Control of lung immunopathology by prostaglandin E2

Prostaglandin E2 is generated in large quantities by stromal cells, epithelial cells, and macrophages during inflammatory responses. Using mice lacking microsomal prostaglandin E2 synthase 1 (Ptges-/- mice), we discovered that selective deficiency of prostaglandin E2 markedly exaggerates features of the type 2 inflammatory response (T2I) in the lung following repetitive intranasal challenges with an extract (Df) from the house dust mite Dermatophagoides farinae. These mice display strong mast cell activation, and high levels of cysteinyl leukotriene (cysLT) generation, and airway hyperresponsiveness. They mimic features of aspirin exacerbated respiratory disease (AERD), a severe form of asthma and sinonasal disease, when challenged with lysine aspirin or other nonselective cyclooxygenase (COX) inhibitors. Administration of selective agonists of E prostanoid 2 (EP2) and EP3 receptors, depletion of platelets, or deletion of the cysLT-generating enzyme LTC4 synthase eliminates all features of T2I and AERD in these mice. Paradoxically, endogenous PGE2 also drives a circuit to amplify macrophage expression of IL-33 through exchange protein activated by adenylate cyclase (EPAC), and Ptges-/- mice display reduced pulmonary pathology in response to challenges with antigens of the mold Alternaria.  Recent studies suggest that selective PGE2 deficiency results in prominent dysplasia of airway epithelial progenitors with altered trajectories toward goblet and tuft cell fates. Current studies use a combination of ex vivo and in vivo approaches to determine the mechanisms responsible. 


Prostaglandin E2 deficiency uncovers a dominant role for thromboxane A2 in house dust mite-induced allergic pulmonary inflammation.

Liu T, et al. Proc Natl Acad Sci U S A. 2012. PMID: 22802632

Prostaglandin E2 deficiency causes a phenotype of aspirin sensitivity that depends on platelets and cysteinyl leukotrienes.

Liu T, et al. Proc Natl Acad Sci U S A. 2013

Endogenous prostaglandin E2 amplifies IL-33 production by macrophages through an E prostanoid (EP)2/EP4-cAMP-EPAC-dependent pathway.

Samuchiwal SK, et al. J Biol Chem. 2017. PMID: 2834

Type 2 inflammatory pathways driven by the type 2 cysteinyl leukotriene receptor.

Cysteinyl leukotrienes (cyLTs) are arachidonic acid metabolites produced by myeloid cells and respiratory chemosensory cells. Well best recognized for their roles as smooth muscle constrictors, their receptors are also expressed by most hematopoietic cells. As such, cysLTs can activate mast cells, dendritic cells, group 2 innate lymphoid cells ex vivo. While many of these effects are mediated by the type 1 cysteinyl leukotriene receptor (the target of FDA-approved asthma drugs), less is known about the type 2 cysLT receptor, which in some systems inhibits CysLT1R signaling. We have found that CysLT2R plays a major role in driving the expression of the potent type 2 cytokine IL-33. Hyperleukotrienemic Ptges-/- mice show marked induction of lung IL-33 expression compared with wild-type mice after dust mite inhalation, a feature that can be mimicked by intransal administration of LTC4 to wild type mice. In both models, alveolar type 2 pneumocytes (the principal site of IL-33 expression) expand dramatically.  These effects are eliminated completely by deletion of the CysLT2 receptor, which also attenuates expansion of group 2 innate lymphoid cells and eosinophilic inflammation. Current studies are using mice with conditional deletion of CysLT2 receptors to identify the mechanisms and confirm the role of endogenous cysLTs in driving type 2 inflammation through actions at epithelial and other cell types. 


Aspirin-Exacerbated Respiratory Disease Involves a Cysteinyl Leukotriene-Driven IL-33-Mediated Mast Cell Activation Pathway.

Liu T, et al. J Immunol. 2015. PMID: 26342029

Type 2 Cysteinyl Leukotriene Receptors Drive IL-33-Dependent Type 2 Immunopathology and Aspirin Sensitivity.

Liu T, et al. J Immunol. 2018. PMID: 29282304 

The role of platelets in type 2 inflammation. 

In addition to their role in hemostasis, platelets play an important role in type 2 inflammation by incompletely understood mechanisms. Platelets possess LTC4 synthase (LTC4S), and can convert LTA4 into LTC4 by a transcellular mechanism when adherent to granulocytes, thus contributing to cysLT generation. We found remarkably large numbers of adherent platelets on circulating eosinophils, neutrophils, and monocytes in the blood of patients with AERD compared with aspirin tolerant asthmatic and healthy controls. Adherent platelets accounted for ~70% of granulocyte associated LTC4S activity and correlated strongly with urinary levels of the stable metabolite LTE4. Recently, we found that endogenously generated LTC4 potently activates platelets exclusively through CysLT2R, resulting in thromboxane and chemokine release. Notably, platelets also contain pre-formed IL-33, and can release abundant bioactive IL-33 in response to exogenous LTC4 or LTA4. Platelet adherent granulocytes are rapidly recruited to the lungs of Ptges-/- mice in response to challenge with Lysine aspirin, in concert with rapid increases in cysLT generation and lung levels of IL-33. Additionally, group 2 innate lymphoid cells (ILC2s), which are targets of both LTC4 and IL-33, expand dramatically. Depletion of platelets completely eliminates these features. Current studies use a series of novel transgenic mice with platelet-specific deletions of LTC4S, CysLT2R, and IL-33 to understand the precise mechanisms by which platelets drive features of type 2 inflammation in our mouse models, and are using biological samples from well-characterized patients with and without AERD to validate the contributions of these mechanisms to human biology. Finally, we are using both pharmacologic and molecular approaches to identify the components responsible for the selective activation of platelets by LTC4


Cysteinyl leukotriene overproduction in aspirin-exacerbated respiratory disease is driven by platelet-adherent leukocytes.

Laidlaw TM, et al. Blood. 2012. PMID: 22262771

Cysteinyl leukotriene receptor 2 drives lung immunopathology through a platelet and high mobility box 1-dependent mechanism.

Liu T, et al. Mucosal Immunol. 2019. PMID: 30664709 

Leukotriene D4 paradoxically limits LTC4-driven platelet activation and lung immunopathology.

Liu T, Barrett NA, Nagai J, Lai J, Feng C, Boyce JA.J Allergy Clin Immunol. 2020 Dec 4:S0091-6749(20)31700-0. doi: 10.1016/j.jaci.2020.10.041. Online ahead of print.PMID: 33285161

Leukotriene D4 paradoxically limits LTC4-driven platelet activation and lung immunopathology.

Mast cell activation and ontogeny

Mast cells are tissue-dwelling leukocytes thought to play a major role in mucosal type 2 immune responses. Both mast cell hyperplasia and mast cell activation are typical findings in all human allergic diseases, but little is understood about potential causative mechanisms. We have addressed these processes using a combination of ex vivo, cell sorting, and single cell genomic approaches. In a transcriptional atlas of human sinonasal tissue, mast cells are the dominant site of expression of transcripts encoding cytokines (IL-13, GM-CSF, amphiregulin) and eicosanoid synthetic enzymes (cyclooxygenase 2, prostaglandin D2 synthase, 5-lipoxygenase). Single cell genomic analysis of sorted mast cells reveal multiple transcriptionally distinct mast cell clusters reflecting a gradient of gene expression. Clusters corresponding to histochemically distinct mast cells expressing tryptase without chymase (“MCT”) and mast cells expressing both tryptase and chymase (“MCTC”) are at opposite poles of a transcriptional continuum, differing by ~300 transcripts. A novel population of transitional mast cells with a high rate of proliferation and distinct cell surface phenotype (KithiCD38hi) is strongly enriched in nasal polyp tissue, especially in AERD, where mast cell expansion, hyperplasia, and activation are especially dramatic. Ex vivo approaches suggest strong influences from innate cytokines (IL-33, thymic stromal lymphopoietin) as well as other factors from regional stromal cells. Ongoing collaborative studies use CITE-Seq combined with ex vivo modeling and gene editing to identify the drivers of mast cell expansion, diversity, and function in type 2 immunopathology. 


Thymic stromal lymphopoietin controls prostaglandin D2 generation in aspirin-exacerbated respiratory disease

Kathleen M. Buchheit, Katherine N. Cahill, Howard R. Katz, Katherine C. Murphy, Chunli Feng, Kathleen Lee-Sarwar, Juying Lai, Neil Bhattacharyya, Elliot Israel, Joshua A. Boyce, Tanya M. Laidlaw

J Allergy Clin Immunol. Author manuscript; available in PMC 2017 May 1.

Published in final edited form as: J Allergy Clin Immunol. 2016 May; 137(5): 1566–1576.e5. Published online 2015 Dec 12. doi: 10.1016/j.jaci.2015.10.020

Allergic inflammatory memory in human respiratory epithelial progenitor cells.

Nature. 2018 Aug;560(7720):649-654. doi: 10.1038/s41586-018-0449-8. Epub 2018 Aug 22

Human airway mast cells proliferate and acquire distinct inflammation-driven phenotypes during type 2 inflammation.

Dwyer DF, Ordovas-Montanes J, Allon SJ, Buchheit KM, Vukovic M, Derakhshan T, Feng C, Lai J, Hughes TK, Nyquist SK, Giannetti MP, Berger B, Bhattacharyya N, Roditi RE, Katz HR, Nawijn MC, Berg M, van den Berge M, Laidlaw TM, Shalek AK, Barrett NA, Boyce JA.Sci Immunol. 2021 Feb 26;6(56):eabb7221. doi: 10.1126/sciimmunol.abb7221.

Purinergic type 6 receptor signaling in pulmonary inflammation.

In addition to their role in nucleic acid synthesis, nucleotides serve as extracellular danger sensors, being released from activated or injured cells and signaling through G protein coupled purinergic (P2Y) receptors and ion channels (P2X). Uridine diphosphate (UDP) is released into the alveolar space rapidly following the intransal administration of house dust mite allergens. Deletion of the UDP-selective P2Y6 receptor before dust mite sensitization, but not afterward, sharply increases the level of pulmonary eosinophilia and type 2 cytokines generated in response to subsequent dust mite challenge in sensitized mice. Alveolar macrophage-intrinsic expression of P2Y6 receptors mediates an innate, IL-12-induced pathway resulting in the recruitment and activation of interferon gamma-expressing natural killer (NK) cells to the alveolar space. Depletion or deletion of NK cells eliminates the protective effect of P2Y6 receptor signaling. Notably, clinically active cysteinyl leukotriene 1 receptor antagonists block P2Y6 receptor signaling in vivo, eliminating the protective effect of UDP/P2Y6 at sensitization. Thus, UDP/P2Y6 signaling prevents inappropriate activation of the type 2 immune system to clinically relevant antigens. The blockade of P2Y6 receptors by clinically available CysLT1R antagonists may account for the highly variable efficacy of these drugs in the treatment of asthma. Ongoing studies focus on the mechanisms responsible for IL-12 induction by P2Y6 signaling, and the function of P2Y6 receptors on epithelial and dendritic cell populations using targeted deletions.


P2Y6 signaling in alveolar macrophages prevents leukotriene-dependent type 2 allergic lung inflammation.

Nagai J, Balestrieri B, Fanning LB, Kyin T, Cirka H, Lin J, Idzko M, Zech A, Kim EY, Brennan PJ, Boyce JA.J Clin Invest. 2019 Dec 2;129(12):5169-5186. doi: 10.1172/JCI129761.PMID: 31638598