Comparison of the sialic acid binding activity of transmissible gastroenteritis coronavirus and E. coli K99.

Transmissible gastroenteritis coronavirus (TGEV) and Escherichia coli K99 are both enteropathogenic for pigs with infections being most severe in neonate animals. For both microorganisms, a sialic acid binding activity has been shown to be an essential pathogenicity factor. Here we demonstrate with haemagglutination and haemagglutination-inhibition assays that TGEV and E. coli K99 differ in their sialic acid binding activities with respect to the type and amount of sialic acid residues required on the erythrocytes surface as well as with respect to the type of sialoglycoconjugate preferentially recognized. Intestinal mucins from piglets (12-14 days old) and adult animals were shown to inhibit TGEV to the same extent. From our results we conclude that E. coli K99 and TGEV interact with different sialoglycoconjugates to establish an intestinal infection. The implications for the enteropathogenicity of TGEV are discussed.

Sensory nerve endings in the hard palate and papilla incisiva of the goat.

The sensory innervation of the papilla incisiva in the hard palate of the domestic goat was studied with light and electron microscopy, supplemented by electrophysiological studies of free nerve endings. The goat lacks incisor teeth. Grass and leaves are not bitten, but pulled off by pressing them between the tongue and papilla incisiva. Thus, the masticatory mucosa is subject to particularly heavy mechanical loads requiring functional specialization of the horny epithelium in the form of thickening, i.e., the papilla incisiva and 12-14 pairs of rugae palatinae. A thin layer of firm connective tissue (lamina propria) attaches the mucosa to the periost of the hard palate. Sensory nerve fibers were found most abundantly in the papilla incisiva. Their number decreased drastically in aboral direction. A section through the first four rugae palatinae contains only about 10% of the number of free nerve endings found in the same area of mucosa from the papilla incisiva. Four types of sensory nerve endings were found. Free nerve endings were seen ubiquitously in the epithelium and superficial layer of the lamina propria. Merkel nerve endings were found in the bases of the epithelial thickenings in the papilla incisiva and rugae palatinae. Few Ruffini corpuscles were found in the deeper layer of the lamina propria, while lamellated corpuscles were seen just below the basement membrane of the epithelial pegs. Thus, a variety of sensory nerve endings were found in the hard palate, especially in those areas that are in close contact with the tongue during chewing of food. This rich innervation suggests an important role in monitoring the mechanical properties of food. Recordings were made from cell bodies supplying these terminals. Classic low-threshold, slowly adapting responses were observed in Ass afferent populations. This activity was probably mediated by Merkel type endings. Alternately, high-threshold and suprathreshold responses obtained from Adelta category afferents were likely to be nociceptive. In support of this, threshold and suprathreshold sensitization was observed following injection of serotonin into the receptive field of Adelta populations. This activity was likely to be derived from the aforementioned free nerve endings.