CD4 and infection: Similar to their inbred counterparts, outbred SPexp mice had increased proinflammatory cytokines (IL-2, IL-6, TNF-α, and IFN-γ), decreased cellularity in the blood, and an increased frequency of Ag-experienced CD4 and CD8 T cells within PBL 5 d after last infection (Supplemental Fig. 1B–E), as seen in inbred SPexp mice (Fig. 2).