Skip to main content

What Are Antibodies? Dr. Kate Sullivan Explains on YouTube

The Immune Deficiency Foundation’s physician adviser gives a patient-friendly explanation in light of the COVID-19 pandemic.



If someone asked you to define “antibodies,” what would you say?

People are increasingly Googling this term – no surprise – due to the global COVID-19 pandemic. Antibodies, part of the immune system response to infection, enable your body to “remember” a bacteria or virus and disarm it before it can make you sick. It’s a complex process and there’s more than just one kind of antibody, explains Dr. Kate Sullivan in a YouTube video shared by the Immune Deficiency Foundation. Sullivan is medical adviser to the IDF and Chief of Allergy and Immunology at the Children’s Hospital of Philadelphia.

“This is really to answer some questions we’ve been getting at the Immune Deficiency Foundation and I have certainly had from patients, friends and neighbors,” she says in the opening to “COVID-19 for Antibody Geeks.”

CSL Behring’s Andrew Koenig, D.O., Global Medical Affairs Lead, Immunology Therapeutic Area, applauded Dr. Sullivan’s outreach to patients on this topic.

The COVID-19 pandemic has brought science and immunology to an all-new level of public awareness,” Koenig said. “The IDF video series with Dr. Sullivan, and specifically this comprehensive feature on antibodies, is a great resource for PI patients and others interested in better understanding the science of this virus, as well as the ways researchers are looking to treat and potentially prevent it in the future.”

Someone who has a primary immune deficiency has one of more than 400 diseases that affect how the immune system works. Sullivan’s video explaining antibodies is one in a series she has created since the start of the pandemic for IDF’s patient community. People with immune system problems are understandably concerned about how the novel coronavirus could affect them.

Here are a few questions Sullivan answers about antibodies:

How many classes (isotypes) of antibodies are there?

There are five classes of antibodies : IgG, IgA, IgM, IgD and IgE. Ig means “immunoglobulin.” Each class has a different structure and a slightly different function, Sullivan said.

Which antibodies do vaccines activate?

Vaccines activate IgG, the most abundant type in the body.

How do antibodies work?

Sullivan constructed – science fair style - her own 3-D model of the COVID-19 virus to better explain. Setting it on a table, she said to imagine the table was a cell and the virus is sitting there. She used an empty K-cup (the kind used in coffee machines) to represent the ACE-2 receptor protein that allows the virus to enter a person’s cell. These ACE-2 receptors, found in the respiratory tract (lungs) and digestive tract (gut), allow the virus to latch on, Sullivan said.

She used red-tipped clothespins for the antibodies and clipped them to the spike proteins to demonstrate how antibodies bind to the virus and prevent it from entering the cell.

“You can think of these antibodies as being like sharp elbows that prevent the virus from gaining entry into the cell,” Sullivan said.

Antibodies get better at binding over a longer exposure, she said. With a coronavirus, the body starts making antibodies after a week and this peaks at about three weeks.

What about a vaccine?

Sullivan closes by explaining why vaccines take time and how scientists must take into account all the complexities they’ve encountered in decades of vaccine development.

But she does find a ray of hope in all the ongoing exploration of more than 100 vaccine candidates: “I’ve never seen science move more quickly and I’ve never seen scientists and clinicians be more willing to share what they’ve learned, to share what they’re doing, and try to help others battle this very serious foe that we’re facing.”