A close interaction between the virus SARS-CoV-2 and the immune system of an individual results in a diverse clinical manifestation of the COVID-19 disease. While adaptive immune responses are essential for SARS-CoV-2 virus clearance, the innate immune cells, such as macrophages, may contribute, in some cases, to the disease progression. Macrophages have shown a significant production of IL-6, suggesting they may contribute to the excessive inflammation in COVID-19 disease. Macrophage Activation Syndrome may further explain the high serum levels of CRP, which are normally lacking in viral infections. In adaptive immune responses, it has been revealed that cytotoxic CD8+ T cells exhibit functional exhaustion patterns, such as the expression of NKG2A, PD-1, and TIM-3. Since SARS-CoV-2 restrains antigen presentation by downregulating MHC class I and II molecules and, therefore, inhibits the T cell-mediated immune responses, humoral immune responses also play a substantial role. Specific IgA response appears to be stronger and more persistent than the IgM response. Moreover, IgM and IgG antibodies show similar dynamics in COVID-19 disease.

Mast cells, activated by antigen via the high affinity receptor for IgE (FcεRI), release an array of pro-inflammatory mediators that contribute to allergic disorders such as asthma and anaphylaxis. The KIT ligand, stem cell factor (SCF), is critical for mast cell expansion, differentiation and survival, and, under acute conditions, enhances mast cell activation. However, extended SCF exposure in vivo conversely protects against fatal antigen-mediated anaphylaxis. In investigating this dichotomy, we identified a novel mode of regulation of the mast cell activation phenotype through SCF-mediated programming. We found that mouse bone marrow-derived mast cells chronically exposed to SCF displayed a marked attenuation of FcεRI-mediated degranulation and cytokine production. The hypo-responsive phenotype was not a consequence of altered signals regulating calcium flux or protein kinase C, but of ineffective cytoskeletal reorganization, with evidence implicating a down-regulation of expression of the Src kinase Hck. Collectively, these findings demonstrate a major role for SCF in the homeostatic control of mast cell activation with potential relevance to mast cell-driven disease and the development of novel approaches for the treatment of allergic disorders.

Increased mast cell burden is observed in the inflamed tissues and affected organs and tissues of patients with mast cell proliferative disorders. However, normal mast cells participate in host defense, so approaches to preferentially target clonally expanding mast cells are needed. We found that mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) are up-regulated in neoplastic and developing immature mast cells compared with their terminally differentiated counterparts. Elevated mTOR mRNA was also observed in bone marrow mononuclear cells of patients exhibiting mast-cell hyperplasia. Selective inhibition of mTORC1 and mTORC2 through genetic and pharmacologic manipulation revealed that, whereas mTORC1 may contribute to mast-cell survival, mTORC2 was only critical for homeostasis of neoplastic and dividing immature mast cells. The cytostatic effect of mTORC2 down-regulation in proliferating mast cells was determined to be via inhibition of cell-cycle progression. Because mTORC2 was observed to play little role in the homeostasis of differentiated, nonproliferating, mature mast cells, these data provide a rationale for adopting a targeted approaching selectively inhibiting mTORC2 to effectively reduce the proliferation of mast cells associated with inflammation and disorders of mast cell proliferation while leaving normal differentiated mast cells largely unaffected. IntroductionMast cells (MCs) are considered to be critical components of both the innate and acquired immune defense systems. 1 Central to these functions is the ability of MCs to release a plethora of inflammatory mediators after activation through cell-surface receptors, primarily the high-affinity receptors for IgE (Fc⑀RI). 2 Although these reactions are considered to have evolved to protect host organisms against invading parasites and other microorganisms, 3 inappropriate or exaggerated activation of MCs manifests the reactions associated with allergic diseases.MCs develop from bone marrow (BM) CD13 ϩ /CD34 ϩ /CD117 (KIT) ϩ progenitor cells that enter into circulation and mature during migration to and residency in their target tissues. 4 MC numbers within tissues appear to be tightly regulated, with a several-fold increase in numbers occurring in inflammatory conditions and even higher numbers in association with parasitic inflammation. Clonal MC disorders may result in 10-fold or greater numbers of MCs in tissues such as the BM, liver, and spleen. [5][6] Similarly, a dysregulated increase in MC numbers is also observed in certain types of cancer, and in that context may contribute to cancer progression. [7][8][9] We observed previously that the mammalian target of rapamycin (mTOR) is overexpressed and constitutively phosphorylated in neoplastic MCs regardless of whether activating mutations in the MC growth factor receptor KIT are present. 10 MTOR is a serine/ threonine kinase that regulates divergent signaling pathways depending on its interactions with 2 regulatory proteins: raptor, a major component of mTOR complex 1 (mTORC1), a...

The exposure of phosphatidylserine (PS) on the cell surface is a general marker of apoptotic cells. Non-apoptotic PS externalization is induced by several activation stimuli, including engagement of immunoreceptors. Immune cells can also be activated by aggregation of glycosylphosphatidylinositol-anchored proteins (GPI-APs). However, it is unknown whether cell triggering through these proteins, lacking transmembrane and cytoplasmic domains, also leads to PS externalization. Here we show that engagement of GPI-APs in rodent mast cells induces a rapid and reversible externalization of PS by a non-apoptotic mechanism. PS externalization triggered by GPI-AP-specific monoclonal antibodies was dependent on the activity of H ؉ -ATP synthase and several other enzymes involved in mast cell signaling but was independent of cell degranulation, free cytoplasmic calcium up-regulation, and a decrease in lipid packing as determined by merocyanine 540 binding. Surprisingly, disruption of actin cytoskeleton by latrunculin B or plasma membrane integrity by methyl-␤-cyclodextrin had opposite effects on PS externalization triggered through GPI-AP or the high affinity IgE receptor. We further show that PS externalization mediated by GPI-APs was also observed in some other cells, and its extent varied with antibodies used. Interestingly, effects of different antibodies on PS externalization were additive, indicating that independent stimuli converge onto a signaling pathways leading to PS externalization. Our findings identify the cell surface PS exposure induced through GPI-AP as a distinct mechanism of cell signaling. Such a mechanism could contribute to "inside-out" signaling in response to pathogens and other external activators and/or to initiation of other functions associated with PS externalization.The plasma membrane exhibits a marked asymmetry in transbilayer distribution of phospholipids. Aminophospholipids, including phosphatidylserine (PS), 2 are usually restricted to the inner leaflet of the membrane. This phospholipid asymmetry is maintained by activity of energy-dependent flippases and floppases that mediate, respectively, inward-directed and outward-directed transfer of phospholipids (1-3). Furthermore, equilibration of phospholipids between the two plasma membrane leaflets seems to be regulated by lipid scramblase, which facilitates bi-directional migration of phospholipids across the bilayer (4, 5). In response to some stimuli, the phospholipid asymmetry is lost, and PS is translocated to the exoplasmic leaflet of plasma membrane (6). Externalized PS is observed in apoptotic, injured, infected, senescent, or necrotic cells and becomes a target for recognition by phagocytes (7-11). PS externalization is also detected at certain stages of cell development (12) and in the course of activation of immune cells by different stimuli, including engagement of immunoreceptors (13-16).It has been described that PS externalization is triggered by stimuli enhancing the concentration of free cytoplasmic calcium, which regulates ...

SUMMARY IL-33 is elevated in afflicted tissues of patients with mast cell-dependent chronic allergic diseases. Based on its acute effects on mouse mast cells (MCs), IL-33 is thought to play a role in the pathogenesis of allergic disease through MC activation. However, the manifestations of prolonged IL-33 exposure on human MC function, which best reflect the conditions associated with chronic allergic disease, are unknown. We now find that long-term exposure of human and mouse MCs to IL-33 results in a substantial reduction of MC activation in response to antigen. This reduction required >72 h exposure to IL-33 for onset and 1–2 wk for reversion following IL-33 removal. This hypo-responsive phenotype was determined to be a consequence of MyD88-dependent attenuation of signaling processes necessary for MC activation including antigen-mediated calcium mobilization and cytoskeletal reorganization; potentially as a consequence of down-regulation of the expression of PLCγ1 and Hck. These findings suggest that IL-33 may play a protective, rather than a causative role in MC activation under chronic conditions and, furthermore, reveal regulated plasticity in the MC activation phenotype. The ability to down-regulate MC activation in this manner may provide alternative approaches for treatment of MC-driven disease.

TRAIL (tumor-necrosis factor related apoptosis-inducing ligand, CD253) and its death receptors TRAIL-R1 and TRAIL-R2 selectively trigger the apoptotic cell death in tumor cells. For that reason, TRAIL has been extensively studied as a target of cancer therapy. In spite of the promising preclinical observations, the TRAIL–based therapies in humans have certain limitations. The two main therapeutic approaches are based on either an administration of TRAIL-receptor (TRAIL-R) agonists or a recombinant TRAIL. These approaches, however, seem to elicit a limited therapeutic efficacy, and only a few drugs have entered the phase II clinical trials. To deliver TRAIL-based therapies with higher anti-tumor potential several novel TRAIL-derivates and modifications have been designed. These novel drugs are, however, mostly preclinical, and many problems continue to be unraveled. We have reviewed the current status of all TRAIL-based monotherapies and combination therapies that have reached phase II and phase III clinical trials in humans. We have also aimed to introduce all novel approaches of TRAIL utilization in cancer treatment and discussed the most promising drugs which are likely to enter clinical trials in humans. To date, different strategies were introduced in order to activate anti-tumor immune responses with the aim of achieving the highest efficacy and minimal toxicity.In this review, we discuss the most promising TRAIL-based clinical trials and their therapeutic strategies.

Background: Chemotaxis is regulated by chemoattractants and poorly understood intrinsic regulators. Results: Aggregation of tetraspanin CD9 leads to activation of mast cells and inhibition of their antigen-driven chemotaxis. Conclusion: Chemotaxis toward antigen involves cross-talk between immunoreceptor, CD9, transmembrane adaptor proteins, and cytoskeleton-regulatory proteins. Significance: Tetraspanin CD9 is defined as a novel regulator of mast cell chemotaxis.

Upregulated Wnt/β-catenin signaling is associated with increased cancer cell resistance and cancer cell-elicited immunosuppression. In non-neoplastic immune cells, upregulated Wnt/β-catenin is, however, associated with either immunosuppression or immunostimulation. Therefore, it is difficult to predict the therapeutic impact inhibitors of Wnt/β-catenin signaling will have when combined with cancer immunotherapy. Here, we evaluated the benefit(s) of the Wnt/β-catenin signaling inhibitor XAV939 in the in vitro elimination of LNCaP prostate cancer cells when cocultured with lymphocytes from patients with localized biochemically recurrent prostate cancer (BRPCa). We found that 5 µM XAV939 inhibited β-catenin translocation to the nucleus in LNCaP cells and CD4+ BRPCa lymphocytes without affecting their proliferation and viability. Preconditioning BRPCa lymphocytes with 5 µM XAV939 accelerated the elimination of LNCaP cells during the coculturing. However, during subsequent re-coculturing with fresh LNCaP cells, BRPCa lymphocytes were no longer able to eliminate LNCaP cells unless coculturing and re-coculturing were performed in the presence of 5 µM XAV939. Comparable results were obtained for PC-3 prostate cancer cells. These findings provide a rationale for combining cell-based immunotherapy of PCa with inhibitors of Wnt/β-catenin signaling.