Beschreibung:
<jats:title>Abstract</jats:title><jats:p>A detailed study of the recently described “nude” rat, which suffers from congenital aplasia of the thymus, has shown that this animal is grossly deficient in functional mature T cells.</jats:p><jats:p>Histological investigation revealed that those areas of lymph node, spleen and Peyer's patches, which are considered to be thymus‐dependent, were markedly depleted of lymphocytes. The areas of lymph node and Peyer's patches, which are normally considered to be thymus‐independent, were also partially depleted of lymphocytes, whereas the thymus‐independent areas of splenic white pulp showed greater activity than in control animals.</jats:p><jats:p>Indirect immunofluorescence with a monoclonal anti‐T cell antibody showed that lymph node and spleen cells were severely depleted of mature T cells, whereas staining with anti‐immunoglobulin antisera revealed an increased percentage of B cells in these organs. The nature of the residual anti‐T<jats:sup>+</jats:sup> cells in rnu/rnu lymph node and spleen is not clear, but at least some of these may be precursor T cells. Spleen cells from rnu/rnu rats gave no response to phytohemagglutinin (PHA), and only occasional small responses to concanavalin A (Con A), but showed normal responses to <jats:italic>Staphylococcus aureus</jats:italic> bacteria. The absence of responses to PHA and Con A was not caused by suppressor cells nor by any defect in helper cell activity. In so far as PHA and Con A are considered to be T cell‐dependent mitogens and <jats:italic>S. aureus</jats:italic> a T cell‐independent mitogen, these results indicate that rnu/rnu rats lack functional T cells.</jats:p>