and MMP‐9 accurately discriminated between stage 1 and stage 2 patients with HAT with 95% sensitivity (SE) for 100% specificity (SP), which was better than CXCL10 (93% SE for 100% SP), one of the most promising known markers. Combination of ICAM‐1 and MMP‐9 with H‐FABP provided a panel that resulted in 100% of SE and SP for staging HAT. Conclusions ICAM‐1 and MMP‐9, alone or in combination, appeared as powerful CSF staging markers of HAT. Final validation of all newly discovered staging markers on a large multi‐centric cohort including both forms of the disease as well as patients with others infections should be performed.     

CD1d-unrestricted NKT cells are endowed with a hybrid function far superior than that of iNKT cells

Invariant natural killer T (iNKT) cells to date represent the best example of cells known to have a hybrid function, representing both innate and adaptive immunity. Shared phenotypic similarities with NK cells together with a rapid response to a cytokine stimulus and a productive TCR engagement are the features that underline the hybrid nature of iNKT cells. Using these criteria, we provide molecular and functional evidence demonstrating that CD1d-independent (CD1d^ind) NKT cells, a population of CD1d-unrestricted NKT cells, are endowed with a hybrid function far superior to that of iNKT cells: (i) an extensive shared program with NK cells, (ii) a closer Euclidian distance with NK cells, and (iii) the ability to respond to innate stimuli (Poly:IC) with cytotoxic potential in the same manner as NK cells identify a hybrid feature in CD1d^indNKT cells that truly fulfills the dual function of an NK and a T cell. Our finding that CD1d^indNKT cells are programmed to act like NK cells in response to innate signals while being capable of adaptive responses is unprecedented, and thus might reemphasize CD1d-unrestricted NKT cells as a subset of lymphocytes that could affect biological processes of antimicrobial and tumor immunity in a unique way.Natural killer T (NKT) cells are increasingly regarded as cells endowed with a hybrid function between an NK cell and a T cell (1, 2). The current classification of NKT cells places them into three categories: type I, type II, and NKT-like cells (1). Type I comprises invariant NKT (iNKT) cells that recognize the glycolipid α-galactosylceramide (α-GalCer) loaded into the MHC class I molecule, CD1d, and contain an invariant TCR repertoire of Vα14-Jα18 (3–5). Type II NKT cells are also CD1d dependent but do not respond to α-GalCer in the same way as iNKT cells do (6, 7). NKT-like cells encompass all other NKT cells and are CD1d independent (CD1d^ind) (8); they are by far the most heterogeneous and the least characterized.Recent studies have increasingly shown a shared expression of NK cell-related receptors on other effector cells. CD8⁺ T cells are known to up-regulate NK markers, such as NK1.1, and can even respond quickly like NK cells (9). Other work has described NKT cells that express NKp46 (10), a marker selectively associated with conventional NK cells and NK22 cells in the gut (11). Moreover, γδ T cells have been shown to express NK markers and display an innate-like response (12). Collectively, these reports converge to raise the following key questions. What qualifies as an NKT cell? Do the cells need to express only NK1.1 and CD3 to be eligible for NKT nomenclature? With the continuous development of both NK and T-cell fields, the simplistic definition that NKT cells are subsets of T cells that express the NK1.1 marker is becoming increasingly misleading and even inaccurate. For instance, NK1.1 complex is expressed in the BALB/c strain but there are allelic divergences with the polymorphism leading to the PK136 antibody not reacting to the BALB/c NK.1.1 (NKrp1) complex (13). This definition is also limited in the C57BL/6 strain because of the discovery of NK1.1⁻CD1d⁺ NKT cells (14). Although phenotypic similarities can be misleading, the criteria that best describes an NKT cell is the ability to perform with a hybrid function between an NK cell and a T cell (2).Nonetheless, the concept of hybrid function is also an elusive notion allowing for a gradient of functions. A number of works refer to an NKT hybrid function as the ability of a T cell with phenotypic similarities to NK cells to perform with innate-like response. The best example of cells endowed with a hybrid NKT cell function are thought to be iNKT cells (2). In this study, we provide molecular and functional evidence demonstrating that CD1d^indNKT cells—a population of MHC-unrestricted T cells—are endowed with a hybrid function that associates them to the NK cell lineage in a manner far superior to the known link between NK and iNKT cells. An extensive shared program with NK cells, a similarity in the gene expression profile with NK cells, and their ability to respond (like NK cells) not only to cytokine signals (IL-12 plus IL-18) but also to innate stimuli [in vivo treatment with Poly:IC (Fisher)] with massive production of key effector players of the cytotoxic pathway collectively identify a hybrid feature in CD1d^indNKT cells that uniquely fulfills the function of an NK cell and a T cell.     

Hiding Lipid Presentation: Viral Interference with CD1d-Restricted Invariant Natural Killer T (iNKT) Cell Activation

The immune system plays a major role in protecting the host against viral infection. Rapid initial protection is conveyed by innate immune cells, while adaptive immunity (including T lymphocytes) requires several days to develop, yet provides high specificity and long-lasting memory. Invariant natural killer T (iNKT) cells are an unusual subset of T lymphocytes, expressing a semi-invariant T cell receptor together with markers of the innate NK cell lineage. Activated iNKT cells can exert direct cytolysis and can rapidly release a variety of immune-polarizing cytokines, thereby regulating the ensuing adaptive immune response. iNKT cells recognize lipids in the context of the antigen-presenting molecule CD1d. Intriguingly, CD1d-restricted iNKT cells appear to play a critical role in anti-viral defense: increased susceptibility to disseminated viral infections is observed both in patients with iNKT cell deficiency as well as in CD1d- and iNKT cell-deficient mice. Moreover, viruses have recently been found to use sophisticated strategies to withstand iNKT cell-mediated elimination. This review focuses on CD1d-restricted lipid presentation and the strategies viruses deploy to subvert this pathway.     

Quaternary Interaction of the HIV-1 Envelope Trimer with CD4 and Neutralizing Antibodies

The entry of HIV-1 into host cells is initiated by the interaction of the viral envelope (Env) spike with the CD4 receptor. During this process, the spike undergoes a series of conformational changes that eventually lead to the exposure of the fusion peptide located at the N-terminus of the transmembrane glycoprotein, gp41. Recent structural and functional studies have provided important insights into the interaction of Env with CD4 at various stages. However, a fine elucidation of the earliest events of CD4 contact and its immediate effect on the Env conformation remains a challenge for investigation. Here, we summarize the discovery of the quaternary nature of the CD4-binding site in the HIV-1 Env and the role of quaternary contact in the functional interaction with the CD4 receptor. We propose two models for this initial contact based on the current knowledge and discuss how a better understanding of the quaternary interaction may lead to improved immunogens and antibodies targeting the CD4-binding site.     

Studies of P-glycoprotein in chronic myelogenous leukaemia patients: expression,activity and correlations with CD34 antigen

Over-expression of the P-glycoprotein (Pgp), transmembrane drug efflux pump, has been shown to cause multidrug resistance of tumour cells (MDR). To investigate the clinical significance of Pgp expression for chronic myeloid leukaemia (CML) diagnosis and monitoring we have studied 38 CML patients in various phases of the disease (chronic phase, CP; accelerated phase, AP; blast crisis, BC). Anti-Pgp monoclonal antibody UIC2 and FACScan analysis were used. Pgp functional activity was investigated by evaluation of verapamil influence upon rhodamine 123 efflux from the cells. Correlations between Pgp and CD34 expression were investigated. In CP, Pgp-expressing cells were found in 2/14 patients; in one of them Pgp proved to be non-functional. There were few Pgp-expressing cells in AP cases. The group of BC patients consisted of cases resistant to chemotherapy. This gave us the opportunity to consider whether drug resistance of BC CML patients is preferentially connected with Pgp-mediated MDR. 11/22 BC patients had 20% or more of Pgp-expressing blasts in the peripheral blood. In all four Pgp⁺ BC cases studied for Pgp activity this protein was functional. Only 4/22 BC patients demonstrated large (40% or more) fractions of Pgp⁺ blasts. Moreover, sequential studies of 11 BC CML patients during treatment revealed an increase in the number of Pgp-expressing cells in only two cases. This suggests that Pgp⁺ cells did not often accumulate in BC CML patients due to chemotherapy and are the cause of drug resistance in only a few cases. A positive correlation between Pgp and CD34 expression was found (r = 0.69; P = 0.0004). 3/22 BC CML patients had large fractions of both Pgp⁺ and CD34⁺ blasts in their peripheral blood. The BC CML patients with this immunophenotype of blast cells may represent a subtype of BC CML resistant to treatment due to Pgp over-expression.     

Evidence for a link between sphingolipid metabolism and expression of CD1d and MHC-class II: monocytes from Gaucher disease patients as a model

Gaucher disease (GD) is an autosomal recessive inherited defect of the lysosomal enzyme glucocerebrosidase (GluCerase) that leads to glucosylceramide (GluCer) accumulation. We previously demonstrated the existence of imbalances in certain lymphocyte populations in GD patients. We now show that GluCerase-deficient monocytes from GD patients or monocytes from healthy subjects treated with conduritol-B-epoxide (CBE), an irreversible inhibitor of GluCerase activity, display high levels of surface expression of the lipid-binding molecule CD1d. GluCerase-deficient monocytes from GD patients also showed increased surface expression of major histocompatibility complex (MHC)-class II, but not of other lysosomal trafficking molecules, such as CD63 and MHC-class I. However, CD1d and MHC-class II mRNA levels were not increased. GluCerase-deficient monocytes from GD patients undergoing enzyme replacement therapy also exhibited increased levels of CD1d and MHC-class II and imbalances in the percentage of CD4+, CD8+, and Valpha24+ T cells. Interestingly, follow-up studies revealed that enzyme replacement therapy induced a decrease in MHC-class II expression and partial correction of the CD4+ T cell imbalances. These results reveal a new link between sphingolipid accumulation in monocytes and the expression of certain MHC molecules that may result in imbalances of regulatory T cell subsets. These immunological anomalies may contribute to the clinical heterogeneity in GD patients.     

Structural reorganization of the antigen-binding groove of human CD1b for presentation of mycobacterial sulfoglycolipids

The mechanisms permitting nonpolymorphic CD1 molecules to present lipid antigens that differ considerably in polar head and aliphatic tails remain elusive. It is also unclear why hydrophobic motifs in the aliphatic tails of some antigens, which presumably embed inside CD1 pockets, contribute to determinants for T-cell recognition. The 1.9-Å crystal structure of an active complex of CD1b and a mycobacterial diacylsulfoglycolipid presented here provides some clues. Upon antigen binding, endogenous spacers of CD1b, which consist of a mixture of diradylglycerols, moved considerably within the lipid-binding groove. Spacer displacement was accompanied by F’ pocket closure and an extensive rearrangement of residues exposed to T-cell receptors. Such structural reorganization resulted in reduction of the A’ pocket capacity and led to incomplete embedding of the methyl-ramified portion of the phthioceranoyl chain of the antigen, explaining why such hydrophobic motifs are critical for T-cell receptor recognition. Mutagenesis experiments supported the functional importance of the observed structural alterations for T-cell stimulation. Overall, our data delineate a complex molecular mechanism combining spacer repositioning and ligand-induced conformational changes that, together with pocket intricacy, endows CD1b with the required molecular plasticity to present a broad range of structurally diverse antigens.