T cell regulation of Bacteroides fragilis-induced intraabdominal abscesses.

Intraabdominal abscesses (IAA) caused by Bacteroides fragilis are a major sequela to colonic spillage into the peritoneum. The development of an animal model that closely reproduces the disease observed in humans permitted careful inspection of the cellular and/or humoral contributions to the development and control of this disease. The results obtained thus far describe an immunoregulatory T cell circuit that governs both the development of and the immunity against these abscesses. T cells of CD4+8+ phenotype induce the development of IAA in response to B. fragilis. CD8+ T cells generated in response to immunization with the B. fragilis capsular polysaccharide confer protection against the development of IAA. These cells elaborate an antigen-specific factor that mediates the observed protection by these cells. Moreover, a third type of T cell, a CD8+ cell that is also present in nonimmune individuals, is required for the immune T cell or its factor to confer protection. Thus, in the specific disease process of IAA induced by the encapsulated microorganism B. fragilis, immunity proceeds by cellular and not humoral mechanisms.