Natural killer cells regulate T-cell proliferation during human parainfluenza virus type 3 infection

A TLR5 mono-agonist restores inhibited immune responses to Streptococcus pneumoniae during influenza virus infection in human monocytes

Influenza A virus (IAV) predisposes individuals to often more severe secondary bacterial infections with Streptococcus pneumonia (S. pneumoniae). The outcomes of these infections may be made worse with the increase in antimicrobial resistance and a lack of new treatments to combat this. Th17 responses are crucial in clearing S. pneumoniae from the lung. We previously demonstrated that early IAV infection of human monocytes significantly reduced levels of S. pneumoniae-driven cytokines involved in the Th17 response. Here, we have further identified that IAV targets specific TLRs (TLR2, TLR4, TLR9) involved in sensing S. pneumoniae infection resulting, in a reduction in TLR agonist-induced IL-23 and TGF-β. The effect of IAV is more profound on the TLR2 and TLR9 pathways. We have established that IAV-mediated inhibition of TLR9-induction is related to a downregulation of RORC, a Th17 specific transcription factor. Other studies using mouse models demonstrated that TLR5 agonism improved the efficacy of antibiotics in the treatment of IAV/S. pneumoniae co-infections. Therefore, we investigated if TLR5 agonism could restore inhibited Th17 responses in human monocytes. Levels of pneumococcus-driven cytokines, which had previously been inhibited by IAV were not reduced in the presence of the TLR5 mono-agonist, suggesting that such treatment may overcome IAV inhibition of Th17 responses. The importance of our research is in demonstrating the IAV directly targets S. pneumoniae-associated TLR pathways. Additionally, the IAV-inhibition of Th17 responses can be restored by TLR5 agonism, which indicates that there may be a different Th17 signalling pathway which is not affected by IAV infection.

Low-dose IL-2 induces CD56bright NK regulation of T cells via NKp44 and NKp46

Low-dose interleukin (IL)-2 has shown clinical benefits in patients with autoimmune and inflammatory diseases. Both regulatory T cells (Tregs ) and natural killer (NK) cells are increased in response to low-dose IL-2 immunotherapy. The role of regulatory T cells in autoimmune diseases has been extensively studied; however, NK cells have not been as thoroughly explored. It has not been well reported whether the increase in NK cells is purely an epiphenomenon or carries actual benefits for patients with autoimmune diseases. We demonstrate that low-dose IL-2 expands the primary human CD56bright NK cells resulting in a contact-dependent cell cycle arrest of effector T cells (Teffs ) via retention of the cycle inhibitor p21. We further show that NK cells respond via IL-2R-β, which has been shown to be significant for immunity by regulating T cell expansion. Moreover, we demonstrate that blocking NK receptors NKp44 and NKp46 but not NKp30 could abrogate the regulation of proliferation associated with low-dose IL-2. The increase in NK cells was also accompanied by an increase in Treg cells, which is dependent on the presence of CD56bright NK cells. These results not only heighten the importance of NK cells in low-dose IL-2 therapy but also identify key human NK targets, which may provide further insights into the therapeutic mechanisms of low-dose IL-2 in autoimmunity.

Quis Custodiet Ipsos Custodes? Regulation of Cell-Mediated Immune Responses Following Viral Lung Infections

Viral lung infections are leading causes of morbidity and mortality. Effective immune responses to these infections require precise immune regulation to preserve lung function after viral clearance. One component of airway pathophysiology and lung injury associated with acute respiratory virus infection is effector T cells, yet these are the primary cells required for viral clearance. Accordingly, multiple immune mechanisms exist to regulate effector T cells, limiting immunopathology while permitting clearance of infection. Much has been learned in recent years about regulation of T cell function during chronic infection and cancer, and it is now clear that many of these mechanisms also control inflammation in acute lung infection. In this review, we focus on regulatory T cells, inhibitory receptors, and other cells and molecules that regulate cell-mediated immunity in the context of acute respiratory virus infection.

Haemagglutinin-neuraminidase from HPIV3 mediates human NK regulation of T cell proliferation via NKp44 and NKp46

HPIV3 is a respiratory virus causing airway diseases, including pneumonia, croup, and bronchiolitis, during infancy and childhood. Currently there is no effective vaccine or anti-viral therapy for this virus. Studies have suggested that poor T cell proliferation following HPIV3 infection is responsible for impaired immunological memory associated with this virus. We have previously demonstrated that NK cells mediate regulation of T cell proliferation during HPIV3 infection. Here we add to these studies by demonstrating that the regulation of T cell proliferation during HPIV3 infection is mediated via NK receptors NKp44 and NKp46 and involves the surface glycoprotein haemagglutinin-neuraminidase but not the fusion protein of the virus. These studies extend our knowledge of the regulatory repertoire of NK cells and provide mechanistic insights which may explain reoccurring failures of vaccines against this virus.

A distinct innate lymphoid cell population regulates tumor-associated T cells

Antitumor T cells are subject to multiple mechanisms of negative regulation. Recent findings that innate lymphoid cells (ILCs) regulate adaptive T cell responses led us to examine the regulatory potential of ILCs in the context of cancer. We identified a unique ILC population that inhibits tumor-infiltrating lymphocytes (TILs) from high-grade serous tumors, defined their suppressive capacity in vitro, and performed a comprehensive analysis of their phenotype. Notably, the presence of this CD56+CD3- population in TIL cultures was associated with reduced T cell numbers, and further functional studies demonstrated that this population suppressed TIL expansion and altered TIL cytokine production. Transcriptome analysis and phenotypic characterization determined that regulatory CD56+CD3- cells exhibit low cytotoxic activity, produce IL-22, and have an expression profile that overlaps with those of natural killer (NK) cells and other ILCs. NKp46 was highly expressed by these cells, and addition of anti-NKp46 antibodies to TIL cultures abrogated the ability of these regulatory ILCs to suppress T cell expansion. Notably, the presence of these regulatory ILCs in TIL cultures corresponded with a striking reduction in the time to disease recurrence. These studies demonstrate that a previously uncharacterized ILC population regulates the activity and expansion of tumor-associated T cells.

Non-invasive Imaging of Sendai Virus Infection in Pharmacologically Immunocompromised Mice: NK and T Cells, but not Neutrophils, Promote Viral Clearance after Therapy with Cyclophosphamide and Dexamethasone

In immunocompromised patients, parainfluenza virus (PIV) infections have an increased potential to spread to the lower respiratory tract (LRT), resulting in increased morbidity and mortality. Understanding the immunologic defects that facilitate viral spread to the LRT will help in developing better management protocols. In this study, we immunosuppressed mice with dexamethasone and/or cyclophosphamide then monitored the spread of viral infection into the LRT by using a noninvasive bioluminescence imaging system and a reporter Sendai virus (murine PIV type 1). Our results show that immunosuppression led to delayed viral clearance and increased viral loads in the lungs. After cessation of cyclophosphamide treatment, viral clearance occurred before the generation of Sendai-specific antibody responses and coincided with rebounds in neutrophils, T lymphocytes, and natural killer (NK) cells. Neutrophil suppression using anti-Ly6G antibody had no effect on infection clearance, NK-cell suppression using anti-NK antibody delayed clearance, and T-cell suppression using anti-CD3 antibody resulted in no clearance (chronic infection). Therapeutic use of hematopoietic growth factors G-CSF and GM-CSF had no effect on clearance of infection. In contrast, treatment with Sendai virus-specific polysera or a monoclonal antibody limited viral spread into the lungs and accelerated clearance. Overall, noninvasive bioluminescence was shown to be a useful tool to study respiratory viral progression, revealing roles for NK and T cells, but not neutrophils, in Sendai virus clearance after treatment with dexamethasone and cyclophosphamide. Virus-specific antibodies appear to have therapeutic potential.

Acute clearance of human metapneumovirus occurs independently of natural killer cells

Human metapneumovirus (HMPV) is a major cause of respiratory disease. The role of NK cells in protection against HMPV is unclear. We show that while HMPV-infected C57BL/6 mice had higher numbers of functional lung NK cells than mock-treated mice, comparing NK cell-depleted and control mice did not reveal differences in lung viral titers, histopathology, cytokine levels, or T cell numbers or function. These data indicate that NK cells are not required for host control of HMPV.

Utilization of mouse models to decipher natural killer cell biology and potential clinical applications

Natural killer (NK) cells represent a key component of innate immunity. The utility of mouse models to recapitulate the human immune response has been a matter of ongoing debate, especially with regard to NK cells. However, mouse models of NK cells have provided significant advancements in our understanding of the biology of the cells that bridge these species. Initial characterization of NK cell activity was in mouse hematopoietic stem cell transplantation models. Recent findings include uncovering functionally disparate subsets of NK cells based on unique inhibitory receptor expression patterns, the existence of memory-like NK cells, and immunoregulatory NK cells that affect hematopoiesis and T-cell function. In addition, the biology of these cells with regard to MHC-binding receptors that affect NK cell subset maturation and function in the context of licensing, the importance of cytokines such as IL-15 in their development and maintenance, and evidence of NK exhaustion have been initially studied in mice. Many of these findings have been validated in clinical studies and demonstrate the significant wealth of knowledge that can be obtained by mouse models. However, it is important to understand the limitations and conditions of the mouse models, particularly when studying NK cells in hematopoietic stem cell transplantation and cancer.

Association between human parainfluenza virus type 1 and smoking history in patients with an abdominal aortic aneurysm

Several studies have suggested that infectious agents may induce the development of abdominal aortic aneurysms and/or accelerate their progression. The aim of this study was to evaluate the presence of the respiratory-transmitted viruses such as influenza A and B and parainfluenza type 1 genomes in bioptic fragments of abdominal aortic aneurysms. Furthermore, the association between viral infection and traditional risk factors for aneurysms was investigated employing multivariate logistic regression models. The genome of parainfluenza 1 was detected in 11 out of 57 patients with abdominal aortic aneurysm, influenza A only in one, whereas none of the specimens analyzed resulted positive for influenza B. After adjustment of age, gender, and clinical diagnosis, being current smokers was associated independently with parainfluenza 1 detection in aneurysms. The identification of parainfluenza 1 in aortic aneurysm biopsies supports previous observations of a possible role of viruses in the lesion development. Smoking, by interfering with the respiratory tract's ability to defend itself and predisposing to upper and lower respiratory tract infections may accelerate the onset and progression of abdominal aortic aneurysms.

Seoul virus-infected rat lung endothelial cells and alveolar macrophages differ in their ability to support virus replication and induce regulatory T cell phenotypes

Hantaviruses cause a persistent infection in reservoir hosts that is attributed to the upregulation of regulatory responses and downregulation of proinflammatory responses. To determine whether rat alveolar macrophages (AMs) and lung microvascular endothelial cells (LMVECs) support Seoul virus (SEOV) replication and contribute to the induction of an environment that polarizes CD4(+) T cell differentiation toward a regulatory T (Treg) cell phenotype, cultured primary rat AMs and LMVECs were mock infected or infected with SEOV and analyzed for viral replication, cytokine and chemokine responses, and expression of cell surface markers that are related to T cell activation. Allogeneic CD4(+) T cells were cocultured with SEOV-infected or mock-infected AMs or LMVECs and analyzed for helper T cell (i.e., Treg, Th17, Th1, and Th2) marker expression and Treg cell frequency. SEOV RNA and infectious particles in culture media were detected in both cell types, but at higher levels in LMVECs than in AMs postinfection. Expression of Ifnβ, Ccl5, and Cxcl10 and surface major histocompatibility complex class II (MHC-II) and MHC-I was not altered by SEOV infection in either cell type. SEOV infection significantly increased Tgfβ mRNA in AMs and the amount of programmed cell death 1 ligand 1 (PD-L1) in LMVECs. SEOV-infected LMVECs, but not AMs, induced a significant increase in Foxp3 expression and Treg cell frequency in allogeneic CD4(+) T cells, which was virus replication and cell contact dependent. These data suggest that in addition to supporting viral replication, AMs and LMVECs play distinct roles in hantavirus persistence by creating a regulatory environment through increased Tgfβ, PD-L1, and Treg cell activity.

Decreased NK cell frequency and function is associated with increased risk of KIR3DL allele polymorphism in simian immunodeficiency virus-infected rhesus macaques with high viral loads

NK cells have been established as an important effector of innate immunity in a variety of viral infections. In HIV-1 infection in humans, alterations of NK cell function, frequency, and expression of various NK receptors have been reported to be associated with differential dynamics of disease progression. Expression of certain alleles of KIR3DL and KIR3DS receptors on NK cells was shown to correlate with levels of virus replication. In the SIV-infected rhesus macaque (RM) model of AIDS, several families of killer inhibitory Ig-related receptors (KIR receptors) corresponding to their human counterparts have been characterized, but only at the level of individual sequence variants. Here we define 14 different alleles of KIR3DL expressed among 38 SIV-infected RM, characterized by either high or low levels of SIV replication, by analyzing multiple sequences from individual animals and show an unequal distribution of certain alleles in these cohorts. High levels of SIV replication were associated with significant increases in KIR3DL mRNA levels in addition to decreases in both the frequency and function of NK cells in these animals. The higher frequency of inheritance of two KIR3DL alleles characterized by a single nucleotide polymorphism 159 H/Q was associated with RM that exhibited high plasma viral load. This data for the first time defines multiple alleles of KIR3DL in RM and shows an association between virus control, NK cell function and genetic polymorphisms of KIR receptors.