Use of Antibody Avidity Assays for Diagnosis of Severe Acute Respiratory Syndrome Coronavirus Infection

Abstract

An indirect immunofluorescent assay (Euroimmun AG, Luebeck, Germany) was used to investigate the avidity of immunoglobulin G (IgG), IgM, IgA, and total Ig (IgGAM) antibody responses to severe acute respiratory syndrome coronavirus (SARS CoV) infections. Serial serum samples from eight patients collected during the first, third, and ninth months after the onset of infection were evaluated. It was found that low-avidity IgG antibodies were detected in 15/15 (100%), 1/5 (20%), and 0/8 (0%) serum samples collected during the first, third, and ninth months after the onset of symptoms, respectively. Low-avidity antibodies of IgA and IgM subclasses were detected in 14/14 (100%) and 3/14 (21%) serum samples, respectively, collected in the first month after the onset of infection. However, IgA antibodies remained low in avidity in a proportion of patients even during late convalescence. As a consequence, IgG antibody avidity assays gave better discrimination between acute-phase and late-convalescent-phase serum samples than IgM, IgA, or IgGAM assays. In two of these patients, sequential serum samples were also tested for IgG avidity against human CoV strains OC43 and 229E in parallel. While SARS CoV infections induced an anamnestic IgG antibody response to the 229E and OC43 viruses, these cross-reactive antibodies remained of high avidity from early (the first month) postinfection. The results showed that assays to detect low-avidity antibody may be useful for discriminating early from late antibody responses and also for distinguishing anamnestic cross-reactive antibody responses from primary specific responses. This may be useful in some clinical situations.

Coexistence of Different Genotypes in the Same Bat and Serological Characterization of Rousettus Bat Coronavirus HKU9 Belonging to a Novel Betacoronavirus Subgroup

“…The absence of cross-reactive antibodies between Ro-BatCoV HKU9 N protein and N proteins from HCoV-HKU1 (Betacoronavirus subgroup A coronavirus), SARSr-Rh-BatCoV (Betacoronavirus subgroup B coronavirus), Ty-BatCoV HKU4, and Pi-BatCoV HKU5 (both Betacoronavirus subgroup C coronaviruses) upon Western blot analysis supports their classification as separate subgroups of Betacoronavirus. In human coronavirus infections, antigenic cross-reactivity has been commonly observed between SARS-CoV and HCoV-OC43 (Betacoronavirus subgroup A coronavirus) by immunofluorescence assays (6,7). When a recombinant SARS-CoV N-proteinbased ELISA was used, cross-reactivity was observed in only 3 of 21 and 1 of 7 serum samples containing antibodies against HCoV-OC43 and HCoV-229E (49).…”

Natural Pig Plasma Immunoglobulins Have Anti-Bacterial Effects: Potential for Use as Feed Supplement for Treatment of Intestinal Infections in Pigs

“…The ppIgG investigated here bound three different E. coli isolates and one S. enterica isolate equally well. Also, the anti-bacterial IgG of ppIgG was found to bind strongly to bacterial epitopes as the binding strength (avidity) of ppIgG towards E. coli was equal to or greater than seen in other studies using urea to interfere with the antibody-antigen binding [24][25][26][27][28]. Thus natural immunoglobulins purified directly from pig plasma (ppIgG) bind strongly to potentially diarrhoeagenic bacteria and inhibit bacterial adhesion to intestinal cells suggesting the use of ppIgG as an antibiotics alternative for prevention and treatment of enteric infections.…”

Epidemiology of Cytomegalovirus among pregnant women in Africa

“…IgG antibody avidity gives a reflection of how long antibodies have been in circulation, following exposure to an antigen. The longer the antibodies would have been in circulation, the higher the avidity and vice versa [27]. Therefore, low avidity antibodies are a better marker of recent and/or active (≤ 6 weeks) infection, following a positive CMV IgM test [28].…”