Researchers from MedUni Vienna's Center for Pathophysiology, Infectiology and Immunology led by Rudolf Valenta developed an ELISA laboratory test to identify patients who had developed protective antibodies after having COVID-19. This showed that only 60% of patients convalescing from COVID-19 developed antibodies that inhibit the interaction of the SARS-CoV-2 receptor-binding domain (RBD) with ACE2. The ACE2 (Angiotensin Converting Enzyme 2) receptor for SARS-CoV-2 occurs predominantly in the respiratory tract and other organs affected by the virus. "The positive outcome is that we now have a test that can identify antibodies and show whether people who have already been infected have protective immunity or not."
However, the research team also discovered that certain immunocomplexes consisting of RBD and patient antibodies, have a higher binding rate to ACE2. This is a hitherto unknown mechanism that enables the virus to dock onto cells more easily. "This is the first study to show elevated binding to ACE2 by immunocomplexes comprising RBD and patient antibodies," explains Principal Investigator Rudolf Valenta. Potentially, this can make it even easier for the virus to infect cells." Further research is now needed to find out exactly what this means in terms of immunity and for vaccine development.
"Antibodies in serum of convalescent patients following mild COVID-19 do not always prevent virus receptor binding." Pia Gattinger, Kristina Borochova, Yulia Dorofeeva, Rainer Henning, Renata Kiss, Bernhard Kratzer, Bernhard Mühl, Thomas Perkmann, Doris Trapin, Martina Trella, Paul Ettel, Inna Tulaeva, Winfried F. Pickl, Rudolf Valenta. doi.org/10.1111/all.14523.