The role of endogenous glucocorticoids in regulating dendritic cell function in vivo

Vaccines are hugely important in the fight against infections. However, vaccines against many infections are ineffective and we are interested in finding ways to boost their activity. Vaccines may require special immune cells, called dendritic cells, to become activated. Thus, one reason why vaccines may not work is that these cells do not become activated enough. We have found that dendritic cells produce large amounts of steroids and that this may prevent them from becoming activated. The dendritic cells contain an enzyme that produces the steroid. Although these findings are very obvious when we culture dendritic cells in a test tube, it is now very important to work out what role this enzyme has in preventing immune responses following a vaccination. This requires that we perform experiments in mice, in which the gene that makes the enzyme has been ?knocked out?. In this case, we can take a mouse that is normal in every respect other than the fact that it cannot make the enzyme. We predict that responses to vaccination will be much better in mice that lack the enzyme in their dendritic cells. If so, this will be important, because new drugs have been developed that can block the enzyme from working. Thus, it may be possible to give a vaccine and an enzyme-stopping drug at the same time in order to get a better response.

A major influence upon the decision between tolerance and immunity is the activation state of dendritic cells (DCs). Although tolerance is induced by ?default? in the absence of DC activation, it can be broken if DCs are exposed to pro-inflammatory stimuli. We are interested in physiological mechanisms that constrain the ability of DCs to undergo activation and the development of novel therapies that will promote DC activation in vivo. We have recently identified a highly conserved pathway in DCs that leads to the generation of active glucocorticoids (GC) and leads to autocrine negative inhibition of DC differentiation and function. Reduction of inactive GC to active GC requires the enzyme, 11beta-dehydroxysteroid dehydrogenase type 1 (11beta-HSD1), whose expression increases upon DC differentiation. 11beta-HSD1 is co-located in the endoplasmic reticulum with a second enzyme, hexose-6-phosphate dehydrogenase (H6PDH) that generates the NADPH required for the reductase reaction. Importantly, the 11beta-HSD1/H6PDH pathway is regulated differently according to the mode of DC activation. Thus, reductase activity is maintained following activation induced by innate signals (e.g. via TLR) but is blocked sharply following CD40 ligation. We hypothesize that 11beta-HSD1/H6PDH is required in the steady state in order to maintain DCs as immature, co-stimulatory molecule cells. We reason that inhibition of this pathway, for example with novel, specific 11beta-HSD1 inhibitors, may help to boost immune responses following vaccination. In order to test these concepts in vivo, we will first determine expression levels and activities of 11beta-HSD1/H6PDH in DCs of wild type mice under normal conditions and following in vivo exposure to TLR agonists or anti-CD40. We will employ bone marrow-chimeric mice, in which haematopoietic cells are derived from H6PDH knockout (ko) or 11beta-HSD1 ko donors, to determine the role of 11beta-HSD1/H6PDH in regulating DC activation in the steady state or following treatment with pro-inflammatory stimuli. Furthermore, we will test whether disabling the 11beta-HSD1/H6PDH system in chimeric mice will boost immunity following vaccination using a model system in which antigen is specifically targeted to DCs. We have also employed Cre-loxP technology to generate a recombined HSD11B1 allele that will allow it?s ?conditional? knockout. Mice containing this conditional allele will be crossed to CD11cCreERT mice, which express a tamoxifen inducible Cre recombinase in differentiated CD11c+ DCs, thus permitting selective ko of 11beta-HSD1 in differentiated DCs. Finally, we will test the feasibility of using transient, specific pharmacological inhibition of 11beta-HSD1 as a means of improving responses to vaccination.