L' activation des neutrophiles par le MNCF a pour conséquence la transcription de gènes et la sécrétion de cytokines, et cela même dans des conditions anti-inflammatoires

Neutrophil activation by MNCF lectin results in gene transcription and secretion of cytokines, even in anti-inflammatory conditions

• Auteur / Autrice : Karina Alves de Toledo
• Direction : Lise Halbwachs-Mecarelli
• Type : Thèse de doctorat
• Discipline(s) : Immunologie
• Date : Soutenance en 2007
• Etablissement(s) : Paris 6

Mots clés

Mots clés libres

Polynucléaires neutrophiles

Lectines

Corticoïdes

Migration des neutrophiles

Inflammation

Chimiokines

Dégranulation

Macrophage

Déxamethasome

Résumé

Le MNCF (Facteur Chimioattractant des Neutrophiles, dérivé des Macrophages) est une lectine qui recrute les neutrophiles, même chez les animaux traités par la déxamethasone. Nous montrons ici que le MNCF se lie à la surface, et provoque la migration, des neutrophiles humains. Le MNCF déclanche : (a) l’inhibition de l’apoptose spontanée ; (b) le relarguage de CD62L ; (c) la phosphorylation de tyrosine-kinases et de la p38MAPkinase ; (e) la dégranulation des vésicules et granules spécifiques sauf les granules azurophiles ; (f) la translocation du facteur de transcription NF-B ; (g) la transcription des gènes et la sécrétion de cytokines et chimiokines. Ces effets du MNCF ne sont modifiés ni par la déplétion en LPS sur detoxigel, ni par le récepteur soluble du TNF, ethanercept , ni par un prétraitement des neutrophiles par la dexamethasone inhibant les effets de chimiokines comme CXCL8 ; ils ne nécessitent pas de pré-activation des cellules par le LPS, à la différence de la galectine 3. Ainsi, l’inflammation induite par le MNCF in vivo serait liée à la production de taux élevés de médiateurs pro-inflammatoires par un mécanisme insensible aux glucocorticoïdes.

Leukocytes are accumulated, in the inflammatory process, because to action of the wide array of stimuli. This event envolved several and coodenated steps whose inhibited by glucocoticoids, such as dexamethasone. Dexamethasone affects human neutrophils in different ways. It shows negative effects (on synthesis and secretion of pro-inflammatory mediators) and positive effects (for example, on annexin I). Among the inducers of leukocyte migration, MNCF, a galactose-binding lectin, has been described as an agonist and chemoattractant for neutrophils, both in vivo and in vitro. MNCF shows as peculiar activity the migration of neutrophils resistant to dexamethasone actions which awakes great interest in undertanding the mechanism of action on polymorphonuclears by this lectin. Our first step was study human MNCF-stimulated neutrophils pre-incubated with dexamethasone. In these conditions, MNCF, in the absence of F-actin polymerization: (a) protects neutrophils from spontaneous apoptosis, (b) induces tyrosine and p38 MAP quinases phosphorylation, (c) induces CD62L shedding, (d) degranulates secretory vesicles and secundary granules, but not azurophilic granules, in the dependent manner of tyrosine and MAP quinases and Src family, (e) translocates the transcription factor NF-kB and, (f) induces transcription and secretion of pro-inflammatory cytokines and chemokines. In parallel, human neutrophils pre-incubated with dexamethasone and stimulated with MNCF did not show CD62L shedding and F-actin polarization, but the in vitro migration was maintained. Besides, we already observe translocation of NF-kB from cytoplasm to nucleous which it activates the genic transcription 14 and secretion of inflammatory mediators, such as CXCL8. The results, showed here, strengthens previous results, demonstranting that MNCF as a agonist to neutrophils, beyond increase the half life them. Although, dexamethasone modifies some effects of MNCF on neutrophis, this glucocorticoid does not inhibit the cellular response to the studied lectin. Thus, the maintenance of inflammatory mediators, dependents to NF-kB, during the inflammatory process, could explain, even parcialy, the break in the resitance to glucocorticoids actions by MNCF in the neutrophil migration.