Altered thymic selection and increased autoimmunity caused by ectopic expression of DRAK2 during T cell development

Area of Science:

• Immunology
• Molecular Biology
• Autoimmunity

Background:

• Negative regulation of T cell receptor (TCR) signaling is crucial for self-tolerance and preventing autoimmune diseases.
• Death-associated protein-related apoptotic kinase-2 (DRAK2) normally increases the TCR activation threshold, affecting T cell selection and activation.
• DRAK2-deficient mice paradoxically resist experimental autoimmune encephalomyelitis despite peripheral T cell hypersensitivity.

Purpose of the Study:

• To investigate the distinct roles of DRAK2 in central versus peripheral immune tolerance.
• To assess the impact of DRAK2 modulation on autoimmune disease development.
• To generate and characterize a transgenic mouse model with ectopic DRAK2 expression.

Main Methods:

• Generation of a transgenic mouse strain (1017-DRAK2 Tg) expressing DRAK2 under the lck proximal promoter.
• Analysis of thymocyte populations (CD4+, CD8+) and negative selection processes.
• Evaluation of peripheral T cell hypersensitivity and susceptibility to experimental autoimmune encephalomyelitis (EAE).

Main Results:

• Ectopic DRAK2 expression was highest in double-positive thymocytes, which normally lack DRAK2.
• 1017-DRAK2 Tg mice showed reduced single-positive CD4+ and CD8+ thymocytes.
• Diminished negative selection was observed in HY TCR x 1017-DRAK2 Tg mice, alongside peripheral T cell hypersensitivity, enhanced EAE susceptibility, and spontaneous autoimmunity.

Conclusions:

• Altering thymocyte signaling thresholds by ectopic DRAK2 expression significantly impacts peripheral T cell pool sensitivity.
• These findings highlight the complex interplay between central tolerance mechanisms in the thymus and peripheral immune responses.
• Modulating DRAK2 levels offers potential insights into the pathogenesis and therapeutic strategies for autoimmune diseases.