Endotoxin tolerance and cross-tolerance in mast cells involves TLR4, TLR2 and FcεR1 interactions and SOCS expression: perspectives on immunomodulation in infectious and allergic diseases

Abstract

BackgroundThe study of the endotoxin tolerance phenomenon in light of the recently defined roles of mast cells and toll-like receptors as essential components of the innate immune response and as orchestrators of acquired immunity may reveal potentially useful mechanisms of immunomodulation of infectious and allergic inflammatory responses, such as sepsis or asthma. Here we evaluated the phenomenon of direct tolerance of endotoxins, as well as the induction of cross-tolerance and synergism by stimulation with toll-like receptor-2 (TLR2) and FcεR1 agonists, in murine mast cells prestimulated with lipopolysaccharide (LPS). Additionally, we evaluated some stimulatory and inhibitory signaling molecules potentially involved in these phenomena.MethodsMC/9 cells and primary bone marrow-derived mast cells obtained from C57BL/6 and TLR4-/- knock-out mice were sensitized to DNP-HSA (antigen) by incubation with DNP-IgE and were prestimulated with LPS for 18 hr prior to stimulation. Cultures were stimulated with LPS or Pam3Cys-Ser-(Lys)4 3HCl (P3C), a TLR2 agonist, individually or in combination with antigen. The production of IL-6 and TNFα, the phosphorylation of NFκB and p38 MAPK, and the expression of TLR4 and SOCS-1 and -3 were analyzed.ResultsWe found that production of TNFα and IL-6 in murine mast cells that have been pretreated with LPS and challenged with TLR4 (LPS) or -2 (P3C) agonists was reduced, phenomena described as endotoxin tolerance (LPS) and cross-tolerance (P3C), respectively. The expression of TLR4 was not affected by LPS pretreatment. Our results show that the FcεR1 agonist DNP-HSA (antigen) interacts synergistically with LPS or P3C to markedly enhance production of cytokines (TNFα and IL-6). This synergistic effect with LPS and P3C was also attenuated by LPS pretreatment and was mediated by TLR4. These results may be attributed to the reduction in phosphorylation of the mitogen-activated protein kinase (MAPK), p38, and the transcription factor NFκB, as well as to an increase in the expression of the suppressors of cytokine signaling (SOCS)-1 and -3 proteins in LPS-pretreated mast cells.ConclusionsThese findings can be explored with respect to the modulation of inflammatory responses associated with infectious and allergic processes in future studies.

Epigenetic Regulation of Tolerance to Toll-Like Receptor Ligands in Alveolar Epithelial Cells

“…Suppressor of cytokine signaling (SOCS) proteins are important negative regulators of the TLR signaling pathway, and have been shown to play a role in the induction of tolerance in macrophages (28,29). The expression of suppressor of cytokine signaling 1 was measured in LPS-tolerized AECs, and was found to significantly increase after secondary LPS ( Figure 5A).…”

Experimental immunology FcεRI-mediated mast cell response is modulated by TLR2 and TLR4 ligation

“…peptidoglycan (PGN) and lipoteichoic acid (LTA), reduced FcεRI-mediated degranulation of human mast cell line LAD2, and only LTA-priming significantly inhibited FcεRI-dependent degranulation of human pulmonary mast cells, as assessed by β-hexosaminidase release [22]. It was also stated that there was no significant change in degranulation of bone marrow-derived mast cells (BMMCs) following stimulation through TLR4 with LPS and FcεRI cross-linking [23]. Substantial enhancement of FcεRI-mediated degranulation of connective as well as mucosal like mast cells was noticed after prolonged exposure (up to 96 h) to LPS.…”

“…On the contrary, some data clearly demonstrated no influence of LPS stimulation on mast cell arachidonic acid metabolite synthesis following FcεRI aggregation [17,26]. Interestingly, it was documented that Aleksandra Słodka, Ewa Brzezińska-Błaszczyk A native, IgE-uncoated mast cells B IgE-coated mast cells the combination of TLR2 or TLR4 stimulation and FcεRI cross-linking resulted in synergistically amplified secretion of many, especially Th2-skewed, cytokines and chemokines from mast cells [14,23,[26][27][28]. The underlying mechanisms by which TLR ligands in combination with FcεRI-mediated activation influence mast cell response remain unclear.…”

“…TLR2 and TLR4 agonists may modulate the surface expression of FcεRI and in consequence can alter mast cell FcεRI-dependent response [17,22,29]. Since it is well documented that TLR ligation stimulates mast cell to various cytokine secretion [5,7,[14][15][16][17] it may be assumed that these secreted cytokines indirectly affect FcεRI-dependent mast cell activity by autocrine feedback loop mechanism [22,23,25]. Little is known about impact of mast cell stimulation mediated via both TLR-and FcεRI-dependent pathway on intracellular signaling events.…”

“…Little is known about impact of mast cell stimulation mediated via both TLR-and FcεRI-dependent pathway on intracellular signaling events. On the one hand, mast cell co-treatment through both FcεRI and TLR2 or TLR4 receptors resulted in the attenuation of mitogen activated protein kinase (MAPK) phosphorylation [23,30] as well as in suppression of intracellular calcium mobilization with no change in calcium influx [26,30,31]. On the other hand, Qiao et al [26] observed the synergistic enhancement of the MAP kinases (p38, JNK) and transcriptional factors phosphorylation (ATF-2, c-Jun, c-Fos) after mast cell activation via TLR2 or TLR4 and FcεRI.…”