Size estimate of the alpha beta TCR repertoire of naive mouse splenocytes

The diversity of the T cell repertoire of mature T splenocytes is generated , in the thymus, by pairing of alpha and beta variable domains of the cup T CR and by the rearrangements of various gene segments encoding these domain s. In the periphery, it results from competition between various T cell sub populations including recent thymic migrants and long-lived T cells, Quanti tative data on the actual size of the T cell repertoire are lacking. Using PCR methods and extensive sequencing, we have measured for the first time t he size of the TCR-alpha beta repertoire of naive mouse T splenocytes, Ther e are 5-8 x 10(5) different nucleotide sequences of BV chains in the whole spleen of young adult mice. We have also determined the size of the alpha b eta repertoire in a subpopulation of AV2(+) T splenocytes, which allows us to provide a minimum estimate of the cup repertoire. We find that the mouse spleen harbors about 2 x 10(6) clones of about 10 cells each. This figure, although orders of magnitude smaller than the maximum theoretical diversit y (estimated up to 10(15)), is still large enough to maintain a high functi onal diversity.