Biochemical studies on glycoproteins secreted by the epithelium of the alimentary canal have been hampered to some extent because the mucosubstances in secretions are products of various cell types. The histochemical stainability of mucins within the same cell type also varies. Considerable differences can be seen when superficial and deep glandular epithelium are compared (Spicer and Sun, 1967). lmmunological techniques offer another way of identifying gastrointestinal glycoproteins. Using specific anti-A, -B or -H sera and the immunofluorescence technique, Glynn and Holborow (1 959), Szulman (1 960, 1962) and Davidsohn et al. (1966) studied the site of production of blood-group substances in gastrointestinal epithelium. The sequential order of sugars which determine the serological specificity of these macromolecules is we1 1 established (Watk ins, 1966). On the other hand, macromolecules having the same serological specificity can be structurally quite different. Examples of this are membrane glycolipids and water-soluble glycoproteins. Differences in molecular structure can also be postulated for water-soluble glycoproteins. Evidence for this comes from immunization experiments with an isolated gastric sulphoglycoprotein fraction possessing blood-group specificity (Hakkinen, 1966Hakkinen and Virtanen, 1967). The immunized rabbits apparently formed antibodies directed not against blood-group antigens, but against some other specific sites in these macromolecules. Molecular configuration in gastric sulphoglycoproteins may be altered in certain pathological conditions such as intestinalization of the gastric epithelium or gastric cancer. A preliminary attempt t o locate the sulphoglycoproteins possessing these antigenic configurations was made by the immunofluorescence technique using specific rabbit antisera . In the present study the same technique has been used to study also the
There have been but few investigations on mucosubstances, i.e. the glycoproteins of the alimentary canal, during foetal development. Blood group specificity, apparently due to glycoproteins, has been detected in the mucosa of the foetal alimentary canal with the aid of immunofluorescence techniques (Szulman, 1960), and the presence of sulphomucins has been demonstrated histochemically in the gastric surface epithelium of a 3-month-old foetus (Stemmermann, 1967). These sporadic observations have not revealed the stage at which the synthesis of mucosubstances starts. Likewise, some other aspects, such as the nature and distribution of these compounds in the foetal alimentary canal, await investigation.Three kinds of specific rabbit antisera have been prepared against the sulphoglycoproteins of the human alimentary canal in adults, namely, normal superficial, intestinal, and cancer antisera (Hakkinen, 1966;1967). The immunohistochemical distribution of compounds reacting with these antisera in the alimentary canal in normal and pathological conditions has been described in previous reports (Hakkinen et al., 1968b); in the present study the same antisera and techniques have been applied to the alimentary canal of human foetuses of various ages.
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