Surface-bound chemokines capture and prime T cells for synapse formation

Area of Science:

• Immunology
• Cell Biology

Background:

• T cell activation requires concurrent signals from chemotaxis and T cell receptor (TCR) engagement within lymphoid tissues.
• Lymphoid tissues provide a complex microenvironment crucial for effective immune responses.

Purpose of the Study:

• To elucidate the mechanism of T cell costimulation mediated by chemokines presented on antigen-presenting cells.
• To investigate the role of chemokine-APC interactions in T cell activation dynamics.

Main Methods:

• Demonstration of T cell zone chemokines, like CCL21, bound to lymph node dendritic cell surfaces.
• Analysis of T cell-APC interactions using a two-step contact model.
• Observation of antigen-independent 'tethered' adhesion formation preceding TCR signaling.

Main Results:

• T cell zone chemokines (e.g., CCL21) are surface-bound to dendritic cells (DCs).
• DCs presenting chemokines induce a two-step costimulatory mechanism on T cells.
• Initial T cell adhesion to chemokine-bearing DCs is antigen-independent, forming 'tethers' that precede TCR signaling and synapse formation.
• Chemokine-tethered T cells exhibit enhanced responsiveness to subsequent APC contacts.

Conclusions:

• T cell costimulation occurs 'in trans' via a sequential, two-step process initiated by chemokine engagement.
• The initial chemokine-mediated adhesion primes T cells for heightened sensitivity to antigen presentation.
• This mechanism highlights the importance of the lymphoid microenvironment in regulating T cell activation.