Innate acting memory Th1 cells modulate heterologous diseases

Area of Science:

• Immunology
• Infectious Disease
• Autoimmunity

Background:

• Immune memory typically enhances responses to familiar pathogens.
• The effect of immune memory on susceptibility to unrelated diseases remains largely unknown.
• T helper 1 (Th1) cells are crucial for cell-mediated immunity.

Purpose of the Study:

• To investigate the function of memory T helper 1 cells beyond specific antigen recall.
• To identify novel subsets of memory T cells with distinct activation pathways.
• To understand how prior infections influence susceptibility to heterologous challenges.

Main Methods:

• Identification and characterization of a novel memory T cell subset, termed innate acting memory T (T_IA) cells.
• In vivo analysis of T_IA cell activation via cytokine signaling (IL-12, IL-18, IL-33) independent of T cell receptor (TCR).
• Assessment of T_IA cell function in heterologous challenge models, including bacterial infection (*Legionella pneumophila*) and an autoimmune disease model (multiple sclerosis).

Main Results:

• A subset of memory Th1 cells, designated T_IA cells, was identified, originating from viral infections.
• T_IA cells produce interferon-gamma (IFN-γ) rapidly upon stimulation with specific cytokines (IL-12/IL-18 or IL-12/IL-33), independent of TCR signaling.
• Rapid IFN-γ production by T_IA cells conferred protection against *Legionella pneumophila* infection.
• Antigen-independent reactivation of CD4+ T_IA cells exacerbated disease in a multiple sclerosis model.

Conclusions:

• Memory Th1 cells can develop TCR-independent, innate-like effector functions.
• These T_IA cells represent a critical link between adaptive memory and innate immunity.
• T_IA cell activity has dual effects, offering protection against certain infections while potentially promoting autoimmunity.