IL-4 IS A DIFFERENTIATION FACTOR FOR TRANSFORMING-GROWTH-FACTOR-BETA SECRETING TH3 CELLS AND ORAL-ADMINISTRATION OF IL-4 ENHANCES ORAL TOLERANCE IN EXPERIMENTAL ALLERGIC ENCEPHALOMYELITIS

We have previously shown that following oral administration of myelin basic protein (MBP), regulatory T cells are generated from gut-associa ted lymphoid tissue and that these cells suppress experimental allergi c encephalomyelitis (EAE). These regulatory T cells produce transformi ng growth factor-beta (TGF-beta) with various amounts of IL-4 and IL-1 0 and these TGF-beta-secreting T cells have been termed Th3 cells. T c ells in lymphoid organs drained by mucosal sites secrete IL-4 as a pri mary T cell growth factor. In the present study, we examined the role of IL-4 on oral tolerance and in the generation of TGF-beta secreting cells. Treatment of (PLJ x SJL)FI mice with intraperitoneal (i.p.) IL- 4 and low-dose oral MBP (0.5 mg) given three times reduced the severit y of EAE, whereas i.p. injection of IL-4 alone or oral MBP alone given in these suboptimal doses, showed no protection. Spleen cells from pr otected mice produced increased amounts of TGF-beta and reduced IFN-ga mma upon stimulation with MBP in vitro. Mucosal MBP-specific IgA produ ction was significantly increased in IL-4 plus MBP fed animals. Moreov er, oral administration of IL-4 (1 mu g per feeding) also enhanced the suppression of EAE by oral MBP and this protective effect was reverse d by administration of anti-TGF-beta antibody in vivo. Reverse transcr iption-PCR showed enhanced suppression of IFN-gamma in Peyer's patch i n animals fed MBP and IL-4 versus those fed MBP alone. We then investi gated the role of IL-4 in the generation of TGF-beta-secreting cells u sing MBP Ac1-11 TCR transgenic animals. Cells were cultured with IL-2, IL-4, or IFN-gamma in the presence of MBP and limiting dilution analy sis for cytokine-secreting cells performed. We found that IL-4, but no t IL-2 or IFN-gamma, generated TGF-beta-secreting T cells from naive s plenic T cells and that these cells provided help for IgA production. These findings demonstrate that IL-4 is a differentiation factor for T GF-beta-secreting Th3 cells and oral IL-4 has a synergistic effect on low-dose oral tolerance that is associated with increased TGF-beta sec retion.