Pectin has protective, anti-inflammatory effects on inflammatory bowel disease (IBD), but the exact mechanism is unknown. Therefore, we investigated the immunological effect of dietary pectin in IL-10(-/-) mice, a murine model for IBD. Cytokine expression, CD4(+) and CD8(+) T cell populations, and immunoglobulin secretion were observed in three groups of mice: normal (BALb/c), IL-10(-/-), and IL-10(-/-) treated with pectin. Pectin treatment reduced expression of TNF-α and GATA-3, an important transcription factor for the Th2 immune response. These mice also expressed lower levels of IgE in the spleen and Peyer's patches (PP) and lower IgG and IgM expression in PP. Interestingly, IL-10 deficiency resulted in lower CD4(+) and CD8(+) populations in the spleen, mesenteric lymph node (MLN), and PP; however, pectin counteracted these declines in the MLN and PP. Therefore, dietary pectin downregulates the inflammatory response in the colon by moderating the production of proinflammatory cytokines and immunoglobulins.