Gestation stage-dependent mechanisms of invariant natural killer T cell-mediated pregnancy loss

Stimulation of CD1d-restricted semiinvariant natural killer T cells by using the CD1d ligand alpha-galactosylceramide (alphaGalCer) induces pregnancy loss in mice through an ill-defined mechanism involving TNF, IFN-gamma, and perforin. In this article, we demonstrate that during early gestation, alphaGalCer efficiently induced pregnancy loss in C57BL/6J and BALB/cJ mice in a perforin-dependent manner. In contrast, during midgestation perforin was no longer required for pregnancy loss. Concomitant with the loss of a perforin requirement at midgestation was the emergence of strain-dependent variations in susceptibility to alphaGalCer-induced pregnancy loss. Whereas pregnant C57BL/6J mice remained susceptible to alphaGalCer at midgestation, pregnant BALB/cJ mice were resistant to its effects. Pregnancy loss during midgestation was correlated with dramatically higher serum cytokine levels, including TNF and IL-2, in the susceptible C57BL/6J strain compared with the resistant BALB/cJ strain. Thus, the stage of gestation defined two distinct mechanisms of pregnancy loss: a perforin-dependent mechanism operating at early gestation and a perforin-independent, cytokine-dominated mechanism operating after midgestation.