Measurement of the Reduction of OC-43 Coronavirus Production by Natural Killer Cell Antibody-Dependent Cell-mediated Cytotoxicity (ADCC) 2260991
The expression of OC-43 coronaviral proteins in the plasma membranes of infected cells [that are needed to support antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) cells] occurs at the same time that virions begin to be released from infected cells. The viral production in the absence of ADCC or cytotoxic T cell death will continue for many days more. We queried the impact of early ADCC on unaffected total viral production. We utilized the cold-causing, endemic human coronavirus OC-43, a virus in the same subfamily as SARS-CoV-2. We used NK-92-CD16A lymphocytes as killer cells, OC-43 from BEI Resources at an moi of 2, plasma antibodies from infected children, and infected lung A549 cells as ADCC ‘targets’. Viral production was monitored by PCR of virions released into the cell-free supernatants and by virions remaining inside cells. We used a Taqman probe from ThermoFisher for a propriety site within the positive RNA OC-43 virus, calibrating assays with genomic OC-43 RNA from BEI. We found that PCR products began to appear in the cell-free supernatants on day 2 post infection (pi) and increased on subsequent days. These viral RNA signals coincided with our previous times for first susceptibility to ADCC and first detection of plasma membrane viral protein in the A549 cells. At day 3 pi, ADCC could eliminate most infected cells. OC-43 gene copies in the supernatants were 16.8 million on day 3 and 24.2 million on day 5 post infection, indicating that some virion production can be curtailed by early ADCC. While substantial viral production before day 3 is observed, ADCC on day 3 reduced the subsequent production by over 75%. Additional conclusions are premature without assessment of infectious virions (by plaque forming units or other means) but the data indicate that early ADCC will substantially reduce the spread of coronaviral infections. This poster was made possible by a grant from the National Institute of General Medical Sciences (GM103440) from the National Institutes of Health and by the T34 GM145539 grant awarded to the University of Nevada, Reno Institute for Neuroscience (MARC program), and the UNR foundation. Viral Immunology (VIR)