Histamine

Summary

Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered in 1910, it has been considered a local hormone (autocoid) because it lacks the classic endocrine glands to secrete it; however, in recent years, histamine has been recognized as a central neurotransmitter. Histamine is involved in the inflammatory response and has a central role as a mediator of itching. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues. It consists of an imidazole ring attached to an ethylamine chain; under physiological conditions, the amino group of the side-chain is proto

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https://en.wikipedia.org/wiki/Histamine

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Co-existence of H1 and H2 histaminergic receptors in individual neurons of rat hypothalamic ventromedial nucleus (VMN)

Christophe Dupré

Histamine is a ubiquitous brain neurotransmitter. Estrogen hormones have been shown to increase histamine effects on neurons located in the ventromedial nucleus of the hypothalamus (VMN) (Kow et al, 2005a). This study has been set up to find candidate pathways to explain the mechanism(s) by which estradiol does this enhancement. Therefore, we decided to look at which histamine receptors are involved in histamine-induced depolarization. Previous studies (Zhou et al, 2007) showed that in mice only the histamine receptor H1 (H1-R) is involved in histamine actions on VMN neurons. It seems however that in rats the mechanism includes more than one receptor. By using histamine agonists (betahistidine and dimaprit) in whole cell patch clamp experiments we revealed that both H1-R and histamine receptor H2 (H2-R) coexist and can mediate opposite actions of histamine on individual VMN neurons. To refine our pharmacological study histamine antagonists were used too. The blocking of both these two receptors revealed that a histamine response is the sum of the depolarization and hyperpolarization by H1-R and H2-R, respectively. Colocalization of H1-R and H2-R on the same cells was therefore suggested and will be evaluated by Immunohistochemistry.

2008

Natural anti-FcepsilonRIalpha autoantibodies may interfere with diagnostic tests for autoimmune urticaria

Lucia Baldi Unser, Martin Vogel

IgG autoantibodies against the alpha-chain of the high affinity IgE receptor are claimed to play a pathogenetic role in autoimmune urticaria. The best methods for detection of functional autoantibodies are currently the autologous serum skin test and the basophil histamine release assay. A simplified and feasible screening test would facilitate the diagnosis of autoimmune urticaria.Here we offer an explanation for the difficulties in establishing a screening test for autoantibodies directed against the alpha-chain of the high affinity IgE receptor in autoimmune urticaria. Identical autoantibodies in chronic urticaria patients and healthy donors belonging to the natural autoantibody repertoire were found by sequence analysis of anti-alpha-chain autoantibodies isolated by repertoire cloning from antibody libraries. These natural autoantibodies bound to the receptor and triggered histamine release but only if IgE was previously removed from the receptor. Diagnostic assays used for detection of antibodies directed against the IgE receptor may require signal comparison with and without the artificial removal of IgE, immune complexes, and complement in order to avoid false positive or negative results. After IgE removal diagnostic tests will detect natural autoantibodies against the high affinity IgE receptor regardless of whether they are pathogenic or not.

2004

Natural antibodies provide an early defense mechanism against pathogens, show a frequent self-reactivity, and are present throughout life. Two questions concern the physiological control of self-reactivity and the pathogenetic link to autoimmune disease. Here we propose a concept of conditional autoimmunity involving natural antibodies against the alpha chain of the high-affinity receptor for IgE (Fc(epsilon)RIalpha ). Like other natural antibodies, anti-Fc(epsilon)RIalpha antibodies are found in sera of healthy donors. We now report the first human recombinant anti-Fc(epsilon)RIalpha autoantibodies isolated by repertoire cloning from a human tonsillar IgM library. These high-affinity antibodies recognize Fc(epsilon)RIalpha on cells and trigger histamine release from freshly isolated blood basophils. However, the latter effect requires IgE removal from the Fc(epsilon)RI. The same conditional histamine release is seen when using sera from individual normal donors and affinity-purified anti-Fc(epsilon)RIalpha antibodies isolated from multidonor therapeutic IgG preparations. We propose that such anti-Fc(epsilon)RIalpha antibodies can become pathogenic and that this is dependent on the state of occupancy of the Fc(epsilon)RIalpha by its natural ligand IgE. We suggest that an imbalance between Fc(epsilon)RIalpha occupancy and natural anti-Fc(epsilon)RIalpha antibodies may be implicated in the pathogenesis of autoimmune urticaria.

2001