Human Extrafollicular CD4⁺ Th Cells Help Memory B Cells Produce Igs

Area of Science:

• Immunology
• Cell Biology

Background:

• Follicular helper T (Tfh) cells are critical for primary immune responses and B cell maturation.
• The specific T cells driving humoral recall responses via memory B cells remain less defined.

Purpose of the Study:

• To characterize a distinct CD4+ T cell subset in human tonsils responsible for promoting humoral recall responses.

Main Methods:

• Analysis of human tonsillar CD4+ T cell subsets.
• Assessment of chemokine receptor expression, cytokine secretion (IL-21), and transcription factor BCL6.
• Evaluation of T cell interaction with memory B cells and antibody production.

Main Results:

• A unique extrafollicular CD4+ T cell subset was identified, distinct from Tfh cells.
• These cells express CXCR5 and PD-1, secrete IL-21, and express BCL6.
• They reside at the T cell zone/B cell follicle border, interacting with memory B cells.
• Promotion of memory B cell antibody production occurs via CD40L, IL-10, and IL-21.

Conclusions:

• A novel extrafollicular CD4+ T cell subset specializes in promoting T cell-dependent humoral recall responses.
• This subset's unique localization and function are critical for adaptive immunity.