Background: Inflammatory bowel disease in interleukin 2 (IL-2) deficient (IL-2^−/−) mice is triggered by the intestinal microflora and mediated by CD4⁺ T cells.

Aims: To determine the characteristics of microflora specific intestinal T cells, including migration and cytokine production.

Methods: Intestinal T cell populations and cytokine mRNA expression of specific pathogen free (SPF) and germ free (GF) IL-2^−/− and IL-2^+/+ mice were compared by flow cytometry and reverse transcription-polymerase chain reaction. Cytokine production of intestinal mononuclear cells on stimulation with microflora antigens was assessed by ELISA. In vivo migration of T cells was assessed by adoptive transfer of ⁵¹Cr labelled CD4⁺CD25⁻αβ⁺ T cells. The ability of intestinal T cell lines to promote colitis was determined by adoptive transfer experiments.

Results: SPF IL-2^−/− mice produced higher interferon γ (IFN-γ) and tumour necrosis factor α mRNA levels than GF IL-2^−/− mice, which was accompanied by an increased number of CD4⁺αβ T cells in the colon. Tracking of ⁵¹Cr labelled and adoptively transferred T cells revealed an increased MAdCAM-1 dependent but VCAM-1 independent recruitment of these cells into the colon of SPF IL-2^−/− mice. Colon lamina propria lymphocytes (LPL) from SPF IL-2^−/− mice showed increased spontaneous IFN-γ production in vitro. On stimulation with bacterial microflora antigens, intraepithelial lymphocytes and LPL did not produce IFN-γ, but high quantities of IL-10, which did not suppress IFN-γ production. Bacterial antigen specific cell lines established from colon LPL of SPF IL-2^−/− mice with colitis showed a regulatory T cell-like cytokine profile and only marginally modulated the course of colitis and survival of IL-2^−/− mice.

Conclusions: Our results suggest that microflora reactive regulatory T cells are present in the colon of SPF IL-2^−/− mice. However, IL-10 produced by these cells did not significantly modulate a possible secondary proinflammatory CD4 Th1 cell population to produce IFN-γ.