Pneumococcal vaccination responses in adults with subnormal IgG subclass concentrations.

BACKGROUND: We sought to compare Pneumovax®23 responses in adults with subnormal IgG subclass concentrations. We studied adults with normal total IgG, frequent/severe respiratory infection, and subnormal IgG1, IgG3, or IgG1 + IgG3 before and after Pneumovax®23. We defined response as serotype-specific IgG > 1.3 µg/mL and aggregate response as IgG > 1.3 µg/mL for ≥70% of all serotypes tested. We compared patients with and without serotype-specific responses and performed logistic regression on aggregate responses using: age; male sex; body mass index; autoimmune condition(s); atopy; other allergies; subnormal IgGSc immunophenotypes; IgA; and IgM. RESULTS: There were 59 patients (mean age 44 ± 13 (SD) years; 83.1% women). Median days between pre- and post-Pneumovax®23 testing was 33 (range 19-158). The median post-vaccination summated concentration of serotype-specific IgG was higher in patients with subnormal IgG1 than subnormal IgG3 (responders and non-responders). All subnormal IgG1 + IgG3 non-responders responded to serotypes 8, 9 and 26, unlike other non-responders. Subnormal IgG3 responders had lower responses to serotypes 1, 4, 12, 23, 26, and 51. Subnormal IgG3 non-responders had higher responses to serotypes 1, 3, 8, 9, 12, 14, 19, 51, and 56. Response rates decreased with increasing age. Aggregate responders were: subnormal IgG1, 54%; IgG3, 46%; and IgG1 + IgG3, 46%. Regression on aggregate response revealed lower response with male sex (odds ratio 0.09 [95% CI 0.01, 0.77]) and atopy (0.17 [0.03, 0.83]). CONCLUSIONS: Serotype-specific IgG responses to Pneumovax®23 were greater in patients with subnormal IgG1 than subnormal IgG3. Male sex and atopy were associated with lower aggregate responses.

Mild Hypogammaglobulinemia Can Be a Serious Condition.

Background: Most patients with primary antibody deficiency (PAD) suffer from less well-described and understood forms of hypogammaglobulinemia (unclassified primary antibody deficiency, unPAD). Because of the moderately decreased immunoglobulin levels compared to CVID, unPAD is generally considered to be clinically mild and not very relevant. Objective: To describe our cohort of-mainly-unPAD patients, and to analyze whether subgroups can be identified. Methods: Data were prospectively collected (February-2012 to June-2016) as part of a standardized, 1-day Care Pathway for suspected primary immunodeficiency. The TNO-AZL Questionnaire for Health-Related Quality of Life (HRQoL) was part of the pre-first-visit intake procedure. Results: Three hundred and twenty patients were referred to the Care Pathway. Data from 23/27 children and 99/113 adults who were diagnosed with PAD and gave informed consent were available for analysis. 89/99 adults had unPAD, the majority (74%) were female and 44% already showed bronchiectasis. HRQoL was significantly decreased in all domains, meaning that a lot of unPAD patients had to cope simultaneously with pain, negative feelings and impairments in cognition, home management tasks, sleep, social interaction, and work. The most prominently impaired HRQoL domain was vitality, indicating these patients feel extremely tired and worn out. Conclusion: These results highlight the need for more attention to the potential patient burden of unPADs. A larger cohort is needed to increase our understanding of unPADs and to analyze whether distinct subgroups can be identified. For now, it is important for the clinician to acknowledge the existence of unPAD and be aware of its potential consequences, in order to timely and appropriately manage its effects and complications.

The Clinical Utility of Measuring IgG Subclass Immunoglobulins During Immunological Investigation for Suspected Primary Antibody Deficiencies.

Measurement of IgG subclass concentrations is a standard laboratory test run as part of a panel to investigate the suspicion of antibody deficiency. The assessment is clinically important when total IgG is within the normal age-specific reference range. The measurement is useful for diagnosis of IgG subclass deficiency, to aid the diagnosis of specific antibody deficiency, as a supporting test for the diagnosis of common variable immunodeficiency, as well as for risk stratification of patients with low IgA. The measurement of IgG subclasses may also help determine a revaccination strategy for patients and support patient management. In certain circumstances, the measurement of IgG subclasses may be used to monitor a patient's humoral immune system. In this review, we discuss the utility of measuring IgG subclass concentrations.

Serum IgG4 Concentration in IgG4-Related Disease.

BACKGROUND: IgG4-related disease (IgG4-RD) is an immune-mediated and chronic fibroinflammatory condition that affects almost any organ and often involves multiple organs in the same patient. In this review article, we address the clinical utility of measuring serum immunoglobulin G subclass 4 concentration ([IgG4]) in IgG4-RD diagnosis and in disease monitoring. METHODS: We discuss the latest literature on the relevance of [IgG4] to the investigation and management of IgG4RDs. In addition, we discuss the potential role of serum [IgG4] measurements in other inflammatory conditions and cancers. RESULTS: Increasing awareness of IgG4-RD among clinicians has led to a growing list of organ systems that can be affected by this chronic condition and the development of new organ-specific diagnostic guidelines. Diagnosis of IgG4-RD depends on multiple clinical and laboratory tests, including serology. Quantification of serum [IgG4] is included in all IgG4-RD diagnostic guidelines available to-date. The scientific literature supports the idea that elevated serum [IgG4], typically > 135 mg/dL, identifies patients with a more active form of the disease, which correlates with increased concentrations of inflammatory serum biomarkers and hypocomplementemia, increased number of organs affected by the disease, and more extensive organ involvement. These patients seem more resistant to treatment and experience a shorter time to disease relapse compared to IgG4-RD patients with normal serum [IgG4] at the time of diagnosis. CONCLUSIONS: Despite better understanding of how to diagnose IgG4-RD, monitoring for accurate prediction of disease relapse, which may involve organs not affected at the time of presentation, is poorly understood. Timely diagnosis and early detection of disease relapse is important to avoid delayed treatment and potential organ damage.

Infection rate and tissue localization of murine IL-12p40-producing monocyte-derived CD103(+) lung dendritic cells during pulmonary tuberculosis.

Non-hematopoietic cells, including lung epithelial cells, influence host immune responses. By co-culturing primary alveolar epithelial cells and monocytes from naïve donor mice, we show that alveolar epithelial cells support monocyte survival and differentiation in vitro, suggesting a role for non-hematopoietic cells in monocyte differentiation during the steady state in vivo. CD103(+) dendritic cells (αE-DC) are present at mucosal surfaces. Using a murine primary monocyte adoptive transfer model, we demonstrate that αE-DC in the lungs and pulmonary lymph nodes are monocyte-derived during pulmonary tuberculosis. The tissue localization may influence the functional potential of αE-DC that accumulate in Mycobacterium tuberculosis-infected lungs. Here, we confirm the localization of αE-DC in uninfected mice beneath the bronchial epithelial cell layer and near the vascular wall, and show that αE-DC have a similar distribution in the lungs during pulmonary tuberculosis and are detected in the bronchoalveolar lavage fluid from infected mice. Lung DC can be targeted by M. tuberculosis in vivo and play a role in bacterial dissemination to the draining lymph node. In contrast to other DC subsets, only a fraction of lung αE-DC are infected with the bacterium. We also show that virulent M. tuberculosis does not significantly alter cell surface expression levels of MHC class II on infected cells in vivo and that αE-DC contain the highest frequency of IL-12p40(+) cells among the myeloid cell subsets in infected lungs. Our results support a model in which inflammatory monocytes are recruited into the M. tuberculosis-infected lung tissue and, depending on which non-hematopoietic cells they interact with, differentiate along different paths to give rise to multiple monocyte-derived cells, including DC with a distinctive αE-DC phenotype.

Mycobacterium tuberculosis infection interferes with HIV vaccination in mice.

Tuberculosis (TB) has emerged as the most prominent bacterial disease found in human immunodeficiency virus (HIV)-positive individuals worldwide. Due to high prevalence of asymptomatic Mycobacterium tuberculosis (Mtb) infections, the future HIV vaccine in areas highly endemic for TB will often be administrated to individuals with an ongoing Mtb infection. The impact of concurrent Mtb infection on the immunogenicity of a HIV vaccine candidate, MultiHIV DNA/protein, was investigated in mice. We found that, depending on the vaccination route, mice infected with Mtb before the administration of the HIV vaccine showed impairment in both the magnitude and the quality of antibody and T cell responses to the vaccine components p24Gag and gp160Env. Mice infected with Mtb prior to intranasal HIV vaccination exhibited reduced p24Gag-specific serum IgG and IgA, and suppressed gp160Env-specific serum IgG as compared to respective titers in uninfected HIV-vaccinated controls. Importantly, in Mtb-infected mice that were HIV-vaccinated by the intramuscular route the virus neutralizing activity in serum was significantly decreased, relative to uninfected counterparts. In addition mice concurrently infected with Mtb had fewer p24Gag-specific IFN-γ-expressing T cells and multifunctional T cells in their spleens. These results suggest that Mtb infection might interfere with the outcome of prospective HIV vaccination in humans.

Antiphagocytic function of an IgG glycosyl hydrolase from Streptococcus equi subsp. equi and its use as a vaccine component.

EndoSe from Streptococcus equi subsp. equi is an enzyme hydrolyzing glycosyl groups on IgG, analogous to EndoS from Streptococcus pyogenes. We here show that the activity of EndoSe leads to an antiphagocytic function and may thus be a contributory factor to immune evasion of S. equi. Despite the damaging effect that EndoSe has on IgG, antibodies against EndoSe can neutralize its function. Antibodies against EndoSe restored the opsonic activity of specific opsonizing antibodies. Mice infected with either S. equi subsp. equi or subsp. zooepidemicus or S. pyogenes could be protected by vaccination with EndoSe. It is speculated that EndoSe could be a suitable vaccine candidate against streptococcal infections.

Tuberculosis and HIV co-infection.

Tuberculosis (TB) and HIV co-infections place an immense burden on health care systems and pose particular diagnostic and therapeutic challenges. Infection with HIV is the most powerful known risk factor predisposing for Mycobacterium tuberculosis infection and progression to active disease, which increases the risk of latent TB reactivation 20-fold. TB is also the most common cause of AIDS-related death. Thus, M. tuberculosis and HIV act in synergy, accelerating the decline of immunological functions and leading to subsequent death if untreated. The mechanisms behind the breakdown of the immune defense of the co-infected individual are not well known. The aim of this review is to highlight immunological events that may accelerate the development of one of the two diseases in the presence of the co-infecting organism. We also review possible animal models for studies of the interaction of the two pathogens, and describe gaps in knowledge and needs for future studies to develop preventive measures against the two diseases.

Failure to recruit anti-inflammatory CD103+ dendritic cells and a diminished CD4+ Foxp3+ regulatory T cell pool in mice that display excessive lung inflammation and increased susceptibility to Mycobacterium tuberculosis.

Susceptibility to Mycobacterium tuberculosis is characterized by excessive lung inflammation, tissue damage, and failure to control bacterial growth. To increase our understanding of mechanisms that may regulate the host immune response in the lungs, we characterized dendritic cells expressing CD103 (α(E) integrin) (αE-DCs) and CD4(+) Foxp3(+) regulatory T (T(reg)) cells during M. tuberculosis infection. In resistant C57BL/6 and BALB/c mice, the number of lung αE-DCs increased dramatically during M. tuberculosis infection. In contrast, highly susceptible DBA/2 mice failed to recruit αE-DCs even during chronic infection. Even though tumor necrosis factor alpha (TNF-α) is produced by multiple DCs and macrophage subsets and is required for control of bacterial growth, αE-DCs remained TNF-α negative. Instead, αE-DCs contained a high number of transforming growth factor beta-producing cells in infected mice. Further, we show that T(reg) cells in C57BL/6 and DBA/2 mice induce gamma interferon during pulmonary tuberculosis. In contrast to resistant mice, the T(reg) cell population was diminished in the lungs, but not in the draining pulmonary lymph nodes (PLN), of highly susceptible mice during chronic infection. T(reg) cells have been reported to inhibit M. tuberculosis-specific T cell immunity, leading to increased bacterial growth. Still, despite the reduced number of lung T(reg) cells in DBA/2 mice, the bacterial load in the lungs was increased compared to resistant animals. Our results show that αE-DCs and T(reg) cells that may regulate the host immune response are increased in M. tuberculosis-infected lungs of resistant mice but diminished in infected lungs of susceptible mice.

Silencing suppressor of cytokine signaling-1 (SOCS1) in macrophages improves Mycobacterium tuberculosis control in an interferon-gamma (IFN-gamma)-dependent manner.

Protection against infection with Mycobacterium tuberculosis demands IFN-γ. SOCS1 has been shown to inhibit responses to IFN-γ and might thereby play a central role in the outcome of infection. We found that M. tuberculosis is a highly efficient stimulator of SOCS1 expression in murine and human macrophages and in tissues from infected mice. Surprisingly, SOCS1 reduced responses to IL-12, resulting in an impaired IFN-γ secretion by macrophages that in turn accounted for a deteriorated intracellular mycobacterial control. Despite SOCS1 expression, mycobacteria-infected macrophages responded to exogenously added IFN-γ. SOCS1 attenuated the expression of the majority of genes modulated by M. tuberculosis infection of macrophages. Using a conditional knockdown strategy in mice, we found that SOCS1 expression by macrophages hampered M. tuberculosis clearance early after infection in vivo in an IFN-γ-dependent manner. On the other hand, at later time points, SOCS1 expression by non-macrophage cells protected the host from infection-induced detrimental inflammation.

Alpha-galactosylceramide as a therapeutic agent for pulmonary Mycobacterium tuberculosis infection.

RATIONALE: Invariant natural killer T (iNKT) cells are a unique subset of T cells that recognize lipid antigens presented by CD1d molecules. Recent studies have shown that iNKT cells can protect mice against Mycobacterium tuberculosis (Mtb) infection. We sought to determine whether pharmacological activation of iNKT cells by α-galactosylceramide (α-GalCer) could be used to treat tuberculosis (TB). OBJECTIVES: We hypothesized that α-GalCer, either alone or in combination with isoniazid, could be used to treat pulmonary TB. METHODS: The ability of α-GalCer-activated iNKT cells to suppress Mtb replication was evaluated using an in vitro coculture system. To test its potency in vivo, mice infected with virulent Mtb were treated with α-GalCer alone or in combination with isoniazid. MEASUREMENTS AND MAIN RESULTS: Quantitative colony-forming unit counts were compared for both experimental systems. Our results show that α-GalCer plus isoniazid controls bacterial growth better than α-GalCer or INH alone, and single or multiple α-GalCer administrations prolong the survival of the mice infected via the aerosol route. CONCLUSIONS: Our results demonstrate that α-GalCer administration can improve the outcome of Mtb infection, even when transmitted by the aerosol route. However, a combination of isoniazid and α-GalCer treatment has a synergistic effect on infection control. We conclude that more efficient treatment of TB will be achieved through a combination of classic chemotherapy and modulation of the host immune response.

Synovial fibroblasts self-direct multicellular lining architecture and synthetic function in three-dimensional organ culture.

OBJECTIVE: To define the intrinsic capacity of fibroblast-like synoviocytes (FLS) to establish a 3-dimensional (3-D) complex synovial lining architecture characterized by the multicellular organization of the compacted synovial lining and the elaboration of synovial fluid constituents. METHODS: FLS were cultured in spherical extracellular matrix (ECM) micromasses for 3 weeks. The FLS micromass architecture was assessed histologically and compared with that of dermal fibroblast controls. Lubricin synthesis was measured via immunodetection. Basement membrane matrix and reticular fiber stains were performed to examine ECM organization. Primary human and mouse monocytes were prepared and cocultured with FLS in micromass to investigate cocompaction in the lining architecture. Cytokine stimuli were applied to determine the capacity for inflammatory architecture rearrangement. RESULTS: FLS, but not dermal fibroblasts, spontaneously formed a compacted lining architecture over 3 weeks in the 3-D ECM micromass organ cultures. These lining cells produced lubricin. FLS rearranged their surrounding ECM into a complex architecture resembling the synovial lining and supported the survival and cocompaction of monocyte/macrophages in the neo-lining structure. Furthermore, when stimulated by cytokines, FLS lining structures displayed features of the hyperplastic rheumatoid arthritis synovial lining. CONCLUSION: This 3-D micromass organ culture method demonstrates that many of the phenotypic characteristics of the normal and the hyperplastic synovial lining in vivo are intrinsic functions of FLS. Moreover, FLS promote survival and cocompaction of primary monocytes in a manner remarkably similar to that of synovial lining macrophages. These findings provide new insight into inherent functions of the FLS lineage and establish a powerful in vitro method for further investigation of this lineage.

Tuberculosis triggers a tissue-dependent program of differentiation and acquisition of effector functions by circulating monocytes.

The origin and function of the different myeloid cell subsets that appear in the lung during pulmonary tuberculosis are unknown. Herein we show that adoptively transferred monocytes give rise to many of the macrophage and dendritic cell (DC) subsets that appear following aerosol infection with virulent Mycobacterium tuberculosis. Monocyte differentiation in infected peripheral tissue is surprisingly heterogeneous and results in the formation of five distinct myeloid subsets, including both classically activated macrophages, that produce inducible NO synthase via an IFN-gamma-dependent mechanism, and DC. In contrast, monocytes recruited to draining pulmonary lymph nodes are functionally different and acquire a mature DC phenotype. Thus, while monocytes are recruited to the lungs of uninfected mice, their differentiation and acquisition of myeloid effector functions are dramatically altered in the presence of inflammation and bacteria and are dependent on tissue localization. Therefore, our results support a model in which recruited monocytes are well poised to influence multiple aspects of host immunity to infections in the lungs. This report provides the first direct evidence for monocyte differentiation into both the macrophage and DC lineages in vivo following infection with a live human pathogen.

Interplay of cytokines and microbial signals in regulation of CD1d expression and NKT cell activation.

In this study we show that like MHC class I and class II molecules, cell surface CD1d expression on APC is regulated and affects T cell activation under physiological conditions. Although IFN-gamma alone is sufficient for optimum expression of MHC, CD1d requires two signals, one provided by IFN-gamma and a second mediated by microbial products or by the proinflammatory cytokine TNF. IFN-gamma-dependent CD1d up-regulation occurs on macrophages following infection with live bacteria or exposure to microbial products in vitro and in vivo. APC expressing higher CD1d levels more efficiently activate NKT cell hybridomas and primary NKT cells independently of whether the CD1d-restricted TCR recognizes foreign or self-lipid Ags. Our findings support a model in which CD1d induction regulates NKT cell activation.

In vivo depletion of CD11c+ cells delays the CD4+ T cell response to Mycobacterium tuberculosis and exacerbates the outcome of infection.

Although dendritic cells (DC) are potent APC that prime T cells against many pathogens, there is no direct evidence that DC are required for immunity to Mycobacterium tuberculosis (Mtb) infection. The requirement for DC to prime the CD4+ T cell response following Mtb infection was investigated using pCD11c-diptheria toxin receptor/GFP transgenic mice, in which DC can be transiently ablated in vivo. We show a critical role for DC in initiation of the CD4+ T cell response to the mycobacterial Ag early secretory Ag of tuberculosis 6. The delay in initiating the Ag-specific T cell response led to impaired control of Mtb replication. Interestingly, DC were not required for the secondary CD4+ T cell response following Mtb infection in peptide-vaccinated mice. Thus, this study shows that DC are essential for the initiation of the adaptive T cell response to the human pathogen Mtb.

The role of group 1 and group 2 CD1-restricted T cells in microbial immunity.

Group 1 and group 2 CD1 present both self and microbial lipid antigens to T cells. While group 1 CD1-restricted T cells are known for their ability to recognize mycobacterial glycolipid antigens, group 2 CD1-restricted T cells are recognized as regulatory T cells that can influence the outcome of innate and adaptive immune responses. The evidence that these T cells contribute to host defense against infectious diseases is reviewed.

Natural killer T-cell populations in C57BL/6 and NK1.1 congenic BALB.NK mice-a novel thymic subset defined in BALB.NK mice.

Natural killer (NK) T lymphocytes are a subpopulation of T lymphocytes regarded as early regulators of immune responses. The majority of NKT cells are restricted by the CD1d molecule. NKT cells have mostly been studied in one single mouse strain, C57BL/6 (B6), because of the absence of NK1.1 in other common mouse strains, and the lack of other reliable surface markers for CD1d-restricted cells. To investigate NKT cell subsets in a mouse strain of a genetic background different from B6, we have back-crossed the NKT cell marker NK1.1 from the B6 mouse to the BALB/c mouse strain. We show that NKT cells in the congenic BALB.B6-NK1.1(b) mouse share many characteristics with their B6 counterparts, but seem to be deficient in the functional NKT cell subtype characterized by low interleukin-4 and high interferon-gamma production, and surface expression of CD49b but not CD69. Moreover, in the thymus but not the spleen of BALB.B6-NK1.1(b) mice we find a novel Valpha14-Jalpha18 invariant NKT cell subset which is devoid of a set of NK markers, suggesting that these cells represent a less differentiated NKT cell stage, and carries high levels of the T-cell receptor and uses a skewed T-cell receptor Vbeta-repertoire.

Surface receptors identify mouse NK1.1+ T cell subsets distinguished by function and T cell receptor type.

Natural killer T (NKT) lymphocytes rapidly produce several cytokines, including IL-4 and IFN-gamma, upon activation, and act as regulatory cells at an early interphase of innate and adaptive immune responses. They have been implicated as important elements in diverse immune responses including the regulation of autoimmune disease, the immune response to infections, and the prevention of tumor metastasis. The broad spectrum of their activities suggested that functionally different subsets of NKT cells may exist. We demonstrate two functionally distinct splenic NKT populations identified by the expression of CD49b and CD69, respectively. Each NKT subset was represented by the amplified transgenic NKT cell population in a distinct transgenic mouse line expressing a CD1d-restricted TCR. CD49bhigh CD69- NKT cells, termed NKT1 cells by us, were high producers of IFN-gamma after stimulation, but essentially devoid of IL-4-synthesizing cells. Most NKT1 cells used diverse (non-Valpha14-canonical) TCR. The CD69+ CD49(-/low) NKT cell population, which we term NKT2, produced large quantities of IL-4 and substantial amounts of IFN-gamma upon activation and were dominated by cells using the canonical Valpha14-Jalpha18 T cell receptor. Knowledge of the unique roles of the different NKT cell subsets in specific situations will be essential for our understanding of NKT cell biology.

MHC-dependent and -independent modulation of endogenous Ly49 receptors on NK1.1+ T lymphocytes directed by T-cell receptor type.

Natural killer (NK) T lymphocytes are thought to act as regulatory cells directing early events during immune responses. Murine NKT cells express inhibitory receptors of the Ly49 family. These receptors have a well-established and crucial role in modulating NK cell activities, but their physiological role in regulating NKT cells is not well understood, nor is the influence of major histocompatibility (MHC) ligands on endogenous Ly49 expression. We have further investigated how the expression of inhibitory NK receptors is regulated on NKT cells, and demonstrate a non-random expression of ligated Ly49 molecules on CD1d-restricted NKT cells. The nature of the T-cell receptor on the NKT cell crucially determines the profile of expressed Ly49 isoforms. Further, we show that MHC class I ligands efficiently modulate the expression levels of the inhibitory receptors, and the frequencies of cells positive for the Ly49 members. In addition, we find a several-fold increase in Ly49C/I-expressing NKT cells in adult thymus, apparently independent of MHC class I molecules. Abundant expression of Ly49 receptors on NKT cells, and the striking differences found in Ly49 isoform patterns on NKT-cell subsets differing in T-cell receptor expression, suggest that the pattern of Ly49 expression is tuned to fit the T-cell receptor and to emphasize further a role for these receptors in NKT immunity.

Structural features of the acyl chain determine self-phospholipid antigen recognition by a CD1d-restricted invariant NKT (iNKT) cell.

Little is known about the antigen specificity of CD1d-restricted T cells, except that they frequently recognize CD1d-expressing antigen-presenting cells in the absence of exogenous antigen. We previously demonstrated that the 24.8.A iNKT cell hybridoma was broadly reactive with CD1d-transfected cell lines and recognized the polar lipid fraction of a tumor cell extract. In the present study, the antigen recognized by the 24.8.A iNKT cell hybridoma was purified to homogeneity and identified as palmitoyl-oleoyl-sn-glycero-3-phosphoethanolamine (16:0-18:1 PE). The 24.8.A iNKT cell hybridoma recognized synthetic 16:0-18:1[cis] PE, confirming that this phospholipid is antigenic. Recognition correlated with the degree of unsaturation of the acyl chains. Using a panel of synthetic PEs, the 24.8.A iNKT cell hybridoma was shown to be activated by PEs that contained at least one unsaturated acyl chain. The configuration of the double bonds was important, as the 24.8.A iNKT cell hybridoma recognized unsaturated acyl chains in the cis, but not the trans, configuration. PEs with multiple double bonds were recognized better than those with a single double bond, and increasing acyl chain unsaturation correlated with increased binding of PE to CD1d. These data illustrate the potential importance of the acyl chain structure for phospholipid antigen binding to CD1d.