Respiratory Syncytial Virus Infection, TLR3 Ligands, and Proinflammatory Cytokines Induce CD161 Ligand LLT1 Expression on the Respiratory Epithelium

Abstract

During respiratory-virus infection, excessive lymphocyte activation can cause pathology both in acute infection and in exacerbations of chronic respiratory diseases. The costimulatory molecule CD161 is expressed on lymphocyte subsets implicated in promoting respiratory inflammation, including Th2, Th17, mucosally associated invariant T (MAIT) cells, and type 2 innate lymphoid cells. We asked whether the CD161 ligand LLT1 could be expressed on respiratory epithelial cells following respiratory-virus infection as a mechanism by which respiratory-virus infection could promote activation of proinflammatory lymphocytes. In response to respiratory syncytial virus (RSV) infection, expression of LLT1 was upregulated in the BEAS-2B respiratory epithelial cell line and primary human bronchial epithelial cells. Imaging studies revealed that LLT1 expression increased in both RSV-infected and cocultured uninfected cells, suggesting that soluble factors produced during infection stimulate LLT1 expression. TLR3 and TLR2/6 ligands led to a rapid increase in LLT1 mRNA in respiratory epithelial cells, as did the proinflammatory cytokines type I interferons, interleukin 1β (IL-1β), and tumor necrosis factor alpha (TNF-α), which are produced early in respiratory-virus infection. Immunohistochemistry confirmed the increase in LLT1 protein on the epithelial cell surface, and live-cell confocal microscopy demonstrated accumulation of epithelial LLT1 at synapses formed with CD161+ T lymphocytes. LLT1 expression by the respiratory epithelium in response to respiratory-virus infection and inflammatory cytokines represents a novel link between innate immunity and lymphocyte activation. As a regulator of CD161+ proinflammatory lymphocytes, LLT1 could be a novel therapeutic target in inflammation caused by respiratory-virus infection.IMPORTANCE The immune response to respiratory-virus infection is essential for clearing the pathogen but, if excessive, can lead to tissue damage and obstruction of the airways. How viral infection activates immune cells in the lungs is not fully understood. Here, we show that LLT1 can be expressed in lung cells in response to infection. LLT1 triggers CD161, a receptor on inflammatory immune cells. This mechanism may promote activation of immune cells in the lungs in viral infection and could be a novel target for therapies aimed at reducing lung inflammation.

Bovine Brain Ribonuclease Is the Functional Homolog of Human Ribonuclease 1

“…Most viruses produce dsRNA at some point during their replication. In mammalian cells, dsRNA is a potent antigen recognized by sensors such as Toll-like receptor (TLR) 3, through which dsRNA can trigger the transcription-based antiviral interferon response (57,58). We found that stimulating endothelial cells with the dsRNA substrate poly(A:U), as well as with the synthetic viral dsRNA analog poly(I:C), increased the secretion of both RNase 1 and BRB significantly, whereas treatment with ssRNA or DNA did not.…”

Functional characterization of a conserved pair of NKR‐P1 receptors expressed by NK cells and T lymphocytes in liver and gut

“…LLT1 is not expressed by resting cells but is upregulated on the surface of various leukocytes upon activation [22,23]. It is also induced in epithelial cells in the lung following RSV infection or activation with proinflammatory cytokines or TLR3 ligands [24]. NKR-P1A has a clear inhibitory effect on human NK-cell functions.…”

Steroid-induced Deficiency of Mucosal-associated Invariant T Cells in the Chronic Obstructive Pulmonary Disease Lung. Implications for Nontypeable Haemophilus influenzae Infection

“…H. influenzae expresses the riboflavin biosynthetic pathway from which the MAIT-cell ligands are derived (30). The costimulatory molecule CD161 is a key expression marker for MAIT cells, which can recognize the ligand lectin-like transcript 1 (LLT1) expressed by respiratory epithelial cells in response to infection and proinflammatory cytokines (48). H. influenzae can invade the lung tissue (49,50) and enter respiratory epithelial cells and macrophages in chronic bronchitis (6)(7)(8)51).…”