TABLE 1.

Preincubation of AKR.H-2^b splenocytes with Fas-Ig fusion protein blocks inhibition of antiviral CTL from immune B6 and B6.gld responder mice^a

Responder mouse strain	Secondary in vitro stimulation		Fas-Ig protein present	E:T ratiob	% Specific lysis
					Control (E♀K1)	Viral
	Tumor cell	Splenocyte				SL1	E♂G2
B6 (expt 1)	None	None	−	50:1	−2	1	3
	E♂G2	None	−	50:1	−3	80	86
				10:1	−3	72	91
				2:1	−2	44	71
	E♂G2	AKR.H-2b	−	50:1	7	24	26
	None	None	+	50:1	−3	1	3
	E♂G2	None	+	50:1	−3	73	77
				10:1	−1	75	79
				2:1	−1	36	49
	E♂G2	AKR.H-2b	+	50:1	3	64	77
				10:1	3	54	66
				2:1	0	24	30
B6.gld (expt 2)	None	None	−	50:1	−4	0	−3
	E♂G2	None	−	50:1	−3	53	55
				10:1	−4	38	43
				2:1	−4	11	15
	E♂G2	AKR.H-2b	−	50:1	−4	12	8
	None	None	+	50:1	−2	4	1
	E♂G2	None	+	50:1	−4	65	55
				10:1	−5	37	42
				2:1	−5	13	16
	E♂G2	AKR.H-2b	+	50:1	−5	65	56
				10:1	−5	35	39
				2:1	−6	13	18

^aB6 (experiment 1) or B6.gld (experiment 2) mice were immunized with 10⁶ B.GV tumor cells 11 (experiment 1) or 13 (experiment 2) days before in vitro stimulation with 2 × 10⁵ E♂G2 tumor cells without or with 2 × 10⁶ AKR.H-2^b splenocytes, as indicated. AKR.H-2^b splenocytes were preincubated for 1 h at 37°C with concentrated supernatant containing Fas-Ig fusion protein, where indicated. At 6 days later, the cells were assayed for the ability to lyse ⁵¹Cr-labeled target cells. AKR.H-2^b-mediated CTL inhibition was substantially blocked by Fas-Ig fusion protein in four of four and two of two experiments when B6 and B6.gld responder cells were used, respectively. The values for spontaneous release by target cells ranged from 7 to 9.4% and 9.1 to 23.7% for experiments 1 and 2, respectively. 

^bE:T ratio, effector-to-target-cell ratio.