Abstract
Macrophages (Mφ) produce histamine (Hm) when activated by bacterial endotoxin (LPS) through induced histidine decarboxylase (HDC). Among the cytokines tested, GM-CSF or IL-3 specifically augmented the LPS-depndent HDC induction by Mφ. Hm formed by Mφ regulates synthesis of cytokines such as IL-1, IL-6, G-CSF and M-CSF by the cells per se and may modulate immune reactions and division and differentiation of various hematopoietic cells. Kupffer cells, Mφ-like cells in the liver, also synthesize Hm in mice injected with hepatotoxins such as tetradecanoylphorbol acetate or LPS. Hm thus produced by Kupffer cells may participate in the regeneration of the injured liver through induction of hepatocyte growth factor. Concanavalin A (Con A) enhanced Hm formation by T lymphocytes. GM-CSF or IL-3 also enhanced the Hm synthesis by CD4+ and CD8+ T cells. Hm formed by T cells regulates immune reactions such as lymphocyte blastogenesis. In animals infected with gram (−) bacteria Hm is produced by the Mφ-T cell system and may regulate immune competence to the bacteria. In addition, Hm may act as a signal transducer between the peripheral immune system and hypothalamus-pituitary-adrenal system, leading to GC secretion, in order to prevent occurrence of tissue injury caused by excess immune reactions.
