Modulation of CD28 expression: distinct regulatory pathways during activation and replicative senescence

Area of Science:

• Immunology
• Molecular Biology
• Cellular Senescence

Background:

• CD28 is a costimulatory molecule expressed on T cells, vital for immune responses.
• CD28 expression decreases with T cell activation, aging, and chronic infections.
• Loss of CD28 impacts T cell function and immune surveillance.

Purpose of the Study:

• To investigate the molecular mechanisms underlying CD28 down-regulation in T cells.
• To explore the role of nuclear protein-binding activities to the CD28 promoter.
• To differentiate CD28 loss patterns in T cell activation, senescence, and chronic conditions.

Main Methods:

• Analysis of CD28 expression on T cells in various conditions (activation, senescence, chronic infection).
• Assessment of nuclear protein-binding activities to specific motifs (site alpha and beta) in the CD28 promoter.
• Comparison of CD28 expression and promoter binding in CD4+ and CD8+ T cells.

Main Results:

• CD28 expression is lost in CD8+ T cells during aging and chronic infections, and less frequently in CD4+ T cells.
• Loss of CD28 correlates with altered protein binding to the CD28 promoter's alpha and beta sites.
• T cell activation reduces both alpha and beta binding, while senescence primarily affects beta binding.
• In vivo expanded CD4+CD28null and CD8+CD28null T cells lack both alpha and beta binding complexes.

Conclusions:

• Differential regulation of CD28 promoter binding sites contributes to CD28 loss in T cells.
• Distinct patterns of CD28 promoter binding changes are associated with T cell activation versus senescence.
• Understanding these mechanisms is crucial for T cell-mediated immunity in aging and disease.