A live-cell assay to detect antigen-specific CD4+ T cells with diverse cytokine profiles

Area of Science:

• Immunology
• Cell Biology

Background:

• Activated CD4(+) T cells express CD154, providing essential costimulatory signals to B cells and antigen-presenting cells (APCs).
• Identifying antigen-specific CD4(+) T cells is vital for understanding immune responses, but previous methods were limited by the transient expression of CD154.

Purpose of the Study:

• To develop a robust assay for identifying and purifying viable antigen-specific CD4(+) T cells based on CD154 expression.
• To characterize the functional heterogeneity of CD4(+) T cells responding to specific antigens.

Main Methods:

• Developed a novel assay using fluorescently conjugated CD154-specific antibodies during cell stimulation.
• Integrated the assay with intracellular cytokine staining for simultaneous assessment of cytokine production.
• Validated the assay's compatibility with long stimulation periods (up to 24 hours) and its nonlethal nature for cell purification.

Main Results:

• The assay successfully identified antigen-specific CD4(+) T cells by detecting de novo CD154 expression post-stimulation.
• Stimulated CD4(+) T cells expressing TNF-alpha, IL-2, or IFN-gamma were predominantly CD154(+).
• CD154 expression was also observed in cytokine-negative cells, indicating broader effector functions.
• Significant heterogeneity in CD154 and cytokine expression was noted in vaccine- or pathogen-specific responses.

Conclusions:

• The developed assay enables reliable identification and purification of viable antigen-specific CD4(+) T cells.
• CD154 expression marks a broader population of activated CD4(+) T cells than previously recognized, including those with non-cytokine-mediated effector functions.
• The findings highlight unrecognized diversity in CD4(+) T cell responses and their capacity to stimulate APCs via CD40.