A spatially-organized multicellular innate immune response in lymph nodes limits systemic pathogen spread.

Area of Science:

• Immunology
• Innate Immunity
• Lymphatic System Biology

Background:

• The lymphatic system transports fluids and antigens, serving as a potential route for pathogen spread.
• Lymph nodes are critical sites for initiating immune responses against invading microorganisms.
• Effective innate immune responses within lymph nodes are crucial for preventing systemic infection.

Purpose of the Study:

• To investigate the role of cellular positioning and intercellular communication in lymph nodes for innate immune defense.
• To elucidate the mechanisms by which innate lymphoid cells contribute to antimicrobial resistance within lymph nodes.
• To understand how pathogen sensing by macrophages influences the activation of nearby innate lymphocytes.

Main Methods:

• Spatial analysis of lymphoid cell populations relative to lymphatic sinus-lining macrophages.
• Detection of inflammasome-generated cytokines (e.g., IL-18) produced by macrophages.
• Assessment of Interferon-gamma (IFNγ) secretion by innate lymphocytes upon stimulation.
• Experimental manipulation of the innate immune response loop to observe effects on bacterial dissemination.

Main Results:

• Diverse innate lymphoid cells (NK cells, γδ T cells, NKT cells, innate-like CD8+ T cells) are located near sentinel macrophages.
• Macrophages release inflammasome-dependent IL-18 and other cytokines upon sensing pathogens.
• Proximity allows rapid cytokine signal reception by innate lymphocytes, leading to swift IFNγ secretion.
• Disruption of this innate immune circuit facilitates systemic spread of lymph-borne bacteria.

Conclusions:

• Cellular positioning and local cytokine signaling within lymph nodes are vital for innate host defense.
• Innate lymphoid cells, activated by pathogen-sensing macrophages, confer antimicrobial resistance.
• Lymph nodes act as active sites of innate immunity, crucial for blocking pathogen dissemination.