Pathogens are sensed by pattern recognition receptors (PRRs), which are germ line-encoded receptors, including transmembrane Toll-like receptors (TLRs) and cytosolic nucleotide oligomerisation domain (NOD) proteins, containing leucine-rich repeats (NLRs). Activation of PRRs by specific pathogen-associated molecular patterns (PAMPs) results in genomic responses in host cells involving activation transcription factors and the induction of genes. There are now at least 10 TLRs in humans and 13 in mice, and 2 NLRs (NOD1 and NOD2). TLR signalling is via interactions with adaptor proteins including MyD88 and toll-receptor associated activator of interferon (TRIF). NOD signalling is via the inflammasome and involves activation of Rip-like interactive clarp kinase (RICK). Bacterial lipopolysaccharide (LPS) from Gram-negative bacteria is the best-studied PAMP and is activated by or ‘sensed’ by TLR4. Lipoteichoic acid (LTA) from Gram-positive bacteria is sensed by TLR2. TLR4 and TLR2 have different signalling cascades, although activation of either results in symptoms of sepsis and shock. This review describes the rapidly expanding field of pathogen-sensing receptors and uses LPS and LTA as examples of how these pathways parallel and diverge from each other. The role of pathogen-sensing pathways in disease is also discussed.

There is increasing evidence that temporal factors are important in allowing cells to gain additional information from external factors, such as hormones and cytokines. We sought to discover how cell responses to glucocorticoids develop over time, and how the response kinetics vary according to ligand structure and concentration, and hence have developed a continuous gene transcription measurement system, based on an interleukin-6 (IL-6) luciferase reporter gene. We measured the time to maximal response, maximal response and integrated response, and have compared these results with a conventional, end point glucocorticoid bioassay. We studied natural glucocorticoids (corticosterone and cortisol), synthetic glucocorticoids (dexamethasone) and glucocorticoid precursors with weak, or absent bioactivity. We found a close correlation between half maximal effective concentration (EC50) for maximal response, and for integrated response, but with consistently higher EC50 for the latter. There was no relation between the concentration of ligand and the time to maximal response. A comparison between conventional end point assays and real-time measurement showed similar effects for dexamethasone and hydrocortisone, with a less effective inhibition of IL-6 seen with corticosterone. We profiled the activity of precursor steroids, and found pregnenolone, progesterone, 21-hydroxyprogesterone and 17-hydroxyprogesterone all to be ineffective in the real-time assay, but in contrast, progesterone and 21-hydroxyprogesterone showed an IL-6 inhibitory activity in the end point assay. Taken together, our data show how ligand concentration can alter the amplitude of glucocorticoid response, and also that a comparison between real-time and end point assays reveals an unexpected diversity of the function of glucocorticoid precursor steroids, with implications for human disorders associated with their overproduction.