Functional α and β T cell chain receptor messages can be detected in old but not in young athymic mice

The expression and sequences of T cell antigen receptor (TcR) α and β‐chain genes were investigated in the spleens from congenitally athymic (nude) mice. A small number of Thy‐1⁺ cells (∼7.0%) was found in nylon wool‐enriched spleen cells from young (8 weeks old) nude mice but no L3T4 or Lyt‐2 surface antigens were detected. These nude mice expressed only a low level of 1.0‐kb β‐chain mRNA and little or no α‐gene transcripts. On the other hand the number of Thy‐1⁺ spleen cells increased slightly (to 24%) in old (20 weeks old) nude mice and a small number of L3T4⁺ (10%) and/or Lyt‐2⁺ (5%) cells were detectable. “Full length” 1.7‐kb α‐chain and 1.3‐kb β‐chain messages could be found in nylon wool‐enriched spleen cells from old nude mice. Sequence analysis of the cDNA revealed that no functional α and β‐chain genes can be detected in the spleen cells of young athymic mice while some of the old mice with nu/nu genotype are composed of completely rearranged V‐(D)‐J‐C‐gene segments which encode potentially functional proteins. Interestingly, two of three independent cDNA clones encoding the α chain used the same V_α and J_α‐gene segments. These results suggest that extrathymic TcR α and β‐chain gene rearrangements do occur, though slowly, to some extent, in nude mice and may be responsible for the limited antigen and/or H‐2‐related T cell functions in these old athymic mice. The data further suggests that the TcR repertoire in athymic mice may also be limited.