Research ArticleClinical Studies

Nine Cases of SARS-CoV-2-PCR-positive Samples Showed No Increase of Antibodies Against SARS-CoV-2

TAKAO KITAGAWA, MASANOBU KOBAYASHI, TOHRU OHTA, MASARU TERASAKI, YOKO TSUKAMOTO, RIE TAKAI, REIKA ISHIZUMI, OSAMU UEHARA, KOJI NAKAGAWA, KOZO AKINO, MASAHIRO ASAKA and YASUHIRO KURAMITSU
In Vivo September 2021, 35 (5) 2947-2949; DOI: https://doi.org/10.21873/invivo.12587

Abstract

Background/Aim: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has been affecting Hokkaido, Japan since late February 2020 until present. The aim of this study was to report the relationship between anti-SARS-CoV-2 antibody-positive and SARS-CoV-2 PCR-positive cases by analyzing anti-SARS-CoV-2 antibodies (IgG and total-Ig). Patients and Methods: Serum samples were collected from care workers and nurses in two nursing homes and two hospitals which underwent virus outbreak. All people were confirmed to be SARS-CoV-2-positive by RT-qPCR and their sera was analyzed for anti-SARS-CoV-2 antibodies (IgG and total-Ig). Results: Although 34 out of 43 samples (79.1%) showed enough amount of anti-SARS-CoV-2 antibodies, 9 RT-qPCR -positive samples (20.9%) showed absence of anti-SARS-CoV-2 antibodies in their sera. Conclusion: The results that 20.9% of RT-qPCR-positive samples with SARS-CoV-2 showed absence of anti-SARS-CoV-2 antibodies provides a possibility that the innate immune reaction could eliminate the virus without activating adaptive immune reaction.

From December 2019, the entire world has been affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that originated in Wuhan, China (1), and the World Health Organization (WHO) declared that coronavirus disease 2019 (COVID-19) a global pandemic on March 11th 2020 (2). Hokkaido, Japan, has been also affected by SARS-CoV-2 beginning late February 2020 (3). In April, May and November, two nursing homes and two hospitals had outbreak and facilities had more than 10 PCR-positive people who are care workers and nurses. All were confirmed to have COVID-19 infection by RT-qPCR for SARS-CoV-2 according to the nationally recommended protocol (4). The PCR-positive samples were analyzed for anti-SARS-CoV-2 antibodies (IgG and total-Ig) to analyze the relationship between antibody-positive and PCR-positive cases.

Patients and Methods

Samples. The study protocol was approved by the Institutional Review Board for Human Use of the Health Sciences, University of Hokkaido and the other four facilities (I) Nursing Home Barato Akashia-Heights (II) Chitose Daiichi Hospital (III) Kin-ikyo Chuo Hospital (IV) Nursing home Dream House. Written informed consent was obtained from all patients before study. The PCR-positive samples collected more than 30 days from the date of PCR positivity from these 4 facilities.

Measurement of antibody. The measurement of anti-SARS-CoV-2 antibodies (IgG and total-Ig) in sera were done by using the Vitros Immunodiagnostic Products anti-SARS-CoV-2 total Ig test and the anti-SARS-CoV-2 IgG test (Ortho Clinical Diagnostics) (5). The sensitivity of the anti-SARS-CoV-2 total Ig test was reported to be 100% in samples collected more than 6 days from the date of PCR positivity (5). The sensitivity of the anti-SARS-CoV-2 IgG test was also reported to be 100% in samples collected at least 15 days following initial disease manifestation (6).

Results

Thirty-four out of 43 PCR-positive samples (79.1%) showed enough amounts of IgG and total-Ig against SARS-CoV-2. However, nine PCR-positive samples (20.9%) (3 out of 11; Nursing Home Barato Akashia-Heights, 3 out of 10; Chitose Daiichi Hospital and 1 out of 8; Kin-ikyo Chuo Hospital; 2 out of 14; Nursing home Dream House) showed absence of anti-SARS-CoV-2 antibodies in their sera (Table I). The three anti-SARS-CoV-2 antibody-absent cases in the nursing home Barato Akashia-Heights showed PCR-positive with high Ct values (32.19, 33.94, and 36.68) and calculated viral copies were less than 100 copies. These three people showed negative results of IgG values and Total Ig values again from sera collected 14 days later.

View this table:
Table I.

Results of RT-PCR and antibody test against SARS-CoV-2.

Discussion

The results of the present study showed that 9 cases out of 43 SARS-CoV-2-PCR-positive samples showed no increase of antibodies against SARS-CoV-2. These results show a possibility of innate immune reaction that could eliminate the virus without activating adaptive immune reaction involving B lymphocytes, helper T cells and plasma cells. Many reports showed an increase of NK cells in SARS-CoV-2-infected people with no symptoms, convalescence and mild symptoms, and decrease of NK cells in SARS-CoV-2-infected people with severe symptoms. (7, 8). In the present study, all cases whose antibodies against SARS-CoV-2 were measured were asymptomatic. It has been reported that the sensitivity of the anti-SARS-CoV-2 total Ig test and the anti-SARS-CoV-2IgG test is greater than 95% (5, 6, 9), and that antibodies are positive in more than 95% of PCR-positive patients. For the first time, our study examined the presence of antibody production in PCR-positive patients, and we found that innate immune response might eliminate SARS-Cov-2 in more than 20% of SARS-CoV-2 PCR-positive patients before adaptive immune system start up. Smetana et al. reported the role of interleukin-6 (IL6) on lung complications in patients with COVID-19 and they mentioned that inhibitors of IL6 signaling represent a promising approach that can be employed for attenuation of a cytokine storm and might be beneficial for patients with COVID-19 (10). IL-6 is involved in the regulation of B cell response into antibody producing cells (11). Presumably asymptomatic SARS-CoV-2-infected people whose antibodies against SARS-CoV-2 were measured in the present study might produce very low levels of IL6 and might not induce enough B cell differentiation to antibody-producing cells. Further studies are needed to clarify the role of innate immunity and IL6 during production of antibodies against SARS-CoV-2 in asymptomatic SARS-CoV-2-infected people.

Acknowledgements

This work was supported, in part, by the Grant from Advanced Research Promotion Centre, Health Sciences University of Hokkaido. We thank Ortho Clinical Diagnostics to lent us Vitros XT7600 integrated system

Footnotes

  • Authors’ Contributions

    All Authors contributed to the study conception and design. Materials preparation, data collection, and analysis were performed by TK, YK, TO, MT, YT, RT, OU, KN and RI. The first draft of the manuscript was written by TK, YK, YT and MK and all authors commented on previous versions of the manuscript. All Authors read and approved the final manuscript.

  • This article is freely accessible online.

  • Conflicts of Interest

    The Authors declare no conflicts of interest.

  • Received May 21, 2021.
  • Revision received June 9, 2021.
  • Accepted June 23, 2021.

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Nine Cases of SARS-CoV-2-PCR-positive Samples Showed No Increase of Antibodies Against SARS-CoV-2
TAKAO KITAGAWA, MASANOBU KOBAYASHI, TOHRU OHTA, MASARU TERASAKI, YOKO TSUKAMOTO, RIE TAKAI, REIKA ISHIZUMI, OSAMU UEHARA, KOJI NAKAGAWA, KOZO AKINO, MASAHIRO ASAKA, YASUHIRO KURAMITSU
In Vivo Sep 2021, 35 (5) 2947-2949; DOI: 10.21873/invivo.12587
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