3D chromatin reprogramming primes human memory T_H2 cells for rapid recall and pathogenic dysfunction.

Area of Science:

• Immunology
• Molecular Biology
• Epigenetics

Background:

• Memory T cells are crucial for long-lasting immunity, but the mechanisms enabling their rapid recall of inflammatory responses are not fully understood.
• CD4+ T helper 2 (T_H2) cells are key players in allergic reactions and immune memory.

Purpose of the Study:

• To investigate the chromatin organization and epigenetic reprogramming that facilitates rapid recall responses in human CD4+ memory T_H2 cells.
• To explore the role of these mechanisms in the context of chronic inflammatory diseases like asthma.

Main Methods:

• Analysis of chromatin landscape at one-dimensional (1D) and three-dimensional (3D) levels in naive and memory T_H2 cells.
• Identification of transcription-permissive chromatin at distal enhancers and their organization into 3D chromatin hubs.
• Characterization of topologically associating domains (TADs) and promoter-enhancer interactions within "memory TADs".

Main Results:

• Memory T_H2 cells exhibit a unique chromatin landscape, reprogrammed at both 1D and 3D levels, distinct from naive T cells.
• Epigenetic priming of recall genes occurs via transcription-permissive chromatin at distal enhancers within long-range 3D hubs.
• Preformed promoter-enhancer interactions within "memory TADs" are exploited by AP-1 transcription factors for rapid gene induction.
• Resting memory T_H2 cells from asthma patients show premature activation of these recall circuits.

Conclusions:

• Stable, multiscale reprogramming of chromatin organization is a fundamental mechanism underlying immunological memory in T cells.
• Aberrant transcriptional control of primed recall responses, driven by faulty chromatin organization, contributes to chronic inflammation in diseases like asthma.