Immunology & Immunological Disorders Poster Session
Lysozyme is an acid- and heat-stable enzyme that is abundant in the breast-milk and in most other mucosal body-fluids (1). The concentration of lysozyme in the colostrum is approximately 40-100 µg/ml and gradually increases as the lactation progresses. Lysozyme catalyzes the hydrolysis of ß (-1,4-) linkage between N-acetylglucosamine and N-acetylmuramic acid in the bacterial cell wall. The enzyme lyses mostly gram positive and a few gram negative bacteria or induces their aggregation (2). In addition, it possesses prominent anti-inflammatory properties.
Lysozyme has been shown to inhibit chemotaxis of activated leucocytes. Other anti-inflammatory functions of lysozyme include inhibition of mitogen-induced lymphoblastogenesis and autologus mixed lymphocyte reaction (at concentrations ranging between 1 and 10 micrograms/ml) (3). Its interaction with the Complement system (Cp) system has so far been found to be indirect, by an inhibition of PMN response towards complement derived chemotaxins. Our present studies have also shown that it is capable of directly modulating the entire activation of Cp reaction cascade. The exact mechanism for this inhibition is however, yet to be fully examined. Lysozyme, some milk proteins, such as alpha lactalbumin, and low molecular-weight ligands, such as citrates and phosphates, are known to have high affinity binding sites for calcium (4), and may therefore act as inhibitors of complement indirectly, by chelating the divalent ions required for complement activation. The inhibitory effect of lysozyme might also be related to its ability to degrade certain glycoprotein components of native Cp factors.
The serum Cp system consist of at least 19 proteins, mostly in pre-activated enzymatic forms, activated in a multi-step cascade reaction via either the classical or alternative pathways. The classical pathway is activated mainly by antigen-antibody complexes (IgG or IgM mostly) starting with C1q, C1r, C1s, C4 and C2, and eventually leading to the activation of C3 by cleavage into C3a and C3b. The alternative pathway (APC) utilizes active sites (such as are present on zymosan, yeast, cobra venom, most gram-negative bacteria, sheep erythrocytes and human cells deficient in the expression of membrane regulatory molecules) in the presence of properdin, serum factors B and D, to activate C3. This step unifies the two pathways and proceeds uniformly thereafter to the formation of (C5b-9) membrane attack complexes (MAC), capable of inserting into biological membranes and producing cell lysis and death. APC activating surfaces are characterised by possession of structures which restrict access to inhibitory factor H to deposited C3b, thereby amplifying the formation of further C3b in the presence of factor B.
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|Ogundele, M.O.; (1998). A Novel Anti-inflammatory Activity of Human Lysozyme: Modulation of Serum Complement Activation. Presented at INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Available at URL http://www.mcmaster.ca/inabis98/immunology/ogundele0178/index.html|
|© 1998 Author(s) Hold Copyright|