Lung megakaryocytes are immune modulatory cells
Daphne N. Pariser, … , James Palis, Craig N. Morrell
Daphne N. Pariser, … , James Palis, Craig N. Morrell
Published October 20, 2020
Citation Information: J Clin Invest. 2021;131(1):e137377. https://doi.org/10.1172/JCI137377.
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Research Article Hematology Inflammation

Lung megakaryocytes are immune modulatory cells

Abstract

Although platelets are the cellular mediators of thrombosis, they are also immune cells. Platelets interact both directly and indirectly with immune cells, impacting their activation and differentiation, as well as all phases of the immune response. Megakaryocytes (Mks) are the cell source of circulating platelets, and until recently Mks were typically only considered bone marrow–resident (BM-resident) cells. However, platelet-producing Mks also reside in the lung, and lung Mks express greater levels of immune molecules compared with BM Mks. We therefore sought to define the immune functions of lung Mks. Using single-cell RNA sequencing of BM and lung myeloid-enriched cells, we found that lung Mks, which we term MkL, had gene expression patterns that are similar to antigen-presenting cells. This was confirmed using imaging and conventional flow cytometry. The immune phenotype of Mks was plastic and driven by the tissue immune environment, as evidenced by BM Mks having an MkL-like phenotype under the influence of pathogen receptor challenge and lung-associated immune molecules, such as IL-33. Our in vitro and in vivo assays demonstrated that MkL internalized and processed both antigenic proteins and bacterial pathogens. Furthermore, MkL induced CD4+ T cell activation in an MHC II–dependent manner both in vitro and in vivo. These data indicated that MkL had key immune regulatory roles dictated in part by the tissue environment.

Authors

Daphne N. Pariser, Zachary T. Hilt, Sara K. Ture, Sara K. Blick-Nitko, Mark R. Looney, Simon J. Cleary, Estheany Roman-Pagan, Jerry Saunders II, Steve N. Georas, Janelle Veazey, Ferralita Madere, Laura Tesoro Santos, Allison Arne, Nguyen P.T. Huynh, Alison C. Livada, Selena M. Guerrero-Martin, Claire Lyons, Kelly A. Metcalf-Pate, Kathleen E. McGrath, James Palis, Craig N. Morrell

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Figure 1

Lung and BM Mks are phenotypically distinct.

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Lung and BM Mks are phenotypically distinct. (A) Mks are present in the ...
(A) Mks are present in the lung. Lung sections from WT mice, TPOR–/– mice, and macaques were immunostained with anti-CD42c antibody (mouse tissue) or anti-CD41 (macaque). Mks were noted in WT mouse and primate lungs (representative images). Original magnification, ×40. (B) Mks are both intravascular and extravascular in the lung. Tissue and vascular discrimination between the lung Mks using anti-CD41 BV421 and BV786 by flow cytometry (unpaired t test). (C) BM Mk ploidy is greater than that of lung Mks. BM and lung Mk ploidy determined by flow cytometry (2-way ANOVA with Šidák’s multiple-comparison test). (D) The percentage of Mks relative to DCs in digested and single-cell resuspended lung tissue. Approximately 2% are Mks compared with 7% resident lung DCs (CD103+CD11b+). (E) Lung and BM Mks upregulate P-selectin (CD62P) in response to thrombin. Isolated lung and BM Mks were stimulated with 1 U/mL thrombin and CD62P surface expression determined by flow cytometry as a marker of degranulation (unpaired t test). (F) Lung Mks produce platelets in vitro. FRET imaging was used to obtain images of proplatelet production from both BM and lung Mks in culture. The red arrows indicate proplatelet formation, while the black arrows indicate an Mk. (G) Flow cytometry confirmation of platelet production in the Mk cultures. Freshly isolated mouse platelets were used as a control. *P = 0.01 to 0.05; **P = 0.001 to 0.01; ***P = 0.0001 to 0.001; ****P < 0.0001.