THYMIC NURSE CELL CLONE SUPPORTS THE DIFFERENTIATION OF CD4-8- THYMOCYTES INTO CD4+8+ THYMOCYTES INVITRO

A previously reported thymic nurse cell clone, TNC-R3.1 could form a unique complex with isolated adult mouse CD4-8- (DN) thymocytes and greatly sustained the cell viability of DN thymocytes in suspension culture. In addition, the TNC-R3.1 clone supported the differentiation of DN thymocytes into CD4+8+ (DP) thymocytes in a short-term culture. Addition of IL-7 into the coculture markedly enhanced DN thymocyte-TNC interaction and induced the proliferation and differentiation of DN thymocytes, though IL-7 alone did not induce the differentiation of DN thymocytes. Separation of DN thymocytes from TNC-R3.1 monolayer using a Millicell caused a great inhibition of the DN thymocyte differentiation, suggesting that direct contact between TNC-R3.1 cells and immature thymocytes was required for the differentiation of DN thymocytes. The kinetics study demonstrated that DN thymocytes started to differentiate into DP thymocytes through CD3-CD4+J11d+ intermediate cells 8-12 h after the initiation of the culture with TNC-R3.1 plus IL-7. The generation of DP thymocytes became maximal 20 h after coculture and gradually decreased thereafter. Furthermore, we demonstrated that TNC-R3.1 could support the differentiation of CD3+CD4+CD8- or CD3+CD4-CD8+ thymocytes from CD3-CD4-CD8- thymocytes in the presence of IL-7 and IL-2. These data indicate that our established in vitro culture system mimics the early stage of the intrathymic T cell developing pathway.