Macrophage Ia expression in athymic nude versus neonatally thymectomized mice.

The requirement of the thymus for the production of Ia-inducing lymphokine was studied in athymic nude, neonatally thymectomized (NTx), and sham-operated (Sham) mice. The peritoneal macrophages from NTx mice immunized with viable Listeria monocytogenes 14 days previously contained as high a proportion of Ia-bearing macrophages as those from Sham mice, while those from athymic nude mice contained only a small proportion. Intraperitoneal injection of a culture supernatant derived from immune spleen cells of NTx mice induced Ia-rich exudates in recipient normal mice just as well as did a corresponding supernatant from cells of Sham mice, but that from cells of athymic nude did not. The production of Ia-inducing lymphokine in culture supernatants of immune spleen cells from both NTx and Sham mice was abolished by pretreatment of cells with anti-Thy-1.2 antibody plus complement. These results suggest that a T cell subset responsible for the production of Ia-inducing lymphokine requires the presence of the thymus for just a short period in the ontogenic development.