Coronavirus
is an enveloped RNA virus that causes mild to severe
respiratory diseases in humans, including HKU1-CoV, 229E-CoV, NL63-CoV,
OC43-CoV, SARS-CoV, MERS-CoV, and SARS-CoV-2. Due to the outbreak
of SARS-CoV-2, it is important to identify the patients and investigate
their immune responses. Protein microarray is one of the best platforms
to profile the antibodies in the blood because of its fast, multiplexed,
and sensitive nature. To fully understand the immune responses and
biological specificities, this study developed a human coronavirus
(HCoV) protein microarray and included all seven human coronaviruses
and three influenza viruses. Each protein was printed in triplicate
and formed 14 identical blocks per array. The HCoV protein microarray
showed high reproducibility and sensitivity to the monoclonal antibodies
against spike and nucleocapsid protein with detection limits of 10ā200
pg. The HCoV proteins that were immobilized on the array were properly
folded and functional by showing interactions with a known human receptor,
e.g., ACE2. By profiling the serum IgG and IgA from 32 COVID-19 patients
and 36 healthy patients, the HCoV protein microarray demonstrated
97% sensitivity and 97% specificity with two biomarkers. The results
also showed the cross-reactivity of IgG and IgA in COVID-19 patients
to spike proteins from various coronaviruses, including that from
SARS-CoV, HKU1-CoV, and OC43-CoV. Finally, an innate immune protein
named surfactant protein D showed broad affinities to spike proteins
in all human coronaviruses. Overall, the HCoV protein microarray is
multiplexed, sensitive, and specific, which is useful in diagnosis,
immune assessment, biological development, and drug screening.