Pulmonary natural killer cells control neutrophil intravascular motility and response to acute inflammation

Abstract

The pulmonary immune system defends a huge surface area directly in contact with the contents of the air we breathe. Neutrophils, the most abundant immune cell in the pulmonary vasculature, are critical to immunity but they are also capable of generating life-threatening pathology. Natural Killer cells are the most highly represented lymphocyte subset in the lung, but relatively little is known about their localization, motility or the specific mechanisms by which they contribute to local homeostasis. Here, we used lung-intravital microscopy to directly visualise and quantify neutrophil and natural killer cell dynamics in the pulmonary vasculature of live mice. This approach revealed unexpected sessile behaviour by intravascular natural killer cells. Interactions with natural killer cells made neutrophils scan the endothelium more slowly over larger distances and reduced the number of neutrophils that accumulated in an LPS-triggered inflammatory challenge. This represents a new paradigm by which natural killer cells contribute to lung physiology by diminishing potentially pathogenic neutrophil accumulation.

Functional visualization of NK cell-mediated killing of metastatic single tumor cells

“…We first assessed the localization of NK cells by intravascular staining with αCD45 antibody (Anderson et al, 2014), followed by flow cytometry with αCD45, αCD3, and αNKp46 antibodies (Figure 2-figure supplement 1). Consistent with previous reports (Gasteiger et al, 2015, Secklehner et al, 2019, more than 95% of pulmonary NK cells (CD45 + , CD3 -, NKp46 + ) were found in the vasculature, compared to 20% of bone marrow NK cells. To study the dynamics of NK cell-mediated immune surveillance in the lung, we developed a reporter line, NK-tdTomato mice, whose NK cells, or more specifically, NKp46 + cells (Narni-Mancinelli et al, 2011), express the fluorescent protein tdTomato.…”

“…Given this sequence of events, it is unknown where NK cell attack on the malignant cells giving rise to a metastatic lesion takes place. Using a newly developed method of intravascular staining of immune cells (Anderson et al, 2014), it was shown that more than 90% of NK cells in the mouse lung are in the vasculature (Secklehner et al, 2019). In agreement with this finding, the major NK cell subset in the lung is similar to that in the peripheral blood (Hayakawa & Smyth, 2006, Marquardt et al, 2017.…”

The Potential Effect of Novel Coronavirus SARS-CoV-2 on NK Cells; A Perspective on Potential Therapeutic Interventions

“…Neutrophils are the most abundant white blood cells in the lung, and they are critical effectors against infections, in particular against bacterial infections, however they are also capable of inducing life-threatening morbidities. Moreover, Natural Killer cells are the most abundant lymphocytes in the lung, and therefore, play an important role not only in curtailment of infection but also in exertion of significant regulatory effect (21). However, little is known regarding the specific mechanisms by which NK cells maintain local homeostasis.…”

“…However, little is known regarding the specific mechanisms by which NK cells maintain local homeostasis. By using lung-intravital microscopy to directly visualize and quantify neutrophil and natural killer cell interaction within the lung of live mice, the authors reported in a preliminary study that NK cells were greatly responsible for the slower pace of scanning of endothelium by neutrophils over a large area, and they were able to reduce the number of neutrophils that accumulated in an LPS-triggered inflammatory challenge (21). Indeed, depletion of NK cells in mice exhibited severe respiratory distress associated with protein-rich, high-permeability alveolar edema accompanied by neutrophil infiltration in myocardial infarction model (22).…”