CHICAGO (CBS) — Saturday morning Chicago police and firefighters who survived COVID-19 donated their plasma Sunday morning to help develop a treatment for the virus.

They got a big show of gratitude from a longtime lawmaker.

“I want to thank the law enforcement officers, the policemen who have had the virus and recovered and are making use of their plasma so that others can get treatment that they need. And the treatment is going to be helpful to those people,” said Rep. Danny Davis.

The plasma they are donating contains COVID-19 antibodies. The treatment is called “convalescence treatment therapy.”

Scientists hope it can be given to patients to boost their ability to fight the virus. It also might keep moderately ill patients from getting sicker.

The Chicago Medical Society is looking for more volunteers.

You can sign up at www.COVID-19CHI.org.