By Jonny Lupsha, News Writer

According to The Boston Globe, the new data about coronavirus exposure comes from a blood test led by Massachusetts General Hospital. Nearly one-third of 200 Chelsea residents who gave a drop of blood to researchers on the street this week tested positive for antibodies linked to COVID-19, the article said. Of the 200 random participants, 64 tested positive for the antibodies that are generated to fight the disease.

Antibodies are produced by our bodies immune systems as part of the bodys natural defense mechanism. They are often involved in cancer therapies.

Antibodies help fight off foreign agents that enter our bodies. In order to do this, the body needs to identify the enemy. According to Dr. David Sadava, Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center, any foreign agent that antibodies attack is called an antigen, in which anti stands for antibody and gen stands for generate. Theyre called antigens specifically because they generate antibodies.

Antigens are not necessarily a large substance, but its a group of atoms linked together in a specific way, Dr. Sadava said. The atoms on, for example, a toxin from a bacterium, like the botulinum toxin, have a unique shape. Some of those are atoms that we dont have in our bodiesonly the bacterium has itso the immune system will recognize that.

How are they recognized? Dr. Sadava said that a type of helper cell in your body called a T-cell recognizes the antigen as being a foreign agent. Essentially, the T-cell is always on the lookout for natural and foreign elements in the body. When it flags an antigen, it sets off a specific two-step response to it that includes both itself and antibodies.

In the first step of the immune response, when the body has been notified of an antigen, cells in the blood serum itself make antibodies against that antigen, if its in the blood. The antibodies mobilize in order to find and bind to the antigen specifically.

Dr. Sadava said this binding is like a lock and key. Antibodies have specific three-dimensional structures, and they will bind to any of the antigen thats in the blood system.

Antibodies can basically escort the antigen out of the body and stop it from causing any trouble along the way. If youre thinking of a bouncer in a nightclub, youre not far off.

The second step of the immune response happens on the cellular level. T-cells can kill some antigens. Dr. Sadava used a surprising example to illustrate how this overall process works.

You have antibodies made in small amounts, and T-cells made in small amounts, that recognize HIV, the virus that causes AIDS, he said. You have a small number of those soldiers that are constantly being made in small numbers. And if you are infected with HIV, all of a sudden, that army gets expandedit gets expanded when this recognition event happens, and all of a sudden those cells will be mobilized.

Once mobilized, the recognizing cells send signals to their siblings to divide and clone themselves to reject or kill cells that contain the antigen.

The residents of Chelsea tested positive for certain antibodies that their bodies made specifically to fight the coronavirus. This means that if they didnt have the coronavirus at the time of the test, they had already encountered it at some point in the past. If they hadnt, those specific antibodies wouldnt be in their blood.

Dr. David Sadava contributed to this article. Dr. Sadava is Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center. He earned a B.S. with first-class honors in biology and chemistry from Carleton University and a Ph.D. in biology from the University of California, San Diego.

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