Using cloned murine large granular lymphocyte (LGL) lines, the expression and the rearrangement of the alpha, beta, and gamma chain genes of the T cell receptor (TCR) were analyzed. Morphological, phenotypical, as well as functional studies indicated that the LGL lines were identical to normal, endogenous NK cells. Northern blot hybridization analysis indicated that the full-length transcripts of all the alpha, beta, and gamma chain genes were expressed in most of the LGL lines, including two lines derived from athymic nude mice. In one line, SPB, however, no transcript of the gamma chain gene was detected, whereas the alpha and beta chain genes were clearly expressed. In every LGL line studied, all of the alpha, beta, and gamma chain genes were rearranged. Conforming to the results of Northern blot hybridization study, the gamma chain gene of the SPB line was aberrantly rearranged, whereas those of all the other lines were productively rearranged. The results clearly revealed that NK cells represented a population of lymphocytes genetically committed to the T cell lineage. It was also suggested that the expression and rearrangement of the TCR genes of NK cells might occur in a thymus-independent fashion. An SPB line without expression of the gamma chain gene could exhibit NK activity indistinguishable from other NK lines. Furthermore, the rearrangement patterns of the beta chain gene did not correlate with the specificity of the cytotoxic activity. These results strongly suggested that the cytotoxic activity in NK cells was not directly mediated by TCR on them. We particularly noted that the beta chain gene of most independently established LGL lines showed identical patterns of rearrangement, indicating that they used the same V beta and J beta gene segments. The significance of the restricted pattern of rearrangement of the beta chain gene in LGL lines, as well as the possible functional roles of TCR on NK cells, was discussed.

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