The identification of novel immunomodulatory factors from Neisseria meningitidis serogroup B.
Anne McNaughton, Dr Alejandro Merino, Dr Ed Lavelle, Professor Dolores Cahill, Professor Kingston Mills
- Start Date:
01 January 2006
Trinity College, Dublin, Ireland
Neisseria meningitidis serogroup B is a major cause of bacterial meningitis and fatal septicaemia. The bacterium colonises the upper nasopharynx of a considerable proportion of the human population without pathogenic consequences but the mechanisms underlying its survival in this environment is not fully understood. Furthermore the mechanisms by which the bacterium can overcome immune defences and cause meningococcal disease have not yet been elucidated. In line with the Foundation's objective of increased understanding of meningococcal pathogenesis and host response, we will investigate novel immunomodulatory factors in Neisseria meningitidis serogroup B that could play a role in immune evasion. Bacterial mono ADP-ribosyltransferases are functionally conserved enzymes, many of which are potent toxins that subvert multiple functions of eukaryotic cells and are major pathogenicity factors. Recent work has identified NarE, a previously undiscovered ADP-ribosyltransferase in Neisseria meningitidis. The enzyme has structural homology with cholera toxin (CT) and heat-labile enterotoxin from Escherichia coli (LT) and possesses both ADP-ribosylating and NAD-glycohydrolase activity. CT and LT are the toxins responsible for cholera and travellers diarrhoea respectively and are among the most potent immunomodulatory molecules and adjuvants yet identified. The toxins selectively modulate dendritic cell activation, suppress inflammatory cytokine production and promote the induction of regulatory T cells. Since ADP-ribosyltransferases are important pathogenicity factors in other bacteria, it is essential that we elucidate the role of NarE in meningococcal pathogenesis and immunity. We will first determine whether NarE exhibits immunoregulatory properties that could promote meningococcal pathogenesis and immune evasion. Secondly, since a systematic analysis of immunomodulatory proteins in N. meningitidis serogroup B has not been previously undertaken, we will use dendritic cells as a model to identify novel immunomodulatory factors that modulate innate immune responses. The activation of dendritic cells by the molecules alone will be tested in addition to measuring the effects of the molecules on meningococcal LPS-induced dendritic cell activation. Since N. meningitidis serogroup B can induce septicaemia, in which LPS plays a significant role, it is important to establish if additional factors are present that can amplify or modulate the innate immune response to LPS. We have strong expertise in protein expression and purification that will enable us to generate a selected group of meningococcal proteins with predicted biological function. We will initially determine if these proteins can modulate the responses of human dendritic cells, an important mechanism of immunomodulation by other bacteria. This will allow us to identify and select potent immunomodulatory molecules. Assays will be carried out to determine if these treated dendritic cells can activate T cells and the nature of the T cell response will be assessed. These molecules will be tested in vivo to assess their ability to activate or suppress T and B cell responses. The molecules will also be tested in vivo to assess whether the proteins can modulate innate immune cell activation and serum cytokine concentrations induced in a murine LPS-induced septic shock model. Since meningococcal LPS plays a vital role in inducing septicaemia it is important to establish if there are additional factors present that amplify the LPS-induced response. We believe that this proposal has the potential to significantly improve our understanding of the relationship between the meningococcus and the immune system and will help in the development of new therapies and vaccines for the disease.