Q&A: Researcher weighs in on long-term COVID-19 immune cell reduction
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Key takeaways:
- Study results add on to previous research on waning immunity with SARS-CoV-2.
- Doctors should urge their patients to protect themselves against SARS-CoV-2 infections.
Patients infected with SARS-CoV-2 saw a reduction of immune cells and a change in growth factor patterns in their blood 10 months after infection, according to a study published in Allergy.
The study, conducted by Bernhard Kratzer, PhD, post-doctoral researcher, center for pathophysiology, infectiology and immunology, Institute of Immunology, Medical University of Vienna, and colleagues, showed that patients experienced a reduction of T cells and B cells after first contracting COVID-19. They also saw a reduction in neutrophils, monocytes and natural killer cells, which proved that a single SARS-CoV-2 infection can have long-lasting effects.
Healio spoke with Janna K. Moen, PhD, postdoctoral researcher at Yale University School of Medicine, about the results of the study and what they mean.
Healio: Do you think these findings are surprising or significant?
Moen: This study aimed to characterize the long-term immune system adaptations in patients infected with the original Wuhan strain of COVID-19 in 2020. The authors collected blood samples from these patients 10 weeks after infection and again 10 months later. They assessed a few different things: levels of SARS-CoV-2-specific antibodies, cytokine levels and immune cell profiling.
Consistent with many other studies, this paper reports a significant decline in antibodies directed against SARS-CoV-2 spike protein, nucleocapsid protein and receptor binding domain at 10 months post-infection. At the 10-month mark, the majority of patients in this study did not produce enough antibodies to protect against COVID-19 infection. This is not surprising, but it does add to the growing body of evidence supporting waning immunity from both natural infection and vaccination for SARS-CoV-2.
They also found that the expression pattern of inflammatory cytokines changed over the course of the 10-month recovery period, shifting toward a different type of inflammation that we call a Th2 response. This corresponded with changes in the levels of circulating immune cells, which, among other things, are responsible for initiating and maintaining inflammatory responses. Many studies have found persistent immune dysregulation following COVID-19 infection, and this study replicates much of this work.
Healio: How do these findings compare with your own experience?
Moen: In the Iwasaki Lab, we are really interested in studying how the immune response to pathogens can drive chronic illnesses such as long COVID and myalgic encephalomyelitis, so the majority of our clinical studies are focused on comparing patients with healthy and convalescent controls.
Using this approach, our group and others have shown that there are distinct changes that occur in people with long COVID vs. those who fully recover from COVID-19. This study is an interesting comparison because the patient group was not stratified by post-acute sequelae, which suggests that immune dysfunction can still persist for at least 10 months even if an infection fully resolves without triggering long COVID symptoms.
Healio: Do you have any recommendations on how doctors and health care professionals can use these findings to help patients who have gone through COVID-19 or are suffering the effects of long COVID?
Moen: These findings add to a wealth of literature suggesting that SARS-CoV-2 infections can induce long-lasting immune dysfunction, even in the absence of severe illness or lingering symptoms. Several immune modulators have been proposed as potential long COVID treatments for clinical trials, which is a very promising line of research that deserves our continued attention.
The observation that over 80% of patients lacked neutralizing antibodies at 10 months post-infection underscores the importance of mitigating potential reinfection events. While it is unclear how reinfections might impact these long-term immune changes, we do know that reinfections are common and can worsen long COVID symptoms in people who already have them, which indicates that repeated infections might exacerbate underlying dysfunction.
Health care professionals should be encouraging their patients to protect themselves against COVID-19 by providing them with education about effective mitigation strategies, such as N95 respirators and air filtration. Ideally, health care professionals can both protect high-risk patients and model proper techniques by employing mitigation measures in their practice.
Healio: How does this research add to our knowledge of long COVID?
Moen: This research study did not specifically address long COVID; approximately 10% of patients in this study reported developing long COVID, which is in line with current estimates on the prevalence of persistent symptoms following COVID-19 infection in the general population. Instead, this study highlights that immune dysfunction can persist for at least 10 months, even in people who ostensibly made a full recovery from their acute illness. Importantly, this study was conducted early in the pandemic before vaccines were available, so these results most closely represent those whose first exposure to SARS-CoV-2 was through direct infection.
Follow-up studies on the impact of vaccination on COVID-19-induced immune dysfunction will be necessary to determine whether prior vaccination can protect against immune dysfunction in breakthrough infections, although we know from other studies that vaccines are not very effective at preventing long COVID.
Healio: What future research do you think should be conducted based on this study?
Moen: I would say there are some clear areas for follow-up. For one, it would be interesting to repeat the study in people who were vaccinated before ever contracting COVID-19 to see whether vaccination offers any protection against immune dysregulation. Similarly, I would love to see data comparing results from people who developed long COVID and those who did not, which, among other things, could determine whether the immune system alterations they observed are amplified in those who go on to develop chronic symptoms.