[Histamine produced by macrophage and T lymphocyte: a new type of signal transducer]

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Macrophages (M phi) and T lymphocytes are key immune cells involved in host defense and tissue homeostasis.
• Histamine (Hm) is a biogenic amine traditionally known for its role in allergic reactions.
• The production and function of histamine by immune cells beyond mast cells are less understood.

Purpose of the Study:

• To investigate the production of histamine by macrophages and T cells.
• To identify factors that regulate histamine synthesis in these immune cells.
• To explore the functional implications of histamine produced by macrophages and T cells in immune responses and tissue repair.

Main Methods:

• Activation of macrophages with bacterial endotoxin (LPS) and assessment of histidine decarboxylase (HDC) activity and histamine production.
• Treatment of T lymphocytes with Concanavalin A (Con A) and analysis of histamine synthesis.
• Investigation of the effects of cytokines, including GM-CSF and IL-3, on histamine production by macrophages and T cells.
• Evaluation of histamine's role in regulating cytokine synthesis and cell differentiation.

Main Results:

• Macrophages produce histamine upon LPS activation, mediated by induced HDC.
• GM-CSF or IL-3 specifically augmented LPS-dependent HDC induction in macrophages.
• Kupffer cells (liver macrophages) synthesize histamine in response to hepatotoxins or LPS, potentially aiding liver regeneration.
• T lymphocytes, stimulated by Con A, also produce histamine, with GM-CSF and IL-3 enhancing this synthesis.
• Histamine produced by macrophages regulates cytokines (IL-1, IL-6, G-CSF, M-CSF) and hematopoietic cell differentiation.
• Histamine from T cells modulates immune reactions like lymphocyte blastogenesis.
• The macrophage-T cell system produces histamine during bacterial infections, potentially regulating immune competence.
• Histamine may signal between the immune system and the HPA axis, influencing glucocorticoid secretion to prevent immune-mediated tissue injury.

Conclusions:

• Macrophages and T cells are significant sources of histamine, contributing to immune regulation and tissue repair.
• Cytokines like GM-CSF and IL-3 play a crucial role in enhancing histamine production by immune cells.
• Histamine produced by these cells influences a range of biological processes, including cytokine synthesis, cell differentiation, and immune responses.
• Histamine acts as a critical mediator in the interplay between the immune system, tissue regeneration, and neuroendocrine pathways.