Effects of 1,25-dihydroxyvitamin D3 on in vitro lymphocyte reactions: arguments for a role at the maternofetal interface.

Calcitriol or 1,25-dihydroxyvitamin D3 is synthesized by successive hydroxylations of vitamin D in the liver and kidney and during pregnancy in the placenta and the decidua. The aim of the present study was to clarify the immunoregulatory role of calcitriol, if any, during pregnancy. Calcitriol concentrations of 10(-10) to 10(-8) M was shown to reduce the proliferation of allogeneically stimulated lymphocytes and cytotoxic cell generation in a dose-dependent manner. However, calcitriol did not inhibit IL-2-dependent proliferation of CTLL-2 cell line. Calcitriol reduced non-MHC restricted cytotoxicity. Calcitriol, therefore, might be involved in the successful engraftment and growth of the fetoplacental unit possibly synergized with other products of placental or decidual origin.