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

Neural Regeneration in Dry Eye Secondary to Systemic Lupus Erythematosus Is Also Disrupted like in Rheumatoid Arthritis, but in a Progressive Fashion

Our objective in this study was to analyze the aberrant neural regeneration activity in the cornea by means of in vivo confocal microscopy in systemic lupus erythematosus patients with concurrent dry eye disease. We examined 29 systemic lupus erythematosus patients and 29 age-matched healthy control subjects. Corneal nerve fiber density (CNFD, the number of fibers/mm²) and peripheral Langerhans cell morphology were lower (p < 0.05) in systemic lupus erythematosus patients compared to the control group. Interestingly, corneal nerve branch density, corneal nerve fiber length, corneal nerve fiber total branch density, and corneal nerve fiber area showed a negative correlation with disease duration. A negative correlation was also demonstrated between average corneal nerve fiber density and central Langerhans cell density. This is in line with our hypothesis that corneal somatosensory terminal Piezo2 channelopathy-induced impaired Piezo2-Piezo1 crosstalk not only disrupts regeneration and keeps transcription activated, but could lead to Piezo1 downregulation and cell activation on Langerhans cells when we consider a chronic path. Hence, Piezo2 containing mechanosensory corneal nerves and dendritic Langerhans cells could also be regarded as central players in shaping the ocular surface neuroimmune homeostasis through the Piezo system. Moreover, lost autoimmune neuroinflammation compensation, lost phagocytic self-eating capacity, and lost transcription regulation, not to mention autoantibodies against vascular heparin sulfate proteoglycans and phospholipids, could all contribute to the progressive fashion of dry eye disease in systemic lupus erythematosus.

Decreased natural killer T-like cells correlated to disease activity in systemic lupus erythematosus

OBJECTIVES

To evaluate the absolute numbers and frequencies of natural killer T-like (NKT-like) cells in systemic lupus erythematosus (SLE) and to characterize the possible role of the cells.

METHODS

Seventy-nine patients with SLE together with 30 age- and sex-matched healthy controls were enrolled. Flow cytometric determination of peripheral NKT-like cells was carried out for all participants by detecting the absolute counts (Abs) and percentage (%) of CD3 + CD16 + CD56 + cells. Disease activity index, laboratory parameters, and clinical manifestations were collected. The correlation between the cells and these parameters was analyzed.

RESULTS

SLE patients had, with respect to controls, considerably decreased values of NKT-like cells (P < 0.001 in both absolute number and percentage). The absolute number of NKT-like cells was found to have positive correlations with WBC, RBC, PLT, C3, C4, IgM and negative correlations with the disease duration, SLEDAI-2 K, anti-dsDNA, anti-nucleosome, anti-ribosomal protein, CRP, ESR. Meanwhile, it was found that the percentage values of NKT-like cells decreased in SLE patients with nephritis which was correlated with anti-ribosomal protein and CRP in comparison to SLE patients without nephritis. Moreover, an increase in the NKT-like cell counts was also observed in the patients with a clinical response to the treatment.

CONCLUSIONS

The absolute counts and frequencies of NKT-like cells decreased in SLE patients significantly, which correlated to disease activities and could recover to normal after the treatment. The NKT-like cells may play an important role in the pathogenesis of SLE and could be a useful marker in the disease assessment. Key Points • The absolute counts and frequencies of NKT-like cells decreased in SLE patients significantly. • NKT-like cells were related to the disease activities and could restore after the treatment. • NKT-like cells may be a useful marker in the disease assessment.

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.

Invariant NKT Cells and Rheumatic Disease: Focus on Primary Sjogren Syndrome

Primary Sjogren syndrome (pSS) is a complex autoimmune disease mainly affecting salivary and lacrimal glands. Several factors contribute to pSS pathogenesis; in particular, innate immunity seems to play a key role in disease etiology. Invariant natural killer (NK) T cells (iNKT) are a T-cell subset able to recognize glycolipid antigens. Their function remains unclear, but studies have pointed out their ability to modulate the immune system through the promotion of specific cytokine milieu. In this review, we discussed the possible role of iNKT in pSS development, as well as their implications as future markers of disease activity.

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

Background

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.

Methods

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.

Results

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.

Conclusions

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.

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.

Differential Activation of Hepatic Invariant NKT Cell Subsets Plays a Key Role in Progression of Nonalcoholic Steatohepatitis

Innate immune mechanisms play an important role in inflammatory chronic liver diseases. In this study, we investigated the role of type I or invariant NKT (iNKT) cell subsets in the progression of nonalcoholic steatohepatitis (NASH). We used α-galactosylceramide/CD1d tetramers and clonotypic mAb together with intracytoplasmic cytokine staining to analyze iNKT cells in choline-deficient l-amino acid-defined (CDAA)-induced murine NASH model and in human PBMCs, respectively. Cytokine secretion of hepatic iNKT cells in CDAA-fed C57BL/6 mice altered from predominantly IL-17+ to IFN-γ+ and IL-4+ during NASH progression along with the downmodulation of TCR and NK1.1 expression. Importantly, steatosis, steatohepatitis, and fibrosis were dependent upon the presence of iNKT cells. Hepatic stellate cell activation and infiltration of neutrophils, Kupffer cells, and CD8+ T cells as well as expression of key proinflammatory and fibrogenic genes were significantly blunted in Jα18-/- mice and in C57BL/6 mice treated with an iNKT-inhibitory RAR-γ agonist. Gut microbial diversity was significantly impacted in Jα18-/- and in CDAA diet-fed mice. An increased frequency of CXCR3+IFN-γ+T-bet+ and IL-17A+ iNKT cells was found in PBMC from NASH patients in comparison with nonalcoholic fatty liver patients or healthy controls. Consistent with their in vivo activation, iNKT cells from NASH patients remained hyporesponsive to ex-vivo stimulation with α-galactosylceramide. Accumulation of plasmacytoid dendritic cells in both mice and NASH patients suggest their role in activation of iNKT cells. In summary, our findings indicate that the differential activation of iNKT cells play a key role in mediating diet-induced hepatic steatosis and fibrosis in mice and its potential involvement in NASH progression in humans.

The Janus Face of NKT Cell Function in Autoimmunity and Infectious Diseases

Natural killer T cells (NKT) are a subset of T lymphocytes bridging innate and adaptive immunity. These cells recognize self and microbial glycolipids bound to non-polymorphic and highly conserved CD1d molecules. Three NKT cell subsets, type I, II, and NKT-like expressing different antigen receptors (TCR) were described and TCR activation promotes intracellular events leading to specific functional activities. NKT can exhibit different functions depending on the secretion of soluble molecules and the interaction with other cell types. NKT cells act as regulatory cells in the defense against infections but, on the other hand, their effector functions can be involved in the pathogenesis of several inflammatory disorders due to their exposure to different microbial or self-antigens, respectively. A deep understanding of the biology and functions of type I, II, and NKT-like cells as well as their interplay with cell types acting in innate (neuthrophils, innate lymphoid cells, machrophages, and dendritic cells) and adaptive immunity (CD4⁺,CD8⁺, and double negative T cells) should be important to design potential immunotherapies for infectious and autoimmune diseases.

NK cells in autoimmune diseases: Linking innate and adaptive immune responses

The pathogenesis of autoimmunity remains to be fully elucidated, although the contribution of genetic and environmental factors is generally recognized. Despite autoimmune conditions are principally due to T and B lymphocytes, NK cells also appear to play a role in the promotion and/or maintenance of altered adaptive immune responses or in peripheral tolerance mechanisms. Although NK cells are components of the innate immune system, they shows characteristics of the adaptive immune system, such as the expansion of pathogen-specific cells, the generation of long-lasting "memory" cells able to persist upon cognate antigen encounter, and the possibility to induce an increased secondary recall response to re-challenge. Human NK cells are generally identified as CD56+CD3-, conversely CD56+CD3+ cells represent a mixed population of NK-like T (NK T) cells and antigen-experienced T cells showing the up-regulation of several NK cell markers. CD56dim constitute about 90% of NK cells in the peripheral blood, they are mature and involved in cytotoxicity responses; CD56bright instead are more immature, mostly involved in cytokine production, having only a limited role in cytolytic responses, keen to leave the blood vessels as the principal population observed in lymph nodes. NK cells have been identified also in non-lymphoid tissues since, in pathologic conditions, they can quickly reach the target organs. A cross-talk between NK with dendritic cells and T cells is established throughout different receptor-ligand bindings. Several studies support the correlation between NK cell number and/or functional alterations, such as a defective cytotoxic activity and several autoimmune conditions. Among the different autoimmune pathologies and even within the same disease, NK cell function is significantly different either promoting or even protecting against the onset of the autoimmune condition. In this Review, we discuss recent literature supporting the role played by NK cells, as a bridge between innate and adaptive immunity, in the onset of autoimmune diseases.

Understanding the Regulatory Roles of Natural Killer T Cells in Rheumatoid Arthritis: T Helper Cell Differentiation Dependent or Independent?

Rheumatoid arthritis (RA) is the most common chronic systemic autoimmune disease. This disease is thought to be caused by pathogenic T cells. Th1, Th2, Th17 and Treg cells have been implicated in the pathogenesis of RA. These Th cells differentiate from CD4+ T cells primarily due to the effects of cytokines. Natural killer T (NKT) cells are a distinct subset of lymphocytes that can rapidly secrete massive amount of cytokines, including IL-2, IL-4, IL-12 and IFN-γ. Numerous studies showed that NKT cells can influence the differentiation of CD4+ T cells via cytokines in vitro. These findings suggest that NKT cells play an important role in RA by polarizing Th1, Th2, Th17 and Treg cells. In view of the complexity of RA, we discussed whether NKT cells really influence the development of RA through regulating the differentiation of Th cells.

What rheumatologists need to know about innate lymphocytes

Many rheumatic diseases are characterized by having an autoimmune background. Determining the mechanisms underlying autoimmunity is, therefore, important to further understand these diseases and to inform future lines of research aimed at developing new treatments and cures. As fast responders, innate lymphocytes have protective or pathogenic roles in the initiation as well as the maintenance of immune responses in general, and they contribute to tissue homeostasis, among other functions. Innate lymphocytes also seem to be involved in autoimmunity in particular. Since 2010, accumulating evidence clearly shows that different populations of innate lymphocytes have roles in responding to antigen-specific autoantibody and autoreactive T cells, thereby amplifying or attenuating disease processes. Cytotoxicity is a cardinal feature of many innate lymphocytes and can contribute to inflammatory tissue damage. Finally, innate lymphocytes can respond to biologic therapies for autoimmune diseases. Consequently, like TNF and other effector molecules, certain innate lymphocyte subsets might be appropriate therapeutic targets to ameliorate various autoimmune diseases. In this Review, we summarize the main characteristics and functions of innate lymphocyte subsets, and describe their roles in autoimmune disease. We also discuss how biologic therapies influence innate lymphocyte function and consider the potential for these cell subsets to act as future therapeutic targets.

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.