Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The expression of T cell‐associated antigens was analyzed on extrathymically differentiated T cells from athymic nude (rnu/rnu) rats. Two‐color flow cytometry and monoclonal antibodies were used to compare the subset structure of the rnu/rnu T cell population with that of normal T cells. In adult nude rats CD4<jats:sup>+</jats:sup> and CD8<jats:sup>+</jats:sup> cells were found which co‐expressed the OX19 antigen (CD5) clearly defining them as T cells. Double‐positive (CD4<jats:sup>+</jats:sup>CD8<jats:sup>+</jats:sup>) cells were not detected in nylon wool‐enriched rnu/rnu T cells. The ratio of CD4<jats:sup>+</jats:sup> to CD8<jats:sup>+</jats:sup> cells in nude rat lymph node cells did not significantly differ from normal T cells. However, the composition of the nude rat CD4<jats:sup>+</jats:sup> and CD8<jats:sup>+</jats:sup> subsets [as identified by the subset‐dividing monoclonal antibodies OX22 and P4/16 (anti‐RT6)] differed from that found in control rats. The most striking observation among the rnu/rnu CD4<jats:sup>+</jats:sup> subset was an inversion in the ratio of OX22<jats:sup>+</jats:sup> to OX22<jats:sup>‐</jats:sup> cells (0.5) compared to normal rats (2.3). Only 61% of the nude rat CD4<jats:sup>+</jats:sup> cells were found to be RT6<jats:sup>+</jats:sup> compared to 85% of rnu/+ CD4<jats:sup>+</jats:sup> cells. In the rnu/rnu CD8 subset the proportion of RT6 co‐expressing cells was also markedly reduced (38% <jats:italic>vs.</jats:italic> 77% of the CD8<jats:sup>+</jats:sup> subset). Furthermore, the nude rat CD8<jats:sup>+</jats:sup> subset contained a substantial number of OX22<jats:sup>‐</jats:sup> cells which were nearly absent in normal rats. The demonstration of cells bearing T cell markers in adult athymic rats further confirms the existence of an extrathymic pathway of T cell differentiation. The unusual T cell subset composition found in athymic rats, however, indicates that T cell subset generation and/or maintenance along this pathway differs from normal T cell development.</jats:p>