Peyer's patches – do they really give a 'gut reaction'?

2001

YEAR BOOK

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University College Dublin

Jane Irwin, Philip Ryan, Stephen Carrington & Alan Baird

Peyer's patches – do they really give a 'gut reaction'?

An intact sheet of nucleated epithelial cells lines the gastrointestinal tract and provides a dynamic interface with the gut contents, which include a mucous gel (blue). Specialised epithelium (PP, yellow) are associated with strategically located cells of the immune system (red).

The mucous membranes lining the inner surface of the gut form a protective barrier preventing pathogens from invading the host animal from within. The surface of the mucosal epithelium consists of epithelial cells that are normally covered in mucus. A mucus gel mostly comprises water, ions and secreted mucin glycoproteins. Mucins are highly glycosylated linear biopolymers of very high molecular weight. The core protein is decorated with chains of linked sugars. These defend the core from proteolytic degradation.

Peyer's patches (PP) are specialised regions of the intestinal tract that may be considered as portals for the surveillance of gut contents. At these sites, specialised phagocytic M cells take up and process particulate antigens, before presenting them to the immune system. It is commonly assumed that the mucus covering of Peyer's patches is attenuated, to allow antigen uptake. The mechanism for this is unclear.

In the Veterinary Pre-Clinical Division, our Departments of Physiology & Biochemistry, and Anatomy, have been collaborating on a study to determine whether glycosidase activity might contribute to the local degradation of the mucins overlying Peyer's patches. As a marker of this, we have developed an assay to quantify and characterise the enzyme ß-galactosidase through its specific action upon the chromogenic substrate, X-Gal. Our approach is to mount PPs in a specially designed chamber that compartmentalises the apical and basolateral sides. We have found a relative abundance of ß-galactosidase on the surface of the epithelium in these areas, but not on the basolateral side. Also, little or no enzyme activity was found in non-PP epithelium adjacent to the PP site. These findings suggest a biochemical mechanism whereby mucus may be locally degraded over Peyer's patches.

This novel 'sided' approach will be extended to examine the activities of other enzymes, such as ß-galactosaminidases, ß-glucosaminidases and a-fucosidase. Homogenates of epithelial tissue have shown the presence of these enzymes in various locations in the gut.

This type of study is crucial to understanding the integrated physiology of the cells which form this important immune-sampling tissue. It is likely that the information generated will have implications for drug and vaccine delivery, as well as for a more complete understanding of the relationships mammals have with the bacteria and viruses which typically inhabit their intestines.

Contact: Dr Jane Irwin,
Department of Veterinary Physiology and Biochemistry,
The Veterinary College,
University College Dublin,
Ballsbridge, Dublin 4;
Tel: +353-1-668-7988;
Fax: +353-1-660-1279;
E-mail: jane.irwin@ucd.ie