Therefore, to investigate the relative contribution of 1° effector CD8+ T cells to ECM development during secondary PbA‐OVA infection we set up a mixed congenic OT‐I cell adoptive transfer model where we could differentiate memory cell‐derived 2° effector OT‐I cells (CD45·1+CD45·2+) compared with 1° effector OT‐I cells (CD45·1+CD45·2−) generated from newly transferred naïve OT‐I cells (experimental schematic in Figure 5a and gating shown in Figure 5b). The gene discussed is CD8A; the disease is infection.