Abstract
The derivation of RT6+ T cells from postthymic RT6- T cells in weanling rats was formally
demonstrated by the intravenous transfer (“parking”) of highly purified populations of RT6- lymph node T cells into thymectomized, irradiated, and bone-marrow-reconstituted (TXBM)
RT6+ and RT7 alloantigen-disparate recipients. Parallel experiments in irradiated and bonemarrow-
reconstituted rats, and in rats whose RT6+ T cells had been depleted by injection of
DS4.23 anti-RT6.1 mAb, suggested that the transit time between the pre-RT6+ and the RT6+ T-cell compartments approximated 4-5 days. A more precise estimate of the transit time was
made by linear regression analysis of the generation of RT6+ T cells in rats that were treated
with DS4.23 mAb at timed intervals after thymectomy. This study indicated that 50% of the
pre-RT6 T cells differentiated into RT6+ cells within 4 days, 75% within 8 days, and more
than 90% within 16 days.Despite the apparent absence of pre-RT6- T cells 3 weeks after thymectomy, numerous
RT6- T cells persisted for at least 10 weeks in thymectomized rats, even after treatment with
DS4.23 mAb. Moreover, these RT6+ T cells failed to generate RT6+ T cells after transfer into adoptive hosts. Quantitative and phenotypic analyses indicated that this population of “true”
RT6- T cells: (1) constitutes approximately 50% of the total RT6- T cells normally found in
control rats; (2) contains CD4 and CD8 subsets; (3) expresses both the CD5 pan-T-cell
antigen (which is absent from NK cells) and the R73