Humoral Immune Response to SARS-CoV-2

Pauline H. Herroelen, MSc; Geert A. Martens, MD, PhD; Dieter De Smet, MD; Koen Swaerts, MSc; An-Sofie Decavele, MSc

Disclosures

Am J Clin Pathol. 2020;154(5):610-619. 

In This Article

Results

Cross-reactivity (Analytical Specificity)

Analytical specificity was evaluated on 57 prepandemic samples from individuals infected with other HCoV viruses (229E/HKU1/OC43), other infectious agents, or with positivity to anti–nuclear factor or rheumatoid factor (Table 1). Wantai SARS-COV-2 Ab ELISA, Elecsys Anti-SARS-CoV-2 assay, EUROIMMUN Anti-SARS-CoV-2 IgG, and Innovita 2019-nCoV Ab Test showed no cross-reactivity Table 2. EUROIMMUN Anti-SARS-CoV-2 IgA and Orient Gene COVID-19 IgG/IgM Rapid Test showed cross reactivity with common cold HCoV viruses, resulting in respective analytical specificities of 91.1% and 92.9%. LIAISON SARS-CoV-2 S1/S2 IgG (96.4% analytical specificity) was the only to show interference by rheumatoid factor (Table 1).

Sensitivity for Detection of Presence of SARS-CoV-2 Antibodies

Study Participants. Sensitivities for detection of SARS-CoV-2 antibodies were compared on 171 samples obtained from 135 subjects, all with PCR-confirmed SARS-CoV-2 infections, pooled or grouped in two distinct cohorts: hospitalized and paucisymptomatic COVID-19 patients. Hospitalized patients included 105 samples from 71 patients hospitalized for severe COVID-19 disease, all with very high level of suspicion of COVID-19 pneumonia on chest computed tomography (COVID-19 Reporting and Data System [CO-RADS] score = 5):[13] 48 males (median age, 65 years; IQR, 53–80) and 23 females (median age, 79 years; IQR, 67–86). Serum samples ranged from 0 to 39 days after patient-reported symptom onset. Paucisymptomatic patients included 66 samples from 64 health care workers with mild (n = 61) or no (n = 3) WHO-listed COVID-19 symptoms: myalgia (present in 62.5%), fever (60.9%), dry cough (56.2%), dyspnea (40.6%), severe fatigue (35.9%), headaches (30.0%), loss of smell or taste (26.6%), or diarrhea (18.8%). None of these patients were hospitalized. Serum samples ranged from 11 to 54 days after patient-reported symptom onset.

Sensitivity for Detection of SARS-CoV-2 Antibodies. Sensitivity was calculated for different patient groups (all patients, hospitalized and paucisymptomatic patients). First, vs SARS-CoV-2 PCR (100% of samples from PCR+ patients) as reference, by measuring the percentage of samples showing antibody titers above the respective assay's cutoff (Table 2). Second, by comparing each individual assay to the consensus outcome of the majority of 7 tested assays Table 3. Wantai SARS-COV-2 Ab ELISA showed highest overall sensitivity for detection of SARS-CoV-2 antibodies: 86.4% (95% confidence interval [CI], 80.3%-91.2%) vs PCR and 100% (95% CI, 97.3%-100%) vs consensus at all time points in both patient cohorts. Its sensitivity was significantly higher (P < .05) than all other assays with the exception of Orient Gene COVID-19 IgG/IgM Rapid Test and EUROIMMUN Anti-SARS-CoV-2 IgG and IgA combined. In a real-world clinical setting, serology assays might be used at later time stages, eg, more than 20 days after onset of symptoms or to document past SARS-CoV-2 infection in paucisymptomatic patients. In these patients, 4 assays showed clinically acceptable sensitivity for detection of SARS-CoV-2 antibodies above 95% vs consensus result (Table 3): Wantai SARS-COV-2 Ab ELISA, Elecsys Anti-SARS-CoV-2 assay, EUROIMMUN Anti-SARS-CoV-2 IgG and IgA combined, and Orient Gene COVID-19 IgG/IgM Rapid Test. In comparison with all other assays, LIAISON SARS-CoV-2 S1/S2 IgG showed significantly (P < .05) lower sensitivities of 83.6% (95% CI, 72.5%-91.5%) vs consensus (Table 3) at greater than 20 days post onset of symptoms and of 84.2% (95% CI, 72.1%-92.5%) in paucisymptomatic patients. Also, EUROIMMUN Anti-SARS-CoV-2-NCP(IgG) and Innovita 2019-nCoV Ab Test showed limited sensitivity at greater than 20 days post onset of symptoms.

Kinetics of Seroconversion. We compared timing of detection of antibodies of the ELISA/CLIA assays on consecutive blood samples of 8 critically ill patients admitted to intensive care units (Figure 1). In all 8 patients, Wantai SARS-COV-2 Ab ELISA was first to exceed the predefined assay cutoff, followed by the EUROIMMUN Anti-SARS-CoV-2 IgA assay. In this cohort of intensive care patients, of the N-targeting assays, EUROIMMUN Anti-SARS-CoV-2-NCP(IgG) provided positive results more rapidly than Elecsys Anti-SARS-CoV-2 assay. LIAISON SARS-CoV-2 S1/S2 IgG was last to detect seroconversion. Seroconversion rates were additionally studied by a pooled analysis in samples from different patients, grouped according to the timeframe after symptom onset ranging from less than 10 days, 10 to 20 days, or more than 20 days post onset of symptoms (Table 2 and Table 3). All tests except Wantai SARS-COV-2 Ab ELISA showed a significantly higher positivity rate between 10 and 20 days post onset of symptoms as compared to less than 10 days post onset of symptoms (P < .05). No significant differences were observed in positivity rates between 10 and 20 days post onset of symptoms and more than 20 days post onset of symptoms (Table 2), indicating that serology testing can be performed starting from 10 days after onset symptoms. In samples less than 10 days after onset of symptoms, all from hospitalized patients, the Wantai SARS-COV-2 Ab ELISA outperformed all other assays, with a sensitivity of 100% (95% CI, 88.1%-100%) vs consensus and 75.5% (95% CI, 61.7%-86.2%) vs PCR, which was significantly lower than its performance in samples from patients greater than 20 days post onset of symptoms (P < .05).

Concordance Analysis of Humoral Immune Response on Individual Samples. For the assays with acceptable overall sensitivity above 95% (Wantai SARS-COV-2 Ab ELISA, Elecsys Anti-SARS-CoV-2 assay, EUROIMMUN Anti-SARS-CoV-2 IgG and IgA combined, and Orient Gene COVID-19 IgG/IgM Rapid Test) a good overall concordance was seen in samples from patients greater than 10 days post onset of symptoms, with 87.7% and 3.5% of samples positive or negative respectively with all 4 methods. No clear differences were observed in kinetics of appearance of antibodies to S or N epitopes. Beyond 10 days, only 1.4% (1/71) of hospitalized and 4.7% (3/64) paucisymptomatic patients developed no detectable antibodies.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....