Jun-ichi Inobe

IL‐4 is a differentiation factor for transforming growth factor‐β 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‐associated lymphoid tissue and that these cells suppress experimental allergic encephalomyelitis (EAE). These regulatory T cells produce transforming growth factor‐β (TGF‐β) with various amounts of IL‐4 and IL‐10 and these TGF‐β‐secreting T cells have been termed Th3 cells. T cells in lymphoid organs drained by mucosal sites secrete IL‐4 as a primary T cell growth factor. In the present study, we examined the role of IL‐4 on oral tolerance and in the generation of TGF‐β secreting cells. Treatment of (PLJ × SJL)F1 mice with intraperitoneal (i.  p.) IL‐4 and low‐dose oral MBP (0.5 mg) given three times reduced the severity 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 protected mice produced increased amounts of TGF‐β and reduced IFN‐γ upon stimulation with MBP in vitro. Mucosal MBP‐specific IgA production was significantly increased in IL‐4 plus MBP fed animals. Moreover, oral administration of IL‐4 (1 μg per feeding) also enhanced the suppression of EAE by oral MBP and this protective effect was reversed by administration of anti‐TGF‐β antibody in vivo. Reverse transcription‐PCR showed enhanced suppression of IFN‐γ in Peyers patch in animals fed MBP and IL‐4 versus those fed MBP alone. We then investigated the role of IL‐4 in the generation of TGF‐β‐secreting cells using MBP Ac1‐11 TCR transgenic animals. Cells were cultured with IL‐2, IL‐4, or IFN‐γ in the presence of MBP and limiting dilution analysis for cytokine‐secreting cells performed. We found that IL‐4, but not IL‐2 or IFN‐γ, generated TGF‐β‐secreting T cells from naive splenic T cells and that these cells provided help for IgA production. These findings demonstrate that IL‐4 is a differentiation factor for TGF‐β‐secreting Th3 cells and oral IL‐4 has a synergistic effect on low‐dose oral tolerance that is associated with increased TGF‐β secretion.

In Vivo Administration of IL-4 Induces TGF-β-producing Cells and Protects Animals from Experimental Autoimmune Encephalomyelitis

FIGURE 1. In vivo administration of IL-4 protects animals from EAE. Two groups of female PLJ x SJL F1 mice, 6 mice per group, were immunized for EAE with MBP in CFA. On the day of immunization, mice received an intraperitoneal (ip) injection of either recombinant mouse IL-4 (5000 U/mouse) in 0.5 mL PBS or PBS alone. The maximum clinical score and fatality of IL-4-treated animals were significantly lower than the PBS-treated group (p = 0.007 and 0.0192, respectively). +, ip PBS; A, ip IL-4.

A Potential Pathway of Th2 Development during Primary Immune Response

Differential cytokine production (Thl versus Th2) by CD4+ T cells during an immune response plays an important role in determining the biological implications of the response. Th1 cells are characterized by the dominance of IFN-γ production while Th2 cells produce predominantly 1L-4. It is now well established that IL-12 is essential for the priming of Thl cytokine secreting T cells1 while IL-4 is critical in the priming of Th2 cytokine secreting T cells2. While it has been suggested that CD1 specific NK1.1 CD4+ T cells in the spleen3, or CD4- CD8-, TCRαβ+ T cells restricted by MHC class I4 might be the potential sources of IL-4 during primary immune responses, these have not been clearly demonstrated.