The immune dysregulation observed in convalescent COVID-19 patients has been the focus of a recent study conducted by the ARUP Laboratories Institute for Clinical and Experimental Pathology and the University of Utah. The research sheds light on the changes in monocyte proportions and responsiveness, providing intriguing evidence of immune dysregulation.
During the acute phase of COVID-19 infection, alterations in myeloid cells, specifically monocytes, have been widely observed. Total monocyte counts tend to decrease, especially in severe cases. Additionally, there are distinct changes in the proportions of different types of monocytes, with a significant decrease in non-classical monocytes in moderate and severe cases. Activation markers on monocytes indicate their activation during acute infection.
However, the behavior of monocytes during the convalescent phase and in long COVID remains less understood. Some studies suggest an increase in non-classical monocytes in convalescent individuals, accompanied by elevated levels of inflammatory genes. Yet, conflicting findings, such as decreased monocyte percentages, highlight the need for more comprehensive studies.
To gain a deeper understanding of monocyte behavior after COVID-19, the researchers conducted a comprehensive study using flow cytometry and functional assays. They analyzed the phenotypic and functional characteristics of monocytes in the blood of convalescent COVID-19 patients, focusing on subset proportions, activation status in response to bacterial lipopolysaccharide (LPS), and cytokine production.
The study found significant alterations in monocytes during the convalescent phase of SARS-CoV-2 infection. There was a decrease in the overall percentage of monocytes in convalescent patients compared to uninfected controls. Specifically, there was a notable decrease in intermediate and non-classical monocytes. Classical monocytes from convalescent patients displayed a hyporesponsive phenotype, with decreased expression of activation markers in response to LPS stimulation. They also exhibited decreased expression of CD142, a key initiator of the coagulation cascade, in response to LPS stimulation. Monocytes from convalescent COVID-19 patients produced lower levels of proinflammatory cytokines in response to LPS stimulation compared to uninfected controls.
These findings provide valuable insights into the immune dysregulation in convalescent COVID-19 patients. The altered proportions, activation status, and cytokine production suggest a complex immune response during the convalescent phase. While the hyporesponsiveness of monocytes may have implications for dampening the inflammatory response and promoting tissue repair, it also raises concerns about the immune response to subsequent bacterial infections. The study acknowledges the need for longitudinal studies to capture changes throughout the acute to convalescent phases and the relevance of these findings to new SARS-CoV-2 variants.
In conclusion, this study contributes to our understanding of the immune dysregulation in convalescent COVID-19 patients, particularly in regard to monocyte behavior. The findings highlight the complexity of the immune response during the convalescent phase and call for further research to fully comprehend the implications and long-term health outcomes in individuals recovering from COVID-19. The study was published in the peer-reviewed journal Frontiers in Immunology.