In this study, we tested the presence of IFN-α Abs in COVID-19 patients and determined their relevance for convalescent plasma treatment and relation to disease outcomes. Using a commercially available ELISA, we found a relatively high detection rate of IFN-α Abs in COVID-19 cases compared to another recent study, including convalescent patients after moderate to mild disease. (7) However, neutralization of IFN-α in a functional assay only occurred in sera with ELISA measured IFN-α Abs well above the LLOD of the commercial assay. Using this neutralization cutoff we found a detection rate that is consistent with that in the aforementioned publication. When measured in the acute phase of COVID-19, this more stringent cutoff identifies patients in whom IFN-α Abs may have contributed significantly to the development of severe disease. Severe COVID-19 is associated with a state of immune hyper activation and the production of a broad spectrum of autoreactive antibodies, which in turn have not been linked to clinically apparent autoimmune disease (12–14). This must be taken into account when interpreting the results of antibody binding assays designed to be performed under more physiologically stable conditions. This includes the ELISA results presented in this study, where a large number of samples were quantified above the ELISA LLOD, without reaching bioactive levels in critical and severe COVID-19 patients. With the aim of controlling for this background, we chose to include a control group of critically ill ICU patients with other infections. Although the rate of IFN-α Abs detection was higher in these patients than is expected from a healthy population, they represent a more diverse group of different types of infections, with a more heterogeneous clinical phenotype. Nevertheless, we argue that this is a more relevant control group than healthy controls with no active inflammatory disease. Only critical COVID-19 cases had serum IFN-α Abs levels that differed significantly from this control group.
An earlier study in a Hepatitis C patient receiving exogenous recombinant IFN-α treatment, demonstrated that low levels of IFN-α Abs before treatment were boosted 1 week after administration of the drug started, to levels which completely blocked the activity of recombinant IFN-α (15). This capacity of IFN-α Abs to be quickly boosted during increased IFN-α exposure indicates that low levels of IFN-α Abs in convalescent or pre-symptomatic individuals could become relevant during an acute infection. Only a single convalescent sample in this study had neutralizing levels of IFN-α Abs. IFN-α Abs positive donors of whom plasma was administered to COVID-19 patients were close to the ELISA detection limit. Given the fact that a single transfusion of 300 mL plasma was administered, this is not expected to result in neutralizing IFN-α Abs levels in the recipient.
Bastard et al. showed a strong overrepresentation of men among COVID-19 patients with type I IFN Abs, and an X-linked genetic association was proposed (7). In contrast, our data show a higher IFN-α Abs detection rate among women. Notably, the convalescent donor cohort consists mainly of males who had had mild disease. Indeed, during the first months of the pandemic only male donors were recruited for convalescent plasma donation for reasons of urgency, since additional HLA and HNA antibody tests are required in female donors before their plasma can be used (16, 17). Therefore, most female subjects analyzed originate from the higher severity groups, which are more likely to have IFN-α Abs. When convalescent donors were excluded from the analysis, the difference in IFN-α Abs detection rate between genders was no longer statistically significant.
Recently an analysis of a subset of the data presented in the aforementioned paper was published, which correlates neutralizing Abs against type I IFN with a higher mortality rate from COVID-19 induced multi-organ failure (18). We found no association between neutralizing IFN-α Abs and mortality, or between SOFA score and IFN-α Abs serostatus, but studies with larger study sizes would be needed before robust conclusions could be drawn. Interestingly, we were able to demonstrate a delay in viral clearance from the respiratory tract in COVID-19 ICU patients with neutralizing levels of IFN-α Abs.
Our finding that most patients who had detectable IFN-α Abs already tested positive at the earliest available time point, and seroconversion during the course of disease was rare, suggests that these individuals already harbored anti-IFN B cell clones before they were infected. The SARS-CoV-2 infection may have boosted the anti-IFN Abs rather than being causally linked to the induction of autoimmunity. Whether this is unique to this virus, or a more widespread phenomenon among primary infections in later adulthood, remains a subject for further study.
In conclusion, we confirm previous finding that IFN-α Abs can be detected in COVID-19 patients, with neutralizing levels being most common in critically ill COVID-19 patients in the acute stage of disease. In these patients, neutralizing IFN-α Abs were associated with delayed viral clearance from the respiratory tract. In contrast, we did not find neutralizing levels of IFN-α Abs in critically ill ICU patients with respiratory illness caused by other infectious diseases. COVID-19 convalescent individuals also had detectable IFN-α Abs, but generally below neutralizing levels. We did not detect any cases were convalescent plasma transfusion was associated with an increase in IFN-α Abs in the recipient.