[Induction of histidine decarboxylase in inflammation and immune responses]

Histamine is a classical, but still interesting inflammatory mediator. Many people have long believed that histamine is derived from mast cells or basophils alone. However, the histamine-forming enzyme, histidine decarboxylase (HDC), is induced in a variety of tissues in response (i) to gram-positive and gram-negative bacterial components (lipopolysaccharides, peptidoglycan, and enterotoxin A) and (ii) to various cytokines (IL-1, IL-3, IL-12, IL-18, TNF, G-CSF, and GM-CSF). HDC is induced even in mast-cell-deficient mice. The histamine newly formed via the induction of HDC is released immediately and may be involved in a variety of immune responses. Reviewing our work and that of Schayer and Kahlson, the pioneers in this field, lead us to the conclusion that nowadays we need to understand that histamine can be produced via the induction of HDC by a mechanism coupled with the cytokine network. We call this histamine "neohistamine", to distinguish it from the classical histamine derived from mast cells or basophils. Neohistamine is involved in physiological reactions, inflammation, immune responses and a variety of diseases such as periodontitis, muscle fatigue (or temporomandibular disorders), stress- or drug-induced gastric ulcers, rheumatoid arthritis, complications in diabetes, hepatitis, allograft rejection, allergic reactions, tumor growth, and inflammatory side effects of aminobisphosphonates.