Very, very interesting study posted in Nature this week! giving more credence to this possible explanation as to why some people have a tough go with the virus and others have a mild case or are asymptomatic. BUT the positive immune response is not tied to antibodies but rather T-Cell response!
https://www.nature.com/articles/s41586-020-2550-z_reference.pdf
SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls
Essentially, SARS-1, and Sars-Cov-2 have identical NSP7 and 13 proteins which can be found in the betacoronavirus that cause milder respiratory infections/common colds (OC43 and HKU1) or more likely other presently unknown coronaviruses that cause similar mild infections.
During an immune response to Sars-Cov-2, a person who had been exposed to one of the endemic or scientifically unknown betacoronaviruses, had previously “informed” T-cells which would recognise and target these familiar proteins and effectively mount a prompt and measured defense. T-cells remember this portion of the virus from its sister virus that you were exposed to and allows the adaptive immune system to effectively target it.
As opposed to antibodies, T-cell memory would be the key to a long lasting/strong immune response and in this theory and prior exposure to these specific betacoronaviruses might be the reason some people have an “immunity” of sorts.
On the other hand when the cytotoxic T-cells don’t recognise the pathogen off the bat, they overcompensate and go ham on your system, causing a cytokine storm while failing to effectively eliminate the virus