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

Saulo F Saturnino,Marcus V Andrade,Roberta O Prado,José R Cunha-Melo

doi:10.1186/1471-2334-10-240

Saulo F Saturnino, Marcus V Andrade + Show 2 more

Open Access

https://doi.org/10.1186/1471-2334-10-240

Copy DOI

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.

Highlights

The 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
Mast cells express endotoxin tolerance not related to the reduction of toll-like receptor-4 expression Pretreatment with 100 ng/ml of LPS for 18 hours did not affect expression of TLR4 in mast cells (Figure 1A)
Assay for cytokine measurement TNFa and IL-6 were measured in the supernatant after 24 hours of stimulation using the enzyme-linked immunosorbent assay (ELISA) method (BioSource kits, Camarillo, CA)

Summary

Introduction

The 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. Additional work from other groups (reviewed in 9) elevated these cells, previously considered mere effectors, to the category of sentinels of the innate immune system and organizers of the adaptive immune response Their permanent location in sites likely to suffer invasion by pathogens - skin, paranasal sinuses, lungs, and intestinal mucosa - places them in a privileged position in terms of detection and subsequent organization of the immune response. The accumulation of evidence defining mast cells as fundamental in the immune response to sepsis [11,12,13] opens up new perspectives on the mechanisms of immunomodulation by this type of cell [14]

Methods

Results

Discussion

Conclusion