Antibody-Dependent Enhancement

Antibody-dependent enhancement (ADE) is a process in which antibodies from an earlier infection or vaccination, instead of blocking a virus, help it to infect cells. It is best known from dengue, where a second infection with a different type of the virus can be more severe than the first.

Antibodies at low levels, or those that bind but do not neutralize, can coat a virus particle. Immune cells such as macrophages carry receptors for the tail of the antibody, so they take up the coated virus and become infected, which increases the number of infected cells. The effect was described for dengue by Scott Halstead in the 1960s and 1970s.

The four types of dengue virus are related, so antibodies made against one type may bind but fail to neutralize another. This is thought to explain why severe dengue, with bleeding and shock, is more common in people infected a second time, as well as in infants carrying maternal antibodies. A dengue vaccine, Dengvaxia, was found to raise the risk of severe disease in people never previously infected, and its use is now restricted to those with prior infection.

Similar effects are suspected or observed in other flaviviruses such as Zika virus and West Nile virus, in feline infectious peritonitis and in some other infections. It is considered when designing vaccines and treatments for arboviruses, and it complicates the use of antibody therapies. Understanding it is a part of immunology.

• Dengue Virus — the virus where it is best known
• Antibody — the molecule involved
• Vaccine — a field affected by the problem