RESUMO
BACKGROUND: 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. 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 FcepsilonR1 agonists, in murine mast cells prestimulated with lipopolysaccharide (LPS). Additionally, we evaluated some stimulatory and inhibitory signaling molecules potentially involved in these phenomena. METHODS: MC/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 TNFalpha, the phosphorylation of NFkappaB and p38 MAPK, and the expression of TLR4 and SOCS-1 and -3 were analyzed. RESULTS: We found that production of TNFalpha 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 FcepsilonR1 agonist DNP-HSA (antigen) interacts synergistically with LPS or P3C to markedly enhance production of cytokines (TNFalpha 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 NFkappaB, 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. CONCLUSIONS: These findings can be explored with respect to the modulation of inflammatory responses associated with infectious and allergic processes in future studies.
Assuntos
Endotoxinas/imunologia , Mastócitos/imunologia , Receptores de IgE/imunologia , Proteínas Supressoras da Sinalização de Citocina/biossíntese , Receptor 2 Toll-Like/imunologia , Receptor 4 Toll-Like/biossíntese , Animais , Células Cultivadas , Endotoxinas/toxicidade , Imunomodulação , Interleucina-6/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , NF-kappa B/metabolismo , Fosforilação , Receptores de IgE/agonistas , Receptor 2 Toll-Like/agonistas , Fator de Necrose Tumoral alfa/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismoRESUMO
Sepsis and septic shock, its more severe form, have shown alarming increases in incidence and a persistently high mortality rate, despite technological advancement allowing adequate support of vital functions in intensive care units. Progress in understanding of physiopathology has directed the therapeutic approach, until recently limited to sustaining failing organ systems and combating infectious agents, towards the alterations provoked by an unbalanced systemic inflammatory response and its deleterious effects on cellular function. Less than 10 years ago, the discovery of Toll-Like Receptor proteins, which allow the detection of pathogen molecular patterns, initiate and modulate the immune response, opened up new and exciting possibilities in approaches to sepsis. The elucidation of the transduction pathways triggered by Toll-Like Receptors activation signals exposes promising therapeutic targets. Currently, mechanisms associated within the context of Toll-Like Receptor signalization are identified in the tolerance phenomena described in the past. The description of genetic polymorphisms associated with Toll-Like Receptors, and the different patterns of response to infectious insults have defined high-risk subgroups of imbalanced immune response with greater specificity. A better understanding of the molecular structures involved in the process and the negative-regulation of some of them have opened up possibilities in antagonizing and modulating the response to the inflammatory activation mediated by Toll-Like Receptors. Having understood how the immune system recognizes pathogens and organizes the inflammatory response upon the discovery of Toll-Like Receptors and their signaling pathways, we gained an insight into the possibilities of specific treatment instead of supportive measures for sepsis.