Defining the molecular basis of H7 flagellin as an adhesin and mucosal adjuvant for vaccine

The overall aim of the research is to understand and exploit the adhesive and mucosal adjuvant properties of H7 flagellin. The two main hypotheses are:
1. That a region within the D2-D3 variable domain of FliC(H7) confers binding specificity to a receptor present in the terminal rectal mucosa of cattle and that vaccination of cattle with this domain can block H7 flagella-mediated adherence without interfering with normal TLR5-activated signalling.
2. That mucosal priming followed by systemic boosting with a TLR5 Binding Domain-linked molecule will result in enhanced mucosal IgA responses to the linked molecule.
The two main aims to test these hypotheses are:
Aim1. To define the molecular basis of H7 flagella binding to the terminal rectal mucosa of cattle and to construct an H7 derivative for use in a vaccine that generates a blocking adaptive response without inhibiting TLR5 activation by wild type H7 flagellin.
Aim2. To determine how H7 flagellin generates a mucosal IgA response following systemic vaccination and to exploit this understanding towards the development of generic mucosal vaccines.

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 are bacteria that cause serious gastrointestinal disease in humans. Toxins released by the bacteria cause life-threatening damage to the kidneys and brain. Cattle are the main reservoir host for the bacteria and humans become infected initially by ingesting food or drink that has been contaminated, directly or indirectly, from animal faeces. One way to guard against human infection with EHEC O157 is to block or limit shedding of the organism from cattle. This can be done via vaccination of cattle. Our previous research has demonstrated that the whip-like 'flagella' of EHEC O157 that are usually used for bacterial movement, can bind to the intestinal lining of cattle to promote colonisation. If we vaccinate cattle with purified flagella, specific antibodies are generated in the gut that block this binding and limit bacterial colonisation. However, a subset of these antibodies have a negative impact in that they bind to a region of the flagella that interferes with how the host recognizes and responds to the real infection when it occurs. There are two main aims of the research. The first is to define the specific region within the flagellin molecule required for flagella binding and to use this in a vaccine preparation to study how it limits colonisation of cattle by EHEC O157. It is anticipated that by using only the region of flagellin required for binding in the gastrointestinal tract of cattle or by altering recognition of the region that stimulates inflammatory responses in mammals, we should be able to produce an effective vaccine containing flagellin that significantly reduces EHEC O157 shedding from cattle. The second part of the research is to understand how the vaccination of cattle with whole flagellin stimulates such a good antibody response on the surface of the animals gastrointestinal tract and then exploit this understanding to generate responses to other molecules linked to flagellin. Finding ways to stimulate this 'mucosal' immunity is important for the development of vaccines to many infectious diseases.

in progress