Role for Complement in Development ofHelicobacter-Induced Gastritis in Interleukin-10-Deficient Mice

Abstract

The mechanisms by which the immune response can eradicate gastric Helicobacter infection are unknown. We hypothesized that Helicobacter-induced activation of the complement system could promote both inflammation and eradication of Helicobacter from the stomach. In vitro studies demonstrated that Helicobacter felis activates complement in normal mouse serum but not in serum from Rag2 ؊/؊ mice, indicating that H. felis activates complement through the classical pathway. Next, we infected complement-depleted wild-type control and interleukin-10-deficient (IL-10 ؊/؊ ) mice with H. felis. Helicobacter infection of wild-type mice elicited a mild, focal gastritis and did not alter serum complement levels. Infection of IL-10 ؊/؊ mice with H. felis elicited severe gastritis. After the initial colonization, the IL-10 ؊/؊ mice completely cleared Helicobacter from the stomach by day 8. In contrast to wild-type mice, H. felis-infected IL-10 ؊/؊ mice had a marked increase in serum complement levels. Complement depletion of wild-type mice did not affect the intensity of gastric inflammation or the extent of Helicobacter colonization compared to that for the wild-type control mice. In contrast, complement depletion of Helicobacter-infected IL-10 ؊/؊ mice decreased the severity of gastritis, decreased the Helicobacter-induced infiltration of neutrophils into the stomach, and delayed the clearance of bacteria. In vitro studies of stimulated splenocytes and neutrophils from IL-10 ؊/؊ mice produced a twofold increase in complement production compared to that for wild-type mice. Pretreatment with IL-10 inhibited this increase. These studies identify a role for complement in the local immune response to gastric Helicobacter in IL-10 ؊/؊ mice and suggest a role for IL-10 in the regulation of complement production.

IgA Antibodies Impair Resistance againstHelicobacter pyloriInfection: Studies on Immune Evasion in IL-10-Deficient Mice

“…In addition, our study is the first to show that IL-10 Ϫ/Ϫ mice develop stronger protection than WT mice following oral immunization. Thus, elicitation of IgA and IL-10 locally in the gastric mucosa appears to be a successful strategy used by H. pylori bacteria to evade host protection against infection (20,21,30,31). In contrast, in the absence of IgA and IL-10, immunized mice developed the strongest protection as compared with that induced in WT mice.…”

“…Finally, an inhibiting effect of IgA Abs on complement activation could account for the reduced inflammatory response seen in the IL-10 Ϫ/Ϫ mice. In fact, a recent report demonstrated that infection in IL-10 Ϫ/Ϫ mice with H. felis resulted in increased levels of serum complement and when complement was depleted in these mice they exhibited decreased gastritis, which delayed the clearance of bacteria (31). It has also been shown that human IgA Abs can significantly inhibit the activation of complement stimulated by Ag-bound IgG Abs (44).…”

“…With this intention, we crossed IgA-onto IL-10-deficient C57BL/6 mice and obtained double and single gene knockout mice, IL-10 Ϫ/Ϫ /IgA Ϫ/Ϫ and IL-10 Ϫ/Ϫ /IgA ϩ/ϩ . Our choice of the IL-10 Ϫ/Ϫ mice was based on previous studies showing that these mice develop severe gastritis and that IL-10 is strongly produced in the gastric mucosa of patients as well as in mice infected with H. pylori (20,(25)(26)(27)(28)(29)(30)(31)(32). Also,…”

“…Of note, the IL-10 Ϫ/Ϫ mice have successfully been used to show the involvement of complement and neutrophilic leukocytes in host resistance against Helicobacter infection (30,31). Moreover, recent investigations have included IL-10 to explain the chronicity of the infection as IL-10-producing regulatory T cells, both in humans and in mice, have been found in infected individuals (21,33).…”

“…Earlier studies have indicated that complement activation may be involved in Helicobacter-induced gastric inflammation and coupled with the notion that IgA Abs poorly activate complement, or even may inhibit IgG-mediated complement activation, we investigated the degree of complement deposition in our IL-10-deficient mice (31,44,45). Because complement activation and tissue deposition could be linked to an increased level of complement receptor expression (CD21/CD35), we analyzed frozen sections of gastric mucosa from infected mice for C3b fragments as well as CD21/CD35 expression (46).…”