Listeria DpgdA mutant in a TLR2-dependent manner A L. monocytogenes pgdA mutant induced a much higher IFN-b response than the parental strain [25] . To definitively establish a role for the peptidoglycan deacetylase PgdA in the downregulation of IFN-b production, we complemented our original pgdA mutant with the wild-type gene and we measured IFN-b secretion of peptone elicited peritoneal macrophages (PEM) infected with wild-type EGDe, DpgdA and a complemented DpgdA strain (Fig. 1) . Inactivation of pgdA led to a strong induction of IFNb secretion in wild-type macrophages. In contrast, the complemented strain did not induce any massive IFN-b secretion, similar to wild-type EGDe. Thus, PgdA directly contributes to downregulation of IFN-b production.