Ligand thresholds at different stages of T cell development

Area of Science:

• Immunology
• T cell biology
• Developmental immunology

Background:

• T cell receptors (TCRs) recognize specific ligands.
• Exposure to T cell ligands during development can lead to T cell deletion or activation.
• Staphylococcal enterotoxin B (SEB) is a T cell ligand that can induce both responses.

Purpose of the Study:

• To quantitatively compare the sensitivity of T cell clonal deletion versus T cell activation to SEB.
• To investigate the dose-dependent responses of T cells to SEB in different contexts.

Main Methods:

• Utilized thymic organ culture to assess clonal deletion of developing T cells.
• Used spleen cell cultures to measure clonal expansion (activation) of T cells.
• Compared the doses of SEB required for each process.

Main Results:

• Clonal deletion of developing T cells was 10- to 100-fold more sensitive to SEB than T cell activation in spleen cells.
• SEB required lower doses to induce deletion in the thymus compared to activation in the periphery.

Conclusions:

• The clonal deletion process has a built-in margin of error, making it more sensitive to T cell ligands than activation.
• Thymic T cell selection is highly sensitive to self-ligands, preventing autoimmunity.
• Findings support observations with naturally occurring ligands and I-E molecules.