Secretory and defensive functions of the duct system of the lactating mammary gland of the African elephant (<Emphasis Type="Italic">Loxodonta africana</Emphasis>, Proboscidea)

The duct system of the lactating mammary gland of the African elephant (Loxodonta africana) was investigated with histochemical and immunohistochemical techniques and with the transmission electron microscope in order to detect specific cell biological differentiations in the ductal epithelia of this species, which is marked by an unusually long lactation period. General histology and electron microscopy allow to distinguish several segments in the entire duct system. The apical membranes of the epithelia have binding sites for several lectins Canavalia ensiformis agglutinin (ConA), Ricinus communis agglutinin (RCA I), Wisteria floribunda agglutinin (WFA), peanut agglutinin (PNA)] and also stain with alcian blue indicating the presence of a highly differentiated negatively charged glycocalyx forming an effective barrier between lumen and epithelium. Cytokeratins, actin, tubulin and vinculin show different expression intensities in the proximal and distal portion of the duct system. Lysozyme, lactoferrin, the secretory component of IgA and human beta defensin-2 are expressed in the epithelium of the entire duct system. In the distal portion of the ducts the staining intensity is stronger than in the proximal portion. We conclude that the duct system of the elephant mammary gland has specific secretory functions and that the secretory products are part of the defensive mechanisms against invading microorganisms.