Figure 6

Aβ1-42-induced extracellular S100A9 depletion resulted in decreased antimicrobial peptide activity. The antimicrobial activities against E coli were assessed with the supernatants from vehicle or Aβ-42 treated THP-1 cells. (A) E coli were cultured with serum-free RPMI-1640 media alone or the conditioned media from THP-1 cells treated with the vehicle or Aβ1-42 (10 μM) for 24 hours. (B) To measure the antimicrobial activities of rS100A9 protein, E coli was cultured with rS100A9 or hi-rS100A9 (each 10 μg/ml). (C) To inactivate antimicrobial activity of S100A9, which was released into the supernatants, the conditioned media from THP-1 cells treated with the vehicle for 24 hours were pretreated with anti-S100A9 antibodies or heat inactivated anti-S100A9 antibodies for 2 hours at 37°C. E coli were then cultured with serum-free RPMI-1640 media alone or the conditioned media treated with anti-S100A9 antibodies or heat inactivated anti-S100A9 antibodies (anti-S100A9_hi) as indicated. Data showed that vehicle treated supernatant, which contained a significant amount of S100A9, demonstrated antimicrobial activity against E coli. Moreover, rS100A9 protein clearly elicited the antimicrobial peptide activity in vitro. Immunodepletion of S100A9 blocked antimicrobial activity of the vehicle treated supernatant. All data are presented as the means ± SEM (n = 3). **P <0.01, versus vehicle treated samples. CM, conditioned media.