(a) Flow cytometric analysis of thoracic and cervical thymus at postnatal day 3 for CD4, CD8, CD25 and CD44 shows changes in the frequency of thymocyte subsets in CT (N>3). (b) Two classes of CT with either very low CD25 and TCRβ expression, or levels similar to thoracic thymus (N>3). Positive gates are indicated. (c) Ratio of CD4/CD8 is lower in parathyroid-derived cervical thymus but shows variety in non-parathyroid-derived cervical thymus, either similar/higher (CT#1, in red) or lower (CT#2, in blue) compared with thoracic thymus (N>3, error bars represent s.e.m.). (d) Percentage of CD25+ cells is significantly lower in pCT but is significantly higher in the CT#2 group of non-parathyroid-derived cervical thymus (N>3; error bars represent s.e.m., *P<0.01 (significant relative to newborn, t-test); †P<0.01 (significant relative to 28 days, t-test)).