Table 3.

Cross-reactive and homologous titers of serum from HCoV S1 immunized rabbit and guinea pig.

Serum	229E IF titer	NL63 IF titer	OC43 IF titer
Rb anti-229E S1	5000	< 50	< 50
Gp anti-229E S1	1000	< 50	< 50
Rb anti-HKU1 S1	< 50	< 50	200
Gp anti-HKU1 S1	50	< 50	200
Rb anti-NL63 S1	200	5000	< 50
Rb anti-NL63 S1	200	5000	< 50
Rb anti-OC43 S1	< 50	200	5000
Gp anti-OC43 S1	< 50	< 50	5000
Rb anti-SARS-CoV-2 S1	< 50	< 50	< 50
Gp anti-SARS-CoV-2 S1	< 50	< 50	< 50

Titers for sera of one rabbit and one guinea pig immunized with three doses of each of the indicated HCoV S1 antigens were determined using immunofluorescence assay. Huh7 cells were infected with 229E or OC43 virus and LLC-MK2 cells with NL63 virus and labelled with a dilution series (1:50 to 1:25,000) of sera against each HCoV S1. Serum titer > 1:50 was considered positive. Of note, infectious HKU1 is globally not available.

Rb, rabbit; Gp, guinea pig; S1, spike subunit 1; IF titer, immunofluorescence titer; < 50, IF titer lower than 1:50.

Significant values are in bold.