Natural Killer T Cell Function Research Articles

Tim-4 alleviates acute hepatic injury by modulating homeostasis and function of NKT cells.

T-cell immunoglobulin and mucin domain-containing molecule 4 (Tim-4) is an immune checkpoint molecule, which involves in numerous inflammatory diseases. Tim-4 is mainly expressed on antigen presenting cells. However, increasing evidences have shown that Tim-4 is also expressed on natural killer T (NKT) cells. The role of Tim-4 in maintaining NKT cell homeostasis and function remains unknown. In this study, we explored the effect of Tim-4 on NKT cells in acute liver injury. This study found that Tim-4 expression on hepatic NKT cells was elevated during acute liver injury. Tim-4 deficiency enhanced IFN-γ, TNF-α expression while impaired IL-4 production in NKT cells. Loss of Tim-4 drove NKT cell effector lineages to be skewed to NKT1 subset. Furthermore, Tim-4 KO mice were more susceptible to α-GalCer challenge. In conclusion, our findings indicate that Tim-4 plays an important role in regulating homeostasis and function of NKT cells in acute liver injury. Therefore, Tim-4 might become a new regulator of NKT cells and a potential target for the therapy of acute hepatitis.

CCR2+TREM-1+ monocytes promote natural killer T cell dysfunction contributing towards HBV disease progression.

Natural killer T (NKT) cells are amongst the most important innate immune cells against hepatitis B virus (HBV) infection. Moreover, previous studies have shown that HBV infection induced TREM-1+ expression in monocyte and secretion of inflammatory cytokines. Thus, this prompted us to elucidate the role of TREM-1+ monocytes in regulating the function of iNKT cells. Ninety patients and 20 healthy participants were enrolled in the study. The percentage and phenotype of iNKT cells and TREM-1+ monocytes were measured in the peripheral blood of healthy controls (HC), patients with chronic HBV infection (CHB), HBV-related liver cirrhosis (LC), and HBV-related acute-on-chronic liver failure (ACLF) via flow cytometry. Moreover, co-culture experiments with iNKT cells and TREM-1 overexpressing THP-1 cells were performed to determine the role of TREM-1 in the regulation of NKT cell function. We observed that the percentage of iNKT cells and CD4-iNKT cells gradually decreased, whereas the percentage of CCR2+TREM-1+ monocytes increased with the progression of the disease. In addition, activation of the TREM-1 signaling pathway induced the secretion of inflammatory cytokines leading to pyroptosis of iNKT cells and secretion of IL-17 contributing towards disease progression. Therefore, this study suggests that blocking the activation of TREM-1 in monocytes could promote the elimination of HBV by inhibiting pyroptosis of iNKT cells and restoring their function. However, further studies are required to validate these results that would help in developing new treatment strategies for patients with HBV infections.

Intrinsic factors and CD1d1 but not CD1d2 expression levels control invariant natural killer T cell subset differentiation

Invariant natural killer T (NKT) cell subsets are defined based on their cytokine-production profiles and transcription factors. Their distribution is different in C57BL/6 (B6) and BALB/c mice, with a bias for NKT1 and NKT2/NKT17 subsets, respectively. Here, we show that the non-classical class I-like major histocompatibility complex CD1 molecules CD1d2, expressed in BALB/c and not in B6 mice, could not account for this difference. We find however that NKT cell subset distribution is intrinsic to bone marrow derived NKT cells, regardless of syngeneic CD1d-ligand recognition, and that multiple intrinsic factors are likely involved. Finally, we find that CD1d expression levels in combination with T cell antigen receptor signal strength could also influence NKT cell distribution and function. Overall, this study indicates that CD1d-mediated TCR signals and other intrinsic signals integrate to influence strain-specific NKT cell differentiation programs and subset distributions.

TGF-β Regulation of TCells.

Transforming growth factor β (TGF-β) is a key cytokine regulating the development, activation, proliferation, differentiation, and death of Tcells. In CD4+ Tcells, TGF-β maintains the quiescence and controls the activation of naive Tcells. While inhibiting the differentiation and function of Th1 and Th2 cells, TGF-β promotes the differentiation of Th17 and Th9 cells. TGF-β is required for the induction of Foxp3 in naive Tcells and the development of regulatory Tcells. TGF-β is crucial in the differentiation of tissue-resident memory CD8+ Tcells and their retention in the tissue, whereas it suppresses effector T cell function. In addition, TGF-β also regulates the generation or function of natural killer Tcells, γδTcells, innate lymphoid cells, and gut intraepithelial lymphocytes. Here I highlight the major findings and recent advances in our understanding of TGF-β regulation of Tcells and provide a personal perspective of the field. Expected final online publication date for the Annual Review of Immunology, Volume 41 is April 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Contradictory Effect of Lymphocyte Therapy and Prednisolone Therapy on CD3+CD8+CD56+ Natural Killer T Population in Women with Recurrent Spontaneous Abortion.

Natural killer T (NKT) cells are influential immune cells in pregnancy failures, including recurrent spontaneous abortion (RSA). Different approaches are used for these disorders due to their effects on maternal immunomodulation. In the present study, we compared the effects of two typical immunotherapies (lymphocyte immunotherapy [LIT] and low-dose prednisolone) on CD3+CD56+CD16+ and CD3+CD56+CD8+ cells as two distinct subsets of NKT cells in Women with RSA. This study was a comparative cohort study conducted from 2021 to 2022. One hundred and five women with RSA were distributed into three treatment groups randomly. Fifty women in the group of low-dose prednisolone therapy, fifty women in the LIT group and five women without any treatment as the control group were included in the study. NK and NKT cell subsets were assessed using flow cytometry. Furthermore, the concentration of interferon-gamma (IFN-γ), transforming growth factor-beta (TGF-β) and interleukin-10 (IL-10) was measured quantitatively using the enzyme-linked immunosorbent assay technique. Normality and comparisons between study groups were performed by non-parametric unpaired Mann-Whitney, Kruskal-Wallis rank sum test, and one-way ANOVA. The percentage of CD56dim NK cells was increased after prednisolone therapy, while this population significantly decreased in the LIT group. In contrast to the LIT group, the administration of prednisolone increased CD3+CD8+CD56+ NKT cells (P < 0.0001), which is helpful for pregnancy. The effect of the investigated treatment approaches on the population of peripheral CD3+CD56+CD16+ NKT cells of women with RSA was not adequately significant. The same situation was also observed regarding the serum level of IFN-γ. However, a significant decrease in serum levels of IL-10 and TGF-β was observed after prednisolone therapy. The lower capability of LIT in changing the population of NKT cells compared to prednisolone therapy may be due to its mechanism of action, which is related to the production of blocking antibodies. These treatment approaches had different effects on NKT cells, indicating that NKT cell population and function can be affected using LIT and prednisolone therapy distinctly. In addition, prednisolone therapy and LIT in women with normal serum levels of IFN-γ have no harmful effects in changing the production of this critical cytokine.

Glycolipids from the gut symbiont Bacteroides fragilis are agonists for natural killer T cells and induce their regulatory differentiation.

Natural Killer T (NKT) cells are a lipid-antigen reactive T cell subset that is restricted to the antigen presenting molecule CD1d. They possess diverse functional properties that contribute to inflammatory and regulatory immune responses. The most studied lipid antigen target for these T cells is α-galactosylceramide (αGC). The commensal organism Bacteroides fragilis (B. fragilis) produces several forms of αGC, but conflicting information exists about the influence of these lipids on NKT cells. Herein, we report the total synthesis of a major form of αGC from B. fragilis (Bf αGC), and several analogues thereof. We confirm the T cell receptor (TCR)-mediated recognition of these glycolipids by mouse and human NKT cells. Despite the natural structure of Bf αGC containing lipid branching that limits potency, we demonstrate that Bf αGC drives mouse NKT cells to proliferate and differentiate into producers of the immunoregulatory cytokine, interleukin-10 (IL-10). These Bf αGC-experienced NKT cells display regulatory function by inhibiting the expansion of naïve NKT cells upon subsequent exposure to this antigen. Moreover, this regulatory activity impacts more than just NKT cells, as demonstrated by the NKT cell-mediated inhibition of antigen-stimulated mucosal-associated invariant T (MAIT) cells (a T cell subset restricted to a different antigen presenting molecule, MR1). These findings reveal that B. fragilis-derived NKT cell agonists may have broad immunoregulatory activity, providing insight into the mechanisms influencing immune tolerance to commensal bacteria and highlighting a potential means to manipulate NKT cell function for therapeutic benefit.

Roles and therapeutic potential of CD1d-Restricted NKT cells in inflammatory skin diseases.

Natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens rather than peptides. Due to their immunoregulatory properties, extensive work has been done to elucidate the immune functions of NKT cells in various immune contexts such as autoimmunity for more than two decades. In addition, as research on barrier immunity such as the mucosa-associated lymphoid tissue has flourished in recent years, the role of NKT cells to immunity in the skin has attracted substantial attention. Here, we review the contributions of NKT cells to regulating skin inflammation and discuss the factors that can modulate the functions of NKT cells in inflammatory skin diseases such as atopic dermatitis. This mini-review article will mainly focus on CD1d-dependent NKT cells and their therapeutic potential in skin-related immune diseases.

Infections, Reactions of Natural Killer T Cells and Natural Killer Cells, and Kidney Injury.

Natural killer T (NKT) cells and NK cells are representative innate immune cells that perform antitumor and antimicrobial functions. The involvement of these cells in various renal diseases, including acute kidney injury (AKI), has recently become evident. Murine NKT cells are activated and cause AKI in response to various stimuli, such as their specific ligand, cytokines, and bacterial components. Both renal vascular endothelial cell injury (via the perforin-mediated pathway) and tubular epithelial cell injury (via the tumor necrosis factor-alpha/Fas ligand pathway) are independently involved in the pathogenesis of AKI. NK cells complement the functions of NKT cells, thereby contributing to the development of infection-associated AKI. Human CD56+ T cells, which are a functional counterpart of murine NKT cells, as well as a subpopulation of CD56+ NK cells, strongly damage intrinsic renal cells in vitro upon their activation, possibly through mechanisms similar to those in mice. These cells are also thought to be involved in the acute exacerbation of pre-existing glomerulonephritis triggered by infection in humans, and their roles in sepsis-associated AKI are currently under investigation. In this review, we will provide an overview of the recent advances in the understanding of the association among infections, NKT and NK cells, and kidney injury, which is much more profound than previously considered. The important role of liver macrophages in the activation of NKT cells will also be introduced.

Natural Killer T (NKT) Cells and Periodontitis: Potential Regulatory Role of NKT10 Cells.

Natural killer T (NKT) cells constitute a unique subset of T lymphocytes characterized by specifically interacting with antigenic glycolipids conjugated to the CD1d receptor on antigen-presenting cells. Functionally, NKT cells are capable of performing either effector or suppressor immune responses, depending on their production of proinflammatory or anti-inflammatory cytokines, respectively. Effector NKT cells are subdivided into three subsets, termed NKT1, NKT2, and NKT17, based on the cytokines they produce and their similarity to the cytokine profile produced by Th1, Th2, and Th17 lymphocytes, respectively. Recently, a new subgroup of NKT cells termed NKT10 has been described, which cooperates and interacts with other immune cells to promote immunoregulatory responses. Although the tissue-specific functions of NKT cells have not been fully elucidated, their activity has been associated with the pathogenesis of different inflammatory diseases with immunopathogenic similarities to periodontitis, including osteolytic pathologies such as rheumatoid arthritis and osteoporosis. In the present review, we revise and discuss the pathogenic characteristics of NKT cells in these diseases and their role in the pathogenesis of periodontitis; particularly, we analyze the potential regulatory role of the IL-10-producing NKT10 cells.

Targeting Natural Killer T Cells in Solid Malignancies.

Natural killer T (NKT) cells are a unique subset of lymphocytes that recognize lipid antigens in the context of the non-classical class I MHC molecule, CD1d, and serve as a link between the innate and adaptive immune system through their expeditious release of cytokines. Whereas NKT have well-established roles in mitigating a number of human diseases, herein, we focus on their role in cancer. NKT cells have been shown to directly and indirectly mediate anti-tumor immunity and manipulating their effector functions can have therapeutic significances in treatment of cancer. In this review, we highlight several therapeutic strategies that have been used to harness the effector functions of NKT cells to target different types of solid tumors. We also discuss several barriers to the successful utilization of NKT cells and summarize effective strategies being developed to harness the unique strengths of this potent population of T cells. Collectively, studies investigating the therapeutic potential of NKT cells serve not only to advance our understanding of this powerful immune cell subset, but also pave the way for future treatments focused on the modulation of NKT cell responses to enhance cancer immunotherapy.

Glutamine metabolism drives NKT cell homeostasis and function

Abstract Cellular metabolism is essential in dictating T cell development and function, but its role in natural killer T (NKT) cells has not been well studied. Activated CD4 T cells undergo a metabolic switch from oxidative to glycolytic metabolism to fuel their proliferation and effector function. We have previously shown that NKT cells operate distinctly different metabolic programming from CD4 T cells. We found that, unlike CD4 T cells, NKT cells rely more on glutamine for their homeostasis. In fact, we observed that resting NKT cells have higher levels of glutamine-derived metabolites than conventional CD4 T cells. However, the precise mechanisms by which NKT cells use glutamine for their proliferation and cytokine production remain unknown. Glutamine is metabolized into glutamate and then into alpha-ketoglutarate (α-KG) and glutathione (GSH). Using the pathway specific inhibitors revealed that NKT cells rely on both pathways for cell homeostasis, but cytokine production is associated with α-KG production. These glutamine oxidation processes control optimal mTORC1 activity and mitochondrial functions. Importantly, we observed a novel role of 5′ AMP-activated protein kinase (AMPK) in regulating glutamine metabolism in NKT cells. Taken together, glutamine metabolism is essential for NKT cell homeostasis and cytokine production.

Integrated computational approach toward discovery of multi-targeted natural products from Thumbai (Leucas aspera) for attuning NKT cells

A multi-omics-based approach targeting the plant-based natural products from Thumbai (Leucas aspera), an important yet untapped potential source of many therapeutic agents for myriads of immunological conditions and genetic disorders, was conceptualized to reconnoiter its potential biomedical application. A library of 79 compounds from this plant was created, out of which 9 compounds qualified the pharmacokinetics parameters. Reverse pharmacophore technique for target fishing of the screened compounds was executed through which renin receptor (ATP6AP2) and thymidylate kinase (DTYMK) were identified as potential targets. Network biology approaches were used to comprehend and validate the functional, biochemical and clinical relevance of the targets. The target–ligand interaction and subsequent stability parameters at molecular scale were investigated using multiple strategies including molecular modeling, pharmacophore approaches and molecular dynamics simulation. Herein, isololiolide and 4-hydroxy-2-methoxycinnamaldehyde were substantiated as the lead molecules exhibiting comparatively the best binding affinity against the two putative protein targets. These natural lead products from L. aspera and the combinatorial effects may have plausible medical applications in a wide variety of neurodegenerative, genetic and developmental disorders. The lead molecules also exhibit promising alternative in diagnostics and therapeutics through immuno-modulation targeting natural killer T-cell function in transplantation-related pathogenesis, autoimmune and other immunological disorders. Communicated by Ramaswamy H. Sarma

Characterization of Immune Dysfunction and Identification of Prognostic Immune-Related Risk Factors in Acute Myeloid Leukemia.

This study aims to provide comprehensive insights into longitudinal immune landscape in acute myeloid leukemia (AML) development and treatment, which may contribute to predict prognosis and guide clinical decisions. Periphery blood samples from 79 patients with AML (at diagnosis or/and after chemotherapy or at relapse) and 24 healthy controls were prospectively collected. We performed phenotypic and functional analysis of various lymphocytes through multiparametric flow cytometry and investigated prognostic immune-related risk factors. Immune defects in AML were reflected in T and natural killer (NK) cells, whereas B-cell function remained unaffected. Both CD8+ T and CD4+ T cells exhibited features of senescence and exhaustion at diagnosis. NK dysfunction was supported by excessive maturation and downregulation of NKG2D and NKP30. Diseased γδ T cells demonstrated a highly activated or even exhausted state through PD-1 upregulation and NKG2D downregulation. Effective therapeutic response following chemotherapy correlated with T and NK function restoration. Refractory and relapsed patients demonstrated even worse immune impairments, and selective immune signatures apparently correlated clinical outcomes and survival. PD-1 expression in CD8+ T cells was independently predictive of poor overall survival and event-free survival. T-cell senescence and exhaustion, together with impaired NK and γδ T-cell function, are dominant aspects involved in immune dysfunction in AML. Noninvasive immune testing of blood samples could be applied to predict therapeutic reactivity, high risk for relapse, and unfavorable prognosis.

Natural Killer T Cells Are Numerically and Functionally Deficient in Patients with Trauma

Natural killer T (NKT) cells rapidly produce Th1 and Th2 cytokines such as interferon-γ (IFN-γ) and interleukin (IL)-4. This study examined the frequency and function of NKT cells in trauma patients. Frequencies, proliferative responses to α-galactosylceramide (α-GalCer), and Th1/Th2 cytokine secretion levels of NKT cells in peripheral blood mononuclear cells from trauma patients and healthy controls (HC) were measured by flow cytometry. Circulating NKT cell levels were significantly reduced in trauma patients. Proliferation and IFN-γ production of circulating NKT cells in response to α-GalCer were markedly decreased in trauma patients. CD69 expression levels produced by NKT cells were significantly upregulated in trauma patients compared to those in HC. In addition, annexin V+ NKT cells were profoundly increased in trauma patients after α-GalCer stimulation. Trauma patients had higher plasma levels of IL-6, IL-8, and TNF-α compared to HC. In particular, the proliferative response of NKT cells to α-GalCer was significantly decreased in the presence of these cytokines. Such decrease was partially recovered after treatment with blocking antibodies against these cytokines. This study demonstrates that circulating NKT cells are numerically deficient and functionally impaired in IFN-γ production in trauma patients. These findings provide an important insight into the trauma-related innate immune response.

Regulatory T cells induce CD4- NKT cell anergy and suppress NKT cell cytotoxic function.

Due to the strong tumoricidal activities of activated natural killer T (NKT) cells, invariant NKT cell-based immunotherapy has shown promising clinical efficacy. However, suppressive factors, such as regulatory T cells (Tregs), may be obstacles in the use of NKT cell-based cancer immunotherapy for advanced cancer patients. Here, we investigated the suppressive effects of Tregs on NKT cells and the underlying mechanisms with the aim to improve the antitumor activities of NKT cells. Peripheral blood samples were obtained from healthy donors, patients with benign tumors, and patients with head and neck squamous cell carcinoma (HNSCC). NKT cells, induced with α-galactosylceramide (α-GalCer), and monocyte-derived dendritic cells (DCs) were co-cultured with naïve CD4+ T cell-derived Tregs to investigate the mechanism of the Treg suppressive effect on NKT cell cytotoxic function. The functions and phenotypes of NKT cells were evaluated with flow cytometry and cytometric bead array. Treg suppression on NKT cell function required cell-to-cell contact and was mediated via impaired DC maturation. NKT cells cultured under Treg-enriched conditions showed a decrease in CD4- NKT cell frequency, which exert strong tumoricidal responsiveness upon α-GalCer stimulation. The same results were observed in HNSCC patients with significantly increased effector Tregs. Tregs exert suppressive effects on NKT cell tumoricidal function by inducing more CD4- NKT cell anergy and less CD4+ NKT cell anergy. Both Treg depletion and NKT cell recovery from the anergy state may be important for improving the clinical efficacy of NKT cell-based immunotherapy in patients with advanced cancers.

Altered Lipid Tumor Environment and Its Potential Effects on NKT Cell Function in Tumor Immunity.

Natural killer T (NKT) cells are CD1d restricted T cells that mostly recognize lipid antigens. These cells share characteristics with both adaptive and innate immune cells and have multiple immunoregulatory roles. In a manner similar to innate immune cells, they respond quickly to stimuli and secrete large amounts of cytokines, amplifying and modulating the immune response. As T cells, they express T cell receptors (TCRs) and respond in an antigen-specific manner like conventional T cells. There are at least two subtypes of NKT cells, type I and type II, that differ in the nature of their TCR, either semi-invariant (type I) or diverse (type II). The two sub-types generally have opposing functions in tumor immunity, with type I promoting and type II suppressing tumor immunity, and they cross-regulate each other, forming an immunoregulatory axis. The tumor has multiple mechanisms by which it can evade immune-surveillance. One such mechanism involves alteration in tumor lipid repertoire and accumulation of lipids and fatty acids that favor tumor growth and evade anti-tumor immunity. Since NKT cells mostly recognize lipid antigens, an altered tumor lipid metabolic profile will also alter the repertoire of lipid antigens that can potentially affect their immune-modulatory function. In this review, we will explore the effects of alterations in the lipid metabolites on tumor growth, antigen cross-presentation, and overall effect on anti-tumor immunity, especially in the context of NKT cells.

NKT Cells in Neurological Diseases.

Natural killer T (NKT) cells are a unique subset of T lymphocytes with the expression of T cell receptor (TCR) and NK cell lineage receptors. These cells can rapidly release large quantities of cytokines and function as a bridge between innate and adaptive immunity. To date, multiple reports have investigated the role of NKT cells under various pathological conditions, such as cancer, autoimmune disease, and infection. Knowledge about NKT cells in neurological diseases is increasing, albeit limited. Here, we review evidence for the involvement of NKT cells in neurological diseases, and discuss immunotherapeutic potential and future study goals. As the development and function of NKT cells become increasingly well understood, the next few years should yield many new insights into NKT cell function, and mechanistic regulation in neurological disorders.

Enhanced oxidative phosphorylation in NKT cells is essential for their survival and function

Cellular metabolism and signaling pathways are key regulators to determine conventional T cell fate and function, but little is understood about the role of cell metabolism for natural killer T (NKT) cell survival, proliferation, and function. We found that NKT cells operate distinct metabolic programming from CD4 T cells. NKT cells are less efficient in glucose uptake than CD4 T cells with or without activation. Gene-expression data revealed that, in NKT cells, glucose is preferentially metabolized by the pentose phosphate pathway and mitochondria, as opposed to being converted into lactate. In fact, glucose is essential for the effector functions of NKT cells and a high lactate environment is detrimental for NKT cell survival and proliferation. Increased glucose uptake and IFN-γ expression in NKT cells is inversely correlated with bacterial loads in response to bacterial infection, further supporting the significance of glucose metabolism for NKT cell function. We also found that promyelocytic leukemia zinc finger seemed to play a role in regulating NKT cells' glucose metabolism. Overall, our study reveals that NKT cells use distinct arms of glucose metabolism for their survival and function.

CD3+CD56+ natural killer T cell infiltration is increased in cervical cancer and negatively correlated with tumour progression

This study investigated the phenotype and function of natural killer T (NKT) cells infiltrating cervical cancer tissues, in an attempt to understand the regulation of NKT cells by cervical cancer cells. Forty-two patients with cervical cancer were included. Flow cytometry was used to analyze the percentage of NKT cells in tumour tissues and its correlation with clinical staging and lymphatic metastasis. The expression of surface receptor and effector molecules on infiltrating NKT cells was determined. The changes of the phenotype, subtype and cytotoxicity of NKT cells were investigated. The regulation of NKT cells by cervical cancer cells was investigated by co-culture with HeLa or SiHa cells. The effect of TGF-β1 on NKT activity regulated by cervical cancer cells was studied. The results showed that the infiltration of NKT cells in cervical cancer tissues was significantly higher than that in tumour-adjacent tissues, and the degree of infiltration was negatively correlated with the progression of the disease. The activity and killing effect of infiltrating NKT were inhibited in cervical cancer tissues, leading to increase of CD4+NKT cells and decrease of CD8−CD4−NKT cells. The activity of NKT cells was down-regulated by co-culture with cervical cancer cells, but subtypes of NKT cells were not altered. Cervical cancer cells inhibited the function of NKT cells by secreting TGF-β1. The study demonstrates that the infiltration of NKT cells in cervical cancer tissues is increased significantly and negatively correlated with tumour progression.

Dysfunction of Circulating Natural Killer T Cells in Patients With Scrub Typhus.

Human natural killer T (NKT) cells are known to serve as regulatory and/or effector cells in infectious diseases. However, little is known about the role of NKT cells in Orientia tsutsugamushi infection. Accordingly, the objective of this study was to examine the level and function of NKT cells in patients with scrub typhus. This study included 62 scrub typhus patients and 62 healthy controls (HCs). NKT cell level and function in peripheral blood samples were measured by flow cytometry. Proliferation of NKT cells and their ability to produce interferon-γ and interleukin-4 (IL-4) were significantly lower in scrub typhus patients compared to those in HCs. However, circulating NKT cell levels were comparable between patients and HCs. Expression levels of CD69, programmed death-1 (PD-1), lymphocyte activation gene-3 (LAG-3), and T-cell immunoglobulin domain and mucin domain-containing molecule-3 (TIM-3) were significantly increased in scrub typhus patients. Elevated expression of CD69, PD-1, LAG-3, and TIM-3, impaired proliferation, and decreased IL-4 production by NKT cells were recovered in the remission phase. This study demonstrates that circulating NKT cells are numerically preserved but functionally impaired in scrub typhus patients. In addition, NKT cell dysfunction is recovered in the remission phase.