CD5 dynamically calibrates basal NF-κB signaling in T cells during thymic development and peripheral activation

Area of Science:

• Immunology
• Cellular Signaling
• Molecular Biology

Background:

• T cell receptor (TCR) signaling during T cell maturation involves positive selection and upregulation of negative regulators like CD5.
• CD5 expression levels correlate with the strength of self-peptide signals, aiming to dampen TCR signaling and prevent autoimmunity.
• Paradoxically, T cells with higher initial CD5 expression (CD5hi) exhibit enhanced persistence as effector/memory cells post-challenge.

Purpose of the Study:

• To elucidate the molecular mechanisms behind the dual role of CD5 in T cell regulation and function.
• To investigate how CD5 influences T cell signaling pathways, particularly NF-κB, in resting and activated states.

Main Methods:

• Conditional ablation of CD5 in T cells.
• Analysis of NF-κB signaling components, including IκBα and p65, in CD5hi versus CD5lo T cells.
• Assessment of protein levels and transcript levels of NF-κB pathway members.

Main Results:

• CD5 influences basal NF-κB signaling activity in resting peripheral T cells.
• Conditional CD5 ablation prevents T cells from maintaining high expression of the NF-κB inhibitor IκBα.
• Resting CD5hi T cells exhibit higher levels of the NF-κB p65 protein compared to CD5lo cells, independent of TCR signals and without increased transcription.

Conclusions:

• CD5 maintains a post-translationally stabilized pool of NF-κB in resting T cells, conferring a survival advantage to CD5hi cells.
• A proposed two-step model suggests that TCR signal strength upregulates CD5, which then maintains NF-κB reserves for subsequent antigen responses.
• This mechanism highlights a novel role for CD5 in pre-conditioning T cells for enhanced responsiveness and survival.