Related Experiment Videos
Direct involvement of the CDR3-like domain of CD4 in T helper cell activation
J M McDonnell1, K J Blank, P E Rao
1Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, PA 19107.
Insights
Researchers modeled the CD4 protein's D1 domain to understand its role in T-helper (Th) cell activation. A designed mimic of the CDR3-like region specifically inhibited Th cell proliferation by disrupting CD4 associations.
Area of Science:
- Immunology
- Structural Biology
- Molecular Mimicry
Background:
- The CD4 glycoprotein is crucial for T-helper (Th) cell activation, but its precise mechanism remains unclear.
- The D1 domain of CD4 shares structural similarities with antibody variable regions, suggesting potential roles in protein interactions.
Purpose of the Study:
- To define the role of CD4 in Th cell activation by modeling its D1 domain.
- To investigate if CD4's CDR-like regions mediate protein-protein interactions.
Main Methods:
- Modeled the D1 domain of murine CD4 (L3T4) based on the human CD4 structure.
- Designed conformational mimics of the CDR3-like region of CD4.
- Tested the inhibitory effects of these mimics on CD4-dependent responses.
Main Results:
- A specific analog mimicking the sequence and conformation of the CDR3-like region potently inhibited CD4-dependent responses.
- The inhibitory activity was localized to the Th cell.
- The analog appeared to uncouple a CD4 association essential for T cell proliferation.
Conclusions:
- The CDR3-like region of CD4 is involved in mediating critical protein-protein interactions necessary for Th cell activation.
- Targeting this region with conformational mimics offers a strategy to inhibit CD4-dependent immune responses.
Abstract:
The CD4 glycoprotein, a member of the Ig super-family, has long been known to play an important role in the immunologic activation of Th cells. The precise manner in which CD4 participates in this activation process is not yet understood. In an attempt to further define its role in Th cell activation, we modeled the D1 domain of the murine CD4 protein (L3T4) based on the experimentally determined high resolution structure of the human CD4 protein. Because the D1 domain of CD4 strongly resembles the V kappa chain of an antibody, we addressed the question of whether the CDR-like regions of CD4 are also involved in mediating protein-protein interactions. Consequently, we used the modeled L3T4 structure as a template in the design of conformational mimics of the CDR3-like region (residues 86-94). Only the analog designed to mimic both the sequence and conformation of this region exhibited highly specific inhibition of CD4-dependent responses. Because the inhibitory activity could be localized to the Th cell itself, it appears that this analog acts by uncoupling a CD4 association (independent of an APC) critical to generating a proliferative response.