Dendritic cells activated with LPS IFNg over 48 hours

Pro-inflammation triggered by microbial lipopolysaccharide (LPS) through Toll-like receptor (TLR) 4 in the presence of interferon (IFN)-g induces cytokine secretion in dendritic cells (DCs) tightly regulated by a defined differentiation program. This DC differentiation is characterized by a dynamic immune activating but also tolerance inducing phenotype associated with irreversible down-modulation of cytokines. CD40L on activated T cells further modifies DC differentiation. Using DNA micro arrays we showed down-regulated mRNA levels of TLR signaling molecules while CD40/CD40L signaling molecules were up-regulated at a time when LPS/IFN-g activated DCs have ceased cytokine expression. Accordingly we demonstrated that CD40/CD40L but not TLR4 or TLR3 signaling mediated by LPS or poly (cytidylic-inosinic) acid (poly I:C) and dsRNA re-established the capacity to secret interleukin (IL)-12 in LPS/IFN-g activated DCs, which have exhausted their potential for cytokine secretion. This resulting TH1 polarizing DC phenotype – which lacked accompanying secretion of the crucial immune suppressive IL-10 - enhanced activation of cytotoxic T lymphocytes (CTLs). We therefore conclude that immune modulation is restricted to a secondary T-cell mediated stimulus at an exhausted DC state which prevents an immune tolerant DC phenotype. These findings impacts on the rational design of TLR activated DC-based cancer vaccines for the induction of anti-tumoral CTL responses. Keywords: time course Monocyte derived DCs were matured for 6 hours with 30 ng/ml lipopolysaccharide (LPS, E. coli strain O111:B4, Calbiochem, San Diego, CA) and 1.000 U/ml IFN-g (Imukin, Boehringer Ingelheim, Austria). RNA of DCs was isolated after 6, 12, 24, or 48 hours of maturation using the RNeasy kit (Qiagen, Hilden, Germany) and analyzed by the RZPD (German Resource Centre for Genome Research, Berlin) using the Affymetrix DNA micro array platform (U133 plus 2.0). DNA array data from different maturation-time experiments were compared to controls that were kept in culture for the same time without stimulation.