ABSENCE OF AN IMMUNOLOGICAL BLOCKING FACTOR FROM SERUM OF WOMEN WITH CHRONIC ABORTIONS

An immunologic mechanism that might explain the apparent tolerant state of the mother during pregnancy was investigated. Cellular-immune reactivity in vitro to paternal alloantigens was demonstrated in multigravid women by production of lymphocyte migration inhibitory factor. Serum from normal multigravid women contained a factor that blocked production of migration inhibitory factor by maternal lymphocytes to paternal antigens in a specific manner. The blocking factor was an IgG [immunoglobulin G] antibody whose activity was removed by absorption with paternal lymphocytes but not with pooled human platelets. The biologic importance of this blocking factor was tested in women who have difficulty maintaining a normal term pregnancy. Women who experience idiopathic spontaneous abortions apparently produce lymphocyte migration inhibitory factor to paternal alloantigens, but their sera lack the blocking factor. The presence of the serum blocking factor during pregnancy may contribute to the success of the fetus as an allograft.