Unique Properties of a Cytotoxic CD4⁺CD8⁺ Intraepithelial T-Cell Line Established from the Mouse Intestinal Epithelium

Abstract

Growth factor-dependent gut intraepithelial lymphocyte (IEL) cell lines were established from a long-term in vitro culture of BALB/c IEL with syngeneic irradiated spleen cells in the presence of concanavalin A-stimulated spleen supernatant fluids. The cell lines were preferentially consisted of very limited thymoindependent subsets of IEL; i.e., Thy-1⁺CD5^-TCRαβ⁺CD4⁺CD8 α⁺β^- (double-positive; DP) IEL and Thy-1⁺CD5^-TCRαβ⁺CD4^-CD8α⁺β^- (CD8 single-positive; CD8 SP) IEL. The CD8 SP IEL cell line had cytotoxic activities and was triggered to proliferate by T-cell receptor (TCR)-directed stimuli. The DP IEL cell line expressed high levels of the CD3-TCRαβ, exhibited cytotoxic activity in redirected lysis assays, and had perform in the cytoplasm, indicating the functional maturity of this cell line. However, the DP IEL cell line did not proliferate in response to TCRαβ-directed stimuli, which indicated that TCRαβ-mediated signalling was able to initiate cytotoxic function but not to induce proliferation of the DP IEL cell line. Although both cell lines were shown to have functional competence, they expressed J11d antigen which marks immaturity in thymocyte differentiation pathways. These results indicate that the established thymoindependent DP and CD8 SP IEL cell lines have unique properties distinct from DP thymocytes and CD8 SP peripheral T cells. Together with a recent report on freshly isolated DP IEL (10), the unique properties of the DP IEL cell line seems to support the notion that DP IEL may undergo a unique maturation process in the gut microenvironment.