Possible Role of Th1, Th2 and Th17 CD4+ T Helper Subpopulations on Human Pregnancy Development

Paternal HLA-C antigens expressed by trophoblast, which liken the trophoblast to a semiallograft, could be presented by the maternal APCs to the specific maternal CD4(+) T helper cells, which could release various cytokines in response to these alloantigens. On the basis of the cytokines produced the effector CD4(+) T helper lymphocytes can be classified in Th1, Th2 and Th17 cells. We focused here the possible role of these 3 human effector CD4+ T helper subpopulations, known to be involved either in allograft rejection (Th1 and Th17 cells) or in allograft tolerance (Th2 cells). Th1 and Th17 cells may compromise pregnancy and be responsible for miscarriage and Th2 cells may be responsible for the success and maintenance of pregnancy. Interestingly, our recent findings showed a beneficial role of Th17 cells, whose major role is the protection against extracellular bacteria and thus may promote adequately the response required to protect the mother against dangerous extracellular pathogens. The chronology of action of Th17 cells remains to be investigated to understand completely the mechanisms by which pregnancy development could or could not be affected by Th17 cells.