Table 1.

Prevalence of BrdU^hi CD8⁺ memory T cells in spleen 8 days after challenge with unrelated viruses

Priming virus*	Challenge†		Tetramer‡	% BrdUhi CD8+§ tetramer+
	Virus	Route
PR8 → HK × 31	Nil		NPP	7  ±  2
	B/HK	i.n.	NPP	15  ±  2¶
	LCMV	i.v.	NPP	29  ±  7¶
LCMV	Nil		LCMV	12  ±  3
	HK × 31	i.n.	LCMV	19  ±  2¶

^*Naïve B6 mice were primed i.p. with 10^7.9 EID₅₀ of the PR8 influenza A virus and then given 10^6.8 EID₅₀ of the HK × 31 virus i.n. 4 weeks later or infected i.v. with 10³ pfu of the Armstrong strain of LCMV. The mice were held for 5–11 weeks before challenge. 

^†Mice were challenged i.n. with 10^5.7 EID₅₀ of the B/HK influenza B virus, i.v. with 10³ pfu of LCMV, or i.n. with 10^6.8 EID₅₀ of the HK × 31 influenza A virus. Unchallenged immune controls (Nil) were used to determine the prevalence of BrdU^hi CD8⁺ tetramer⁺ T cells in “resting” spleen. 

^‡Virus-specific CD8⁺ T cells were stained with the D^d-NP_366-374 (NPP) or the D^b-LCMV NP_396-404 (2) tetramers. 

^§The percentage of CD8⁺ tetramer⁺ T cells that were BrdU^hi (R3 region of Fig. 3) was determined after feeding water that contained BrdU for 8 days. The results show the mean ± SD for at least five individual mice, compiled from two experiments (bottom two lines) or from a contemporary comparison (top three lines). 

^¶P < 0.01 compared with the unchallenged group (Nil). The data were analyzed with the Mann–Whitney U test.