Regulatory T cells in pregnancy: V. Allopregnancy-induced T-cell-suppressor factor is H-2 restricted and bears la determinants

Spleen cells of allogeneically pregnant mice at the second week of second to fourth parity contain suppressor T cells capable of suppressing an MLR of maternal responders and releasing a soluble factor. The genetic restrictions of this factor have been studied in a $\text{H}\text{-2}{}^{\mathrm{<mtext>k</mtext>}}\text{H}\text{-2}{}^{\mathrm{<mtext>d</mtext>}}$ system using $\text{k}\text{d}$ or $\text{d}\text{k}$ pregnancies, and responder cells from $\text{k}\text{d}$ recombinants. The factor appeared to be IC subregion restricted. Furthermore, its activity could be removed by passage on insolubilized anti-Ia immune serum. Although factor-releasing suppressor cells are antigen specific the factor itself does not appear so, possibly implicating a mixture of fine specificities.