Identification of a new type of invariant V alpha 14(+) T cells and responsiveness to a superantigen, Yersinia pseudotuberculosis-derived mitogen

We examined the expression of the H4 T cell activation marker in thymic T c ell subpopulations and found that TCR-alpha beta(+) CD4(+) thymic T cells a re segregated into three subpopulations based upon H4 levels. Thymic T cell s with either no or low H4 expression differentiate via the mainstream diff erentiation pathway in the thymus, H4(int) thymic T cells, which express a skewed V beta repertoire of V beta 2, -7, and -8 in their TCRs, show the ph enotype of NKT cells: CD44(high), Ly6C(high), NK1.1(+), and TCR-alpha beta( low), H4(high) thymic T cells also show a skewed V beta repertoire, V beta 2, -7, and -8, and predominantly express an invariant V alpha 14-J alpha 28 1(+) alpha-chain in their TCRs but constitute a distinct population in that they are CD44(int), Ly6C(-), NK1.1(-), and TCR-alpha beta(high). Thus, inv ariant V alpha 14(+) thymic T cells consist of ordinary NKT cells and a new type of T cell population. V beta 7(+) and V beta 8.1(+) invariant V alpha 14(+) thymic T cells are present in DBA/2 mice, which carry mammary tumor virus-7-encoded superantigens, in comparable levels to those in BALB/c mice . Furthermore, V beta 7(+) invariant V alpha 14(+) thymic T cells in DBA/2 mice are in the immunologically responsive state, and Yersinia pseudotuberc ulosis-derived mitogen-induced V beta 7(+) invariant V alpha 14(+) thymic T cell blasts from DBA/2 and BALB/c mice exhibited equally enhanced response s upon restimulation with Y. pseudotuberculosis-derived mitogen, Thus, inva riant V alpha 14(+) thymic T cells that escape negative selection in DBA/2 mice contain T cells as functionally mature as those in BALB/c mice.