How do natural killer T cells help B cells?

NKT Agonist-Antigen Conjugates as Cancer Vaccines

Natural killer T (NKT) cells are a population of innate-like T cells capable of enhancing both innate and adaptive immune responses. Co-delivering an NKT cell agonist and antigen can provide molecular signals to antigen-presenting cells, such as dendritic and B cells, that facilitate strong antigen-specific adaptive immune responses. Accordingly, there has been a significant number of developmental NKT cell-dependent vaccine therapies developed, particularly in the last decade, with many incorporating cancer antigens. In this review, we summarize studies that chemically conjugate the NKT cell agonist and antigen as an effective strategy for agonist-antigen co-delivery to drive antitumor responses.

Lysosomal processing of sulfatide analogs alters target NKT cell specificity and immune responses in cancer

In a structure-function study of sulfatides that typically stimulate type II NKT cells, we made an unexpected discovery. We compared analogs with sphingosine or phytosphingosine chains and 24-carbon acyl chains with 0-1-2 double bonds (C or pC24:0, 24:1, or 24:2). C24:1 and C24:2 sulfatide presented by the CD1d monomer on plastic stimulated type II, not type I, NKT cell hybridomas, as expected. Unexpectedly, when presented by bone marrow-derived DCs (BMDCs), C24:2 reversed specificity to stimulate type I, not type II, NKT cell hybridomas, mimicking the corresponding β-galactosylceramide (βGalCer) without sulfate. C24:2 induced IFN-γ-dependent immunoprotection against CT26 colon cancer lung metastases, skewed the cytokine profile, and activated conventional DC subset 1 cells (cDC1s). This was abrogated by blocking lysosomal processing with bafilomycin A1, or by sulfite blocking of arylsulfatase or deletion of this enyzme that cleaves off sulfate. Thus, C24:2 was unexpectedly processed in BMDCs from a type II to a type I NKT cell-stimulating ligand, promoting tumor immunity. We believe this is the first discovery showing that antigen processing of glycosylceramides alters the specificity for the target cell, reversing the glycolipid's function from stimulating type II NKT cells to stimulating type I NKT cells, thereby introducing protective functional activity in cancer. We also believe our study uncovers a new role for antigen processing that does not involve MHC loading but rather alteration of which type of cell is responding.

A Case Study to Dissect Immunity to SARS-CoV-2 in a Neonate Nonhuman Primate Model

Most children are less severely affected by coronavirus-induced disease 2019 (COVID-19) than adults, and thus more difficult to study progressively. Here, we provide a neonatal nonhuman primate (NHP) deep analysis of early immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in blood and mucosal tissues. In addition, we provide a comparison with SARS-CoV-2-infected adult NHP. Infection of the neonate resulted in a mild disease compared with adult NHPs that develop, in most cases, moderate lung lesions. In concomitance with the viral RNA load increase, we observed the development of an early innate response in the blood, as demonstrated by RNA sequencing, flow cytometry, and cytokine longitudinal data analyses. This response included the presence of an antiviral type-I IFN gene signature, a persistent and lasting NKT cell population, a balanced peripheral and mucosal IFN-γ/IL-10 cytokine response, and an increase in B cells that was accompanied with anti-SARS-CoV-2 antibody response. Viral kinetics and immune responses coincided with changes in the microbiota profile composition in the pharyngeal and rectal mucosae. In the mother, viral RNA loads were close to the quantification limit, despite the very close contact with SARS-CoV-2-exposed neonate. This pilot study demonstrates that neonatal NHPs are a relevant model for pediatric SARS-CoV-2 infection, permitting insights into the early steps of anti-SARS-CoV-2 immune responses in infants.

Effect of Immune Cell Infiltration on Occurrence of Pulmonary Hypertension in Pulmonary Fibrosis Patients Based on Gene Expression Profiles

Pulmonary hypertension (PH) is a frequent complication in patients with pulmonary fibrosis (PF), whereas the mechanism was not well-understood. This study aimed to explore the influence of immune cell infiltration on PH status based on the genomic expression profiles. Microarray data of GSE24988 were downloaded from the GEO database, including 116 lung tissue samples derived from PF patients with various PH status. Proportion of infiltrated immune cells was evaluated using CIBERSORT, a gene expression-based de-convolution algorithm. A random forest classifier was constructed and out of bag (OOB) cross-validation was carried out for PH prediction. The proportions of immune infiltration cells varied differently in PH samples except T regulatory cells (p-value = 0). Compared with non-PH samples, increased number of naive B cells and plasma cells were identified in PH samples, whereas activated dendritic cells and M2 macrophages were relatively lower (p < 0.05). In the random forest model, these four types of immune cells obtained a higher variable importance score than other cells, including mean decreased accuracy and mean decreased gini evaluation. We ran the OOB cross-validation in each sample of datasets (training set and testing set) and obtained 79 and 69% accuracy, respectively. Abnormal proportions of four types of immune cells were identified in PH samples compared with non-PH samples, suggesting their involvement in PH development. In summary, the immune cell infiltration in PF patients is associated with the PH status of patients, which deserves further investigation in the future.

Mendelian randomization integrating GWAS and eQTL data revealed genes pleiotropically associated with major depressive disorder

Previous genome-wide association studies (GWAS) have identified potential genetic variants associated with the risk of major depressive disorder (MDD), but the underlying biological interpretation remains largely unknown. We aimed to prioritize genes that were pleiotropically or potentially causally associated with MDD. We applied the summary data-based Mendelian randomization (SMR) method integrating GWAS and gene expression quantitative trait loci (eQTL) data in 13 brain regions to identify genes that were pleiotropically associated with MDD. In addition, we repeated the analysis by using the meta-analyzed version of the eQTL summary data in the brain (brain-eMeta). We identified multiple significant genes across different brain regions that may be involved in the pathogenesis of MDD. The prime-specific gene BTN3A2 (corresponding probe: ENSG00000186470.9) was the top hit showing pleiotropic association with MDD in 9 of the 13 brain regions and in brain-eMeta, after correction for multiple testing. Many of the identified genes are located in the human major histocompatibility complex (MHC) region on chromosome 6 and are mainly involved in the immune response. Our SMR analysis indicated that multiple genes showed pleiotropic association with MDD across the brain regions. These findings provided important leads to a better understanding of the mechanism of MDD and revealed potential therapeutic targets for the prevention and effective treatment of MDD.

Modulation of Immune Responses to Influenza A Virus Vaccines by Natural Killer T Cells

Influenza A viruses (IAVs) circulate widely among different mammalian and avian hosts and sometimes give rise to zoonotic infections. Vaccination is a mainstay of IAV prevention and control. However, the efficacy of IAV vaccines is often suboptimal because of insufficient cross-protection among different IAV genotypes and subtypes as well as the inability to keep up with the rapid molecular evolution of IAV strains. Much attention is focused on improving IAV vaccine efficiency using adjuvants, which are substances that can modulate and enhance immune responses to co-administered antigens. The current review is focused on a non-traditional approach of adjuvanting IAV vaccines by therapeutically targeting the immunomodulatory functions of a rare population of innate-like T lymphocytes called invariant natural killer T (iNKT) cells. These cells bridge the innate and adaptive immune systems and are capable of stimulating a wide array of immune cells that enhance vaccine-mediated immune responses. Here we discuss the factors that influence the adjuvant effects of iNKT cells for influenza vaccines as well as the obstacles that must be overcome before this novel adjuvant approach can be considered for human or veterinary use.

Histocompatibility Complex Status and Mendelian Randomization Analysis in Unsolved Antibody Deficiency

The pathogenesis in the majority of patients with common variable immunodeficiency (CVID), the most common symptomatic primary immunodeficiency, remains unknown. We aimed to compare the minor and major histocompatibility complex (MHC) markers as well as polygenic scores of common genetic variants between patients with monogenic CVID and without known genetic mutation detected. Monogenic patients were identified in a CVID cohort using whole exome sequencing. Computational full-resolution MHC typing and confirmatory PCR amplicon-based high-resolution typing were performed. Exome-wide polygenic scores were developed using significantly different variants and multi-variant Mendelian randomization (MR) analyses were used to test the causality of significant genetic variants on antibody levels and susceptibility to infectious diseases. Among 83 CVID patients (44.5% females), monogenic defects were found in 40 individuals. Evaluation of the remaining CVID patients without known genetic mutation detected showed 13 and 27 significantly associated MHC-class I and II alleles, respectively. The most significant partial haplotype linked with the unsolved CVID was W^*01:01:01-DMA^*01:01:01-DMB^*01:03:01:02-TAP1^*01:01:01 (P < 0.001), where carriers had a late onset of the disease, only infection clinical phenotype, a non-familial form of CVID, post-germinal center defects and a non-progressive form of their disease. Exclusion of monogenic diseases allowed MR analyses to identify significant genetic variants associated with bacterial infections and improved discrepancies observed in MR analyses of previous GWAS studies with low pleiotropy mainly for a lower respiratory infection, bacterial infection and Streptococcal infection. This is the first study on the full-resolution of minor and major MHC typing and polygenic scores on CVID patients and showed that exclusion of monogenic forms of the disease unraveled an independent role of MHC genes and common genetic variants in the pathogenesis of CVID.

Tissue-Specific Phenotype and Activation of iNKT Cells in Morbidly Obese Subjects: Interaction with Adipocytes and Effect of Bariatric Surgery

BACKGROUND

The immune response of visceral adipose tissue (VAT) in obesity, in particular the role of invariant natural killer T (iNKT) cells, has not yet been fully elucidated.

OBJECTIVE

To characterize iNKT cells and its activation status in VAT and peripheral blood mononuclear cells (PBMC) in morbidly obese subjects (MO), and to analyze their association with metabolic parameters.

SUBJECTS AND METHODS

Twenty non-obese and 20 MO subjects underwent Roux-en-Y gastric bypass (RYGB) and were studied before and 6 months after RYGB. VAT and PBMC were obtained.

RESULTS

A decrease in VAT iNKT cells from MO was found, however, not in PBMC. Visceral adipocytes from MO presented increased CD1d expression (p = 0.032). MO presented an increase in early activated CD69+ iNKT cells in PBMC before RYGB (p < 0.001), but not after RYGB nor in VAT, and an increase in later activated CD25+ iNKT in VAT (p = 0.046), without differences in PBMC. The co-expression of early and later markers (CD69+CD25+) in iNKT cells was increased in MO in VAT (p = 0.050) and PBMC (p = 0.006), decreasing after RYGB (p = 0.050). CD69+ iNKT and CD69+CD25+ iNKT cells in PBMC after RYGB correlated negatively with glucose, insulin, and insulin resistance levels.

CONCLUSIONS

There is a tissue-specific phenotype and activation of iNKT cells in VAT in morbid obesity, which could be involved in VAT immunometabolism dysregulation. Also, the increase in CD1d expression could be to offset the lack of VAT iNKT cells.

Phenotypic identification of CD19+CD5+CD1d+ regulatory B cells that produce interleukin 10 and transforming growth factor β1 in human peripheral blood

INTRODUCTION

Regulatory B cells (Bregs), a novel subpopulation of B cells, are a significant area of research due to their immune regulatory function in the immunological response. Bregs have been reported to regulate acute inflammation and immunity through the production of anti-inflammatory cytokines.

MATERIAL AND METHODS

A B cell subpopulation was identified using flow cytometric analysis in two different processes: 1) after preparation and storage of peripheral blood mononuclear cells (PBMCs) using Ficoll density gradient centrifugation from a human blood sample, 2) followed by isolation and storage of B cells through magnetic separation using a B cell isolation kit and MS column. ELISA assays were performed to observe the cytokine production of interkleukin 10 (IL-10) and transforming growth factor β₁ (TGF-β₁) by this novel B cell subpopulation.

RESULTS

Double positive staining of CD5+CD1d+ Bregs represents (19.27 ±1.52) from PBMCs, (33.32 ±2.95) from B cells accordingly (n = 40). Through ELISA assays, it has been found that B cell subpopulation produces IL-10 (0.56 ±0.08) and TGF-β₁ (0.90 ±0.12) (n = 40).

CONCLUSIONS

These methods should be able to facilitate progress in research on Bregs through the following steps: 1) the regulatory role may be observed in comparison with particular autoimmune diseases, inflammation, cancer, and immunologic responses to find out whether Breg alteration and/or cytokine production is altered as well in these disorders or conditions. 2) If the alteration of Bregs and cytokine production is significant along with the clinical correlation, a further in vitro study can be initiated with exposure of certain drugs to overcome the alteration of the cytokine production; then, an in vivo study can be initiated.

Differences of the immune cell landscape between normal and tumor tissue in human prostate

BACKGROUND

Over the past few decades, immunological checkpoint therapy has been an increasingly prominent strategy in the treatment of tumors, including prostate cancer (PC). There are few systematic studies of the phenotypic of tumor-infiltrating immune cells in PC tissues.

METHODS

CIBERSORT is an analytical tool for estimating the abundance of member cell types in mixed cell population by gene expression data. Herein, we analyzed different levels of tumor-infiltrating immunity cells in normal tissue compared with PC using CIBERSORT.

RESULTS

The results showed that proportion of M1 macrophages and resting mast cells presented significant differences in prostate tumor than these normal tissues. A higher proportion of resting mast cells was associated with a worse outcome and M1 macrophages was associated with a favorable outcome. Moreover, the radiotherapy and targeted molecular therapy can affect the immune infiltration of M1 macrophages and resting mast cells.

CONCLUSIONS

Resting mast cells and M1 macrophages has an important role in the prognosis of prostate cancer. Our data provides valuable information about the future treatment of PC.

Natural Killer and Natural Killer T Cells in Juvenile Systemic Lupus Erythematosus: Relation to Disease Activity and Progression

The contribution of innate immune cells, including natural killer (NK) and natural killer T (NKT) cells, in systemic lupus erythematosus (SLE) is still unclear. Herein, we examined the frequency of peripheral NK cells, CD56^dim and CD56^bright NK cells, and NKT cells in patients with juvenile SLE and their potential relations to SLE-related clinical and laboratory parameters. The study included 35 SLE children and 20 apparently healthy controls. After baseline clinical and lab work, SLE Disease Activity Index (SLEDAI-2K) and Pediatric Systemic Lupus International Collaborative Clinics/American College of Rheumatology (SLICC/ACR) Damage Index (Ped-SDI) scores were assessed. The frequency of peripheral NK cells, CD56^dim and CD56^bright NK cells, and NKT cells was examined using flow cytometry. SLE patients showed significantly lower frequency of NK cells and NKT cells and higher frequency of CD56^bright NK cells compared to controls. Disease activity, urea, and creatinine correlated negatively with NK, but positively with CD56^bright NK cells. NK and NKT cells exhibited inverse correlation with the renal biopsy activity index; however, CD56^bright NK cells showed direct correlations with both activity and chronicity indices. Regarding Ped-SDI, renal, neuropsychiatry disorders, and growth failure correlated inversely with NK but directly with CD56^bright NK cells. NKT cell inversely correlated with renal damage and delayed puberty. In conclusion, low frequency of NK and NKT and expansion of CD56^bright NK cells are marked in juvenile SLE, particularly with activity. These changes have direct effect on renal impairment and growth failure, reflecting their potential influence on disease progression.

Immune Ecosystem of Virus-Infected Host Tissues

Virus infected host cells serve as a central immune ecological niche during viral infection and replication and stimulate the host immune response via molecular signaling. The viral infection and multiplication process involves complex intracellular molecular interactions between viral components and the host factors. Various types of host cells are also involved to modulate immune factors in delicate and dynamic equilibrium to maintain a balanced immune ecosystem in an infected host tissue. Antiviral host arsenals are equipped to combat or eliminate viral invasion. However, viruses have evolved with strategies to counter against antiviral immunity or hijack cellular machinery to survive inside host tissue for their multiplication. However, host immune systems have also evolved to neutralize the infection; which, in turn, either clears the virus from the infected host or causes immune-mediated host tissue injury. A complex relationship between viral pathogenesis and host antiviral defense could define the immune ecosystem of virus-infected host tissues. Understanding of the molecular mechanism underlying this ecosystem would uncover strategies to modulate host immune function for antiviral therapeutics. This review presents past and present updates of immune-ecological components of virus infected host tissue and explains how viruses subvert the host immune surveillances.

Protection induced by virus-like particle vaccine containing tandem repeat gene of respiratory syncytial virus G protein

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract illness in infants, young children and the elderly. However, there is no licensed vaccine available against RSV infection. In this study, we generated virus-like particle (VLP) vaccine and investigated the vaccine efficacy in a mouse model. For VLP vaccines, tandem gene (1–780 bp) for V1 VLPs and tandem repeat gene (repeated 450–780 bp) for V5 VLPs were constructed in pFastBac^TM vectors, respectively. Influenza matrix protein 1 (M1) was used as a core protein in the VLPs. Notably, upon challenge infection, significantly lower virus loads were measured in the lung of mice immunized with V1 or V5 VLPs compared to those of naïve mice and formalin-inactivated RSV immunized control mice. In particular, V5 VLPs immunization showed significantly lower virus titers than V1 VLPs immunization. Furthermore, V5 VLPs immunization elicited increased memory B cells responses in the spleen. These results indicated that V5 VLP vaccine containing tandem repeat gene protein provided better protection than V1 VLPs with significantly decreased inflammation in the lungs. Thus, V5 VLPs could be a potential vaccine candidate against RSV.

The early activation of memory B cells from Wiskott-Aldrich syndrome patients is suppressed by CD19 downregulation

Wiskott-Aldrich syndrome (WAS) pediatric patients exhibit a deficiency in humoral immune memory. However, the mechanism by which Wiskott-Aldrich syndrome protein (WASP) regulates the differentiation and activation of memory B cells remains elusive. Here we examine the early activation events of memory B cells from the peripheral blood mononuclear cells of WAS patients and age-matched healthy controls (HCs) using total internal reflection fluorescence microscopy. In response to stimulation through the B-cell receptor (BCR), memory B cells from HCs showed significantly higher magnitudes of BCR clustering and cell spreading than naive B cells from the same individuals. This was associated with increases in CD19 recruitment to the BCR and the activation of its downstream signaling molecule Btk and decreases in FcγRIIB recruitment and the activation of its downstream molecule Src homology 2-containing inositol 5' phosphatase (SHIP). However, these enhanced signaling activities mediated by CD19 and Btk are blocked in memory B cells from WAS patients, whereas the activation of FcγRIIB and SHIP was increased. Although the expression levels of CD19, Btk, and FcγRIIB did not change between CD27(-) and CD27(+) B cells of HCs, the protein and mRNA levels of CD19 but not Btk and FcγRIIB were significantly reduced in both CD27(-) and CD27(+) B cells of WAS patients, compared with those of HCs. Overall, our study suggests that WASP is required for memory B-cell activation, promoting the activation by positive regulating CD19 transcription and CD19 recruitment to the BCR.

Immunoregulation of NKT Cells in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease with different variety of clinical manifestations. Natural killer T (NKT) cells are innate lymphocytes that play a regulatory role during broad range of immune responses. A number of studies demonstrated that the quantity and quality of invariant NKT (iNKT) cells showed marked defects in SLE patients in comparison to healthy controls. This finding suggests that iNKT cells may play a regulatory role in the occurrence and development of this disease. In this review, we mainly summarized the most recent findings about the behavior of NKT cells in SLE patients and mouse models, as well as how NKT cells affect the proportion of T helper cells and the production of autoreactive antibodies in the progress of SLE. This will help people better understand the role of NKT cells in the development of SLE and improve the therapy strategy.

Cd1d regulates B cell development but not B cell accumulation and IL10 production in mice with pathologic CD5(+) B cell expansion

Background

CD1d is a widely expressed lipid antigen presenting molecule required for CD1d-restricted invariant natural killer T (iNKT) cell development. Elevated CD1d expression is detected in CD5⁺ IL10-producing B cells, called B10 B cells, and is correlated with poorer prognosis in chronic lymphocytic leukemia (CLL), a CD5⁺ B cell malignancy with B10-like functional properties. Whether CD1d expression regulates CD5⁺ B cell accumulation, IL10 competence, and antibody production in naïve mice with pathologic CD5⁺ B cell expansion remains untested.

Results

Using three different transgenic mouse models of benign or leukemic CD5⁺ B cell expansion, we found that CD1d was differentially expressed on CD5⁺ B cells between the three models, but loss of CD1d expression had no effect on CD5⁺ B cell abundance or inducible IL10 expression in any of the models. Interestingly, in the CLL-prone Eμ-TCL1 model, loss of CD1d expression suppressed spontaneous IgG (but not IgM) production, whereas in the dnRAG1xEμ-TCL1 (DTG) model of accelerated CLL, loss of CD1d expression was associated with elevated numbers of splenic CD4⁺ and CD8⁺ T cells and an inverted CD4⁺:CD8⁺ T cell ratio. Unexpectedly, before leukemia onset, all three transgenic CD1d-deficient mouse strains had fewer splenic transitional B cells than their CD1d-proficient counterparts.

Conclusions

The results show that CD1d expression and iNKT cells are dispensable for the development, accumulation, or IL10 competence of CD5⁺ B cells in mice prone to benign or leukemic CLL-like B cell expansion, but reveal a novel role for iNKT cells in supporting B cell progression through the transitional stage of development in these animals. These results suggest CD1d-directed therapies to target CLL could be evaded by downregulating CD1d expression with little effect on continued leukemic CD5⁺ B cell survival. The data also imply that iNKT cells help restrain pro-leukemic CD8⁺ T cell expansion in CLL, potentially explaining a reported correlation in human CLL between disease progression, the loss of NKT cells, and a paradoxical increase in CD8⁺ T cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-015-0130-z) contains supplementary material, which is available to authorized users.

The importance of B cell CD1d expression for humoral immunity

It was reported over a decade previously that CD1d-restricted Natural Killer T (NKT) cells could interact with CD1d-expressing B cells and facilitate antibody secretion. Since then, several studies have observed that NKT cells can provide B-cell help for production of antibody against model and pathogen-derived glycolipids, carbohydrates and proteins. In regard to T cell-dependent protein antigens, it is still not entirely clear to what extent cognate interactions between CD1d-expressing B cells and NKT cells contribute to initial and long-lived B-cell responses that are characteristic of such antigens. In this editorial, we review evidence that NKT cells provide CD1d-dependent cognate and non-cognate forms of B-cell help following immunization with protein antigen. Elucidating these mechanisms will be important for harnessing NKT cells during vaccination.

BAFF- and APRIL-dependent maintenance of antibody titers after immunization with T-dependent antigen and CD1d-binding ligand

CD1d-restricted invariant NKT (iNKT) cells boost humoral immunity to T-dependent Ags that are coadministered with the CD1d-binding glycolipid Ag α-galactosylceramide (α-GC). Observations that mice lacking iNKT cells have decaying Ab responses following vaccination have led to the hypothesis that iNKT cells express plasma cell (PC) survival factors that sustain specific Ab titers. Bone marrow chimeric mice in which the entire hematopoietic compartment or iNKT cells selectively lacked BAFF, a proliferation-inducing ligand (APRIL), or both BAFF and APRIL were created and immunized with nitrophenol hapten-conjugated keyhole limpet hemocyanin adsorbed to Imject aluminum hydroxide-containing adjuvant or mixed with α-GC. In comparison with BAFF- or APRIL-sufficient bone marrow chimeras, absence of hematopoietic compartment- and iNKT-derived BAFF and APRIL was associated with rapidly decaying Ab titers and reduced PC numbers. The iNKT cell-derived BAFF or APRIL assumed a greater role in PC survival when α-GC was used as the adjuvant for immunization. These results show that iNKT cell-derived BAFF and APRIL each contribute to survival of PCs induced by immunization. This study sheds new light on the mechanisms through which iNKT cells impact humoral immunity and may inform design of vaccines that incorporate glycolipid adjuvants.

Fine tuning a well-oiled machine: Influence of NK1.1 and NKG2D on NKT cell development and function

Natural killer T cells (NKT) represent a group of CD1d-restricted T-lineage cells that provide a functional interface between innate and adaptive immune responses in infectious disease, cancer, allergy and autoimmunity. There have been remarkable advances in understanding the molecular events that underpin NKT development in the thymus and in the complex array of functions in the periphery. Most functional studies have focused on activation of T cell antigen receptors expressed by NKT cells and their responses to CD1d presentation of glycolipid and related antigens. Receiving less attention has been several molecules that are hallmarks of Natural Killer (NK) cells, but nonetheless expressed by NKT cells. These include several activating and inhibitory receptors that may fine-tune NKT development and survival, as well as activation via antigen receptors. Herein, we review the possible roles of the NK1.1 and NKG2D receptors in regulating development and function of NKT cells in health and disease. We suggest that pharmacological alteration of NKT activity should consider the potential complexities commensurate with NK1.1 and NKG2D expression.

Type II NKT cells facilitate Alum-sensing and humoral immunity

Alum-based adjuvants facilitate vaccine-driven humoral immunity, but their mechanism of action remains poorly understood. Herein, we report that lack of type II NKT cells is associated with intact, mature B cells but dampened humoral immunity following immunization with Alum-adsorbed T-dependent antigen. Type II NKT cells facilitated production of IL-4, IL-5, IL-10, IL-13, and antibody by LN and splenocyte cultures following Alum/antigen administration in vivo and antigen restimulation in vitro. Addition of IL-4 and IL-5 to type II NKT-deficient cultures restored in vitro antibody production. Intracellular staining revealed that Alum-primed type II NKT cells coordinated IL-4 secretion by T cells. Alum did not significantly affect CD1d expression in vivo, but addition of CD1d-blocking mAb diminished cytokine production and in vitro antibody production. Type II NKT cells therefore function as part of the Alum-sensing apparatus and in a CD1d-dependent manner, facilitate T(H)2-driven humoral immunity. This may have important consequences for understanding the mechanism of action of Alum-containing vaccines.

SAP expression in invariant NKT cells is required for cognate help to support B-cell responses

One of the manifestations of X-linked lymphoproliferative disease (XLP) is progressive agammaglobulinemia, caused by the absence of a functional signaling lymphocyte activation molecule (SLAM)-associated protein (SAP) in T, invariant natural killer T (NKT) cells and NK cells. Here we report that α-galactosylceramide (αGalCer) activated NKT cells positively regulate antibody responses to haptenated protein antigens at multiple checkpoints, including germinal center formation and affinity maturation. Whereas NKT cell-dependent B cell responses were absent in SAP(-/-).B6 mice that completely lack NKT cells, the small number of SAP-deficient NKT cells in SAP(-/-).BALB/c mice adjuvated antibody production, but not the germinal center reaction. To test the hypothesis that SAP-deficient NKT cells can facilitate humoral immunity, SAP was deleted after development in SAP(fl/fl).tgCreERT2.B6 mice. We find that NKT cell intrinsic expression of SAP is dispensable for noncognate helper functions, but is critical for providing cognate help to antigen-specific B cells. These results demonstrate that SLAM-family receptor-regulated cell-cell interactions are not limited to T-B cell conjugates. We conclude that in the absence of SAP, several routes of NKT cell-mediated antibody production are still accessible. The latter suggests that residual NKT cells in XLP patients might contribute to variations in dysgammaglobulinemia.

Differential contribution of dendritic cell CD1d to NKT cell-enhanced humoral immunity and CD8+ T cell activation

CD1d-restricted type I NKT cells provide help for specific antibody production. B cells, which have captured and presented a T-dependent, antigen-derived peptide on MHC class II and CD1d-binding glycolipid α-GC on CD1d, respectively, activate Th and NKT cells to elicit B cell help. However, the role of the DC CD1d in humoral immunity remains unknown. We therefore constructed mixed bone marrow chimeras containing CD1d-expressing, DTR-transgenic DCs and CD1d(+) or CD1d(-) nontransgenic DCs. Following DT-mediated DC ablation and immunization, we observed that the primary and secondary antibody responses were equivalent in the presence of CD1d(+) and CD1d(-) DCs. In contrast, a total ablation of DCs delayed the primary antibody response. Further experiments revealed that depletion of CD1d(+) DCs blocked in vivo expansion of antigen-specific cytotoxic (CD8(+)) T lymphocytes. These results provide a clear demonstration that although CD1d expression on DCs is essential for NKT-enhanced CD8(+) T cell expansion, it is dispensable for specific antibody production.

Developing understanding of the roles of CD1d-restricted T cell subsets in cancer: reversing tumor-induced defects

Invariant natural killer T-cells ('iNKT') are the best-known CD1d-restricted T-cells, with recently-defined roles in controlling adaptive immunity. CD1d-restricted T-cells can rapidly produce large amounts of Th1 and/or Th2//Treg/Th17-type cytokines, thereby regulating immunity. iNKT can stimulate potent anti-tumor immune responses via production of Th1 cytokines, direct cytotoxicity, and activation of effectors. However, Th2//Treg-type iNKT can inhibit anti-tumor activity. Furthermore, iNKT are decreased and/or reversibly functionally impaired in many advanced cancers. In some cases, CD1d-restricted T-cell cancer defects can be traced to CD1d(+) tumor interactions, since hematopoietic, prostate, and some other tumors can express CD1d. Ligand and IL-12 can reverse iNKT defects and therapeutic opportunities exist in correcting such defects alone and in combination. Early stage clinical trials have shown potential for reconstitution of iNKT IFN-gamma responses and evidence of activity in a subset of patients, with rational new approaches to capitalize on this progress ongoing, as will be discussed here.

Invariant NK T cells: potential for immunotherapeutic targeting with glycolipid antigens

Invariant NK T (iNKT) cells are a subset of T lymphocytes that recognize glycolipid antigens bound with the antigen-presenting molecule CD1d. iNKT cells have potent immunoregulatory activities that can promote or suppress immune responses during different pathological conditions. These immunoregulatory properties can be harnessed for therapeutic purposes with cognate glycolipid antigens, such as the marine sponge-derived glycosphingolipid α-galactosylceramide. Preclinical studies have shown substantial promise for iNKT cell-based treatments of infections, cancer and autoimmune and inflammatory diseases. Translation of these preclinical studies to the clinic, while faced with some obstacles, has already had some initial success. In this article, we review the immunodulatory activities of iNKT cells and the potential for developing iNKT cell-based prophylactic and curative therapies of human disease.

Specific humoral immunity versus polyclonal B cell activation in Trypanosoma cruzi infection of susceptible and resistant mice

Background

The etiologic agent of Chagas Disease is Trypanosoma cruzi. Acute infection results in patent parasitemia and polyclonal lymphocyte activation. Polyclonal B cell activation associated with hypergammaglobulinemia and delayed specific humoral immunity has been reported during T. cruzi infection in experimental mouse models. Based on preliminary data from our laboratory we hypothesized that variances in susceptibility to T. cruzi infections in murine strains is related to differences in the ability to mount parasite-specific humoral responses rather than polyclonal B cell activation during acute infection.

Methodology/Principal Findings

Relatively susceptible Balb/c and resistant C57Bl/6 mice were inoculated with doses of parasite that led to similar timing and magnitude of initial parasitemia. Longitudinal analysis of parasite-specific and total circulating antibody levels during acute infection demonstrated that C57Bl/6 mice developed parasite-specific antibody responses by 2 weeks post-infection with little evidence of polyclonal B cell activation. The humoral response in C57Bl/6 mice was associated with differential activation of B cells and expansion of splenic CD21^highCD23^low Marginal Zone (MZ) like B cells that coincided with parasite-specific antibody secreting cell (ASC) development in the spleen. In contrast, susceptible Balb/c mice demonstrated early activation of B cells and early expansion of MZ B cells that preceded high levels of ASC without apparent parasite-specific ASC formation. Cytokine analysis demonstrated that the specific humoral response in the resistant C57Bl/6 mice was associated with early T-cell helper type 1 (Th1) cytokine response, whereas polyclonal B cell activation in the susceptible Balb/c mice was associated with sustained Th2 responses and delayed Th1 cytokine production. The effect of Th cell bias was further demonstrated by differential total and parasite-specific antibody isotype responses in susceptible versus resistant mice. T cell activation and expansion were associated with parasite-specific humoral responses in the resistant C57Bl/6 mice.

Conclusions/Significance

The results of this study indicate that resistant C57Bl/6 mice had improved parasite-specific humoral responses that were associated with decreased polyclonal B cell activation. In general, Th2 cytokine responses are associated with improved antibody response. But in the context of parasite infection, this study shows that Th2 cytokine responses were associated with amplified polyclonal B cell activation and diminished specific humoral immunity. These results demonstrate that polyclonal B cell activation during acute experimental Chagas disease is not a generalized response and suggest that the nature of humoral immunity during T. cruzi infection contributes to host susceptibility.

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, affects 10–12 million people in Latin America. Patent parasitemia develops during acute disease. During this phase, polyclonal B cell activation has been reported to generate high levels of serum antibody with low parasite specificity, and delayed protective humoral immunity, which is necessary to prevent the host from succumbing to infection. In this manuscript, data show that relatively resistant mice have improved parasite-specific humoral immunity and decreased polyclonal B cell activation compared to susceptible mice. Parasite-specific humoral immunity was associated with differential expansion of B cell subsets and T cells in the spleen, as well as with increased Th1 and decreased Th2 cytokine production. These data suggest that host susceptibility/genetic biases impact the development of humoral responses to infection. Th2 cytokines are generally associated with improved antibody responses. In the context of T. cruzi infection of susceptible mice, Th2 cytokines were associated with increased total antibody production concomitant with delayed pathogen-specific humoral immunity. This study highlights the need to consider the effect of host biases when investigating humoral immunity to any pathogen that has reported polyclonal B cell activation during infection.