Characteristics of cross-reactive serum and memory B-cells between SARS-CoV-2 and endemic HCoVs 

A group from Scripps Research Institute has reported about characteristics of cross-reactive serum and memory B-cells between SARS-CoV-2 and endemic HCoVs.
https://www.nature.com/articles/s41467-021-23074-3

COVID-19 convalescent sera from 36 donors showed strong reactivity to the SARS-CoV-2 spike in the vast majority of infected donors, somewhat lower reactivity with the SARS-CoV-1 spike and much lower reactivity with the MERS-CoV spike. COVID-19 sera also exhibited strong cross-reactivity with endemic HCoV spikes, especially with the HCoV-HKU1 and HCoV-OC43 β-HCoVs. The α-HCoV-derived HCoV-NL63 spike was least reactive among the four endemic HCoVs. From a cohort of 36 HIV seropositive but otherwise healthy human donors whose samples were collected SARS-CoV-2 pre-pandemic. The sera showed almost no reactivity to SARS-CoV-2/CoV-1 and MERS-CoV spikes but showed strong binding to the endemic HCoV spikes, especially against the HCoV-HKU1 and HCoV-OC43 β-HCoVs (see a figure below).

In sera from SARS-CoV-2 pre-pandemic cohort, there was no evidence of pre-existing SARS-CoV-2 S-protein reactive antibodies that resulted from endemic HCoV infections. A recent study has, however, reported the presence of SARS-CoV-2 S-protein reactive antibodies in a small fraction of pre-pandemic human sera from children and adolescents as explained in the following paper.
Preexisting immunity to SARS-CoV-2 before the pandemic

The SARS-CoV-2/HKU1-CoV cross-reactive mAbs failed to bind any of the S1 subunit domains or subdomains, suggesting targeting to the more conserved S2 subunit

Interestingly, SARS-CoV-2 infection boosted titers to endemic HCoV-HKU1 S protein, but not for other HCoVs, suggesting that SARS-CoV-2 infection activated cross-reactive endemic HCoV-HKU1 S-protein-specific B cells.