A positively selecting thymic epithelial cell line lacks costimulatory activity

Area of Science:

• Immunology
• Cell Biology
• T lymphocyte development

Background:

• Costimulatory molecules are essential for T cell activation in peripheral tissues.
• The role of costimulation in thymic T cell selection is not fully understood.
• Thymic epithelial cells (TECs) are critical for T cell development and selection.

Purpose of the Study:

• To investigate the role of costimulatory molecule interactions in the positive selection of T lymphocytes.
• To determine if the lack of costimulation on TECs contributes to their non-stimulatory phenotype.
• To elucidate the mechanisms underlying T cell positive selection in the thymus.

Main Methods:

• Utilized a TEC line (427.1) to assess allospecific CTL responses.
• Manipulated MHC class I expression and transfected B7/BB1-encoding DNA into TECs.
• Performed intrathymic injections of transfected TECs into beta 2-microglobulin negative mice.
• Assessed the rescue of CD8+ mature thymocytes.

Main Results:

• The TEC line 427.1, lacking B7/BB1, failed to stimulate CTL responses, indicating a role for costimulation in peripheral responses.
• Transfection of B7/BB1 restored the stimulatory phenotype of 427.1 cells for peripheral T cells.
• However, B7/BB1 expression did not enhance the ability of TECs to induce positive selection in the thymus.
• Intrathymic injection of B7/BB1-transfected TECs resulted in fewer rescued thymocytes compared to mock-transfected cells.

Conclusions:

• Positive selection of T cells in the thymus may not rely on costimulatory signals provided by presenting cells, unlike peripheral T cell responses.
• The absence of costimulatory molecules on TECs does not impede their capacity to mediate positive selection.
• This suggests distinct requirements for T cell activation in the thymus versus the periphery.