Histochemical distribution of sialic acids and antimicrobial substances in porcine carpal glands.

The localization of sialic acids and antimicrobial products (lysozyme, IgA, lactoferrin, β-defensin 2) as well as Rab3D in the carpal glands of pig was studied by sialoglycoconjugate histochemistry and immunohistochemistry. The secretory epithelium of the carpal glands consisted of dark and clear cells. The dark cells of these glands exhibited high levels of sialoglycoconjugates, including O-acetylated sialic acids, whereas the localization of sialic acids linked to α2-3Gal1-4GlcNAc was confined to a subpopulation of the dark cells. Furthermore, all antimicrobial substances and Rab3D were mainly detectable in a subpopulation of the dark cells. The results obtained are discussed with regard to the functional significance of these glands. Our findings suggested that Rab3D is involved in the secretory regulation of sialoglycoconjugates and antimicrobial substances. These secretory products may create a defensive barrier against microbial invasion and play an essential role in the preservation of skin integrity.