Fig. 4

Activated THP-1 stimulates C5a-C5aR1 axis. The relative level of complement factor C5a was measured by ELISA from the culture supernatant of THP-1 cells (A) treated with IL-6, IL-1α, HMGB1, or TNF-α for four days; and (B) exposed to CM from spike expressing cells in the presence or absence of ST2825 or Peps A for four days. C Relative C5a level in the CM from A549 cells transfected with SARS-CoV-2 spike gene construct or empty vector is shown. D mRNA expression status of C5aR1 and C5aR2 analyzed by qRT-PCR from the total RNA of THP-1 cells exposed to the CM from SARS-CoV-2 spike expressing cells in the presence or absence of ST2825 or Peps A and exogenous C5a incubation for four days. E Expression of C5aR1, phospho-PKC, and cryopyrin were analyzed by Western blot from THP-1 cell lysates prepared after exposure to CM in the presence or absence of ST2825, Peps A, or exogenous C5a for four days. Expression level of actin in each lane from the same gel is shown as a total protein load for comparison. F Intracellular reactive oxygen spices were measured by fluorometric assay of THP-1 cells prior exposed to CM from virus spike expressing cells in the presence or absence of ST2825, Peps A, or exogenous C5a for four days. G The concentration of complement factor C5a was measured by ELISA from sera of uninfected healthy volunteers (n = 4), severe COVID-19 patients (n = 6) and post-COVID-19 patients (n = 6). The results are presented as mean ± standard deviation and ‘*’ represents analyses of data only showing statistical significance p < 0.05