Animal studies have demonstrated that feeding Ags induces regulatory (Th2, Th3) cells in Peyer’s patches (PP), which migrate to the periphery and produce immunomodulatory cytokines such as IL-4, IL-10, or TGF-β. In this work we have attempted to extend this paradigm to man by analyzing the response of human PP T cells to in vitro challenge with the common dietary Ag β-lactoglobulin (βlg) of cow’s milk. PP T cells stimulated with βlg showed enhanced proliferation compared with blood T cells from the same patient. Increased expression of CD25 and the Th1-associated chemokine receptor CCR5 was also seen on CD4+ and CD8+ PP T cells, but not blood T cells, stimulated with βlg. By enzyme-linked immunospot assay and RT-PCR, the PP T cell recall response to βlg and casein was dominated by IFN-γ, with negligible IL-4, IL-5, IL-10, or TGF-β. To help explain the PP T cell response to βlg, we examined IL-12 expression. Both IL-12p40 and-p35 transcripts were abundantly expressed in PP, but not in adjacent normal ileal mucosa. Immunoreactive IL-12p40-containing cells were present below the PP dome epithelium. Furthermore, in culture, PP, but not paired PBMC, spontaneously released IL-12p70. These results suggest that the human response to oral Ags in the gut may be different from that in rodents.