Study Sheds Light On Immune Processes Involved In Long COVID
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Researchers in the United States have provided important insights into the immune processes that may be associated with post-acute sequelae of severe acute respiratory syndrome coronavirus 2 infection. Approximately 10 to 40% of people who recover from COVID-19 experience post-acute sequelae of SARS-CoV-2 infection (PASC) – a condition characterized by the persistence or recurrence of symptoms that cannot be explained by another health condition.

However, the biological processes associated with PASC are unknown, and there are limited data on immunologic trends over time associated with ongoing clinical symptoms. Now, researchers have shown that among individuals recovering from COVID-19, those who went on to develop PASC generally exhibited higher levels of the cytokines tumor necrosis factor-alpha (TNF-alpha) and interferon gamma-induced protein 10 (IP-10) during the early recovery period.

Individuals with PASC also exhibited a trend towards higher levels of the cytokine interleukin 6 (IL-6) during early recovery that became more pronounced during late recovery. In a prospective cohort study of 121 individuals with a history of documented SARS-CoV-2 infection, the researchers compared blood plasma levels of inflammation markers between individuals with and without PASC during the early recovery period (less than 90 days since symptom onset) and the late recovery period (beyond 90 days since onset).

Seventy-three (60%) of the 121 participants reported one or more symptoms at the late recovery timepoint, with the most common symptoms including memory or concentration problems (57%), fatigue (56%), shortness of breath (38%), and a loss of sense of smell (37%). During early recovery, levels of TNF-alpha and IP-10 were an average of 14% and 28% higher, respectively, among those who went on to develop PASC, compared with those who did not develop PASC.

The level of IL-6 was also an average of 29% higher during early recovery among individuals who developed PASC, with this trend becoming more pronounced during late recovery. The IL-6 level was an average of 44% higher among those with versus without PASC during the late recovery period. The researchers say that these observations may inform about the biological pathways that lead to PASC and facilitate the identification of potential therapeutic strategies.

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