The dynamic of anti-dengue antibodies over time.

Dengue virus is transmitted to man by the bite of an infected mosquito. Infection is usually not life threatening either causing no symptoms, resulting in a mild flu-like syndrome or leading to an unpleasant but limited disease called dengue fever. However the infection can have more serious consequences with a significant number of infected individuals developing what is called dengue haemorrhagic fever (DHF), which can be fatal in up to 20% of patients unless they receive expert medical care. This disease is common in tropical and subtropical countries where around 2.5 billion people are at risk of infection. It is estimated that 390 million infections occur per year of which around 25% develop into dengue disease. In Thailand millions of people become infectioned each year and in some years hundreds of thousands of those infected go on to develop life-threatening DHF. Dengue circulates as four related viruses. Infection with one serotype will not provide protection against other serotypes. Therefore it is common to get a dengue infection on more than one occasion. In fact, those experiencing a second infection with a different serotype are more likely to develop DHF. This suggests that pre-existing immunity can have a detrimental effect. This feature is an obstacle to vaccine development. Because of the scale of the problem, there is an urgent need for a vaccine. However it has proved an enormous challenge. After almost 50 years of effort two phase III trials showed limited protection. In this study, we will interrogate the development of acute antibody responses as well as memory B cell responses. We will also study the antibody response in dengue-infected individuals who do not develop the disease. The antibody profiles will be compared with the responses found in dengue-infected patients. In addition, the contribution of antibodies recognizing the dengue non-structural protein 1 in the pathogenesis and protection will be studied. The study will provide useful information to direct vaccine design and monitoring.

Dengue virus infection is a growing problem in many tropical and subtropical areas such as Thailand. Four dengue serotypes co-circulate. These 4 serotypes have 60-70% amino acid sequence homology. Primary infection with dengue virus is often mild and the more severe form of the infection, dengue haemorrhagic fever tends to occur when individuals are infection on a second or subsequent occasion by another dengue serotype. The antibody dependent enhancement (ADE) theory has been put forward as one explanation for this phenomenon. ADE occurs when pre-existing heterologous antibodies generated during a primary infection, may not be of sufficient avidity or concentration to neutralize a secondarily encountered virus. Studies show that serum from an acute dengue infection frequently show cross-reactivity and neutralize a number of dengue serotypes. However the heterologous immunity wanes over the first year following infection leaving serotype-specific immunity to the previously encountered serotype. Interestingly, surveillance suggests symptomatic cases caused by third or fourth infections are rare, implying that following secondary infection there is some degree of cross protection towards the remaining serotypes.
Non structural protein 1(NS1) has been suggested to have effects on complement activation. In this application, we have proposed:
1. Generation of human monoclonal antibodies using 2 techniques, EBV transformation and molecular cloning of immunoglobulin genes as described by Lanzavecchia and Wilson respectively
2. Characterisation of human monoclonal antibodies: antigen recognition, epitope mapping, neutralization, antibody dependent enhancement
3. Comparison of antibody repertoires over a time course and between symptomatic and asymptomatic cases
4. Understanding the role of anti-NS1 antibodies in pathogenesis and protection during secondary infection

The work will foster a strong collaboration between the UK and Thailand. It will be used as a platform for training the next generation in scientific research. Any knowledge generated from this study will be beneficial to other researchers working towards vaccine development and, most importantly, to people living in areas of transmission around the world.