Biomedical subjects

H Lepesant

Publications and source records attributed to H Lepesant.

3 recordsLinked to original sources

PubMed1995

Deficient antigen presentation by thymic epithelial cells reveals differential induction of T cell clone effector functions by CD28-mediated costimulation.

Thymic epithelial cells participate in tolerance induction by deleting or inducing anergy of autoreactive lymphocytes. To explore this process in vitro, the antigen-presenting function of thymic epithelial cell lines was evaluated using a panel of T hybridoma and cloned cells displaying the same antigenic specificity. These mouse thymic epithelial cell lines could process different exogenous antigens and stimulate T hybridoma cells but only induced a partial activation of helper cloned T cells. This state of incomplete activation was characterized by the inability to produce IL-2 and IFN-gamma upon antigenic stimulation, whereas T cell IL-2R alpha expression and cytolytic potential were optimally induced. Thymic epithelial cells failed to express CD28 ligands detected by a CTLA-4/Ig probe even after induction by IFN-gamma. Optimal cloned T cell activation was only observed in the presence of LPS blasts or exogenous IL-2. Costimulation with anti-CD28 mAb was found to restore IFN-gamma but not IL-2 production. Thus, T cell activation by thymic epithelial cell lines provides a useful model to further dissect the requirements for costimulatory molecules, which, in addition to CD28, are required for optimal T cell activation.

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PubMed1990

Mouse thymic epithelial cell lines interact with and select a CD3lowCD4+CD8+ thymocyte subset through an LFA-1-dependent adhesion--de-adhesion mechanism.

Differentiation of bone-marrow-derived precursor cells into mature mouse T lymphocytes occurs in the thymus and involves sequential interactions with MHC-positive hemopoietic and epithelial stromal cells. To study the in vitro molecular mechanisms at play during the lympho-epithelial cell adhesion, we derived thymic stromal cell lines which were shown to possess cytokeratin filaments and tight junctions. These mouse thymic epithelial (MTE) cell lines did not express the classical hemopoietic stromal cell surface markers (i.e. LFA-1, Mac-1, and CD45) but expressed ICAM-1, NCAM, J11d, CD44, and MHC molecules. A quantitative cell adhesion assay was used to evaluate the interaction of various lymphoid cell subsets with MTE cells. Two cell interaction patterns could be defined: first, a rapid adhesion of a fraction of CD4+CD8+ and of a few CD4-CD8- immature thymocytes to MTE cells was observed at 4 degrees C. The CD8 molecule was shown to be partially involved in this initial contact. The strength of adhesion between MTE cells and distinct thymocyte subsets was evaluated and found to be maximal with neonatal thymocytes. Second, a temperature-dependent adhesion step characterized by a rapid and active stabilization of the interaction of MTE cells with 20% of CD4+CD8+CD3low thymocytes was seen, followed by a more progressive de-adhesion step. This active process of engagement was highly LFA-1-dependent, involved the CD4 and CD8 molecules, and required protein kinase C activation and cytoskeletal integrity. The results are consistent with the involvement of LFA-1 in a transient and regulated cell adhesion under the control of the TCR-CD3 complex that progressively appears on maturing cells. This phenomenon might contribute to the selection of a subset of immature thymocytes by epithelial cells occurring during the process of maturation of these cells.

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PubMed1989

Establishment and characterization of mouse thymic epithelial cell lines.

Primary stromal cell cultures from fetal day-16 thymuses of Swiss mice were developed using a combination of D-valine-containing DMEM and Ham's F-12 medium supplemented with epidermal growth factor, insulin and cortisone. Using cloning cylinders and subsequent limiting dilution techniques, we obtained two clones, MTE-1 and MTE-2. The presence of cytokeratin filaments established their epithelial origin. These cells expressed class I and class II MHC antigens after induction by gamma-interferon, and lacked conventional lymphoid cell-surface markers. Their ability to form rosettes with thymocytes should allow us to identify cell-surface antigens involved in thymocyte-epithelial cell interaction. Moreover, these lines will be used to set up in vitro thymocyte maturation assays.

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