Organ culture studies of nude mouse thymus

There is evidence that peripheral lymphoid organs of nude mice, born from homozygous matings, contain a small proportion of theta-positive lymphocytes indicating that nude mice may not be totally devoid of T cell function. It has been suggested that such lymphocytes may develop within the dysplastic nude thymus itself. While this suggestion receives no support from morphological studies, it has been claimed that on explanation to organ culture the developing nude thymus becomes lymphoid. In this present study we confirm the presence of theta-positive lymphocytes in peripheral lymphoid tissues of homozygous nude mice born of nude parents. However, when we have organ-cultured nude thymus, explained from homozygous nude embryos at days 13, 14, 16 and 18 of gestation, we have found no histological sign of lymphopoiesis nor have we detected any theta-positive cells in such cultured material. On the contrary, the nude thymus in vitro develops into the polycystic structure characteristic of the adult nude thymus. We conclude that the small number of theta-positive cells present in the periphery result from extrathymic differentiation.