No abstract

Multiple sclerosis (MS) lesions are associated with infiltration of T lymphocytes and macrophages that appear to mediate myelin destruction and gliosis (scarring). Mast cells are located perivascularly in the brain, are juxtaposed to neurons, and have been shown to secrete vasoactive and inflammatory mediators in response to neuropeptides and direct nerve stimulation. Mast cells have been previously identified in MS lesions, are activated by myelin basic protein, and can participate in the regulation of blood-brain barrier permeability, as well as in myelin destruction. Here, cerebrospinal fluid from MS patients and controls with other neurologic diseases was assayed for histamine, its major metabolite methylhistamine, and the specific mast cell marker tryptase. Histamine and methylhistamine were not elevated in MS. However, the mast cell specific proteolytic enzyme tryptase was significantly elevated in MS, suggesting that mast cell activation may be involved in the pathophysiology of this disease.

Mast cells have been studied extensively for their involvement in allergic reactions, where they secrete numerous powerful mediators in response to immunoglobulin E and specific antigens. However, they are also triggered by neuropeptides, they have been found in close contact with neurons, and they are activated in diseases such as angioedema, interstitial cystitis and irritable bowel disease, the prevalence of which is much higher in women. When tested on purified rat peritoneal mast cells, 17β-estradiol augmented secretion of histamine and serotonin, starting at 1 μM and in a dose-dependent manner, whether stimulated by the mast cell secretagogue compound 48/80 or the neuropeptide substance P. However, 17β-estradiol did not augment mast cell secretion stimulated by immunoglobulin E and specific antiserum indicating that immunologic stimulation is under different regulation. Testosterone inhibited secretion induced by compound 48/80. Tamoxifen, an estrogen receptor antagonist used in the treatment of breast cancer, inhibited serotonin and histamine release from purified rat peritoneal mast cells triggered by compound 48/80 or substance P. Tamoxifen also inhibited the increase in intracellular free Ca²⁺ originating from an influx of extracellular Ca²⁺ in response to compound 48/80. Moreover, tamoxifen antagonized the synergistic effect of phorbol myristate and the cation ionophore A23187 on mast cell secretion, suggesting that tamoxifen’s inhibition may be due to regulation of protein kinase C activity. Tamoxifen may, therefore, have a beneficial effect in other neuroimmunoendocrine disorders both through estrogen receptor blockade and inhibition of mast cell secretion.