CD4 and infection: Finally, given the increasingly established heterogeneity and functional specialization among Foxp3+ CD4 cells that utilize distinct cell-associated and secreted molecules to mediate context specific immune suppression [42], [43], [44], establishing the Treg-associated molecule(s) that sustain fetal tolerance and distinguishing them from those required for host defense against infection have salient implications for developing therapies for dissociating the beneficial and detrimental impacts of expanded maternal Tregs.