Replication of Crohn's disease-associated AIEC within macrophages is dependent on TNF- α secretion

Adherent and invasive Escherichia coli (AIEC) associated with Crohn's disease are able to survive and to replicate extensively in active phagolysosomes within macrophages. AIEC-infected macrophages release large amounts of tumour necrosis factor-alpha (TNF- α ) and do not undergo cell death. The aim of the present study was to determine what benefit AIEC bacteria could gain from inducing the release of large amounts of TNF- α by infected macrophages and to what extent the neutralization of TNF- α could affect AIEC intramacrophagic replication. Our results showed that the amount of TNF- α released by infected macrophages is correlated with the load of intramacrophagic AIEC bacteria and their intracellular replication. TNF- α secretion was not related to the number of bacteria entering host cells because when the number of bacteria internalized in macrophage was decreased by blocking lipid raft-dependent and clathrin-coated pits-dependent endocytosis, the amount of TNF- α secreted by infected macrophages was not modified. Interestingly, dose-dependent increases in the number of intracellular AIEC LF82 bacteria were observed when infected macrophages were stimulated with exogenous TNF- α , and neutralization of TNF- α secreted by AIEC-infected macrophages using anti-TNF- α antibodies induced a significant decrease in the number of intramacrophagic bacteria. These results indicate that AIEC bacteria use TNF- α as a Trojan horse to ensure their intracellular replication because replication of AIEC bacteria within macrophages induces the release of TNF- α , which in turn increases the intramacrophagic replication of AIEC. Neutralizing TNF- α secreted by infected macrophages may represent an effective strategy to control AIEC intracellular replication.