TABLE 2.

Relationship between Stx2 and TNF-α in induction of apoptosis in HUVEC^a

Initial exposure (6 h)	% Apoptotic cells after secondary exposure (42 h) to:
	Medium	TNF-α	Stx2	Stx2 + TNF-α
Medium only	3.0 ± 1.4	5.2 ± 2.7	9.8 ± 5.6	42.8 ± 6.7e
Stx2 (100 ng/ml)	3.5 ± 1.6	9.8 ± 3.3b	11.4 ± 3.9d	14.9 ± 4.8f
TNF-α (20 U/ml)	3.1 ± 0.8	6.6 ± 3.7c	43.8 ± 7.5e	46.7 ± 5.9e

^aSimultaneous addition of Stx2 and TNF-α as a positive control resulted in 44.9 ± 6.4% of HUVEC becoming TUNEL positive after 48 h of incubation. 

^bNot significant compared to HUVEC first exposed to Stx2 and subsequently cultured in Stx2. 

^cP < 0.01 compared to HUVEC first exposed to TNF-α and subsequently cultured in Stx2. 

^dP < 0.01 compared to HUVEC first exposed to TNF-α and subsequently cultured in Stx2. 

^eNot significant compared to positive controls. 

^fP < 0.01 compared to HUVEC first exposed to medium and subsequently cultured in Stx2 and TNF-α.