Complete but curtailed T-cell response to very low-affinity antigen

Area of Science:

• Immunology
• Cellular Biology
• Infectious Disease

Background:

• CD8(+) T cells play a crucial role in adaptive immunity following infection.
• Naive T cells exhibit diverse T-cell antigen receptor (TCR) affinities for antigens.
• The impact of TCR-ligand binding affinity on T-cell activation kinetics was previously unclear.

Purpose of the Study:

• To investigate how varying TCR-ligand interaction strengths influence naive CD8(+) T-cell activation and response kinetics in vivo.
• To determine the threshold of TCR stimulation required for T-cell activation, proliferation, and memory formation.

Main Methods:

• In vivo studies of T-cell responses to microbial infection.
• Analysis of T-cell activation, proliferation, and contraction phases.
• Assessment of effector and memory T-cell generation.

Main Results:

• Very weak TCR-ligand interactions are sufficient to activate naive T cells and initiate proliferation.
• TCR-ligand interaction strength dictates the duration of T-cell expansion and the onset of contraction.
• Strongly stimulated T cells exhibit delayed contraction and exit from lymphoid organs compared to weakly stimulated cells.

Conclusions:

• The prevailing notion that strong TCR ligation is essential for CD8(+) T-cell activation is challenged; weak interactions suffice for initial activation.
• Sustained T-cell expansion requires strong TCR ligation.
• Microbial challenge initially recruits T-cell clones with a wide range of avidities, with high-affinity clones expanding longer, leading to affinity maturation of the T-cell pool.