Detection of SARS‐CoV‐2‐independent immunoregulatory activity of COVID‐19 convalescent plasma

BACKGROUND: Convalescent plasma has emerged as a potential specific treatment for coronavirus disease 2019 (COVID‐19), since it contains severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) antibodies. Several studies are currently investigating the efficacy of convalescent plasma for treatment of COVID‐19, with a focus on neutralizing antibodies. However, there is little information on whether convalescent plasma may contain additional immunoregulatory constituents produced by the blood donor during convalescence. Therefore, using a standardized whole blood assay employing synthetic toll‐like receptor (TLR) ligands, we have investigated the immunoregulatory capacity of convalescent plasma in direct comparison to ABO‐matched allogeneic control plasma. STUDY DESIGN AND METHODS: Whole blood samples from healthy blood donors were collected, and autologous plasma was replaced by convalescent plasma or ABO‐matched control plasma. Standardized innate immune triggering and monitoring was performed by adding different TLR ligands (Pam3CsK4 [TLR1/2], HKLM [TLR2], LPS [TLR4], flagellin [TLR5], ssRNA40 [TLR8], imiquimod [TLR7], and FSL‐1 [TLR2/6]) and subsequent quantitative analysis of pro‐ and anti‐inflammatory cytokines (IP‐10, IL‐1β, TNF‐α, MCP‐1, IL‐6, IL‐10, and IFN‐γ) by cytometric bead array. Negative controls included unstimulated samples as well as samples spiked with autologous plasma. RESULTS: COVID‐19 convalescent plasma (CCP) significantly decreased pro‐inflammatory cytokines production triggered by different TLR ligands in healthy donors as compared with healthy control plasma. IL‐6, MCP‐1, and IFN‐γ represented the cytokines that are most frequently downregulated by convalescent plasma. CONCLUSION: Our experiments reveal a potential novel, SARS‐CoV‐2‐independent immunomodulatory activity of CCP, which may be beneficial for COVID‐19 patients.