Protein Tyrosine Kinase Fyn Regulates TLR4-Elicited Responses on Mast Cells Controlling the Function of a PP2A-PKCα/ß Signaling Node Leading to TNF Secretion.

Mast cells produce proinflammatory cytokines in response to TLR4 ligands, but the signaling pathways involved are not fully described. In this study, the participation of the Src family kinase Fyn in the production of TNF after stimulation with LPS was evaluated using bone marrow-derived mast cells from wild-type and Fyn-deficient mice. Fyn(-/-) cells showed higher LPS-induced secretion of preformed and de novo-synthesized TNF. In both cell types, TNF colocalized with vesicle-associated membrane protein (VAMP)3-positive compartments. Addition of LPS provoked coalescence of VAMP3 and its interaction with synaptosomal-associated protein 23; those events were increased in the absence of Fyn. Higher TNF mRNA levels were also observed in Fyn-deficient cells as a result of increased transcription and greater mRNA stability after LPS treatment. Fyn(-/-) cells also showed higher LPS-induced activation of TAK-1 and ERK1/2, whereas IκB kinase and IκB were phosphorylated, even in basal conditions. Increased responsiveness in Fyn(-/-) cells was associated with a lower activity of protein phosphatase 2A (PP2A) and augmented activity of protein kinase C (PKC)α/ß, which was dissociated from PP2A and increased its association with the adapter protein neuroblast differentiation-associated protein (AHNAK, desmoyokin). LPS-induced PKCα/ß activity was associated with VAMP3 coalescence in WT and Fyn-deficient cells. Reconstitution of MC-deficient Wsh mice with Fyn(-/-) MCs produced greater LPS-dependent production of TNF in the peritoneal cavity. Our data show that Fyn kinase is activated after TLR4 triggering and exerts an important negative control on LPS-dependent TNF production in MCs controlling the inactivation of PP2Ac and activation of PKCα/ß necessary for the secretion of TNF by VAMP3(+) carriers.

Chemokine-Derived Peptides: Novel Antimicrobial and Antineoplasic Agents.

Chemokines are a burgeoning family of chemotactic cytokines displaying a broad array of functions such as regulation of homeostatic leukocyte traffic and development, as well as activating the innate immune system. Their role in controlling early and late inflammatory stages is now well recognized. An improper balance either in chemokine synthesis or chemokine receptor expression contributes to various pathological disorders making chemokines and their receptors a useful therapeutic target. Research in this area is progressing rapidly, and development of novel agents based on chemokine/ chemokine receptors antagonist functions are emerging as attractive alternative drugs. Some of these novel agents include generation of chemokine-derived peptides (CDP) with potential agonist and antagonist effects on inflammation, cancer and against bacterial infections. CDP have been generated mainly from N- and C-terminus chemokine sequences with subsequent modifications such as truncations or elongations. In this review, we present a glimpse of the different pharmacological actions reported for CDP and our current understanding regarding the potential use of CDP alone or as part of the novel therapies proposed in the treatment of microbial infections and cancer.

Oral immunotherapy induces IgG antibodies that act through FcγRIIb to suppress IgE-mediated hypersensitivity.

BACKGROUND: Food-induced anaphylaxis is triggered by specific IgE antibodies. Paradoxically, some subjects with significant IgE levels can ingest allergenic foods without incident. Similarly, subjects completing oral immunotherapy (OIT) tolerate food challenges despite persistent high-titer food-specific IgE. OBJECTIVE: We sought to test whether IgG antibodies induced by food immunotherapy prevent food-induced anaphylaxis and whether this occurs through the inhibitory receptor FcγRIIb. METHODS: Food allergy-susceptible Il4raF709 mice were enterally sensitized to ovalbumin (OVA). Similarly sensitized IgE-deficient (IgE(-/-)) Il4raF709 mice, which can ingest OVA without anaphylaxis, were subjected to a high-dose enteral OVA desensitization protocol (OIT). Sera from both groups were tested for the ability to activate or inhibit bone marrow mast cells (BMMCs) exposed to allergen or to passively transfer allergy to naive hosts. In parallel experiments sera obtained from patients with peanut allergy before and after undergoing OIT were interrogated for their ability to enhance or suppress peanut-induced activation in an indirect assay by using basophils from nonallergic donors. RESULTS: Il4raF709 mice exhibited strong OVA-specific IgE responses. Their sera efficiently sensitized BMMCs for activation by antigen challenge. Sera from Il4raF709/IgE(-/-) mice subjected to OVA OIT suppressed BMMC responses. This inhibition was IgG mediated and FcγRIIb dependent. Similarly, pre-OIT but not post-OIT sera from patients efficiently sensitized basophils for peanut-induced activation. IgG antibodies in post-OIT sera suppressed basophil activation by pre-OIT sera. This inhibition was blocked by antibodies against FcγRII. CONCLUSION: Food-specific IgG antibodies, such as those induced during OIT, inhibit IgE-mediated reactions. Strategies that favor IgG responses might prove useful in the management of food allergy.

IgE-dependent sensitization increases responsiveness to LPS but does not modify development of endotoxin tolerance in mast cells.

OBJECTIVE: Effects of immunoglobulin E (IgE)-dependent sensitization on the response to bacterial lipopolysaccharide (LPS) were analyzed in mast cells. METHODS: Murine bone marrow-derived mast cells (BMMCs) were sensitized or not with IgE before stimulation with LPS. TLR4 and co-receptors expression was analyzed by flow cytometry and RT-PCR, TNF-α production by ELISA, IKK and IκB activation by western blot or immunoprecipitation. NFκB nuclear translocation was determined by EMSA. RESULTS: IgE-sensitized BMMCs secreted larger amounts of TNF-α than non-sensitized cells shortly after LPS challenge. No change in TLR4, CD14 or MD-2 expression was detected after the IgE-dependent sensitization process, whereas TLR4-dependent phosphorylation of IKK and IκB was augmented. IgE-dependent sensitization increased basal NFκB activity. Endotoxin tolerance was not affected by the IgE-dependent sensitization process. CONCLUSIONS: IgE-induced sensitization primes mast cells for higher response to LPS through pre-activation of NFκB transcription factor. IgE-dependent sensitization does not modify events leading to endotoxin tolerance.

Angiotensin II increases mRNA levels of all TGF-beta isoforms in quiescent and activated rat hepatic stellate cells.

AII (angiotensin II) is a vasoactive peptide that plays an important role in the development of liver fibrosis mainly by regulating profibrotic cytokine expression such as TGF-beta (transforming growth factor-beta). Activated HSCs (hepatic stellate cells) are the major cell type responsible for ECM (extracellular matrix) deposition during liver fibrosis and are also a target for AII and TGF-beta actions. Here, we studied the effect of AII on the mRNA levels of TGF-beta isoforms in primary cultures of rat HSCs. Both quiescent and activated HSCs were stimulated with AII for different time periods, and mRNA levels of TGF-beta1, TGF-beta2 and TGF-beta3 isoforms were evaluated using RNaseI protection assay. The mRNA levels of all TGF-beta isoforms, particularly TGF-beta2and TGF-beta3, were increased after AII treatment in activated HSCs. In addition, activated HSCs were able to produce active TGF-beta protein after AII treatment. The mRNA expression of TGF-beta isoforms induced by AII required both ERK1/2 and Nox (NADPH oxidase) activation but not PKC (protein kinase C) participation. ERK1/2 activation induced by AII occurs via AT1 receptors, but independently of either PKC and Nox activation or EGFR (epidermal growth factor receptor) transactivation. Interestingly, AII has a similar effect on TGF-beta expression in quiescent HSCs, although it has a smaller but significant effect on ERK1/2 activation in these cells.