TABLE 2.

Effects of various mutant strains of Y. enterocolitica on O₂⁻ production by granulocytes in response to different stimuli^a

Preincubation substance	O2− production by granulocytes during stimulation with:
	Medium	PMA	f-MLP	pYV−	pYV+
Medium	1.53 ± 0.42	19.13 ± 1.46	19.98 ± 1.58	18.48 ± 0.8	9.48 ± 0.96
pYV−	1.73 ± 0.42	14.19 ± 2.17	11.24 ± 1.25	5.91 ± 1.04	3.46 ± 0.63
pYV+	1.50 ± 0.85	12.04 ± 2.23	1.89 ± 1.26b	1.44 ± 0.34b	0.94 ± 0.17b
pBC7 YadA− Yops+	1.34 ± 0.59	11.94 ± 1.76	2.63 ± 1.63b	NDc	ND
pSW2276 YadA+ Yops−	2.42 ± 0.47	13.39 ± 1.46	12.48 ± 0.85	ND	ND
pGC1152 YadA+ YopH−	2.49 ± 1.19	20.07 ± 6.03	3.61 ± 1.84b	ND	ND

^aGranulocytes were preincubated with medium or a Y. enterocolitica strain (ratio of 10 bacteria to 1 granulocyte) for 30 min. After removal of nonadherent bacteria, O₂⁻ production by granulocytes during stimulation was assessed by measuring the reduction of the level of ferricytochrome c. Stimulation with pYV⁻ or pYV⁺ Y. enterocolitica was performed at a ratio of 50 bacteria to 1 granulocyte. Results are expressed in nanomoles per 10⁶ cells per 30 min (means ± standard errors of results from at least three independent experiments). 

^bSignificantly different (P < 0.05) from values found for granulocytes preincubated with pVY⁻ Y. enterocolitica in response to the same stimulus, according to Student’s paired two-tailed t test. 

^cND, not done.