Histochemical localization of sialic acids and antimicrobial substances in eccrine glands of porcine snout skin

Abstract

The distribution of sialic acids and antimicrobial products (lysozyme, IgA, lactoferrin, β-defensin 2) as well as Rab3D in the eccrine glands of porcine snout skin was studied by sialoglycoconjugate histochemistry and immunohistochemistry. The secretory epithelium consisted of two types of secretory cells: dark and clear cells. The dark cells exhibited considerable amounts of sialoglycoconjugates, which included O-acetylated sialic acids, whereas sialic acids in the sequence Siaα2-3Gal1-4GlcNAc were confined to some of the dark cells. All antimicrobial substances and Rab3D were demonstrated to be also mainly present in some of the dark cells. Additionally, in the cytological and cytochemical features, the different characteristics were observed among the dark cells. The results obtained are discussed with regard to the functional significance of the eccrine glands. The secretory products elaborated by this gland type may function as protective agents in order to preserve the skin integrity of the snout region, considering that sialic acids and antimicrobial substances are important in general defense mechanisms.

Figure 1

General structure of the eccrine glands in the porcine snout skin. a) Mallory-Azan, GRP: gland of rostral plate, asterisk: excretory duct; b) higher magnification of the eccrine glandular acini, Mallory-Azan, arrows: dark cells, arrowheads: clear cells.

Figure 2

General carbohydrate histochemical appearance of the eccrine glands in the snout skin. a) AB pH 2.5-PAS, GRP: gland of rostral plate, asterisk: excretory duct; b) AB pH 2.5-PAS, arrows: dark cells, arrowhead: clear cell.

Figure 3

Histochemical visualization of sialic acids in the eccrine glands of the snout skin. a) AB pH 2.5, arrows: dark cells, arrowhead: clear cell; b) KOH-Sial-AB pH 2.5; c) PA-P-TCH-SP-PD, arrows: dark cells, arrowhead: clear cell; d) KOH-PA-P-TCH-SP-PD; e) KOH-PA-P-TCH-SP-PD, arrows: dark cells, arrowhead: clear cell; f) KOH-Sial-PA-P-TCH-SP- PD0.

Figure 4

Lectin histochemical staining in the eccrine glands of the snout skin. a) WGA, arrows: dark cells, arrowhead: clear cell; b) SSA, arrows: dark cells, arrowhead: clear cell; c) MAM, arrow: dark cell; d) control.

Figure 5

mmunohistochemical staining in the eccrine glands of the snout skin. a) Lysozyme, arrow: dark cell; b) IgA, C: capillary, arrow: dark cell; c) lactoferrin, arrow: dark cell; d) β-defensin 2, arrow: dark cell; e) Rab3D, arrow: dark cell; f) control.

Figure 6

Ultrastructure of the eccrine glands in the porcine snout skin stained with uranyl acetate and lead citrate. a) The secretory portion consists of type I dark cells, type II dark cells and clear cells. BL: basal lamina, CC: clear cell, DC1: type I dark cell, DC2: type II dark cell, L: lumen; b) Higher magnification of dark cells in the eccrine glandular acini. DC1: type I dark cell, DC2: type II dark cell, Go: Golgi apparatus, L: lumen, Me: myoepithelial cell, Mv: microvilli, N: nucleus, PM: plasma membrane, rER: rough-surfaced endoplasmic reticulum, SG: secretory granule.

Figure 7

Cytochemical PA-TCH-SP-PD staining of the eccrine glands in the snout skin. a) Ultrastructures exhibit positive reactions. CC: clear cell, DC1: type I dark cell, DC2: type II dark cell, L: lumen, Mv: microvilli, PM: plasma membrane, SG: secretory granule; b) Part of the apical cytoplasm of secretory cells. CC: clear cell, DC2: type II dark cell, Go: Golgi apparatus, Mv: microvilli, N: nucleus, PM: plasma membrane, SG: secretory granule; c) Part of the basal cytoplasm of secretory cells. BL: basal lamina, DC1: type I dark cell, DC2: type II dark cell, Go: Golgi apparatus, Me: myoepithelial cell, N: nucleus, PM: plasma membrane, SG: secretory granule.