MAIT cells express IL-18Rα at birth and rapidly acquire a memory phenotype. (A) Representative CD45RO and IL-18Rα staining of MAIT cells (gated as in Figure 1A) from human cord blood (left panel) or 2-day-old (middle panel) and 3-month-old (right panel) infant blood. (B) Proportion of MAIT cells in blood T lymphocytes of healthy donors from 0.1 to 1000 months of age. Each symbol represents an individual donor.