CD28 shapes T cell receptor signaling by regulating Lck dynamics and ZAP70 activation

Area of Science:

• Immunology
• Cellular Signaling
• Molecular Biology

Background:

• T cell activation is crucial for adaptive immunity, initiated by T cell receptor (TCR) engagement.
• CD28 co-stimulation is essential for a robust immune response, but its molecular mechanism remains unclear.
• TCR engagement triggers proximal signaling events, including tyrosine phosphorylation and kinase activation.

Purpose of the Study:

• To investigate the molecular mechanism of CD28 co-stimulation in T cell activation.
• To delineate how CD28 signaling affects the kinetics and stoichiometry of TCR proximal signaling events.
• To understand the impact of CD28 on the formation and function of TCR microclusters (MCs).

Main Methods:

• Utilized TIRF microscopy to study spatial and kinetic relationships of signaling molecules in live T cells.
• Triggered TCR microclusters using anti-TCR (CD3) antibodies.
• Analyzed the effects of CD28 co-stimulation on TCR proximal signaling within MCs.

Main Results:

• CD28 co-stimulation accelerated ZAP70 recruitment to the TCRζ chain within MCs.
• CD28 enhanced ZAP70 activation.
• Increased Lck recruitment to MCs drove the accelerated ZAP70 recruitment, with greater spatial separation of active/inactive Lck species.

Conclusions:

• CD28 co-stimulation enhances TCR signaling by promoting Lck activation and recruitment.
• This enhancement of Lck activity within TCR MCs may lower the TCR activation threshold.
• Understanding these mechanisms provides insight into generating effective immune responses.