CD28 and CTLA-4 coreceptor expression and signal transduction

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• T-cell activation requires TCR/CD3 and CD4-CD8-p56lck complexes plus coreceptor signals.
• Coreceptors like CD28 and ICOS provide positive signals, while CTLA-4 and PD-1 provide inhibitory signals.
• The balance of these co-signals dictates T-cell response outcomes, preventing excessive inflammation and autoimmunity.

Purpose of the Study:

• To review current knowledge of CD28 and CTLA-4 signaling pathways in T-cell immunity.
• To present recent findings on TRIM regulation of CTLA-4 expression.
• To describe the CTLA-4 signaling pathway involving PI3K and PKB/AKT in anergy induction.

Main Methods:

• Review of existing literature on T-cell coreceptor signaling.
• Analysis of signaling pathways involving PI3K, Grb2, Filamin A, PKCtheta, and phosphatases.
• Examination of TRIM's role in CTLA-4 regulation and CTLA-4-mediated PI3K/PKB/AKT activation.

Main Results:

• CD28 and ICOS promote T-cell responses, while CTLA-4 and PD-1 limit them.
• Specific signaling molecules like PI3K, Grb2, Filamin A, and PKCtheta are involved in CD28 and CTLA-4 pathways.
• TRIM regulates CTLA-4 surface expression, and CTLA-4 signaling can activate PI3K/PKB/AKT to ensure cell survival during anergy.

Conclusions:

• The balance between stimulatory (CD28, ICOS) and inhibitory (CTLA-4, PD-1) coreceptor signals is critical for T-cell immunity.
• Understanding these signaling mechanisms provides insight into controlling T-cell responses and preventing autoimmune diseases.
• CTLA-4 plays a dual role in limiting T-cell activation and promoting survival in anergic states through PI3K/PKB/AKT signaling.