Ligand density determines the efficiency of negative selection in the thymus

Area of Science:

• Immunology
• T-cell biology
• Transgenic mouse models

Background:

• Negative selection in the thymus is crucial for preventing autoimmunity.
• The role of antigen density in thymocyte deletion is not fully understood.
• MHC class I (K(b)) and T-cell receptor (TCR) interactions are key in T-cell development.

Purpose of the Study:

• To investigate how varying surface densities of MHC class I (K(b)) affect negative selection.
• To determine the role of CD8 coreceptor in thymocyte deletion.
• To assess the functional consequences of altered negative selection on graft-versus-host disease.

Main Methods:

• Generation of transgenic mice expressing K(b) at low (K(b-lo)) and high (K(b-hi)) densities.
• Crossing these mice with anti-K(b) T-cell receptor (Des-TCR) transgenic mice.
• Flow cytometry analysis of thymocyte populations and functional assays for graft-versus-host disease.

Main Results:

• High K(b) density (K(b-hi)) led to complete elimination of Des-TCR T cells.
• Low K(b) density (K(b-lo)) resulted in two T-cell populations: Des-TCR(int)CD8(-) and Des-TCR(lo)CD8(lo).
• Deletion occurred before the CD4(+)CD8(+) stage, and CD8 expression was necessary for negative selection in K(b-lo) mice.
• K(b-lo) mice were protected from lethal graft-versus-host disease by Des-TCR lymph node cells.

Conclusions:

• Antigen density critically regulates negative selection efficiency in the thymus.
• CD8 coreceptor expression is essential for initiating negative selection at lower antigen densities.
• Modulating thymic selection offers potential therapeutic strategies against graft-versus-host disease.