As I hypothesized months ago, the researchers who looked at T-cell activation thought it was from previous exposure to one or more of those other four corona viruses that circulate around the world as common colds. They don't have the SARS-COV2 spike protein, but they do have other antigens very similar or identical to SARS-COV2 antigens. The reason I hypothesized that is because early antibody test makers warned users a positive test could mean they had been exposed to antigens on one of the other four corona viruses. There is no reason to assume somebody could react to those antigens and NOT have some immunity to SARS-COV2.

So that means all the so-called "false positive" antibody tests are not really false. They do mean you have some immunity. They just don't tell you it was SARS-COV2.