THE EXPRESSION OF COMPLEMENT PROTEIN-4 AND IGG3 IN LUMINAL SECRETIONS

Background: Factors regulating proximal small-intestinal luminal conce ntrations of IgG3, the predominant IgG subclass at this site, are uncl ear. This study determined whether luminal IgG3 concentrations are rel ated to those of complement protein 4 (C4), an acute-phase reactant pr edominantly derived from local mucosa. Methods: Proximal small-intesti nal luminal and peripheral blood Ige subclass and C4 concentrations we re measured by radial immunodiffusion in 30 adult subjects without pre disposition to disturbed mucosal immunity. Mucosal C4 immunoreactivity and the presence or absence of small-intestinal bacterial overgrowth were determined in all subjects. Caecal luminal concentrations of IgG3 and C4 were measured in a separate cohort of eight asymptomatic subje cts. Results: Proximal small-intestinal luminal C4 and IgG subclass co ncentrations were not significantly influenced by the presence or abse nce of small-intestinal bacterial overgrowth (P > 0.2). Nor did plasma C4 levels significantly influence C4 concentrations in small-intestin al luminal secretions (P > 0.2). Mucosal immunoreactivity for C4 was p resent in every subject. A significant correlation was found between C 4 and IgG3 concentrations in proximal smalt-intestinal luminal secreti ons (P < 0.0005) and also in caecal secretions (P < 0.05) but not in p eripheral brood (P > 0.1). Conclusions: Common factors, not including the presence or absence of small-intestinal bacterial overgrowth, regu late luminal concentrations of C4 and IgG3. Local investigation is man datory when assessing mucosal immune mechanisms.