The role of NK cells in the development of autoantibodies

Exhausted signature and regulatory network of NK cells in myasthenia gravis

Introduction

NK cells are dysfunctional in myasthenia gravis (MG), but the mechanism is unclear. This study aims to measure associations and underlying mechanisms between the NK cells and the development of MG.

Methods

Twenty healthy controls (HCs) and 53 MG patients who did not receive glucocorticoids and immunosuppressants were collected. According to the Myasthenia Gravis Foundation of America (MGFA) classification, MG patients were categorized into MGFA I group (n = 18) and MGFA II-IV group (n = 35). Flow cytometry, cell sorting, ELISA, mRNA-sequencing, RT-qPCR, western blot, and cell culture experiments were performed to evaluate the regulatory mechanism of exhausted NK cells.

Results

Peripheral NK cells in MGFA II-IV patients exhibit exhausted phenotypes than HCs, marked by the dramatic loss of total NK cells, CD56dimCD16- NK cells, elevated PD1 expression, reduced NKG2D expression, impaired cytotoxic activity (perforin, granzyme B, CD107a) and cytokine secretion (IFN-γ). Plasma IL-6 and IL-21 are elevated in MG patients and mainly derived from the aberrant expansion of monocytes and Tfh cells, respectively. IL-6/IL-21 cooperatively induced NK-cell exhausted signature via upregulating SOCS2 and inhibiting the phosphorylation of STAT5. SOCS2 siRNA and IL-2 supplement attenuated the IL-6/IL-21-mediated alteration of NK-cell phenotypes and function.

Discussion

Inhibition of IL-6/IL-21/SOCS2/STAT5 pathway and recovery of NK-cell ability to inhibit autoimmunity may be a new direction in the treatment of MG.

COVID-19: captures iron and generates reactive oxygen species to damage the human immune system

Currently, the novel coronavirus pneumonia has been widespread globally, and there is no specific medicine. In response to the emergency, we employed bioinformatics methods to investigate the virus's pathogenic mechanism, finding possible control methods. We speculated in previous studies that E protein was associated with viral infectivity. The present study adopted the domain search techniques to analyse the E protein. According to the results, the E protein could bind iron or haem. The iron and haem bound by the E protein came from the attacked haemoglobin and phagocytes. When E protein was attached to haem, it synthesised oxygen and water into superoxide anions, hydrogen peroxide and hydroxyl radicals. When the iron-bound E protein and the haem-bound E protein worked together, they converted superoxide anions and hydrogen peroxide into oxygen and water. These were the "ROS attack" and "ROS escape" of the virus. "ROS attack" damaged the tissues or cells exposed on the surface of the virus, and "ROS escape" decomposed the superoxide anion and hydrogen peroxide that attacked the virus. When NK cells were exposed to infected cells, viruses that had not shed from the infected cells' surface damaged them through "ROS attack". In addition, lymphocytes such as T cells and B cells, which could be close to the antigen of the virus surface, were also easily damaged or killed by the "ROS attack", generating a decrease in lymphocytes. When memory B cells were exposed to the virus's surface antigen, they were also damaged by "ROS attack", resulting in the patient's re-infection. The virus applied the "ROS escape" to decompose hydrogen peroxide released by phagocytes into oxygen and water. The surrounding cells were replenished with oxygen, and the patient was in a "happy hypoxia" state. When the phagocytes swallowed the virus, the E protein converted superoxide anions into oxygen and water. In this way, the virus parasitized in the vesicles of the phagocyte. While virus was in the lysosome, the E protein generated ROS to damage nearby hydrolases. In this way, the virus parasitized the lysosome. Excessive hydroxyl free radicals destroyed the membrane structure of the lysosome, causing the hydrolase release from lysosome, autophagy of phagocytic cells and subsequent cell death. As a result, the colonizing phagocytes of the virus was associated with asymptomatic infection or retest-positive. Briefly, the virus inhibited the immune system through "ROS escape", and damaged the immune system by "ROS attack". The destruction instigated a strong cytokine storm, leading to organ failure and complications.

BAFF Produced by Neutrophils and Dendritic Cells Is Regulated Differently and Has Distinct Roles in Antibody Responses and Protective Immunity against West Nile Virus

B cell activating factor (BAFF) is essential for B cells to develop and respond to Ags. Dysregulation of BAFF contributes to the development of some autoimmune diseases and malignancies. Little is known about when, where, and how BAFF is produced in vivo and about which BAFF-producing cells contribute to B cell responses. To better understand BAFF functions, we created BAFF reporter (BAFF-RFP) mice and Baff floxed (Bafffl/fl ) mice. Splenic and bone marrow neutrophils (Nphs) from BAFF-RFP mice expressed the highest constitutive levels of BAFF; other myeloid subsets, including conventional dendritic cells (cDCs) and monocyte (MO) subsets, expressed lower levels. Treatment of BAFF-RFP mice with polyinosinic:polycytidylic acid increased BAFF expression in splenic Ly6Chi inflammatory MOs, CD11bhi activated NK subset, and in bone marrow myeloid precursors. Postinfection with West Nile virus (WNV), BAFF increased in CD8- cDCs and Nphs, and BAFF+ CD11bhi NK cells expanded in draining lymph nodes. The cell- and tissue-specific increases in BAFF expression were dependent on type I IFN signaling. MAVS also was required or contributed to BAFF expression in dendritic cell and MO subsets, respectively. Mice with deletion of Baff in either cDCs or Nphs had reduced Ab responses after NP-Ficoll immunization; thus, BAFF produced by both cDCs and Nphs contributes to T cell-independent Ab responses. Conversely, mice with a cDC Baff deficiency had increased mortality after WNV infection and decreased WNV-specific IgG and neutralizing Ab responses. BAFF produced by Nphs and cDCs is regulated differently and has key roles in Ab responses and protective immunity.

The complement receptor 3 (CD11b/CD18) agonist Leukadherin-1 suppresses human innate inflammatory signalling

Complement receptor 3 (CR3, CD11b/CD18) is a multi‐functional receptor expressed predominantly on myeloid and natural killer (NK) cells. The R77H variant of CD11b, encoded by the ITGAM rs1143679 polymorphism, is associated robustly with development of the autoimmune disease systemic lupus erythematosus (SLE) and impairs CR3 function, including its regulatory role on monocyte immune signalling. The role of CR3 in NK cell function is unknown. Leukadherin‐1 is a specific small‐molecule CR3 agonist that has shown therapeutic promise in animal models of vascular injury and inflammation. We show that Leukadherin‐1 pretreatment reduces secretion of interferon (IFN)‐γ, tumour necrosis factor (TNF) and macrophage inflammatory protein (MIP)‐1β by monokine‐stimulated NK cells. It was associated with a reduction in phosphorylated signal transducer and activator of transcription (pSTAT)‐5 following interleukin (IL)‐12 + IL‐15 stimulation (P < 0·02) and increased IL‐10 secretion following IL‐12 + IL‐18 stimulation (P < 0·001). Leukadherin‐1 pretreatment also reduces secretion of IL‐1β, IL‐6 and TNF by Toll‐like receptor (TLR)‐2 and TLR‐7/8‐stimulated monocytes (P < 0·01 for all). The R77H variant did not affect NK cell response to Leukadherin‐1 using ex‐vivo cells from homozygous donors; nor did the variant influence CR3 expression by these cell types, in contrast to a recent report. These data extend our understanding of CR3 biology by demonstrating that activation potently modifies innate immune inflammatory signalling, including a previously undocumented role in NK cell function. We discuss the potential relevance of this to the pathogenesis of SLE. Leukadherin‐1 appears to mediate its anti‐inflammatory effect irrespective of the SLE‐risk genotype of CR3, providing further evidence to support its evaluation of Leukadherin‐1 as a potential therapeutic for autoimmune disease.

NK cells and their receptors in naive and rituximab-treated patients with anti-MAG polyneuropathy

BACKGROUND

Natural killer (NK) cells can bridge innate and acquired immunity, and play a role in autoimmunity. A few studies evaluated the distribution of NK cells and the expression of their receptors in chronic immune-mediated demyelinating polyneuropathies. We investigated NK cell distribution and NK cell receptor expression in 20 naïve patients with anti-MAG polyneuropathy (MAG-PN).

METHODS

Using flow cytometry, we analysed NK cells and a series of NK cell receptors in the peripheral blood of patients with MAG-PN, and, as controls, in patients with chronic inflammatory demyelinating peripheral polyradiculoneuropathy (CIDP) and in healthy subjects. Six MAG-PN patients were also tested after rituximab treatment.

RESULTS

At baseline the percentage of NK cells did not differ among the groups. KIR2DL2 receptor expression in MAG-PN patients was higher, andCD94/NKG2A receptor expression in both MAG-PN and CIDP patients was lower than in healthy controls. These abnormalities did not correlate with any clinical or demographic variable. No modification was found after rituximab therapy.

CONCLUSIONS

The data suggest that MAG-PN shows abnormalities in NK cell receptors that characterise other autoimmune diseases, and cannot help in differential diagnosis with CIDP. The impairment of the relevant CD94/NKG2A inhibitory pathway, which might play a central role in the development and perpetuation of MAG-PN, warrants further functional investigations.

Natural killer cells in human autoimmune disorders

Natural killer (NK) cells are innate lymphocytes that play a critical role in early host defense against viruses. Through their cytolytic capacity and generation of cytokines and chemokines, NK cells modulate the activity of other components of the innate and adaptive immune systems and have been implicated in the initiation or maintenance of autoimmune responses. This review focuses on recent research elucidating a potential immunoregulatory role for NK cells in T-cell and B-cell-mediated autoimmune disorders in humans, with a particular focus on multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematous. A better understanding of the contributions of NK cells to the development of autoimmunity may lead to novel therapeutic targets in these diseases.

Enhancement of antigen-specific immunoglobulin G responses by anti-CD48

CD48 is a glycosylphosphatidylinositol-anchored protein expressed ubiquitously on many cell types. Despite the poor ability to signal on its own, CD48 can activate cells via interaction with its counter receptors CD2 and CD244 as well as influence the function of other cell surface molecules by costimulatory activities. We show, herein, that injection of anti-CD48 antibodies into mice can augment the antibody response to a T-independent antigen, NP-Ficoll, that is representative of antigenic determinants expressed on the surface of various pathogens, such as Streptococcus pneumoniae. In C57BL/6 mice, enhancement of the response is dependent on natural killer (NK) cells as well as on the presence of CD2 and CD244, ligands for CD48, suggesting a requirement for direct interaction between NK and B cells. Interestingly, in this case, despite a similar augmentation by anti-CD48 in BALB/C mice, the response is independent of NK or T cells, suggesting that help for this response can be derived from other innate cell types. These results provide a pathway by which CD48, when appropriately activated, can influence the course of an antigen-specific antibody response via the innate system.

Regulatory NK cells in autoimmune disease

As major components of innate immunity, NK cells not only exert cell-mediated cytotoxicity against tumor cells or infected cells, but also act to regulate the function of other immune cells by secretion of cytokines and chemokines, thus providing surveillance in early defense against viruses, intracellular bacteria and cancer cells. However, the effector function of NK cells must be exquisitely controlled in order to prevent inadvertent attack against self normal cells. The activity of NK cells is defined by integration of signals coming from inhibitory and activation receptors. Inhibitory receptors not only distinguish healthy from diseased cells by recognize self-MHC class I molecules on cell surfaces with "missing-self" model, but also provide an educational signal that generates functional NK cells. NK cells enrich in immunotolerance organ and recent findings of different regulatory NK cell subsets have indicated the unique role of NK cells in maintenance of homeostasis. Once the self-tolerance is broken, autoimmune response may occur. Although data has demonstrated that NK cells play important role in autoimmune disorders, NK cells seemed to act as a two edged weapon and play opposite roles with both regulatory and inducer activity even in the same disease. The precise role and regulatory mechanisms need to be further determined. In this review, we focus on recent research on the association of NK cells and antoimmune diseases, particularly the genetic correlation, the immune tolerance and misrecognition of NK cells, the regulatory function of NK cells, and their potential role in autoimmunity.

IFN type I and type II independent enhancement of B cell TLR7 expression by natural killer cells

The PRR TLR7 plays a key role in the activation of autoantigen-reactive B cells. This response is increased markedly by IFN-α, produced by accessory cells, as a result of the up-regulation of TLR7. We report herein an alternative pathway by which TLR7 expression can be augmented. This finding was derived from continuation of ongoing studies to uncover interactions between NK and B cells. Here, we have compared gene expression profiles by microarray analysis of B cells before and after their interaction with purified NK cells. The most outstanding alteration of genes transcribed in B cells is a significant increase in the expression of many members of the ISG family, among which is TLR7. Further analysis revealed that the enhancement of TLR7 on B cells is not mediated via type I or type II IFN but by another cytokine, IL-28, a type III IFN, which acts in concert with contact-mediated interactions with NK cells. This increased expression allows B cells to respond more readily upon stimulation by its ligand and may increase in vivo responses to other TLR7 ligands, such as autoantigens, prior to or jointly with stimulation by other cytokines.