How do Covid-19 antibodies work?
Covid-19

How do Covid-19 antibodies work?

The macro and micro point of view.

By Ava Mainieri, PhD
Senior Director of Research, She/her

5 min read

Did you know you have an extensive microscopic collection living on your skin, inside your body, and in your cells? The majority of them are bacteria, some are tiny fungi microbes, and others are viruses that can infect microorganisms and cells. Every day your body is attacked by billions of microscopic invaders.

The immune system, composed of a network of cells, tissues, and their products, is on a constant lookout for pathogens (microorganisms, bacteria, or viruses that can cause disease) that are trying to infiltrate your body. As a result, your body is swimming with different kinds of immune cells — some bear the memory of past infections in preparation for future encounters, some vigorously destroy foreign microbes, and others act as a patrol.

The Immune System

The immune system can be divided into two main groups: the innate immune system and the adaptive immune system.

If a foreign virus slips past the physical and chemical mechanisms (eg. the skin or mucus lining the inside the nose), it is met by the innate immune system. The innate immune system responds rapidly with inflammation and engages macrophages and neutrophils, white blood cells that devour, eat, and engulf foreign particles. They express receptors that can sense the presence of a foreign invader and sound a cytokine alarm to the rest of the body, like a loudspeaker announcing that an intruder has sneaked in. Innate immunity is activated in all kinds of injuries and illnesses, everything from a scrape on your leg to a splinter on your big toe.

Now and again, a microbe comes along that gets past the innate immune system. That is when the adaptive immune system, a true powerhouse, rallies to fight back. Only vertebrates (species with backbones like us) have adaptive immune systems, the third layer of defense that adapts to protect against foreign pathogens. Over 99% of organisms on Earth don’t have adaptive immune systems and get along fine with only natural barriers and the innate immune system for defense.

When you get a cold, flu, or the novel coronavirus, cells within your adaptive immune system rush out to identify the sickness. Your adaptive defenses come to the rescue by recruiting and activating a specialized team of while blood cells that are best equipped to fight the specific pathogen. For example, if you get infected with E. coli (the pesky bacteria that can cause food poisoning), white blood cells that recognize particular molecules on E. coli are activated. When the human immune system is given time to prepare, it can produce defenses that protect against foreign invaders.

On Antibodies

The adaptive immune system is unique because it creates a special protein complex called an antibody (also referred to as immunoglobulin). Specialized white blood cells produce antibodies, which are uniquely designed to look for antigens, a specific structure found on a foreign virus or particle. Antibodies adhere to antigens, which then signal the immune system to destroy the foreign invader. Although antibodies are incredibly important to defend against pathogens, they do not kill anything! Their job is only to plant the kiss of death on the microbe — tagging it for destruction.

White blood cells created in bone marrow can mature and become antibody factories. It can take antibodies a couple of weeks to develop after being exposed to a virus. IgG has reliably shown up on antibody tests 3- 14 days after a Covid-19 infection.

Antibodies stick around for differing amounts of time depending on the illness, creating an immunological memory. This means you are reinfected, the adaptive immune system can bounce into action quickly. Scientists believe SARS antibodies stay in the body for 2 years and MERS antibodies are maintained for almost 3 years. Because Covid-19 is a novel virus, we do not know for sure how long these antibodies last. However, experts generally agree that, based on experience with other viruses, the presence of antibodies does confer some level of protection. In a recent study, researchers infected volunteers with a seasonal coronavirus and around a year later, infected them with the same or similar virus. All of the participants either experienced full or partial protection.

Antibody Tests

Antibody tests also called serology tests, take a sample of your blood to test if your immune system has produced any antibodies in response to an infection. These tests can tell you if you were previously infected but they cannot detect active infections or recovery.

The is currently a lot of concern about the accuracy of Covid-19 antibody tests. Accuracy is based on sensitivity and specificity, this is tricky because the tests have to be sensitive enough to detect the presence of IgG-specific antibodies and specific enough to avoid accidentally produce a positive result.

Tia is now offering in partnership with Quest the Abbott antibody test, which is 99.1% accurate.

As such, we stand by the quality of the test but because no antibody test can tell you if you are immune we recommend continuing to wear a mask and practicing social distancing even if you have developed antibodies.

Why Test?

Widespread antibody testing will help give epidemiologists a clearer understanding of the scope of this disease. A study from random testing around 3,000 people in New York City recently postulated that as many as one in five residents, or about 2.7 million people, might have contracted the disease without knowing. Antibody testing research may also help identify groups who are more susceptible to infection, and why. It is small steps and bits of information that help scientists build a robust understanding and system to address disease, not much different than the information an antibody holds to respond to infection and protect.

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