NK Cell Subpopulations and Receptor Expression in Recovering SARS-CoV-2 Infection

The Role of Killer Ig-like Receptors in Diseases from A to Z

Killer Ig-like Receptors (KIRs) regulate immune responses, maintaining the balance between activation and inhibition of the immune system. KIRs are expressed on natural killer cells and some CD8 T cells and interact with HLA class I molecules, influencing various physiological and pathological processes. KIRs' polymorphism creates a variability in immune responses among individuals. KIRs are involved in autoimmune disorders, cancer, infections, neurological diseases, and other diseases. Specific combinations of KIRs and HLA are linked to several diseases' susceptibility, progression, and outcomes. In particular, the balance between inhibitory and activating KIRs can determine how the immune system responds to pathogens and tumors. An imbalance can lead to an excessive response, contributing to autoimmune diseases, or an inadequate response, allowing immune evasion by pathogens or cancer cells. The increasing number of studies on KIRs highlights their essential role as diagnostic and prognostic biomarkers and potential therapeutic targets. This review provides a comprehensive overview of the role of KIRs in all clinical conditions and diseases, listed alphabetically, where they are analyzed.

Organ-Dysfunction Markers in Mild-to-Moderate COVID-19 Convalescents

Background: A coronavirus disease 2019 (COVID-19) outbreak led to a worldwide pandemic. COVID-19 not only caused acute symptoms during the severe phase of the disease, but also induced long-term side effects on the functioning of many organs and systems. Symptoms that were associated with the disease and present at least 3 months after recovery were named long COVID. The aim of this study was to assess if mild-to-moderate COVID-19 may lead to the dysfunction of respiratory, cardiovascular, neural, and renal systems in healthy blood donors who recovered from the disease at least 6 months earlier. Methods: Here, we examined 294 adults among volunteer blood donors divided into convalescents (n = 215) and healthy controls (n = 79). Concentrations of soluble CD163, TGF beta, Lp-PLA2, NCAM-1, S100, NGAL, and creatinine were measured either by ELISA or automated methods. The probability value p < 0.05 was considered as statistically significant. Results: We found significant differences in Lp-PLA2, S100, and NCAM-1 between convalescents and never-infected subjects. Lp-PLA2 and NCAM-1 were lower, and S100 higher, in convalescents than in the control group. Conclusion: Mild-to-moderate COVID-19 convalescents are at a low risk of developing lung fibrosis or chronic kidney disease. However, they should regularly carry out their prophylaxis examinations for early detection of possible negative outcomes of COVID-19.

Association of KIR Genes with Middle East Respiratory Syndrome Coronavirus Infection in South Koreans

BACKGROUND

Middle East respiratory syndrome (MERS) is a lower respiratory tract disease caused by a beta coronavirus (CoV) called MERS-CoV, characterized by a high mortality rate. We aimed to evaluate the association between genetic variation in killer cell immunoglobulin-like receptors (KIRs) and the risk of MERS in South Koreans.

METHODS

KIR genes were genotyped by multiplex polymerase chain reaction with sequence-specific primers (PCR-SSP). A case-control study was performed to identify the odds ratios (OR) of KIR genes for MERS and the association of KIR genes and their ligands, human leukocyte antigens (HLA) genes.

RESULTS

KIR2DS4D and KIR3DP1F showed higher frequencies in the group of all patients infected with MERS-CoV than in the control group (p = 0.023, OR = 2.4; p = 0.039, OR = 2.7). KIR2DL1, KIR2DP1, and KIR3DP1D were significantly associated with moderate/mild (Mo/Mi) cases. KIR2DL2, KIR2DS1, and KIR3DP1F were affected in severe cases. When we investigated the association between KIR genes and their ligands in MERS patient and control groups, KIR3DL1+/Bw4(80I)+, KIR3DL1+/Bw6+, KIR3DL1+/Bw6-, KIR2DS1+/C2+, and KIR3DS+/Bw4(80I)+ were associated with MERS. KIR3DL1+/Bw6- was found in Mo/Mi cases. KIR2DS1+/C2+ and KIR2DS2+/C1+ were found in severe cases.

CONCLUSION

Further investigations are needed to prove the various immune responses of MERS-CoV-infected cells according to variations in the KIR gene and ligand gene. A treatment strategy based on current research on the KIR gene and MERS-CoV will suggest potential treatment targets.

Immune inhibitory receptor-mediated immune response, metabolic adaptation, and clinical characterization in patients with COVID-19

Immune inhibitory receptors (IRs) play a critical role in the regulation of immune responses to various respiratory viral infections. However, in coronavirus disease 2019 (COVID-19), the roles of these IRs in immune modulation, metabolic reprogramming, and clinical characterization remain to be determined. Through consensus clustering analysis of IR transcription in the peripheral blood of patients with COVID-19, we identified two distinct IR patterns in patients with COVID-19, which were named IR_cluster1 and IR_cluster2. Compared to IR_cluster1 patients, IR_cluster2 patients with lower expressions of immune inhibitory receptors presented with a suppressed immune response, lower nutrient metabolism, and worse clinical manifestations or prognosis. Considering the critical influence of the integrated regulation of multiple IRs on disease severity, we established a scoring system named IRscore, which was based on principal component analysis, to evaluate the combined effect of multiple IRs on the disease status of individual patients with COVID-19. Similar to IR_cluster2 patients, patients with high IRscores had longer hospital-free days at day 45, required ICU admission and mechanical ventilatory support, and presented higher Charlson comorbidity index and SOFA scores. A high IRscore was also linked to acute infection phase and absence of drug intervention. Our investigation comprehensively elucidates the potential role of IR patterns in regulating the immune response, modulating metabolic processes, and shaping clinical manifestations of COVID-19. All of this evidence suggests the essential role of prognostic stratification and biomarker screening based on IR patterns in the clinical management and drug development of future emerging infectious diseases such as COVID-19.

Defining the role of natural killer cells in COVID-19

Natural killer (NK) cells are critical effectors of antiviral immunity. Researchers have therefore sought to characterize the NK cell response to coronavirus disease 2019 (COVID-19) and the virus that causes it, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The NK cells of patients with severe COVID-19 undergo extensive phenotypic and functional changes. For example, the NK cells from critically ill patients with COVID-19 are highly activated and exhausted, with poor cytotoxic function and cytokine production upon stimulation. The NK cell response to SARS-CoV-2 is also modulated by changes induced in virally infected cells, including the ability of a viral peptide to bind HLA-E, preventing NK cells from receiving inhibitory signals, and the downregulation of major histocompatibility complex class I and ligands for the activating receptor NKG2D. These changes have important implications for the ability of infected cells to escape NK cell killing. The implications of these findings for antibody-dependent NK cell activity in COVID-19 are also reviewed. Despite these advances in the understanding of the NK cell response to SARS-CoV-2, there remain critical gaps in our current understanding and a wealth of avenues for future research on this topic.

Thiopurine therapy in inflammatory bowel disease in the pandemic era: Safe or unsafe?

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract. Crohn's disease (CD) and Ulcerative colitis (UC) are the two major types affecting millions across the globe. Various immunomodulatory drugs consisting of small molecules (thiopurines, methotrexate and tofacitinib) and biologics are used to treat IBD. Thiopurines (TP) are widely used in the treatment of IBD and it plays an important role both alone and in combination with anti-TNF agents as IBD maintenance therapy. Although the advent of biologics therapy has significantly advanced the management of IBD, TP remains the mainstay of treatment in resource-limited and low economic settings. However, the recently commenced pandemic has raised uncertainty over the safety of the use of immunosuppressant drugs such as TP among healthcare care providers and patients, as there is a scarcity of data on whether IBD patients are at higher risk of COVID-19 infection or more prone to its severe outcomes.

AIM

This review aims to encapsulate evidence on the risk of COVID-19 infection and its severe prognosis in IBD patients on TP. Additionally, it also evaluates the role of TP in inhibiting the viral protease, a potential drug target, essential for the replication and pathogenesis of the virus.

CONCLUSION

Emerging evidence suggests that TP therapy is safe during the current pandemic and does not carry an elevated risk when used as monotherapy or in combination with other IBD drugs. In-vitro studies demonstrate that TP is a potential therapeutic for present and future betacoronavirus pandemics.

Distribution of KIR Genes and Their HLA Ligands in Different Viral Infectious Diseases: Frequency Study in Sicilian Population

Natural killer (NK) cells play a role in defence against viral infections by killing infected cells or by producing cytokines and interacting with adaptive immune cells. Killer immunoglobulin-like receptors (KIRs) regulate the activation of NK cells through their interaction with human leucocyte antigens (HLA). Ninety-six Sicilian patients positive to Human Immunodeficiency Virus-1 (HIV) and ninety-two Sicilian patients positive to SARS-CoV-2 were genotyped for KIRs and their HLA ligands. We also included fifty-six Sicilian patients with chronic hepatitis B (CHB) already recruited in our previous study. The aim of this study was to compare the distribution of KIR-HLA genes/groups of these three different infected populations with healthy Sicilian donors from the literature. We showed that the inhibitory KIR3DL1 gene and the KIR3DL1/HLA-B Bw4 pairing were more prevalent in individual CHB. At the same time, the frequency of HLA-C2 was increased in CHB compared to other groups. In contrast, the HLA-C1 ligand seems to have no contribution to CHB progression whereas it was significantly higher in COVID-19 and HIV-positive than healthy controls. These results suggest that specific KIR-HLA combinations can predict the outcome/susceptibility of these viral infections and allows to plan successful customized therapeutic strategies.

Innate immune responses to three doses of the BNT162b2 mRNA SARS-CoV-2 vaccine

To explore the effects of SARS-CoV-2-mRNA vaccines on innate immune responses we enrolled 58 individuals who received 3 doses of the BNT162b2 vaccine in a longitudinal study; 45 of these individuals had never been SARS-CoV-2 infected. Results showed that vaccination significantly increased: 1) classical and intermediate inflammatory monocytes, 2) CD56^bright, CD56^dim, and CD56^dim/CD16^dim NK cells, and 3) IFN-γ+ ;production as well as perforin and granzyme content by NK cells. Vaccination also reduced expression of the NK inhibitory receptor ILT-2, increasing that of the stimulatory molecule 2DS2. These effects were long-lasting and were boosted by every vaccine dose. Notably, ILT-2 expressing NK cells were reduced even more robustly in COVID-19-recovereed vaccines. BNT162b1 mRNA vaccine is known to induce potent adaptive immune responses; results herein show its ability to modulate innate immune responses as well, offering further support to the indication to proceed with worldwide vaccination efforts to end the SARS-CoV-2 pandemic.

Exploring the Utility of NK Cells in COVID-19

Coronavirus disease 2019 (COVID-19) can manifest as acute respiratory distress syndrome and is associated with substantial morbidity and mortality. Extensive data now indicate that immune responses to SARS-CoV-2 infection determine the COVID-19 disease course. A wide range of immunomodulatory agents have been tested for the treatment of COVID-19. Natural killer (NK) cells play an important role in antiviral innate immunity, and anti-SARS-CoV-2 activity and antifibrotic activity are particularly critical for COVID-19 control. Notably, SARS-CoV-2 clearance rate, antibody response, and disease progression in COVID-19 correlate with NK cell status, and NK cell dysfunction is linked with increased SARS-CoV-2 susceptibility. Thus, NK cells function as the key element in the switch from effective to harmful immune responses in COVID-19. However, dysregulation of NK cells has been observed in COVID-19 patients, exhibiting depletion and dysfunction, which correlate with COVID-19 severity; this dysregulation perhaps contributes to disease progression. Given these findings, NK-cell-based therapies with anti-SARS-CoV-2 activity, antifibrotic activity, and strong safety profiles for cancers may encourage the rapid application of functional NK cells as a potential therapeutic strategy to eliminate SARS-CoV-2-infected cells at an early stage, facilitate immune–immune cell interactions, and favor inflammatory processes that prevent and/or reverse over-inflammation and inhibit fibrosis progression, thereby helping in the fight against COVID-19. However, our understanding of the role of NK cells in COVID-19 remains incomplete, and further research on the involvement of NK cells in the pathogenesis of COVID-19 is needed. The rationale of NK-cell-based therapies for COVID-19 has to be based on the timing of therapeutic interventions and disease severity, which may be determined by the balance between beneficial antiviral and potential detrimental pathologic actions. NK cells would be more effective early in SARS-CoV-2 infection and prevent the progression of COVID-19. Immunomodulation by NK cells towards regulatory functions could be useful as an adjunct therapy to prevent the progression of COVID-19.

Innate Immune Response in SARS-CoV-2 Infection

An efficient host immune response is crucial in controlling viral infections. Despite most studies focused on the implication of T and B cell response in COVID-19 (Corona Virus Disease-19) patients or in their activation after vaccination against SARS-CoV-2, host innate immune response has raised even more interest as well. In fact, innate immunity, including Natural Killer (NK) cells, monocytes/macrophages and neutrophils, represent the first line of defense against the virus and it is essential to determine the correct activation of an efficient and specific acquired immune response. In this perspective, we will report an overview on the main findings concerning SARS-CoV-2 interaction with innate host immune system, in correlation with pathogenesis and viral immune escape mechanisms.