Physical and functional bivalency observed among TCR/CD3 complexes isolated from primary T cells

Area of Science:

• Immunology
• Molecular Biology
• Cellular Signaling

Background:

• The conventional model posits that T-cell receptor (TCR) expression is monovalent, unlike B-cell receptors (BCRs) and secreted immunoglobulins (Ig).
• Previous studies using digitonin-solubilized complexes did not detect bivalent TCR/CD3 complexes, supporting the monovalent model.

Purpose of the Study:

• To investigate the valency of TCR/CD3 complexes in primary αβ T cells.
• To determine if bivalent TCR/CD3 complexes influence T-cell function and antigen recognition.

Main Methods:

• Solubilization of TCR/CD3 complexes from primary αβ T cells using digitonin.
• Immunoprecipitation coupled with flow cytometry to analyze TCR complex formation.
• Assessment of functional performance using peptide/MHC-Ig fusion proteins.

Main Results:

• Unexpectedly observed bivalent TCR/CD3 complexes containing two TCRs per complex in primary T cells.
• Identified that standard bivalent anti-TCR antibodies could mask TCR bivalency in certain assays.
• Demonstrated that TCR bivalency impacts the functional binding of TCRs to soluble peptide/MHC ligands.

Conclusions:

• TCR/CD3 complexes in primary T cells can exist in both physically and functionally bivalent forms.
• The presence of bivalent TCRs has significant implications for understanding antigen-triggered T-cell signaling mechanisms.
• Bivalent expression of T-cell receptors may be a general feature of antigen receptors.