Carnosic acid inhibits secretion of allergic inflammatory mediators in IgE-activated mast cells via direct regulation of Syk activation

Mast cells are essential regulators of inflammation most recognized for their central role in allergic inflammatory disorders. Signaling via the high-affinity immunoglobulin E (IgE) receptor, FcεRI, leads to rapid degranulation of preformed granules and the sustained release of newly-synthesized pro-inflammatory mediators. Our group recently established rosemary extract (RE) as a potent regulator of mast cell functions, attenuating MAPK and NF-κB signaling. Carnosic acid (CA)-a major polyphenolic constituent of RE-has been shown to exhibit anti-inflammatory effects in other immune cell models, but its role as a potential modulator of mast cell activation is undefined. Therefore, we sought here to determine the modulatory effects of CA in a mast cell model of allergic inflammation. We sensitized bone marrow-derived mast cells (BMMCs) with anti-trinitrophenyl (TNP) IgE and activated with allergen (TNP-BSA) under stem cell factor (SCF) potentiation, in addition to treatment with CA. Our results indicate that CA significantly inhibits allergen-induced early phase responses including Ca²⁺ mobilization, ROS production, and subsequent degranulation. We also show CA treatment reduced late phase responses, including the release of all cytokines and chemokines examined following IgE stimulation, and corresponding gene expression excepting that of CCL2. Importantly, we determined that CA mediates its inhibitory effects through modulation of tyrosine kinase Syk and downstream effectors TAK1 (Ser412) and Akt (Ser473) as well as NF-κB signaling, while phosphorylation of FcεRI (γ chain) and MAPK proteins remained unaltered. These novel findings establish CA as a potent modulator of mast cell activation, warranting further investigation as a putative anti-allergy therapeutic.

Out of the frying pan and into the fire? Due diligence warranted for ADE in COVID-19

Antibody-dependent enhancement (ADE) is an atypical immunological paradox commonly associated with dengue virus re-infection. However, various research models have demonstrated this phenomenon with other viral families, including Coronaviridae. Recently, ADE in SARS-CoV-2 has emerged as one hypothesis to explain severe clinical manifestations. Whether SARS-CoV-2 is augmented by ADE remains undetermined and has therefore garnered criticism for the improper attribution of the phenomenon to the pandemic. Thus, critical evaluation of ADE in SARS-CoV-2 vaccine development will be indispensable to avoid a global setback and the erosion of public trust.

Zika virus infection of mast cells is not associated with a degranulation response

Dengue virus (DENV) infection is augmented by a process called antibody-dependent enhancement (ADE), in which pre-existing DENV immunity can render an individual more susceptible to a subsequent DENV exposure. Based on Zika virus (ZIKV) and DENV structural similarities, emerging evidence suggests anti-DENV antibodies can cross-react with ZIKV at non-neutralizing levels characteristic of ADE. Mast cells (MC), sentinel white blood cells integral in coordinating early immune defences, have been identified as a principle contributor to DENV vascular leakage. This clinical manifestation is attributed to significant histamine release caused by MC degranulation, a characteristic MC activation response. However, to our knowledge ZIKV-MC interactions remain unexplored. MC responses to virus can be modelled in vitro, including via use of the well-characterized KU812 cell line which express Fcγ receptors. Here, we sought to determine if the KU812 MC is susceptible to (1) direct ZIKV infection; and (2) ADE in the presence of anti-DENV antibodies that cross-react with ZIKV. A significant increase in viral titre (104 PFU/mL) was detected, by plaque assay, in MC directly infected with ZIKV compared to MC infected with UV-inactivated ZIKV (0 PFU/mL). Furthermore, a significant viral titre (106 PFU/mL) was detected in MC infected with ZIKV pre-incubated with anti-DENV antibodies when compared to MC infected with ZIKV pre-incubated with isotype control antibodies (104 PFU/mL). Furthermore, unlike DENV induced degranulation of MC, ZIKV did not activate a degranulation response in this model or in a primary murine model. Therefore, MC may be a contributor in ZIKV pathogenesis without the classical degranulation response seen in DENV infected MC.

Decoding communication patterns of the innate immune system by quantitative proteomics

The innate immune system is a collective network of cell types involved in cell recruitment and activation using a robust and refined communication system. Engagement of receptor-mediated intracellular signaling initiates communication cascades by conveying information about the host cell status to surrounding cells for surveillance and protection. Comprehensive profiling of innate immune cells is challenging due to low cell numbers, high dynamic range of the cellular proteome, low abundance of secreted proteins, and the release of degradative enzymes (e.g., proteases). However, recent advances in mass spectrometry-based proteomics provides the capability to overcome these limitations through profiling the dynamics of cellular processes, signaling cascades, post-translational modifications, and interaction networks. Moreover, integration of technologies and molecular datasets provide a holistic view of a complex and intricate network of communications underscoring host defense and tissue homeostasis mechanisms. In this Review, we explore the diverse applications of mass spectrometry-based proteomics in innate immunity to define communication patterns of the innate immune cells during health and disease. We also provide a technical overview of mass spectrometry-based proteomic workflows, with a focus on bottom-up approaches, and we present the emerging role of proteomics in immune-based drug discovery while providing a perspective on new applications in the future.