The epithelium provides a first line of defense against potentially pathogenic microorganisms. AM is produced by epithelial cells at mucosal surfaces, such as skin, oral cavity, and respiratory and gastrointestinal tract, and AM has antimicrobial properties against both Gram-positive and Gram-negative bacteria in these spots (Allaker et al., 1999). AM has also been shown to stimulate proliferation and inhibit apoptosis of cultured immature rat thymocytes, suggesting AM may play a role in the development of immunity (Belloni et al., 2003).
AM gene is expressed in peripheral blood monocytes and is rapidly up-regulated during their transformation to macrophages. Some studies showed that AM suppresses the secretion of proinflammatory cytokines such as tumor necrosis factor-a in Swiss 3T3 cells, macrophage cell line, and rat Kupffer cells (Isumi et al., 1999; Wu et al., 2003). The antiinflammatory effect of AM was also demonstrated in different in vivo models of inflammation (Clementi et al., 1999).
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