IL-2 mediates protection against abscess formation in an experimental model of sepsis

Little is known regarding the mechanism by which T cells control intraabdominal abscess formation. Treating animals with polysaccharide A (PS A) from Bacteroides fragilis shortly before or after challenge protects against abscess formation subsequent to challenge with different abscess-inducing bacteria. Although bacterial polysaccharides are considered to be T cell-independent Ags, T cells from PS A-treated animals mediate this protective activity. In the present study, we demonstrate that CD4+ T cells transfer PS A-mediated protection against abscess formation, and that a soluble mediator produced by these cells confers this activity. Cytokine mRNA analysis showed that T cells from PS A-treated animals produced transcript for IL-2, IFN-gamma, and IL-10, but not for IL-4. The addition of IL-2-specific Ab to T cell lysates taken from PS A-treated animals abrogated the ability to transfer protection, whereas the addition of Abs specific for IFN-gamma and IL-10 did not affect protection. Finally, administration of rIL-2 to animals at the time of bacterial challenge prevented abscess formation in a dose-dependent manner. These data demonstrate that PS A-mediated protection against abscess formation is dependent upon a CD4+ T cell-dependent response, and that IL-2 is essential to this immune mechanism.