In the present study, we report the establishment of a monoclonal antibody (Mab) designated F10 that recognized an antigen commonly shared by human trophoblasts and leucocytes. F10 MAb was obtained using cell membrane components from a trophoblast cell line HT as immunogen. Based on immunochemical studies, the F10 reactive antigen (F10-Ag) could be located on both villous and nonvillous trophoblasts from early and term placental tissues and on all trophoblastic cell lines. In addition, flow cytometry revealed that most ( > 95%) peripheral blood lymphocytes, monocytes, as well as polymorphonuclear leukocytes (PMN) were positively stained with F10 MAb. Immunoblotting with F10 MAb identified two protein bands with apparent molecular mass of 62 and 56 kDa. Furthermore, the antigens were glycoproteins and were glycosylated via the O-linkage. Scatchard plot analyses of the binding data between 125I-labeled MAb F10 IgG and HT cells revealed a single class of F10 binding sites with an apparent dissociation constant (Kd) of 10.54 +/- 2.03 pM and maximum binding-site (Bmax) value of 2.1 +/- 0.11 x 10(6) sites per cell. We suggest that F10 may be useful for the identification of a novel epitope that is commonly shared by all trophoblasts and leukocytes and such an epitope may be potentially active in maternal-fetal interactions.