Decreased responseof neutrophils from endotoxin tolerant mice towards lipopolysaccharide

LOPEZ M.F; LANDONI V.I; REARTE B; CHIARELLA P; LABORDE E; RAMOS M.V; BENTANCOR LV; FERNANDEZ-BRANDO R.J; ISTURIZ M.A; PALERMO M.S; FERNANDEZ G.C

Rio de Janeiro Brasil

Congreso; 13th International Congress of Immunology; 2007

  Septic shock is a heterogenic clinical situation associated to bacterial or fungal infection. However, 50% of the cases of sepsis are associated to infections with Gram-negative bacteria. Lipopolysaccharide (LPS) is the main component of the cell membrane of Gram-negative bacteria and it is a potent stimulator of the release of pro-inflammatory cytokines (TNF-a, IL-1b, IL-8) associated to septic shock (Lehner, M., et al., 2001, Infection and Immunity, Vol. 69). The inoculation of a high dose of LPS induces pathologic symptoms similar to those observed in septic patients. However, the repetitive exposure to LPS induces a refractory state towards its effects, known as tolerance to LPS. Previous studies have demonstrated a decreased cytokine production (TNF-á, IL-1, IL-6) in monocytes pre-treated in vitro with LPS and ex vivo in monocytes from patients with sepsis (Karp, C.L., et al., 1998, Eur. J. Immunol., Vol. 28 ). Neutrophils (PMN) are central elements in the response against infectious agents and even though their activation is beneficial for the resolution of the infection, deactivation of PMN has been observed in several pathologies. In this regard, PMN from septic patients or healthy donors inoculated with LPS showed a decreased IL-8 production (Marie, C., et al., 1998, Blood, Vol. 91; Marie, C., et al., 2000, Cytokine, Vol 12). Characterize the functional state of PMN in a murine model of tolerance to LPS, in order to comprehend the mechanisms involved in the refractory state of the immune system observed in late stages of sepsis. For this purpose, we evaluated the LPS effects on the kinetic of peripheral PMN counts, and determined the expression of activation markers such as CD62L and CD11b on PMN of animals rendered tolerant to LPS. Additionally we evaluated the LPS co-receptor TLR4 expression, the production of reactive oxygen species (ROS) and the in vivo migratory capacity of PMN. We studied the modulation of all these parameters  after a challenge with a high dose of LPS. The administration of LPS to normal animals (challenge) induces a high and explosive activation of PMN as evidenced by: disappearance of PMN from the periphery, an increase in CD11b expression and in ROS generation. Even though a conserved TLR4 expression was observed in PMN from Tolerant animals, they showed attenuated functional responses after the challenge with a higher dose of LPS, i.e. the disappearance from periphery was abolished and the increase in CD11b expression and ROS generation were lower.         PMN from tolerant animals have distinctive characteristics. Their conserved migratory, and their increased cytotoxic capacities (ROS) suggest that tolerance to LPS is an adaptation to a new situation that still have the ability to face an infection minimizing the processes associated to the injury mediated by a possible massive activation of PMN in response to an exposure to a high quantity of bacterial load (challenge).