Human CD8⁺ T Cells Exhibit a Shared Antigen Threshold for Different Effector Responses

Area of Science:

• Immunology
• Cellular Biology
• Adaptive Immunity

Background:

• T cells are crucial for adaptive immunity, mediating responses like target cell killing and cytokine secretion.
• It was hypothesized that different T cell effector responses might have distinct antigen (Ag) dose and affinity thresholds.
• This suggests that the nature of the Ag could encode pathogen-specific information.

Purpose of the Study:

• To investigate whether different T cell responses exhibit varying antigen dose and affinity thresholds.
• To determine if antigen recognition properties encode specific information for distinct T cell effector functions.

Main Methods:

• Experiments were conducted using primary human CD8+ T cell blasts stimulated with recombinant peptides presented on MHC Ag.
• Systematic variations in Ag dose and affinity were employed in a reductionist system.
• Primary human memory CD8+ T cells were also studied responding to autologous antigen-presenting cells (APCs).

Main Results:

• Different inflammatory cytokines showed comparable Ag dose thresholds despite a 25,000-fold variation in affinity.
• Costimulation via CD28, CD2, and CD27 enhanced cytokine production but did not alter the Ag threshold.
• Equivalent thresholds for cytokines and killing were observed in memory CD8+ T cells responding to APCs.

Conclusions:

• Multiple T cell responses appear to share a common rate-limiting threshold in T cell receptor (TCR) signaling.
• A simple model of CD8+ T cell Ag recognition suggests Ag dose and affinity do not provide response-specific information.
• These findings challenge the notion that varying Ag properties dictate distinct T cell effector functions.