CD27 and infection: Phenotypic progression or non-progression of memory CD8 T cells in outbred hosts appeared to be correlated to the size of the memory CD8 T cell pool generated following infection, as mice with high levels of CD127, CD62L, and CD27 and low levels of KLRG1 at day 121 following infection had lower levels of memory CD8 T cells than mice with low expression of CD127, CD62L, and CD27 and high expression of KLRG1 (Figures S4A,B in Supplementary Material).