EFFECTS OF THYMUS SUPERNATANTS ON THE PHENOTYPE OF DIFFERENT SUBSETS OF PERITONEUM ANTIGEN-PRESENTING CELLS

Peritoneal cells (PC) obtained 2 h subsequent to intraperitoneal (i.p. ) injection of low doses (200 mu g) of a purified fraction of rat male accessory glands (FI-RAG) are phenotypically and functionally differe nt from those obtained 24 h after i.p. injection. In fact, PC obtained 2 h after FI-RAG injection are mainly IE(+) and are involved in induc ing specific suppression to RAG. In contrast, PC obtained 24 h after F I-RAG injection are mainly IA(+) and capable of inducing specific resp onse to RAG. For their induction, IA(+) PC require cells within or rec ently derived from bone marrow. In order to analyze the mechanisms inv olved in IA(+) bone marrow-dependent cell generation in the peritoneum , we studied the distribution of FI-RAG following i.p. injection. It w as established that FI-RAG is found mainly in the thymus 2 h after inj ection and remains there for at least 24 h. Subsequently, we analyzed, in 4 groups of rats, the influence of thymic culture supernatants on the phenotype of cells appearing in the peritoneal cavity 2 h after FI -RAG injection. An increase in IA(+) PC was observed 2 h after i.p. in jection of FI-RAG in animals that had received either supernatants fro m normal thymic cells cultured with FI-RAG or those from thymic cells taken from animals injected with FI-RAG 2 h prior to being killed. Sup ernatants of thymic cells from animals injected with FI-RAG 24 h prior to being killed or from normal thymic cells do not increase the perce ntage of IA(+) PC. Contrasting with these results obtained in peritone um, there was no increase in IA(+) lymph node cells (LNC) immediately after collection. For the effect to become apparent, an additional 24 h contact with FI-RAG was necessary. Our results infer that, under spe cific conditions, thymic supernatants can induce an increase in the pe rcentage of IA(+) cells in the peritoneum.