Increased relative frequency of suppressor monocytes in peripheral blood in early pregnancy

The adherent cell fraction (AdC) of human peripheral blood mononuclear cells (PBM) contains two cell types of opposing function in vitro. Dendritic cells (DC) act as antigen presenting cells (APC) in vitro, while monocytes (Mo) have a suppressive effect on antigen activation of T cells. In this report we show that pregnant women (PW) during the first trimester have a significantly increased relative frequency of suppressor Mo compared with nonpregnant healthy controls. The T cell response to PPD (purified protein derivative of tuberculin) was significantly lower in the PW, but after removal of Mo by adherence the T cell response was about the same in the two groups. These observations indicate the PW during the first trimester have the same number of T cells reactive to PPD and normal functioning DC. The relative suppression expressed on a per Mo basis was the same in both groups, which indicates that the increased suppression in the PW was caused by an increased number of Mo, and not by changes in their activation state.