Immune system histamines

L-Tyrosine metabohsm and catecholamine biosynthesis occur largely in the brain, central nervous tissue, and endocrine system, which have large pools of L-ascorbic acid (128). Catecholamine, a neurotransmitter, is the precursor in the formation of dopamine, which is converted to noradrenaline and adrenaline. The precise role of ascorbic acid has not been completely understood. Ascorbic acid has important biochemical functions with various hydroxylase enzymes in steroid, dmg, andhpid metabohsm. The cytochrome P-450 oxidase catalyzes the conversion of cholesterol to bUe acids and the detoxification process of aromatic dmgs and other xenobiotics, eg, carcinogens, poUutants, and pesticides, in the body (129). The effects of L-ascorbic acid on histamine metabohsm related to scurvy and anaphylactic shock have been investigated (130). Another ceUular reaction involving ascorbic acid is the conversion of folate to tetrahydrofolate. Ascorbic acid has many biochemical functions which affect the immune system of the body (131). 

The classical cellular sources of histamine are mast cells and basophils, gastric enterochromaffin-like cells, platelets and histaminergic neurons. Interestingly the cells in the immune system, which do not store histamine, show high HDC activity and are capable of production of high amounts of histamine, which is secreted immediately after synthesis [20]. These cells include platelets, monocytes/macrophages, DCs, neutrophils, and T and B lymphocytes. 

Histamine may be released from mast cells by mechanisms that do not require prior sensitization of the immune system. Drugs, high-molecular-weight proteins, venoms, and other substances that damage or disrupt cell membranes can induce the release of histamine. Any thermal or mechanical stress of sufficient intensity also will result in histamine release. Cytotoxic compounds, may release histamine as the result of disruption of cell membranes. 

Biomolecules - Other types of molecules and macromolecules are active during the immune response. Histamine and serotonin were encountered in our discussion of the nervous system. They are factors which act to intensify the response to a nonself presence. Heparin, the anticoagulant. 

Receptors for histamine, which probably acts as a neuromodulator,801 occur in the brain.802 Histamine is formed by decarboxylation of histidine (p. 745)803 and is inactivated by histidine N-methyltransferase. Histamine is best known for its presence in mast cells,804 components of the immune system that release histamine during inflammatory and allergic reactions (Chapter 31). However, histaminergic neurons of the hypothalamus extend throughout the whole forebrain,805 and specific receptors have been found both in the brain and in peripheral tissues.806 Several other amines that are formed by decarboxylation of amino acids are present in trace amounts but may have im-... 

In conclusion, the role of histamine H3 receptors in the immune responses has not yet been completely identified. The H3 receptor, located on mast cells, may represent a mechanism for a negative feedback through histamine autoregulation in tissue inflammation. The presence of this receptor on both mast cells and nerve endings suggests an important role for H3 receptors, especially when we consider that the immune system and the nervous system behave as separate arms of a unified, coordinated body defence system (McKay and Bienenstock, 1994). 

It is thought that the T-cell balance can be different in different people. If T-helper cells predominate, then their immune system can be hyperactive and react even with relatively harmless particles like dust or pollen. This causes the mast cells to release chemicals including histamine and other chemicals that cause inflammation, dilation of blood vessels and the production of mucus. This occurs in the nose for hay-fever... 

HRF is one of the many immune system protein molecules called cytokines that trigger allergic reactions. Unlike other cytokines, HRF stimulates basophils to release histamine (MacDonald, 1996). 

An allergic reaction occurs when the patient develops sensitivity to a medication. When a medication is first administered, the patient s immune system develops antibodies to the medication, sensitizing the patient to the medication. The next administration of the medication causes a reaction with the antibodies, resulting in the production of histamine. Histamine causes allergic symptoms. 

Additional studies are needed to understand the immunotoxic potential of OPs and CMs. Since e.stcrase activation has a role at various steps of complement cascade, release of histamine or other bioaetive substances from cells, and chemo-laxis of. sensitized lymphocytes, the inhibition of cstcrasc.s may produce opposite effects. Anticholinesterase pc.sticidcs have potent effects on various processes of the immune response in some cases. It has not been established whether these are mediated directly via inhibition of cholinesterases or via other esterases that mediate the immune reactions since potent anticholinesterase insecticides have the potential to inhibit different esterases in the body. It is not known if the anticholinesterase property can be effectively used for therapeutic modulation of the immune system. The cytotoxic... 

---