Effects of p75NTR knockout on IL-1β, IL-6, and TNF-α secretion and mRNA expression. Controls or p75NTR knockout U937 cells were further induced to differentiate into macrophages and then stimulated with LPS with the presence of culture medium, a low concentration of BDNF (20 ng/mL), or a high concentration of BDNF (200 ng/mL) for 48 h (for cytokines secretion) or 4 h (for mRNA expression). The effects of p75NTR knockout on IL-1β (A) secretion and (B) mRNA expression. The effects of p75NTR knockout on IL-6 (C) secretion and (D) mRNA expression. The effects of p75NTR knockout on TNF-α (E) secretion and (F) mRNA expression (ns, not significant; * p < 0.05; ** p < 0.01; *** p < 0.001).