Incomplete IgG avidity maturation after seasonal coronavirus infections.

Struck, Friedhelm; Schreiner, Patrick; Staschik, Eva; Wochinz-Richter, Karin; Schulz, Sarah; Soutschek, Erwin; Motz, Manfred; Bauer, Georg

In classical viral infections, the avidity of IgG is low during acute infection and high a few months later. As recently reported, SARS-CoV-2 infections are not following this scheme, but they are rather characterized by incomplete avidity maturation. This study was performed to clarify whether infection with seasonal coronaviruses also leads to incomplete avidity maturation. The avidity of IgG towards the nucleoprotein (NP) of the seasonal coronaviruses 229E, NL63, OC43, HKU1 and of SARS-CoV-2 was determined in the sera from 88 healthy, SARS-CoV-2-negative subjects and in the sera from 70 COVID-19 outpatients, using the recomLineSARS-CoV-2 assay with recombinant antigens. In the sera from SARS-CoV-2-negative subjects, incomplete avidity maturation (persistent low and intermediate avidity indices) was the lowest for infections with the alpha-coronaviruses 229E (33.3 %) and NL63 (61.3 %), and the highest for the beta-coronaviruses OC43 (77.5%) and HKU1 (71.4%). In the sera from COVID-19 patients, the degree of incomplete avidity maturation of IgG towards NP of 223E, OC43 and HKU1 was not significantly different from that found in SARS-CoV-2-negative subjects, but a significant increase in avidity was observed for IgG towards NP of NL63. Though there was no cross-reaction between SARS-CoV-2 and seasonal coronaviruses, higher concentrations of IgG directed towards seasonal coronaviruses seemed to indirectly increase avidity maturation of IgG directed towards SARS-CoV-2. Our data show that incomplete IgG avidity maturation represents a characteristic consequence of coronavirus infections. This raises problems for the serological differentiation between acute and past infections, and may be important for the biology of coronaviruses. This article is protected by copyright. All rights reserved.