Figure 4. No further activation of HA-specific CD4+ T cells in response to challenge virus in pre-infected mice.

Mice received 2.5 × 10⁶ naïve HA-specific CD4+ T cells on the same day with pre-infection (50 PFU, intranasal inoculation) or intramuscular injection (500 PFU) of PR8 virus. On day 7-post virus exposure, half of the mice were sacrificed to study activation status of HA-specific CD4+ T cells (Before) and rest of the mice were challenged with 1.25 × 10⁴ PFU of PR8 virus. On day 4- post challenge, mice were sacrificed to study activation status of HA-specific CD4+ T cells similarly (After). Data are representative of at least three similar experiments and presented as mean ± s.d. (n = 6/group).