Spleen and bronchoalveolar lavage (BAL) samples were recovered from mice at acute phases of the primary and secondary infections (d10 and d8 respectively), and the BAL samples were incubated on plastic petri-dishes for 1hr at 37 0 C to remove macrophages. The spleens were disrupted and enriched for CD8 + T cells using goat anti-mouse IgG and IgM antibodies (Jackson ImmunoResearch Labs, West Grove, PA, USA). For assessment of naïve precursor frequency of N3A 366 + CD8 + T cells, spleens and lymph nodes (inguinal, brachial, axillary, superficial cervical, and mesenteric) were collected from naïve mice and processed to single-cell suspensions.