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Effects of immunoglobulin E (IgE)-dependent sensitization on the response to bacterial lipopolysaccharide (LPS) were analyzed in mast cells. 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. 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. 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.

Background High concentrations of plasmatic IgE have been related to distinct systemic inflammatory conditions that frequently predispose individuals to hypersensitivity reactions. Although effects of IgE have been suggested to relay on the low-intensity activation of distinct effector elements of the immune system, such as mast cells (MC), experimental evidence on the role of IgE-induced production of inflammatory mediators on specific pathologies is scarce. MC are an important component in tumor microenvironment where they seem to secrete a number of immunomodulatory and angiogenic mediators, such as the Vascular Endothelial Growth Factor (VEGF) by not well-described mechanisms. In this work, we investigated the effect of monomeric IgE (in the absence of antigen) on the production of VEGF in MC, analyzed if monomeric IgE could exacerbate the pro-tumorigenic properties of that cell type and characterized some of the molecular mechanisms behind the effects of IgE on VEGF production and tumor growth. Methods For in vitro studies, murine bone marrow-derived mast cells (BMMCs) were used. Pharmacological inhibitors and phosphorylation of key elements controlling VEGF secretion and protein translation were used to characterize the mechanism of VEGF production triggered by IgE. In vivo, the effect of a single i.v. administration of monomeric IgE on B16 melanoma tumor weight, intratumoral blood vessel formation and tumor-associated MC was assessed in four groups of mice: MC-proficient (WT), MC-deficient (Wsh), Wsh reconstituted with MC derived from WT mice (Wsh Rec WT) and Wsh reconstituted with MC derived from Fyn −/− mice (Wsh Rec Fyn −/−). Results Monomeric IgE induced VEGF secretion through a Fyn kinase-dependent mechanism and modulated de novo protein synthesis modifying the activity of the translational regulator 4E-BP1 in BMMCs. In vivo, monomeric IgE increased melanoma tumor growth, peritumoral MC and blood vessel numbers in WT but not in Wsh mice. The positive effects of IgE on melanoma tumor growth were reproduced after reconstitution of Wsh mice with WT but not with Fyn −/− BMMCs. Conclusion Our data suggest that monomeric IgE, in the absence of antigen, induces VEGF production in MC and in vivo contributes to melanoma tumor growth through a Fyn kinase-dependent mechanism.