TNF and infection: Having shown that monocytes, which had internalized TNFR1 in response to external TNF-α became apoptotic (Fig. 6B,C), that TNF-α was produced (Fig. 4A), and TNFR1 was down-regulated during infection with E. coli (Fig. 6A), we analyzed TNFR1-internalization in our E. coli-GFP model: GFP-negative monocytes internalized TNFR1 significantly more than GFP-positive cells 30 min p.i. (Fig. 6D).