Most vaccines contain adjuvants which boost their effectiveness by stimulating the immune system. The mode of action of these adjuvants however remained misunderstood. Researchers at ULg discovered how alum, the most frequent adjuvant, acts during vaccination. A process where our own DNA plays a key role.

It would seem that the first form of vaccination (read Vaccines in action) was introduced in China centuries ago to protect people from smallpox. This practice, called variolation, involved putting the person to be immunised in contact with the content of vesicles of an ill person with the hope that this person was affected by a non-virulent form of smallpox... Since then vaccines have changed and are no longer based on luck!

Since the end of the 19th century we have thus seen the emergence of vaccines against a large number of illnesses such as polio, hepatitis B, diphtheria or tetanus. In particular vaccination allowed smallpox to be completely eradicated. There remain, however, infectious illnesses such as AIDS or malaria that are also real scourges for society and against which, to date, no effective vaccine is available. Aside from studying these illnesses, the in-depth understanding of the mechanisms of vaccination is essential in order to develop new vaccines.

A vaccine contains a killed or weakened form, certain components of or a synthetic substitute of an infectious disease-causing agent. In contact with these antigens, the immune system is stimulated and prepares to defend itself against the enemy. When our organism is genuinely attacked by this infectious agent, the immune system can directly use adequate ammunition and strikes down the attacker without it having the time to provoke the illness for which it is responsible.

An adjuvant that is a well-kept secret!

Although the basic principle of vaccination is well known, the mode of action of current adjuvants, which are added to many vaccines to increase their immunogenicity and their effectiveness, is less so. Aluminium salts, often collectively referred to as alum, are the most frequently used type of addititives. "Adjuvants boost the responsiveness of the immune system in the face of the antigen but also direct this response towards a certain type of immunity. They allow an increase in the production of antibodies directed against the elements of the vaccine», explains Christophe Desmet, FNRS Researcher at the Laboratory of Cellular and Molecular Physiology at the GIGA. «Alum has been used since the 1930s. Once injected, the aluminium salt forms spongy-looking macroscopic deposits. Several hypotheses linked to this spongy form have been put forward to explain why alum might increase the effectiveness of vaccines", continues the researcher.