TABLE 1.

Analysis of IFN-γ⁺ CD8⁺ T cells from spleen in a secondary response following homologous challenge^a

Day	Virus	% IFN-γ+ CD8+ T cells (mean ± SD)
		NP	PA	PB1	NS2	M1
0	WT	0.6 ± 0.1	0.3 ± 0.08	0.4 ± 0.1	0.07 ± 0.04	0.01 ± 0.02
	−NP	0.02 ± 0.03*	0.24 ± 0.07	0.3 ± 0.15	0.07 ± 0.03	0.01 ± 0.02
	−PA	1.0 ± 0.1	0.01 ± 0.03*	0.15 ± 0.05	0.08 ± 0.05	0.01 ± 0.01
	−NP−PA	0.04 ± 0.03*	0.02 ± 0.03*	0.16 ± 0.1	0.08 ± 0.06	0.02 ± 0.02
7	WT	10.9 ± 0.4	1.0 ± 0.5	1.5 ± 0.6	0.5 ± 1.3	0.14 ± 0.07
	−NP	0.2 ± 0.1*	2.7 ± 1.0	5.6 ± 1.8*	1.7 ± 0.8	0.17 ± 0.06
	−PA	13.4 ± 4.9	0.5 ± 0.09*	4.3 ± 0.9*	3.1 ± 1.3*	0.16 ± 0.15
	−NP−PA	0.2 ± 0.06*	0.4 ± 0.3*	3.8 ± 1.0*	4.69 ± 1.8*	0.48 ± 0.40
10	WT	15.2 ± 6.1	1.3 ± 0.1	2.3 ± 1.0	0.9 ± 0.2	0.05 ± 0.02
	−NP	0.2 ± 0.1*	4.1 ± 0.8*	10.0 ± 2.9	4.5 ± 0.7*	0.3 ± 0.2*
	−PA	13.4 ± 1.5	0.1 ± 0.09*	6.2 ± 2.0	4.8 ± 1.0*	0.4 ± 0.4
	−NP−PA	0.03 ± 0.01*	0.1 ± 0.1*	3.4 ± 0.7	4.8 ± 1.3*	0.3 ± 0.2
30	WT	17.5 ± 9.0	2.0 ± 0.8	3.1 ± 1.3	1.7 ± 1.0	0.07 ± 0.05
	−NP	0.1 ± 0.02*	4.9 ± 1.7*	9.3 ± 1.5*	3.7 ± 2.3*	0.05 ± 0.04
	−PA	14.6 ± 4.7	0.5 ± 0.1*	4.1 ± 2.0	1.3 ± 0.9	0.05 ± 0.03
	−NP−PA	0.1 ± 0.02*	0.3 ± 0.1*	4.7 ± 2.6	4.6 ± 1.3*	0.2 ± 0.1

^aTen-week-old, female B6 mice were primed i.p. with 10⁸ EID₅₀ of PR8 WT and mutants per mouse. The mice were challenged i.n. with homologous X31 viruses at 10⁷ EID₅₀ per mouse. Spleens were harvested on days 0 (8 weeks after priming), 7, 10, and 30, and the IFN-γ⁺ assay was performed as described in Materials and Methods. The significant differences from the WT are indicated as * (P < 0.05).