Regulation of thymocyte development through CD3. I. Timepoint of ligation of CD3 epsilon determines clonal deletion or induction of developmental program.
Several recent observations suggest that successful rearrangement of the T cell receptor (TCR) beta locus induces several important events in thymocyte maturation. Allelic exclusion is achieved by interruption of further rearrangement of the beta locus, and CD4-8- interleukin (IL)-2R+ cells enter the CD4+8+IL-2R- stage. The actual molecular events regulating this important control point are unknown, but may be related to the expression of the TCR-beta locus in immature CD4-8- thymocytes. It is not clear whether maturation is induced by intracellular appearance of TCR-beta chain or by signal transduction through an immature TCR complex on the thymocyte membrane, possibly involving TCR-beta chain homodimers and CD3. Here we show that early addition of anti-CD3 mAb to fetal thymic organ cultures induces all known events associated with the acquisition of the CD4+8+ stage. Expression of CD4 and CD8 is accelerated, IL-2R alpha is downregulated, and the cells fail to produce TCR-beta, possibly based on premature cessation of beta gene rearrangement. Upon stimulation with anti-CD3 antibodies, we see calcium mobilization in 15% of all CD4-8- thymocytes with no detectable surface TCR expression. These results suggest that functional CD3 is expressed on immature thymocytes at very low concentrations before the appearance of a complete TCR-beta chain. Ligation of CD3 at this stage may mimic the maturation signal normally generated by the immature TCR-beta homodimer-CD3 complex. The results are consistent with the notion that acquisition of the CD4+8+ stage involves signal transduction through an immature TCR complex. Later in thymocyte development, ligation of CD3 results in deletion of CD4+8+ cells. Thus, signal transduction through CD3 may result in entirely different cellular responses, depending on the stage of thymocyte differentiation. These results suggest an involvement of CD3 as a link in signal transduction for at least two different decision points in the development of a thymocyte.
Levelt
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Max-Planck-Institut für Immunbiologie, Freiburg, Germany.
Ehrfeld
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A
Eichmann
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D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015152:Blotting, Northern; D017252:CD3 Complex / Q000276:immunology / Q000494:pharmacology*; D015704:CD4 Antigens / Q000032:analysis; D016827:CD8 Antigens / Q000032:analysis; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D005434:Flow Cytometry; D015333:Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D011247:Pregnancy; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000032:analysis / Q000235:genetics / Q000276:immunology; D015375:Receptors, Interleukin-2 / Q000032:analysis; D015398:Signal Transduction / Q000502:physiology; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000648:ultrastructure; D013997:Time Factors
D000911:Antibodies, Monoclonal; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D016693:Receptors, Antigen, T-Cell, alpha-beta; D015375:Receptors, Interleukin-2; D002118:Calcium