ATP content and energy efficiency of CCR7⁻ versus CCR7⁺CD8⁺ T cells. (A) ATP contents of sorted CCR7⁻ and CCR7⁺CD8⁺ T cells were measured in a luminescence-based assay (left panel); mRNA levels of PGC-1β, ERRα, cytochrome C (Cycs), and ATP synthase (Atp5o) were quantified using RT-PCR technology (right panels). CCR7⁻CD8⁺ T cells contained less ATP and expressed less mRNA for PGC-1β, ERRα, Cycs, and Atp5o than their CCR7⁺ counterparts. *P < .05. (B) In calorimetric analyses heat production of sorted CCR7⁻ and CCR7⁺CD8⁺ T cells was quantified. After a calibration period of 24 hours, heat production was quantified every minute for 12 hours. The insert shows the heat flow diagram of a representative experiment (left panel). mRNA levels of the uncoupling proteins 2 and 3 of the respiratory chain (UCP-2 and UCP-3) were quantified by RT-PCR (right panels). CCR7⁻CD8⁺ T cells contained significantly less mRNA for both UCP-2 and UCP-3 than their CCR7⁺ counterparts. *P < .05.