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The worldwide pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has continued to date. Given that some of the patients with coronavirus disease 2019 (COVID-19) are asymptomatic, antibody tests are useful to determine whether there is a previous infection with SARS-CoV-2. In this study, we measured IgM and IgG antibody titers against SARS-CoV-2 in the serum of asymptomatic healthy subjects in The University of Tokyo, Japan. From June 2020, we recruited participants, who were students, staff, and faculty members of The University of Tokyo in the project named The University of Tokyo COVID-19 Antibody Titer Survey (UT-CATS). Following blood sample collection, participants were required to answer an online questionnaire about their social and health information. We measured IgG and IgM titers against SARS-CoV-2 using iFlash-SARS-CoV-2 IgM and IgG detection kit which applies a chemiluminescent immunoassay (CLIA) for the qualitative detection. There were 6609 volunteers in this study. After setting the cutoff value at 10 AU/mL, 32 (0.48%) were positive for IgG and 16 (0.24%) for IgM. Of six participants with a history of COVID-19, five were positive for IgG, whereas all were negative for IgM. The median titer of IgG was 0.40 AU/mL and 0.39 AU/mL for IgM. Both IgG and IgM titers were affected by gender, age, smoking status, and comorbidities. Positive rates of IgG and IgM titers were relatively low in our university. Serum levels of these antibodies were affected by several factors, which might affect the clinical course of COVID-19. [ABSTRACT FROM AUTHOR]

Primary cytomegalovirus (CMV) infection during pregnancy often results in congenital CMV infection with severe clinical complications. IgM antibodies are one of the indices of primary infection. The IgG avidity index (AI) is also known to remain low for 3 months after primary infection. Here, we evaluated and compared the performance of CMV IgM and IgG avidity assays. Because sensitivity and specificity reportedly differ between CMV IgM kits, CMV IgM detection was compared between the two commercially available ELISA kits that are most commonly used in Japan. Sera for CMV IgM were first screened using a traditional indirect ELISA kit. Selected samples were then tested for CMV IgM and CMV AI using a CMV IgM‐capture ELISA kit and a CMV IgG avidity assay, respectively. The rate of concordance between the IgM kits was 89% (42/47), indicating the absence of any significant difference. Most of the CMV IgM‐positive plasma samples showed high CMV IgG AI; however, 18 commercially available plasma samples with low CMV IgG AI were all CMV IgM‐positive. One plausible explanation for this discrepancy is that the duration of low IgG AI is shorter than that of IgM positivity. Alternatively, CMV IgM tests may generate pseudo‐positive readouts in cases of congenital infection. Nevertheless, our study confirms that CMV IgG AI can be a reliable indicator of CMV primary infection. [ABSTRACT FROM AUTHOR]

Primary Toxoplasma gondii (T. gondii) infection during pregnancy could result in congenital disease with severe clinical complications. IgM antibodies are one of the indices of primary infection. The IgG avidity index (AI) is also known to remain low for at least 3 months after primary infection. Here, we evaluated and compared the performance of T. gondii IgG avidity assays as confirmed by T. gondii IgM serostatus and number of days post-exposure. Four assays preferentially used in Japan were employed to measure the T. gondii IgG AI. Results for the T. gondii IgG AI showed good concordance, particularly in cases with a low IgG AI. This study confirms that the combination of T. gondii IgM and IgG AI tests is a reliable and suitable method for identifying T. gondii primary infections. Our study proposes the necessity of measuring the T. gondii IgG AI as an additional indicator of T. gondii primary infection. [ABSTRACT FROM AUTHOR]

This study aimed to calibrate hepatitis E virus (HEV) serological assays. We optimized the previously developed in-house HEV antibody enzyme-linked immunosorbent assay (ELISA) by setting the cutoff with an in-house serological performance panel consisting of broad HEV antibody titers and subtracting nonspecific background values for anti-HEV IgM, IgA, and IgG. We also compared the assay's performance with that of commercial serological assay kits (four kits for IgM, one for IgA, and two for IgG). Although all serological assays readily detected HEV antibodies at high titers in the symptomatic hepatitis E population, considerable variations between assays were observed in the asymptomatic population. The in-house ELISA showed a higher sensitivity for HEV IgM, IgA, and IgG than the commercial kits and detected the seroconversion of HEV IgM and IgG earlier when testing a commercially available HEV seroconversion panel. The low sensitivity of the commercial kits was due to the high setting of the original cutoff, which was demonstrated by receiver operating characteristic analysis. However, the corrected cutoff value reduced assay specificity. Background subtraction is essential to achieve high specificity because the in-house ELISA without background subtraction reduced its specificity. These results indicate that asymptomatic specimens and background subtraction contribute to the optimization of HEV serological assays. IMPORTANCE Accurate diagnosis of hepatitis E virus (HEV) infection is essential for public health surveillance and for preventing HEV-contaminated blood transfusion. Anti-HEV IgM or IgA is used as a reliable marker of recent HEV infection. However, considerable variability in the sensitivity and specificity of HEV antibody detection is observed among several commercially available assay kits. In addition, none of the HEV antibody detection methods have been approved by the U.S. Food and Drug Administration (FDA). Here, we show that the in-house enzyme-linked immunosorbent assay (ELISA) could detect HEV IgM and IgA more sensitively than commercial kits in the asymptomatic population. We also suggest that the assay performance of commercial kits might be improved by optimizing the cutoff and reducing nonspecific background noise. A sensitive serological (IgM or IgA) assay in addition to HEV RNA testing will contribute to accurate diagnosis of acute HEV infection because HEV RNA-positive duration is relatively short.

A human-mouse hybridoma clone #86 secreting IgM-class human monoclonal antibody to peanut allergen protein Ara h1 was newly established. To detect an antibody-binding sequence (epitope) on Ara h1, the monoclonal antibody #86 was reacted with multi-pin apparatus with a series of peptides synthesized from the amino acid sequence of Ara h1. The antibody #86 was found to bind to a peptide with amino acid sequence of 481EEEEDEDEEEEGSNREVRRY500. Further analysis with shorter pin-peptides with ten amino acid-long showed that the peptides reacted with the antibody #86 contained a sequence of 485DEDEEEE491. This might be an essential linear sequence of this epitope. When the 485DED487 part of the peptide was replaced by alanine, decreased binding of antibody #86 was observed. [ABSTRACT FROM AUTHOR]

There have been reports from several countries that hepatitis E virus (HEV) infection is frequently associated with Guillain-Barré syndrome (GBS). This study aimed to determine the frequency of HEV infection associated with GBS in Japanese patients, and to clarify the clinical characteristics of these patients. Sera obtained from 63 patients with GBS or Miller Fisher syndrome (MFS) and 60 control subjects were examined for both HEV-IgM and HEV-IgG. Of the 63 patients, three were positive for both HEV-IgM and elevated hepatic enzymes: Two had GBS, and one had MFS. No control subjects were positive for HEV-IgM. Our study demonstrated that 4.8 % of patients with GBS or MFS from our institution had associated acute HEV infection. There were no clinical differences between GBS with HEV infection and other GBS cases. To our knowledge, this is the first survey in Japan of HEV-associated GBS or MFS. [ABSTRACT FROM AUTHOR]

To better understand the immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in individuals with COVID-19, it is important to investigate the kinetics of the antibody responses and their associations with the clinical course in different populations, since there seem to be considerable differences between Western and Asian populations in the clinical features and spread of COVID-19. In this study, we serially measured the serum titers of IgM, IgG and IgA antibodies generated against the nucleocapsid protein (NCP), S1 subunit of the spike protein (S1), and receptor-binding domain in the S1 subunit (RBD) of SARS-CoV-2 in Japanese individuals with COVID-19. Among the IgM, IgG, and IgA antibodies, IgA antibodies against all of the aforementioned viral proteins were the first to appear after the infection, and IgG and/or IgA seroconversion often preceded IgM seroconversion. In regard to the timeline of the antibody responses to the different viral proteins (NCP, S1 and RBD), IgA against NCP appeared than IgA against S1 or RBD, while IgM and IgG against S1 appeared earlier than IgM/IgG against NCP or RBD. The IgG responses to all three viral proteins and responses of all three antibody classes to S1 and RBD were sustained for longer durations than the IgA/IgM responses to all three viral proteins and responses of all three antibody classes to NCP, respectively. The seroconversion of IgA against NCP occurred later and less frequently in patients with mild COVID-19. These results suggest possible differences in the antibody responses to SARS-CoV-2 antigens between the Japanese and Western populations., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Bartonella henselae strains genetically differ among nations. The utility of Japanese-specific YH-01 strain was investigated in developing indirect fluorescence antibody assay (IFA) for IgM in comparison with conventional IFA employing Houston-1 strain by testing 100 Japanese patients suspected of cat scratch disease. The country-specific IFA greatly improved the accuracy of diagnosis., (Copyright © 2016 Elsevier Inc. All rights reserved.)