NEW YORK — New York City will test 140,000 people for coronavirus antibodies between next week and early June, Mayor Bill de Blasio announced Thursday.

The antibody tests, which indicate whether a person has been infected with the virus at some point, will be offered for free by appointment at five locations around the city, de Blasio said. The results will be available to the individual in one to two days and will also be used for epidemiological research, he said.

Researchers have said it is unclear whether antibodies for the coronavirus provide immunity or whether people who test positive for the antibodies can still be sickened by the virus.

"We are not promising people a rose garden here," de Blasio said. "We're not saying the antibody test is the last word. It's not. But it tells you something."

The city will use tests made by BioReference Laboratories for the free testing program.

Blood tests are different from the nasal swab tests currently used to diagnose active COVID-19 infections. Instead, the tests look for blood proteins called antibodies, which the body produces days or weeks after fighting an infection. Most use a finger-prick of blood on a test strip.

Health officials in the U.S. and around the world have suggested the tests could be helpful in identifying people who have previously had the virus — with or without getting sick — and developed some immunity to it. But researchers haven't yet been able to answer many questions about the tests  including what level of antibodies it takes to be immune and how long that immunity lasts.