Antibody dependent enhancement
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Antibody dependent enhancement (ADE) occurs when antiviral antibodies enhance viral entry into host cells, leading to increased infectivity in the host cells.

ADE in dengue fever

The most common example of ADE occurs during dengue infection. There are four serotypes of the dengue virus, numbered from 1 to 4. ADE occurs when a patient suffering from a dengue infection is infected with a different serotype of the dengue virus. These patients have severe clinical outcomes and high viremia compared with other dengue sufferers.^{citation needed}

Mechanism

There are several possibilities to explain the phenomenon:

1. A viral surface protein laced with antibodies against a virus of one serotype binds to a similar virus with a different serotype. The binding is meant to neutralize the virus surface protein from attaching to the cell, but the antibody bound to virus also binds to the receptor of the cell, the Fc-region antibody receptor clarifyme. This brings the virus into close proximity to the virus-specific receptor, and the cell endocytoses the virus through the normal infection route. ¹
2. A virus surface protein may be attached to antibodies of a different serotype, activating the classical pathway of the complement system. The complement cascade system instead binds C1q attached to the virus surface protein via the antibodies, which in turn bind C1q receptor found on cells, bringing the virus and the cell close enough for a specific virus receptor to bind the virus, beginning infection.^{citation needed}
3. When an antibody to a virus is present for a different serotype, it is unable to neutralize the virus, which is then ingested into the cell as a sub-neutralized virus particle. These viruses are phagocytosed as antigen-antibody complexes, and degraded by macrophages. Upon ingestion the antibodies no longer even sub-neutralize the body due to the denaturing condition at the step for acidification of phagosome before fusion with lysosome^clarify. The virus becomes active and begins its proliferation within the cell.^{citation needed}

References