Characterization of peripheral blood leukocytes and monocyte-derived dendritic cells in individuals with acute and convalescent COVID-19

The COVID-19 pandemic continues to be a major global health challenge. The World Health Organization (WHO) reports that from the end of 2019 through February 2024, Brazil alone recorded 37,519,960 confirmed cases of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and 702,116 related deaths. While initially categorized as an acute respiratory illness, some individuals experience persistent symptoms such as fatigue, memory loss, and hair loss. This study aims to investigate whether alterations in surface markers on leukocytes, particularly monocyte-derived dendritic cells, are associated with long COVID. Additionally, it explores whether dendritic cells from individuals with mild acute COVID-19 exhibit changes in cytokine production. Insights gained could help explain the prolonged symptoms observed in some individuals post-infection.To address these questions, we recruited a cohort of individuals with mild acute COVID-19 and those with persistent symptoms during convalescence. Flow cytometry analyses conducted by our team revealed no significant differences in monocytes, CD3⁺CD8⁺ T lymphocytes, or monocyte-derived dendritic cells (DCs) between healthy controls, mild acute cases, and convalescent individuals. However, a notable reduction in CD16i^ntCD66b⁺ neutrophils was observed in the circulation of convalescent individuals with persistent symptoms. This reduction may be linked to some of the reported long COVID symptoms, such as increased susceptibility to opportunistic infections following the acute phase. Further research is needed to fully elucidate the mechanisms underlying long COVID.