Understanding Human Coronavirus HCoV-NL63

Abdul-Rasool, Sahar; Fielding, Burtram C

Serum samples have been screened for antibodies against HCoV-NL63 using enzyme-linked immunosorbent assays (ELISA) [75, 76] . An ELISA assay based on the N protein showed high seropositive results for serum samples from children younger than 20 years old [76] . Interestingly, the presence of maternally-acquired N-directed antibodies was detected in serum by ELISA [75, 76] , usually decreasing within the first 4-5 months of life [76] . Potent neutralizing activity directed against HCoV-NL63 S protein was detected in virtually all serum samples from patients eight years of age or older, suggesting that HCoV-NL63 infection of humans is common and usually acquired during childhood [42] . Alarmingly, SARS-CoV infections appear to stimulate cross-reactive antibody responses to other human coronaviruses, including HCoV-NL63 [77] . Such cross reaction between human coronaviruses has been reported previously for immunoflourescence and complement fixation tests [78, 79] . In fact, false positive results were also reported for SARS-CoV detection using ELISA tests based on the recombinant N antigen [80] . This cross-reactivity is most likely due to the presence of cross-reactive antigenic epitopes of the coronaviruses [77] . An awareness of this ( cross-reactivity is important when developing antigenand/or antibody-diagnostic assays and selecting the most suitable antigen or antigen target is important.