Antibody-dependent enhancement (ADE) is an intriguing mechanism by which certain antibodies actually enhance viral replication by promoting entry of the pathogen into immune cells (eg, macrophages) resulting in worsening of the infection.^1-4 Although these antibodies are pathogen-specific, they are commonly not neutralizing or only sub-neutralizing.⁴  So aside from not being able to protect the host from infection, they actually help the virus attack host cells!

Fortunately, there is no evidence that ADE contributes to pathogenesis of Covid-19 or SARS. ^2,3 In fact, in contrast to the dengue virus, a classic cause of ADE,  SARS-CoV-2 does not seem to target or grow in macrophages; a related coronavirus, SARS-CoV is also unable to grow in macrophages infected through ADE.^2,3

ADE was initially proposed as an explanation for severe Covid-19 cases in China.¹ More specifically, it was thought that prior infection due to other coronaviruses (eg, common cold, SARS-CoV) in these patients was predisposing them to the development of severe Covid-19 following.   This hypothesis never panned out, however.  

Bonus Pearl: Did you know that in experimental studies, cats and ferrets have been found to be highly susceptible to  SARS-CoV-2, while dogs had low susceptibility and livestock, including pigs and chickens were not susceptible at all? ⁵

Liked this post? Download the app on your smart phone and sign up below to catch future pearls right into your inbox, all for free!

 References

1. Francesco N. Is antibody-dependent enhancement playing a role in COVID-19 pathogenesis. Swiss Med Wkly 2020;150:w20249. https://smw.ch/article/doi/smw.2020.20249
2. Iwasaki A, Yang Y. The potential danger of suboptimal antibody responses in COVID-19. https://www.nature.com/articles/s41577-020-0321-6.pdf
3. Peeples L. New feature: avoiding pitfalls in thepursuit of a COVID-19 vaccine. PNAS 2020:117:8218-8221. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7165470/
4. Wan Y, Shang J, Sun S, et al. Molecular mechanism for antibody-dependent enhancement of coronavirus entry. J Virol 2020; 94:e02015.  https://jvi.asm.org/content/jvi/94/5/e02015-19.full.pdf 
5. Shi J, Wen Z , Zhong G, et al. Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS-coronavirus 2.  Science 2020;10.1126/science.abb7015 https://pubmed.ncbi.nlm.nih.gov/32269068/

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!