CD45RA expression on γδ and αβ T cells emigrating from the fetal and postnatal thymus

We have compared the expression of CD45RA on αβ and γδ T cells emigrating from the fetal and postnatal thymus. The fetal and postnatal thymus export both CD45RA⁺ and CD45RA^- T cells. The number of γδ⁺CD45RA⁺ T cells was remarkably constant regardless of stage of ontogeny or T cell maturity. Around 5--8% of γδ thymic emigrants, thymocytes and peripheral blood lymphocytes expressed CD45RA in both fetal and postnatal animals. In contrast to γδ T cells, up to one quarter of both fetal and postnatal αβ emigrants expressed CD45RA. Post-thymic maturation of CD45RA expression on αβ emigrants, which occurred both before and after birth, appeared to be antigen independent.