PubMed · 7930296
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R E Reisman. 1994. Venom hypersensitivity.. https://doi.org/10.1016/0091-6749(94)90167-8
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The pathophysiological responses to immune stress (IS) include activation of several processes which are dependent on cytosolic Ca2+ elevation. Magnesium frequently acts as a natural Ca2+ antagonist. In this study we have observed that Mg2+ can protect guinea-pigs against IS. Antigen-sensitized guinea-pigs, which had been fed a magnesium-deficient diet, were given a single dose (15 mg) of MgCl2 intraperitoneally 1 h before antigen challenge. The development of anaphylactic shock (AS) was observed during the next 2 h, and the hearts were subsequently examined histologically for signs of cardiac myolysis (CM). Magnesium (i) reduced the incidence of CM from 40% to 10% (p < 0.05); (ii) reduced the incidence of AS from 61% to 35% (p < 0.05); (iii) attenuated the severity of the AS; and (iv) lowered mortality from 39% in the control to 19% in the Mg(2+)-treated group (p = 0.1). Serum and tissue total [Mg2+] were not affected by the administration of MgCl2. Also, the serum and heart Mg2+ levels were the same whether or not the guinea-pigs developed AS or CM. In cell culture we demonstrated that by elevating the [Mg2+] in the medium bathing sensitized rat basophilic leukemia (RBL) cells, the increase in cytosolic [Ca2+] subsequent to antigen challenge was reduced from 174 +/- 23.28% (1 mM) to 82.74 +/- 13.22% (3 mM). We conclude that a single treatment with Mg2+ can considerably diminish damage induced by immune stress, probably by its altering the Ca2+: Mg2+ ratio. Since the physiological reaction to different types of stress is similar, Mg2+ could prove beneficial in preventing stress-induced shock in general. Studies examining the mechanisms by which Mg2+ exerts its effects thus provide a scientific basis for the current clinical use of Mg2+ in acute myocardial infarction (AMI) and asthma.
Mouse mast cell protease (mMCP) 7 is a tryptase of unknown function expressed by a subpopulation of mast cells that reside in numerous connective tissue sites. Because enzymatically active mMCP-7 is selectively released into the plasma of V3 mastocytosis mice undergoing passive systemic anaphylaxis, we used this in vivo model system to identify a physiologic substrate of the tryptase. Plasma samples taken from V3 mastocytosis mice that had been sensitized with immunoglobulin (Ig) E and challenged with antigen were found to contain substantial amounts of four 34-55-kDa peptides, all of which were derived from fibrinogen. To confirm the substrate specificity of mMCP-7, a pseudozymogen form of the recombinant tryptase was generated that could be activated after its purification. The resulting recombinant mMCP-7 exhibited potent anticoagulant activity in the presence of normal plasma and selectively cleaved the alpha-chain of fibrinogen to fragments of similar size as that seen in the plasma of the IgE/antigen-treated V3 mastocytosis mouse. Subsequent analysis of a tryptase-specific, phage display peptide library revealed that recombinant mMCP-7 preferentially cleaves an amino acid sequence that is nearly identical to that in the middle of the alpha-chain of rat fibrinogen. Because fibrinogen is a physiologic substrate of mMCP-7, this tryptase can regulate clot formation and fibrinogen/integrin-dependent cellular responses during mast cell-mediated inflammatory reactions.