Th17 alloimmunity prevents neonatal establishment of lymphoid chimerism in IL-4-deprived mice.

Immune responses in newborn mice are known to be biased toward the helper type 2 phenotype. This may account for their propensity to develop tolerance. Herein, we evaluated the effects of IL-4 deprivation on CD4(+) T-cell activities elicited by neonatal exposure to allogeneic spleen cells. We showed that chimerism, Th2-type polarization and pathology, as well as skin allograft acceptance were inhibited in BALB/c mice immunized at birth with (A/J x BALB/c) F(1) spleen cells upon in vivo IL-4 neutralization. While IL-4 neutralization inhibited the development of Th2 cells in this model, it led to the accumulation of IL-17A, IL-17F, IL-22, IL-6 and RORγt mRNA in the spleen or graft tissues. Moreover, IL-4 deprivation led to the differentiation of donor-specific Th17 cells with a concomitant Th1 response characterized by IFN-γ production. The Th17-type response emerging in IL-4-deprived mice was found to mediate both intragraft neutrophil infiltration and the abrogation of B-cell chimerism. Neutralization of this Th17 response failed however to restore functional skin graft acceptance. Collectively, our observations indicate that the neonatal Th2 response opposes the development of Th17 cells, and that Th17 cells are responsible for controlling lymphoid chimerism in mice neonatally injected with semiallogeneic cells.

Expansion of regulatory CD8+ CD25+ T cells after neonatal alloimmunization.

Transplantation tolerance induced by neonatal injection of semi-allogeneic spleen cells is associated with a pathological syndrome caused by T helper type 2 (Th2) differentiation of donor-specific CD4(+) T lymphocytes. We have shown previously that this Th2-biased response is inhibited by host CD8(+) T cells. Herein, we demonstrate that upon neonatal immunization with (A/J × BALB/c)F(1) spleen cells, BALB/c mice expand a population of CD8(+) T cells expressing both CD25 and forkhead box P3 (FoxP3) markers. In this setting, CD8(+) CD25(+) T cells predominantly produce interferon (IFN)-γ and interleukin (IL)-10 and are efficient in controlling IL-4, IL-5 and IL-13 production by donor-specific CD4(+) T cells in vitro. CD8(+) FoxP3(-) T cells are single producers of IFN-γ or IL-10, whereas CD8(+) FoxP3(+) T cells are double producers of IFN-γ and IL-10. We further demonstrate that IFN-γ and IL-10 are two major cytokines produced by CD8(+) T cells involved in the in vivo regulation of Th2-type pathology. In this setting, we conclude that neonatal alloimmunization induces the expansion of several regulatory CD8(+) T cells which may control Th2 activities via IFN-γ and IL-10.