Non-specific immunoregulatory factors in the cytosol fraction of human trophoblast.

Cytosol extracts from syncytiotrophoblast of human placenta (HP) have been shown to contain substances capable of suppressing the proliferation of normal human lymphocytes stimulated by mitogens. This suppressive effect has also been observed on lymphocytes stimulated by mitogens and by allogenic cells in various species. The extracts did not, however, inhibit spontaneous (i.e. unstimulated) lymphoproliferation. In addition, HP in some cases exercised an immunostimulatory effect solely on stimulated fractionated lymphocytes. In preliminary experiments the suppressive activity was shown to depend on at least two factors: the first had the ability to bind the mitogen while the second acted irreversibly after 8 h of contact on the lymphocyte itself and was thermostable.