THE EXPANSION AND SELECTION OF T-CELL RECEPTOR-ALPHA-BETA INTESTINAL INTRAEPITHELIAL T-CELL CLONES

In conventional mice, the T cell receptor (TCR)alpha beta(-) CD8 alpha alpha(+) and CD8 alpha beta(-) subsets of the intestinal intraepithel ial lymphocytes (IEL) constitute two subpopulations. Each comprise a f ew hundred clones expressing apparently random receptor repertoires wh ich are different in individual genetically identical mice (Regnault, A., Cumano, A., Vassalli, P., Guy-Grand, D. and Kourilsky, P., J. Exp. Med. 1994. 180: 1345). We analyzed the repertoire diversity of sorted CD8 alpha alpha and CD8 alpha beta TCR alpha beta(-) IEL populations from the small intestine of individual germ-free mice that contain ten times less TCR alpha beta(+) T cells than conventional mice. The TCR beta repertoire of the CD8 alpha alpha and the CD8 alpha beta IEL popu lations of germ-free adult mice shows the same degree of oligoclonalit y as that of conventional mice. These results show that the intestinal microflora is not responsible for the repertoire oligoclonality of TC R alpha beta(+) IEL. The presence of the microflora leads to an expans ion of clones which arise independently of bacteria. To evaluate the d egree of expansion of IEL clones in conventional mice, we went on to m easure their clone sizes in vivo by quantitative PCR in the total and in adjacent sections of the small intestine of adult animals. We found that both the CD8 alpha alpha and the CD8 alpha beta TCR alpha beta I EL clones have a heterogeneous size pattern, with clones containing fr om 3 x 10(3) cells up to 1.2 x 10(6) cells, the clones being qualitati vely and quantitatively different in individual mice. Cells from a giv en IEL clone are not evenly distributed throughout the length of the s mall intestine. The observation that the TCR alpha beta IEL population s comprise a few hundred clones of very heterogeneous size and distrib ution suggests that they arise from a limited number of precursors, wh ich may be slowly but continuously renewed, and undergo extensive clon al expansion in the epithelium.