Pathogen-specific inhibition of the innate immune response during mastitis

Bovine mastitis usually arises as a result of intramammary infection by bacteria. The inflammatory reaction associated with mastitis results in a lower rate of milk production and a gross deterioration of the quality of the secretion. Our understanding of how mastitis-causing pathogens evade the local immune system is incomplete. Yet, a good understanding of this process at the molecular level is of strategic importance to the dairy industry as well as for treatments of these infections in cattle. Recent evidence from the groups of both supervisors as well as unpublished information from collaborating partners (H.-M. Seyfert, FBN Dummerstorf, Germany) suggests that several mastitis-causing agents interact with receptors of the innate immune system, such as Toll-like receptors (TLR) in a different way. Thus, whereas Escherichia coli or its cell-wall component LPS seems to induce a dose-dependent stimulation of the signalling cascade downstream of TLRs, others such as Streptococcus (S).uberis or its cell-wall component peptidoglycan (PGN) and lipoteichoidacid (LTA) fail to do so. This is accompanied by the failure of the immune system to produce cytokines in response to these stimuli, potentially due to thee fact that some mastitis-causing bacteria may secrete proteins which prevent TLR signalling, similar to those recently described((1); Metcalfe and Werling, unpublished data). These factors represent a unique family of bacterial Toll/interleukin-1 receptor domain-containing proteins (Tcps) which interact with the main adaptor protein of TLRs, MyD88, preventing downstream signalling. Related strains of S.uberis have recently been isolated from cows with transient and persistent mastitis (2), and the above described observation may contribute to the differences in persistence of these pathogens. Furthermore, mastitis-causing pathogens isolated from cattle or women have been shown to originate from a common ancestor, suggesting that evasion strategies are identical between different host species (3). Our hypothesis is that Gram-positive and Gram-negative mastitis-causing pathogens have developed a number of strategies to evade immune recognition in the udder. To test the hypothesis, the student will identify the presence/absence of Tcps in bacterial strains isolated from mastitis cases and assess their potential interactions with TLR-signalling by: 1) Analysing the genomes of different mastitis-causing bacteria for the presence of Tcps and compare their structures to known inhibitors of TLR signalling 2) Cloning the identified genes into mammalian expression-systems and assess their effects in established TLR-reporter assays 3) Assessing the response of milk-derived macrophages to either recombinant Tcps, whole bacteria or a combination of both Understanding how different bacterial strains are able to evade immune recognition in the udder has the potential to revolutionize novel drug/vaccine development and lead to advances in the control of this important infectious disease across species. 1. Cirl, C., Wieser, A., Yadav, M., Duerr, S., Schubert, S., Fischer, H., Stappert, D., Wantia, N., Rodriguez, N., Wagner, H., Svanborg, C., and Miethke, T. (2008) Nat Med 14, 399-406 2. Pullinger, G. D., Coffey, T. J., Maiden, M. C., and Leigh, J. A. (2007) Vet Microbiol 119, 194-204 3. Coffey, T. J., Pullinger, G. D., Urwin, R., Jolley, K. A., Wilson, S. M., Maiden, M. C., and Leigh, J. A. (2006) Appl Environ Microbiol 72, 1420-1428